Book - Oral Histology and Embryology (1944) 5

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Orban B. Oral Histology and Embryology (1944) The C.V. Mosby Company, St. Louis.

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Chapter V - Pulp

I. FUNCTION Formative Nutritive Sensory Defensive

II. ANATOMY

Pulp Chamber Root canal Apical Poramen

HI. DEVELOPMENT

IV. STRUCTURAL ELEMENTS

Fibroblasts and Fibers Odontoblasts Defense Cells

3.. Histiocytes b. Undifferentiated Mesenchymal cells c. Lymphocytes Blood Vessels

Lymph Vessels Nerves

V. REGBESSIVE CEANGES

Pulp Stones Galcifications Secondary Dentin Fibrosis

VI. GLDTICAI. CONSIDERATIONS

I. FUNCTION

The dental pulp is of mesenchymal origin and contains most of the cellular and fibrous elements which are present in connective tissue. The primary function of the dental pulp is the production of dentin. This function is discussed in the chapter on Dentin. The pulp furnishes nourishment through the odontoblastie processes to the dentin. Nutritional elements are contained in the tissue fluid. The pulp also contains nerves. Some of these nerves give sensation to the tooth structures, others serve to regulate the blood supply of the pulp itself by ending on the muscular ele—

ments of the vessels.

First draft submitted by Balint Orban. 127 Defensive

128 (um. HISTOLOGY AND EMBRYOLOGY

The pulp is well protected against external irritations as long as it is surrounded by an intact wall of dentin. It can evolve a very effective reaction if exposed to irritation whether it is of mechanical, thermal, chemical or bacterial nature. The defenive reaction may be expressed in the formation of irregular dentin (see chapter on Dentin) if the irritation is mild, or as an inflammatory reaction in cases of more severe irritation. While the rigid dentinal wall has to be considered as a protection to the pulp it also endangers its existence under certain conditions. During inflammation of the pulp the hyperemia and the exudate cause increasing pressure which, by occlusion of the blood vessels, may lead to necrosis—self-strangulation of the pulp.

H. ANATOMY

The dental pulp occupies the pulp cavity which consists of the coronal pulp chamber and the root canals. The pulp is continuous with the periapical tissues through the apical foramen or foramina. Roughly the

--:-qr’; v-,"'* "—— ~.ws¢§§

Fig. 97.—Age changes in the pulp chamber or the first permanent molar. Decalcifled sections; enamel lost.

4. Age 8 years. B.Ase55 years.

Reduction of the pulp chamber in height is greater than in mesiodlsfal diameter. Pulp stones narrowing the entrance into the root canals in B. (Kronteld, R34)

shape of the pulp chamber follows, in young individuals, the outline of the tooth. The extensions into the cusps of the tooth are called pulpal horns. At the time of eruption the pulp chamber is large, but becomes smaller with advancing age, due to continuous deposition of dentin“ (Fig. 97). The decrease in the size of the pulp cavity in molars does not occur at the same rate throughout the pulp chamber. Formation of dentin PULP 129

progresses fastest on the floor‘ of the pulp chamber; some is formed at the occlusal wall and, lem still, on the side walls of the pulp chamber so that the pulp dimension is reduced in an occlusal direction. The chamber may

be further narrowed and its shape may become irregular by formation of irregular dentin. The formation of pulp stones (Fig. 97, B) may also

reduce the size and change the shape of the formerly Wide pulp cavity, occasionally even occluding it.

=_ ' ‘,“""’”'.j

Pulp

lEpithella.l iiaphragm

Apical foramen

Fig. 98.—Deve1opment of the apical toramen. A. Undeveloped root end; wide apical foramen, partly limited by epithelial diaphragm

B. Apical foramen fully formed. Root canal straight; apical roramen surrounded by cementum (Coolidge, E. D.’)

Advancing age induces similar changes in the root canals. During Root canal root formation the apical foramen is a wide opening, limited by the epithelial diaphragm (Fig. 98, A), the continuation of Hertwig’s root sheath at the root end. The dentinal walls taper and the shape of the pulp

canal is like a wide, open tube. As growth proceeds more dentin is formed so that, when the root of the tooth has matured, the root canal is considerably narrower. In the course of root formation Hertwig’s epithelial root sheath breaks up into epithelial rests, and cementum is laid down on the root surface (Fig. 98, B). This cementum will influence the size and shape of the apical foramen in the fully formed tooth. Root canals are not

‘The floor oi.’ the pulp chamber is the wall opposite the occlusal wall (root) regardless of the position of the tooth in the Jaws. 130 ORAL HISTOLOGY AND EMBRYOLOGY

Fig. 99.-Drawings of teeth a.1.'t_er filling or the _root canals with India. ink and clear_ing. (After Okumura. 1“ and Apr1le.1) A. Upper incisors. B. Upper cuspids. C‘. Lower mcisors. D. Lower cuspids. F. Upper molars. G. Lower premolars. molars.

Fig. 99 Contd.—E. Upper premolars.

H. Lower

.3

PULP

131 132 ORAL HISTOLOGY AND nmmzvonocv

always straight and single but vary by the occurrence of accessory canals, as seen in corrosion specimens“ or after filling of the root canals with india ink and clearing (Fig. 99).

At any distance from the apex of the tooth (Fig. 100, A) side branches of the root canal may be present. In multi-rooted teeth these are observed even at, or close to, the floor of the pulp chamber (Fig. 100, B and C). A possible explanation for the development of all side branches of the pulp canals may be a defect in HertWig’s epithelial root sheath during development of the root at the site of a larger supernumerary blood vessel.

‘ p Accessory

canal

Fig. 100.—Accessory canals in microscopic sections. A. Close to the apex. B. Close to the bifurcation.

Apical There are variations in shape, size, and location of the apical foramen.’ Poramen A regular, straight apical opening is rare (Fig. 98, B); occasionally, the cementum can be traced from the outer surface of the dentin into the pulpal canal. Sometimes, the apical opening is found on the lateral side of the apex (Fig. 101, B) although the root itself is not curved. Frequently, there are two or more distinct apical foramina, separated by a band of

dentin and cementum, or cementum only. The location and shape of the apical foramen may also undergo changes,due to functional influences upon the teeth.“ A tooth maybe tipped, due Flg. 1000.—Roentgenogram or lower molar with accessory canal filled. (H. B. J'ohnston.")

Fig. 101.—Varlatlons of the apical to:-amen.

A. sum ot the apical roramen by resorption of dentin and cementum on one surface md apposition of cementum on the other.

8. Apical fornmen on the side of the apex (Coolidge. E. D’).

Apex 134 ORAL HISTOLOGY AND EMBRYOLOGY

to horizontal pressure, or may migrate mesially causing the apex to deviate in the opposite direction. Under these conditions the tissues entering the pulp through the apical foramen exert pressure on one wall of the foramen, causing resorption. At the same time cementum

is laid down on the opposite side of the apical root canal, resulting in a change in the relative position of the original opening (Fig. 101, A).

III. DEVELOPMENT

The development of the dental pulp begins at a very early stage of embryonic life, about the fifty-fifth day, in the region of the incisors; later in the other teeth. The first indication is a proliferation and condensation of mesenchymal elements, lmown as the dental papilla, at the

Oral epithelium

Epithelial enamel organ

Basement membrane

._ Dental papilla

i Mandi bular bone

Fig. 102.——Development at the pulp. Dental papilla or an embryo two and one-halt months old. The papilla contains a. rich network of tine argyrophil fibers. Basement

membrane between mesenchyrne and epithelium. Silver impregnation.’ (Courtesy Dr. P. Gruenwald.) ‘ ' w A ' ‘ PULP 135

basal end of the enamel organ (Fig. 102). Due to the rapid development of the epithelial elements of the tooth germ into a bell-shaped enamel organ. the future pulp is well defined in its outline. In a silver-impregnated section the arrangement of the fibers in‘ the embryonic dental papilla, is clearly visible (Fig. 102). ' In the future pulp area the fibers are fine and irregularly grouped, and much denser than in the surrounding tissue. At the boundary toward the epithelium a basement membrane is formed, and the fibers of the dental papilla radiate into it.

The fibers in the embryonic pulp are pre-collagenous, i.e., reticular or argyrophil. There are no collagenous fibers in the embryonic pulp, ex cept where the fibers follow the course of the blood vessels." °~ ”' As the development of the tooth germ progresses the pulp becomes increasingly vascular, and the cells develop into star-shaped connective tissue cells (fibroblasts) (Fig. 103, A). The cells are more numerous in the periphery of the pulp. Between the epithelium and the pulp cells is a cell-free layer. This contains numerous fibers, forming the basement or limiting membrane (see chapter on Development of Dentin);

IV. STRUCTURAL ELEMENTS

The pulp is a specialized loose connective tissue. It consists of cells (fibroblasts) and the intercellular substance. The latter, in turn, consists of fibers and a cementing substance. In addition, defense cells and the cells of the dentin, the odontoblasts, are part of the dental pulp. The fibroblasts of the pulp and the defense cells are identical to those found elsewhere in the body. The fibers of the pulp are in part collagenous, in part precollagenous. Elastic fibers are absent. The cementing substance of the pulp seems to be of a much higher consistency than that in the loose connective tissue outside of the pulp.

‘In the course of development the relative number of cellular elements in the dental pulp decreases, whereas the intercellular substance increases (Fig. 103, B). With advancing age there is a progressive reduction in the number of fibroblasts, accompanied by an increase in the number of fibers (Fig. 103, C’). In the embryonic and immature pulp, the cellular elements are predominant, in the mature tooth the fibrous constituents. In a fully developed tooth the cellular elements decrease in number toward the apical region and the fibrous elements become more numerous (Fig. 106).

A microscopic specimen of a mature pulp, stained with hematoxylin eosin, does not present a complete picture of the structure of the pulp, because not all the fibrous elements are stained by means of this method (Fig. 104, A). A great abundance of fibers are revealed by silver impregnation (Fig. 104, B), especially, the so-called Korfl:"s fibers between the odontoblasts. These fibers are the primary elements in forming dentin ground substance (see chapter on Dentin).

Argyrophil Fibers B. Nine months old. 0. Adult.

. Newborn in1a.nt_

6'. Fig. 103.—Age changes of the dental pulp. Cellu cellular substance increases with advancing age.

epithelium Blood vesel P Blood vessel ‘ Blood vessel lax elements decrease, fibrous inter 136

ORAL HISTOLOGY AND EMBRYOLOGY PULP 137

The Korff’s fibers originate from among the pulp cells as thin fibers, thickening at the periphery of the pulp, to form relatively thick bundles which pass between the odontoblasts. They are pre-collagenous, staining black with silver; hence the term argyrophil fibers. The remaining part of the pulp contains a dense irregular network of collagenous fibers.

Dentin-— Odontobiasts — A. . . n, H is Q!" U 3: L 3:" 9: ' - s. .e' _ l "N r: 15‘ H . Dentin ~ V/3; . ‘ c ,_ _ _,_ _ , capillary

Collagenous fibers

Arzyrophu fibers =--‘ “ or Kori!

B.

Fig. 104.-Cellular and fibrous elements in the pulp. .4. Cellular elements stained with hematoxylin and eosin.

gi Fibrous elements stained by silver impregnation. Specimms are from the same too .

The most significant change in the dental pulp during development Odonfioblagtg is that the connective tissue cells adjacent to the enamel epithelium diiferentiate into odontoblasts. Dentin development sets in approximately in the fifth embryonic month and, shortly before this, the odontoblasts begin to differentiate. The development of odontoblasts starts at the highest point in the pulpal horn and progresses apically. T

Odontoblasts are highly differentiated connective tissue cells, columnar in shape, with an oval nucleus (Fig. 105). From each cell a cytoplasmic OR.-\L HISTOLOGY AND EMBRYOLOGY

process extends into a tubule in the dentin matrix. These processes are known as Tomes’, or dentinal, fibers. The ends of the odontoblasts, adjacent to the dentin, are separated from each other by intercellular eondensations, the so-called terminal bars. In a section the terminal bars appear as fine dots or lines. The odontoblasts are connected with each other and with the adjacent cells of the pulp by intercellular bridges. Some odontoblasts are long, others short, the nuclei being irregularly placed.

Odon toblasls

Predentin __.

Dentin

Odontoblastic ___ _ process

, Pulp

/,:\,

Terminal bars ___

Odontoblastic __ , . process

Odontoblasts

at

i.~J.

.

Fig. 105.——Odontobla.sts.

The form and arrangement of the odontoblasts are not uniform throughout the pulp. They are more cylindrical and longer in the crown (Fig. 106, A), and become cuboid in the middle of the root (Fig. 106, B). Close

to the apex of an adult tooth the odontoblasts are flat and spindle-shaped,

and can be recognized as odontoblasts only by their processes entering

the dentin as odontoblastic processes. In areas close to the apical foramen PULP

Odontoblaata

Dentin —

Odontob last!

.’ If ? c-. g

Fig. 106.—Varia.tlon o! odontablasts in different regions of one tooth. A. High columnar odontoblasts in the pulp chamber.

3. Low columnar odontoblasts in the root canal.

0. Flu odontoblasns in the apical region.

139 Defense cells

140 om. HISTOLOGY AND EMBRYOLOGY

the dentin is irregular (Fig. 106, C). This change in the shape of odontoblasts, toward the apical foramen, may be caused by mechanical factors, e.g., movement of the apex when the tooth is in function, or by changes in the blood and lymph stream producing varying pressure at the narrow apical portion of the root} canal.

The odontoblasts are associated with the formation of the dentin matrix (see Chapter on Dentin) -and mediate its nutrition. Histogenetically and biologically they have to be regarded as cells of the dentin. Whether they play a part in the sensitivity of the dentin is still debatable.

".2s<

wig‘,

' * "“‘ “ ' ‘ " Cell-rich zone

Odontoblasts

Predentin

Dentin —-—» - .g ,

Flg. 10'I.—Ce11-tree subodontoblastic zone of Well.

In the crown of the pulp a cell-free layer can be found, just inside the layer of odontoblasts (Fig. 107). This layer is known as the zone of Weil or subodontoblastic layer and it contains nerve fibers. Most unmyelinated nerve fibers are a continuation of the myelinated fibers of the deeper layers and continue to their terminal arborization in the odontoblastic layer. The zone of Weil can be found but rarely in young teeth.

In addition to fibroblasts and odontoblasts there are other cellular elements in the human pulp, usually associated with small blood vessels and PULP 141

Undiflerentlated -

mesenchymal Capillary B. Endothelial cell Capillary _ . ~- _"f"3.Und1flerent1atad

ifilsmcbrmu

""'57-I-Iiatiocyte ii “ Hf" """“J;T ‘“'* 0. . qi Lymphoid wan- —» ~-vi‘ dering cell A M ‘*1? Fibroblast Undifrerentiated — °‘“’m”’ mesenchymal cell , " '7 ' "‘Histiocyte

Fix. 108.-Defense cells in the Pulp. Blood Vessels

142 ORAL msronocr AND EMBRYOLOGY

capillaries. They are important for the defense activity of the tissues, especially in inflammatory reaction.” Several types of cells belong to this group; they are classified partly as blood elements and partly as belonging to the reticuloendothelial system. In the normal pulp these

cells are in a resting state.

One group of these cells is that of the histiocytes or adventitial cells or, according to Maximow’s nomenclaturefil» 1“ the resting wandering cells. These cells are, generally, located along the capillaries. Their cytoplasm has a notched, irregular, branching appearance; the nuclei are dark and oval. They may have diverse forms in the human pulp but, usually, can be easily recognized (Fig. 108). Intravital staining methods have revealed that histiocytes are able to store dyes. It is assumed that they produce antibodies and, consequently, have an important relation to immune reactions. During an inflammatory process the histiocytes withdraw their cytoplasmic branches, assume rounded shape, migrate to the site of inflammation, and develop into macrophages.

Another cell type of the reticulo-endothelial system is described by Maximow as undifferentiated mesenchymal cells (Fig. 108). These are also associated with capillaries, have oval elongated nuclei similar to those of fibroblasts or endothelial cells, and long, faintly visible cytoplasmic bodies. They are in close proximity to the vessel wall. These cells can be differentiated from endothelial cells only by their location outside the vessel wall. According to Maximow, they possess multipotency which means that, under the proper stimulus, they can develop into any type of connective tissue element. In an inflammatory reaction they form macrophages.

A third type of cell which cannot be classified as belonging strictly to the reticulo-endothelial system, but which plays an important part in defense reactions, is the ameboid wandering cell, or lymphoid wandering cell (Fig. 108, 0). These cells are migrating elements which probably originate in the blood stream. Their cytoplasm is sparse and shows fine extensions, pseudopodia, suggesting a migratory character. The dark nucleus fills almost the entire cell and is often kidney-shaped. In chronic inflammatory reactions they migrate to the site of injury and, according to Maximow, change into macrophages. They may develop into plasma cells which are a cell type characteristic of chronic inflammation. However, their function is not as yet fully known.

The blood supply of the pulp is abundant. The blood vessels of the dental pulp enter through the apical foramen. Usually, one artery and one or two veins enter each foramen. The artery, carrying the blood into the pulp, branches out into a rich network of blood vessels, soon after entering the root canal. The veins gather blood from this capillary network and carry it back through the apical foramen into larger vessels (Fig. 109). The arteries are clearly identified by their straight 1=~u1,p 143

course and thicker walls, whereas the thin-walled veins are wider and, frequently, have an outline similar to a row of beads. The capillaries form loops close to the odontoblasts, near the surface of the pulp, and may even reach into the odontoblast layer.

Vein _.. ’.

Artery _ _T_f_,___.

,itA__.--__

Fig. 109.-—-Blood vessels or the pulp. A. La.rger vessels in the center of the pulp.

B. Dense 111 tw rk in the periphery or the pulp. Arteries narrow, with thick walls and ev3pou?:l11'1y1eI:evel2:s wide with thin walls and irregular outline.

The larger vessels in the pulp, especially the arteries, have a typical circular muscular coating (Fig. 110). These muscular elements can be traced to the finer branches. Along the capillaries are found branching Lymph Vessels

144 ORAL HISTOLOGY AND EMBRYOLOGY

cells, the pericytes (R0uget’s cells). It has been claimed that they are modified muscular eleinents.“

Occasionally, it is difiicult to differentiate between pericytes and undifferentiated mesenehymal cells. However, some specimens show both types of cells and, thereby, it is possible to identify them (Fig. 11111). The nuclei of the pericytes can be distinguished as round or slightly oval bodies outside the endothelial wall of the capillary. A very thin cytoplasm can be seen between the nuclei and the outside of the endothelium.

, E ., .

Circular muscle coating

Circular muscle coating '

1 ‘ ' I-Iistlocyte

Fig. 110.—Branching artery in the pulp; circular muscle coating.

The endothelial cells can be recognized in the continuation of the vessel wall. The undiflerentiated mesenchymal cells lie outside the pericytes, and have finger-like projections. If no pericytes are present the undifferentiated mesenchymal cells are in close proximity to the endothelial wall (Fig. 108).

It has been repeatedly stated that lymph vessels are present in the dental pulp. Special methods are required to render them visible; the PULP 145

common histological technique does not reveal them. The presence of

lymph vessels has been demonstrated by the application of dyes into the

pulp1°’ 21' 22 which are carried into the regional lymph nodes. Injection methods have also been tried successfully.” 2’

' The nerve supply of the dental pulp is abundant. Thick nerve bundles mm. enter the apical foramen and pass into the crown portion of the pulp

where they split into numerous fiber groups and, ultimately, into single

fibers and branches (Fig. 112). Usually, the nerve bundles follow the

blood vessels into the root canal; the finer branches can be seen following

the smaller vessels and capillaries.

Undlflerentlated mesenchymal cell

,..,..;...

pay A...

Undifferentiated » mtlalsenchymal

Fig. 111.—Perlcyte.s of capillaries in the pulp. Note the differences in location and nuclear shape between endothellal cells, pez-Icytes and undifferentiated mesenchymal

Most nerve elements which enter the pulp are of the myelinated type; but, there are also unmyelinated elements. These unmyelinated nerve fibers are of the sympathetic nervous system and are the nerves of the blood vessels, regulating their contraction and dilation.

The bundles of myelinated fibers follow closely the arteries, dividing coronally into-smaller and smaller branches. Individual fibers form a 146 ORAL HISTOLOGY AND EMBRYOLOGY

layer beneath the subodontoblastic zone of Wei], the parietal layer. From there the individual fibers pass through the subotlontoblastic zone and, losing their myelin sheath, begin to branch. Their te1'1ni11al arborization occurs in the odontoblastic layer (See chapter on Dentin).

Histlocyte .- .4 far-Af ‘ ‘

Blood vessel v._

Fig. 112.—Nerves in the pulp.

It is a peculiar feature that, whatever stimulus reaches the pulp, it will always elicit only pain sensation. There is no possibility in the pulp to differentiate between heat, cold, touch, pressure, chemicals, and so forth; the result is always pain. The cause of this behavior is the fact PULP 147

that only one type of nerve endings, free nerve endings, are found in the P111P- The free nerve endings are specific for the reception of pain. The nerves do not have the faculty of localizing the stimulus.

_.ié____ _ 2

'4

_~/‘ *

• 1

”=:“""* ‘ "" ‘ True denticle

False denticle

False dentlcle

‘ Difluse calciflcations

"** Dentln

Fig. 113.—Denticles (pulp stones). A. True denticle.

B. False denticle.

0. Diflluse calciflcations. Pulp stones

148 omu. HISTOLOGY AND EMBRYOLOGY

V. REGRESSIVE CHANGES

Certain formations in the dental pulp, such as pulp stones or denticles, are on the borderline of pathologic conditions. Their discussion in this chapter is justified only by their frequent occurrence. Pulp stones are often found in teeth which appear to be quite normal in all other re spects. They have been found not only in functioning teeth but also in embedded teeth.

' '4 '¢.c-1-hp:-nu =1 . E .

'5».

s

i ‘ Free dentlcle

Adherent dentlcle

’ Embedded dentlcle

Fig. 114.—Free, attached, and embedded denticles.

Pulp stones are classified, according to their structure, as true denticles, false denticles, and diffuse calcifications (Fig. 113). True denticles consist of dentin, showing traces of dentinal tubuli and odontoblasts (Fig. 113, A). They are comparatively rare and are usually found close to the apical foramen. A theory has been advanced“ that the development of this type of pulp stones is caused by remnants of Hertwig’s epithelial root sheath, which become enclosed in the pulp, due to some local disturbance during development. These epithelial remnants may inPULP 149

duce cells of the pulp to form true denticles. This explanation is based upon frequent observation of true denticles, close to the apical foramen, and also the frequent presence of epithelial rests in this region. It is an accepted fact that epithelial cells (enamel epithelium) are necessary for the differentiation of odontoblasts and the onset of dentin formation.‘ False clenticles are calcified formations in the pulp Which do not show the structure of true dentin. They consist of concentric layers of calcified

Pulp stone ""' ' *‘ if

Nerve

1?‘ ”"‘ —’ Pulp stone

‘. ,Z'l:*'A‘§

Fig. 115p-Pulp stones in close proximity to a nerve.

tissue (Fig. 113, B). In the center of these concentric calcified structures there are usually remnants of necrotic and calcified cells. Calcification of thrombi in blood vessels (phlebolite) may also be the starting point for false denticles. Once calcification has begun, more layers of calcified tissue are laid down on the surface of the pulp stones, thereby increasing their size continuously. The surrounding pulp tissue may be quite normal (Fig. 113, B); no pathologic changes can be detected in the cells or intercellular Calcification:

Secondary Dentin

fibrous

150 ORAL n1s'ro1.ocY AND nmnmronocr

fibrous matrix. Sometimes, pulp stones of this character fill the pulp chamber almost completely. They increase in number and size with advancing age. Overdoses of vitamin D may cause formation of numerous denticles.‘

Diffuse calcifications (Fig. 113, C‘) are irregular calcific deposits in the pulp tissue, usually following collagenous fiber bundles or blood vessels. Sometimes, they develop into large bodies; at other times they persist as fine spicules. They are amorphous, having no specific structure, and are usually the final outcome of a hyalin degeneration of the pulp tissue. The pulp, in its coronal portion, may be quite normal without any sign of inflammation or other pathologic changes. These diffuse calcifications are, usually, located in the root canal, seldom in the pulp chamber; advancing age favors their development.

Pulp stones are classified, not only according to their structure, but also according to their location in relation to the dentiual wall. Free, attached, and embedded denticles can be distinguished (Fig. 114). The free denticles are entirely surrounded by pulp tissue; attached denticles are partly fused with the dentin; embedded denticles are entirely surrounded by dentin. They are formed free in the pulp, and some become attached or embedded as formation of the dentinal wall progresses.

Pulp stones are frequently found close to nerve bundles, as shown in Fig. 115. Occasionally, this may bring about a disturbance if the pulp stones come close enough to the nerves to exert pressure. This may entail pain in the jaw in which the affected tooth is located, rendering a satisfactory diagnosis difficult. The close proximity of pulp stones to blood vessels may cause atrophy of the pulp if the growing pulp stones exert pressure upon the vessels. It is improbable that the pulsation of the blood in the arteries, close to pulp stones, causes suflicient movement of the stone to irritate nerves and cause pain. Pulp calcifications are more common in older teeth. Diffuse calcium deposits may be found in and around the pulpal vessels especially in the roots of older teeth. Well-outlined calcified bodies are more frequently found in the coronal portion of the pulp. In twenty-nine teeth from individuals between ten and thirty years of age, Hill" found pulp calcifications in 66 per cent; in sixty-two teeth from individuals between thirty and fifty years of age, 80 to 82.5 per cent showed calcification in the pulp, and in thirty-one teeth from individuals over fifty years of age, 90 per cent had pulp calcification.

With advancing age the pulp chamber and the root canals become narrower due to secondary dentin formation. In secondary dentin the dentinal tubuli are sparse and irregular. This is due to the fact that odontoblasts degenerate with advancing age, or are destroyed by some

irritation, whereas the matrix formation persists or even increases (see chapter on Dentin).

It has been pointed out that, with advancing age, the cellular elements decrease 111 number whereas the fibrous components increase in the pulp. PULP 151

In older individuals this shift in tissue elements can be considerable and fibrosis may thus develop in the pulp. Thereby, the vitality of the pulp may be lowered without any consequence to the function of the teeth.

VI. CLINICAL CONSIDERATIONS

For all operative procedures it is important to bear in mind the shape of the pulp chamber, and its extensions into the cusps, the pulpal horns. The wide pulp chamber, in the tooth of a young person, will make a deep cavity preparation hazardous to the pulp, and it should be avoided if possible. In some rare instances the pulpal horns remain projected high into the cusps and this may, in some cases, explain the exposure of a pulp when it is least anticipated” (Fig. 116). Sometimes, a roentgenogram will help to determine the size of a pulp chamber and the extensions of the pulpal horns. Roentgenograms of anterior maxillary teeth often lack detail concerning the exact location of pulp horns and the presence of denticles. Information on this subject can be obtained by allowing the rays to strike the crown at almost right angles and double the exposure. Such a film will not only show greater detail concerning pulp horns and pulp calcification, but also orient the position of the pulp chamber more reliably.

If it becomes necessary to open a pulp chamber for treatment, its size and variation in shape must be taken into consideration. With advancing age the pulp chamber becomes smaller and, due to excessive dentin formation at the roof and floor of the chamber, it is sometimes difficult to locate the root canals. In such cases, it is advisable, when opening the pulp chamber, to advance toward the distal root in a lower molar and toward the lingual in the upper molar; in this region, one is most likely to find the opening of the pulp canal without risk of perforating the floor of the pulp chamber. In the anterior teeth the extreme coronal part of the pulp chamber may be filled with secondary dentin, making it difficult to locate the root canal. Pulp stones lying at the opening of the root canal may cause considerable difficulty when an attempt is made to locate the canals (Fig. 97, B).

The shape of the apical foramen, and its location, may play an important part in the treatment of root canals, especially as regards the root canal filling. When the apical foramen is narrowed by cementum formation it is more readily located, because further progress of the broach will be stopped at the foramen. If the apical opening is at the side of the apex, as shown in Fig. 101, A, not even the roentgenograms will reveal the true length of the root canal, and this may lead to misjudging the length of the canal and the root canal filling.

The problem of accessory canals, in root canal work, plays an important part in making the outcome of the root canal treatment questionable. Side branches of the pulp are rarely seen in the roentgenograms and are usu152 oruu. HISTOLOGY AND EMBRYOLOGY

ally overlooked in the treatment and filling of the root canal. If these accessory canals are infected they may cause a recurrence of inflammation.

There "is another condition in which accessory canals may play an important part, especially if they are located in the bifurcation, or high up toward the crown (Fig. 100, B). In periodontal diseases, e.g., where pocket formation progresses, accessory canals may be exposed and infection of the pulp may follow. This may account for some causes of pulp necrosis in periodontal diseases, not only in molars but also in single-rooted teeth.

Enamel (lost in decals]flcatlon)

Fig. 116.-—Pulp horn reaching far into the cusp of a molar. (0rba,n.")

For a long time it was believed that an exposed pulp meant a lost pulp. The fact that “defense cells’ ’ have been recognized in the pulp has changed this contention.” Extensive experimental work has shown that exposed pulps can be preserved if proper pulp capping or pulp amputation procedures are applied.“ 2° This is especially so in noninfected, accidentally exposed pulps in young individuals. In many instances new dentin was formed at the site of the exposure, forming a dentin barrier or bridge. Thus, the pulp may remain in a healthy and vital condition. Pulp capping of deciduous teeth has been shown to be remarkably successful. PULP 153

References

1. Aprile, E. C. de and Aprile, H.: Topografia de los conductos radiculares, Rev. Odontologia 35: 686, 1947. la. Becks, Hermann: Dangerous Eifects of Vitamin D Overdosage on Dental and Paradental Structures, J. A. D. A. 29: 1947, 1942. Bodecker, C. F.: The Soft Fiber of Tomes, J. Nat. Dent. A. 9: 281, 1922. . Bodeglsrerbgg. 117‘S.),3and Applebaum, E.: Metabolism of the Dentin, Dental Cosmos

1.

Bodecker, C: F., and Lefkowitz, W.: Concerning the “Vitality” of the Calcified Dental Tissues, J. Dent. Research 16: 463, 1937. Boling, L. R.: Blood Sup ly of Dental Pulp, J. Dent. Research 20: 247, 1941. Brunn, A. v.: Die Aus ehnung des Schmelzorganes und seine Bedeutung fiir die Zahnbildung (The Extension of the Enamel Organ and Its Significance in the Formation of Teeth), Anat. Anz. 1: 259, 1886. Formation of Teeth, Anat. Anz. 1: 259, 1886. 7. Cooligge,‘ 1151 Anatomy of Root Apex in Relation to Treatment Problems, . . . . 6: 1456 1929. 8. Ebner, V. v.: Ueber die Entwicklung der leimgebenden Fibrillen im Zahnbein lglgtse Development of Collagenous Fibrlls in Dentin), Anat. Anz. 29: 137, 9. Ebner, V: v.: Histologie der Ziihne (Histology of the Teeth, Schefi’s Handbook of Dentistry), ed.' 4, Vienna, 1922, A. Hoelder. 10. Fish, E. W.: An Experimental Investigation of Enamel, Dentin and the Dental Pulp, London, 1932, John Bale Sons & Danielsson, Ltd. 11. Hess, W., and Zurcher, E.: The Anatomy of the Root Canals, London, 1925, John Bale Sons & Danielsson, Ltd. 12. Hill, T. J.: Pathology of the Dental Pulp, J. A. D. A. 21: 820, 1934. 13. Johnston, H. B., and Orban, B.: Interradicular Pathology as Related to Accessory Root Canals, J. Endodontia 3: 21, 1948. 14. Kronfggif Igefitgl Histology and Comparative Dental Anatomy, Philadelphia, 1 ea e iger. 15. Lehner J., and Plenk H.: Die Ziihne (The Teeth) M6llendorfi’s Handb. der Mikrosk. Anat. vol. 5, pt. 3, p. 449, 1936. 16. Magnus, G.: Ueber den Nachweis der Lymphgefiisse in der Zahn Pulpa §D;n]11on:tr4:(1)t1o1:5 of Lymph Vessels in the Dental Pulp), Deutsche Monatschr. . an. :611922. 17. Maximow, A. A.: Morphology of the Mesenchymal Reactions, Arch. Path. &: Lab. Med. 4: 557, 1927. 18. Maximow, A. A., and Bloom, W.: Textbook of Histology, Philadelphia, W. B. Saunders Co. ed. 4 1942. 19. Meyer, W.: Ist’ das ’Foramen Apicale stationiirl (Is the Apical Foramen Stationary?) Deutsche Monatschr. f. Zahnh. 45: 1016, 1927. 20. Noyes, F. B., and Dewey, K.: Lymphatics of the Dental Region, J. A. M. A. 71: 1179 1918. 21. Noyes, F.’ B.: Review of the Work of Lymphatics of Dental Origin, J. A. D. A. 14: 714 1927. 22. Noyes, F. Bi, and Ladd, R. L.: The Lymphatics of the Dental Region, Dental Cosmos 71: 1041 1929. 22a. Okumura, '11: Anat’om_v of the Root Canals, .T. A. D. A. 14: 632,1927. 23. Orban B.: Contribution to the Histolo of the Dental Pulp J. A. D. A. 16: 9%" 1929 gy ’ o, . 24. Orban, B.: Epithelial Rests in the Teeth, Proc. Am. Assn. of Dental Schools, 5th Annual Meeting Washington, D. C. 1929, p. 121. 25. Orban, B.: Biologic Cohsiderations in Restorative Dentistry, J. A. D. A. 28: 1069 194]. 26. Restarski: J. S.: Preserving Vitality of Pulps Exposed by Caries in Young Children Illinois Dent. J. 9: 2, 1940. 27. Schweizer, Gt: Die Lymphgefiisse des Zahnfleisches und der Ziihne (Lymph Vessels of the Gingiva and Teeth), Arch f. mikr. Anat. 69: 807, 1907; 74: 927 1909. 28. Wasserniann, F.: The Innervation of Teeth, J. A. D. A. 26: 1097, 1939. 29. Zander, H. A.: Reaction of the Pulp to Calcium Hydroxide, J. Dent. Research

13: 373, 1939.

Chapter VI - Cementum

1. DEFINITION

2. PHYSICAL CHARACTERISTICS

3. CHEMICAL COMPOSITION

4. CI‘-MIE‘-NTOGENESIS

5 MORPHOLOGY

6. CEMENTO-ENAMEL JUNCTION 7. CEMI'.NTO~DENTINAL JUNCTION 8. FUNCTION

9. EYPERCEMENTOSIS

10. CLINICAL CONSIDERATIONS

1. DEFINITION

Cementum is the hard dental tissue covering the anatomical roots of the human teeth. It was first microscopically demonstrated in 1835 by two pupils of Purkinje.5 It begins at the cervical portion of the tooth at the cemento-enamel junction, and continues to the apex. Cementum furnishes a medium for the attachment of the fibers that bind the tooth

to the surrounding structures. It can be defined as a specialized, calcified tissue of mesodermal origin, a modified type of bone covering the anatomic

root of the teeth.

2. PHYSICAL CHARACTERISTICS

The hardness of adult or fully formed cementum is less than that of dentin.“ 2‘ It is light yellowish and is easily distinguished from the enamel by its darker hue; it is somewhat lighter in color than dentin. By means of vital staining and other chemical-physical experiments the cell containing cementum has been proved to be permeable.”

3. CHEMICAL COMPOSITION

Adult cementum consists of about 45 to 50 per cent inorganic substances and 50 to 55 per cent organic material and water (see table in chapter on Enamel). The inorganic substances consist mainly of calcium salts. The molecular structure is hydroxyl apatite which, basically, is the same as that of enamel, dentin and bone. The chief constituent of the organic material is collagen.

4. CEMENTOGENESIS

The development of cementum is known as cementogenesis. During enamel formation the crown of the tooth is covered by the enamel epithelium. The basal part of the epithelium (inner and outer layers) is the

First draft submitted by Emmerich Kotanyi. 154 CEMENTUM 155

He1'twig‘s epithelial root sheath which is of particular importance in root development; it forms the mold into which the root dentin is deposited. Therefore, the newly formed dentin, in this region, is covered at first by the epithelium, and is separated by it from the surrounding connective tissue (Fig. 117). Cementum is formed by this connective tissue but it

I‘. x

Epithelial sheath " broken, separated from root

\‘ 5 Epithelial sheath-,-.—‘ . in contact with . .'- ‘dentin

- Epithelial diaphragm

Fig. 117.—-Hertwig’s epithelial root sheath at end of forming root. At the side of the root the sheath is broken up and cementum formation begins. (Gottliel).“)

cannot be deposited on the outer surface of the root dentin as long as the epithelial sheath separates it from the dentin. A contact between connective tissue and tooth is accomplished by invasion of connective tissue through the epithelial layers. By this process the epithelial sheath loses its continuity but persists as a network of epithelial strands which Gementobluts

156 om. HISTOLOGY AND nnnaronocr

lie fairly close to the root surface. The remnants of the epithelial sheath are known as “epithelial rests” of Malassez.“ (See chapter on Periodontal Membrane.) When the separation of the epithelium from the surface of the root dentin has been accomplished, the periodontal connective tissue comes into contact with the root surface and cementum is laid down.

‘x

Enamel epithelium; , it

- Enamel

— Cemento-enamel junction

Remnants at epithelial sheath

L’.

Fig. 118.—Epithelia.I sheath is broken and separated from root surface by connective US$116.

In the first stage of cementum formation two tissue elements can be observed; First, cells of the connective tissue (undiflferentiated mesonchymal cells) are arranged along the outer surface of the dentin (Fig. 118). These change into flat," cuboidal cells and are the cementoblasts. At the same time the second tissue element, pre-collagenous (argyrophil) fibers,

can be seen at right angles to the root surface, and attached to the outer surface of the dentin (Fig. 119). These fibers soon assume a collagenous CEMENTUM 157

1% numa“ .9» ’ Argyrophil H.‘ nbera _ ,

59.; —— Dentin

"V 4’ ”" " Attach an ‘e . 111 .'$w$ :~_ of fibers

fibers

w‘

Fig. 119.—Argy1-ophil fibers of the periodontal membrane. attached to the dentin (silver impregnation).

Couagenous _ __M__ ___,_..,,~:, , WW , _ '- Dentin fibers

• Cementum

M _ _

Fir. 120.—-Cementum ground substance develops from fibers of the periodontal membrane - (silver impregnation). 158 ORAL HISTOLOGY AND EMBRYOLOGY

character and become a. part of the ground substance of the cementum (Fig. 120). This mechanism is similar to that observed in dentinogonesis (see chapter on Dentin).

Definite knowledge of the function of the cementoblasts is incomplete, but it is presumed that they play the same role in cementum formation

Dentln '1. Cementoblastsfr ' >-' ' :7 - ‘—:~=~-= ’ " " "*ex ——-V-n--—-~ W cementum Periodontal ” ’ '—,membrane ,.__—_—————~— -r—— Cementold ' tissue Cementoblast ' ‘ ’” "'-‘"“:““‘ ' "f"

Fig. 121.—Cementoid tissue on the surfaceflgf calcified cementum. Cementoblasts between ers.

as the osteoblasts play in bone formation. In the first phase of development the cementoblasts, apparently by enzymatic action, elaborate a homogenous material, the cementoid tissue. In the second phase, calcification takes place by the deposit of calcium salts in the cementing substance of the intercellular substance. Simultaneously the organic component changes radically, becoming soluble by proteolytic enzymes.“ GEMENTUM 159

During the continuous apposition of cementum a thin layer of non- °¢m°“"°i° calcified matrix, termed cementoid tissue, which is analogous to osteoid tissue and predentin, is seen on the surface of the cementum (Fig. 121). This cementoid tissue is lined by cementoblasts. Connective tissue fibers from the periodontal membrane pass between the cementoblasts into the cementum. These fibers are embedded in the cementum and serve as an attachment for the tooth to the surrounding bone. Their embedded portions are known as Sharpey’s fibers. These were accurately described in 18872 as an essential part of the suspensory apparatus.

-—» —— -1

3:355 25' 7 -f, if In ' .4‘ J» gag‘!

at . ' ‘r 7 i

Periodontal membrane

T-»"'"‘, .A.ceuu1a.r 3:?“ cementum ax» .

Alveolar bone

Fig. 122.——Increment2.l lines in the accellular cementum.

5. MORPHOLOGY

From a morphologic standpoint two kinds of cementum can be differentiated: (a) acellular, and (b) cellular cementum. Functionally, however there is no difference between the two. Acellular cementum

160 om. HISTOLOGY AND EMBRYOLOGY

Acellular cementum may cover the root dentin from the cemento-enamel junction to the apex, but is often missing on the apical third of the root. Here the cementum may be entirely of the cellular type. The aeellular cementum is thinnest at the cemento-enamel junction (20 to 50 microns), and thickest toward the apex (150 to 200 microns). The apical foramen is surrounded by cementum. Sometimes the cementum extends to the inner wall of the dentin for a short distance, forming a lining of the root canal.

Both acellular and cellular cementum are separated by incremental lines‘ into layers that indicate periodic formation (Fig. 122). Acellular

" "— " ‘“. ‘ .3‘: ' j

_. Principal fibers of periodontal membrane

Dentin .

Cementum _

F1E- 123.——'1‘he principal fibers ot the periodontal membrane continue into the surface layer of the cementum.

cementum consists of the calcified matrix and the embedded Sharpey’s fibers. The matrix is composed of two elements: the collagenous fibrils and the calcified cementing substance. The fibrils in the matrix are perpendicular to the embedded Sharpey’s fibers and parallel to the cementum surface. The fibrils are less numerous than in lamellated bone and about as numerous as those of bundle bone. Due to identical

‘The term incremental lines was introduced by Salter in 1874 as including the stripes

of Remus In the enamel, the contour lines at Owen in the dentin and the stratification In the cementum. U1‘JJ.V.l.EJN'l'UL1 .10.].

optical qualities, i.e., the same refractive index, the fibrils and interfibrillar cementing substance can be made visible only by special staining methods. Fibrils and Sharpey’s fibers are easily distinguished by means of silver impregnation. In dried ground sections Sha.rpey’s fibers are disintegrated and the spaces and channels which they formerly occupied are filled with air; the areas thereby become discernible as dark lines.

 ‘ 'r.-,z Dentin

. ‘

Periodontal ‘

“L I Acellular membrane —

cementum

Cementoid

tissue ’——«g Cellular

1 cementum

F--“fl Acellular

cementum

.e

Alveolar bone A

Fig. 124.——Cellula.r cementum on the surface or acellular cementum, and again cov ercd by acellular cementum (incremental lines). The _la.cunae _of the cellular cementum are empty, indicating that this part of the cementum is necrotic.

While the cementum remains relatively thin, Sharpey’s fibers can be observed crossing the entire thickness of the cementum. With further apposition of cementum a larger part of the fibers is incorporated in the cementum. At the same time, the portion of the fibers lying in the deeper layers of the cementum becomes obscure. The attachment proper is probably confined to the most superficial or recently formed layers of 162 ORAL HISTOLOGY AND EMBRYOLOGY

Periodontal Dentin membrane ‘ ‘ Cementoid __ __ _____

tissue _— — cellular

cementum

Fig. 125.—Cel1u1'ar cementum forming the entire thickness of cementum. (Orban.W)

F_? - -—-—-——-v---—-———-—J..-g‘

Dentin

Apex formed » ~.—_.—— I-~~———~———— by cemen-. tum

2‘-T ‘

373- 136-——Cementum tyiickest at apex contributing to the length or the root, cnmrmrun 163

cementum (Fig. 123). This would seem to indicate that the thickness of the cementum does not enhance functional efficiency by increasing the strength of attachment of the individual fibers. Continuous apposition of cementum is essential for the continuous eruptive movements of the functioning tooth and the continuous reorganization of the periodontal membrane which is necessitated by these movements. The surface of the cementum is vital Whereas the inner layers become necrotic as recognized by empty lacuni in the cellular cementum (Fig. 124) .

The location of acellular and cellular cementum is not definite. Layers of acellular and cellular cementum may alternate in almost any arrangement. The acellular cementum, which is normally laid down on the surface of the dentin, may occasionally be found on the surface of cellular cementum (Fig. 124). Cellular cementum is usually formed on the sur

Fig. 127.—Cementum lacuna and canaliculi filled with air (ground section).

face of acellular cementum (Fig. 124), but it may comprise the entire thickness of the apical cementum (Fig. 125). It is always thickest around the apex and, in this manner, contributes to the lengthening of the root (Fig. 126).

The cells in cellular cementum (cementocytes) are similar to osteocytes. They lie in spaces designated as lacunae. Frequently, the cell body has the shape of a plum stone, with numerous long processes radiating from the cell body. These processes may branch, and frequently anastomose with those of a neighboring cell. Most of the processes are directed toward the periodontal suflface of the cementum, differing in this respect from the evenly distributed processes of the bone cells.

Cellular cementum 164 ORAL HISTOLOGY AND EMBRYOLOGY

Some canaliculi, containing processes of the cementocytes, have been said to anastomose with peripheral branches of the dentinal tubulifi» 9" The cells are irregularly distributed throughout the thickness of the cellular cementum. The cavities can be best observed, however, in ground sections of dried teeth, where they appear as dark spider-like figures (Fig. 127). The dark appearance is due to the fact that the spaces are filled with air; these spaces also can easily be filled with dyes.

Enamel I Enamel

Enamel ,_,___._-_.__, , ‘ Enamel epithelium epithelium . ff‘ ‘EC: , Z t .,l u

"’ I  - ‘- ‘ ‘="'::—:-—- cementum over_ . _ lapping enamel

Cemento-enamel «— . ' 7 ~ ‘ .i junction ‘ Cementum—— -

A. B.

Fig. 128.-—Cemento—enamel junction. A. cementum and enamel meet in a. sharp line. B. cementum overlaps enamel.

6. CEMENTO-ENAMEL JUNCTION

The relation between cementum and enamel at the cervical region of the teeth is variable.“ In about 30 per cent of the examined teeth the cementum meets the cervical end of the enamel in a sharp line (Fig. 128, A). Here, the cementum, as Well as the enamel, tapers into a knife-edge. In other teeth, about 60 per cent, the cementum overlaps the cervical end of the enamel for a short distance (Fig. 128, B). Developmentally, this CEMENTUM 165

may occur only when the enamel epithelium, which normally covers the entire enamel, degenerates in its cervical end, permitting the connective tissue, which is responsible for the deposition of cementum, to come in contact With the enamel surface.

Enamel

i . Enamel

epithelium End of — enamel Enamel epithelium Q7‘ Cemente enamel - junction ‘ ‘; Cementum epithelium Cementum

Fig. 129.—Variations at the cemento-enamel junction. 4. Enamel epithelium attached to dentin surface preventing cementum formation.

1 BhEnamel epithelium breaking continuity of cementum near the cemento-enamel unc on.

In about 10 per cent of all teeth various aberrations of the cementeenamel junction may be observed. Occasionally, the enamel epithelium which covers the cervical part of the root does not separate from the dentin surface at the proper time.‘ In other words, it remains attached to the dentin of the root for variable distances (Fig. 129, A), and prevents the formation of cementum. In such cases there is no cemento-enamel junction, but a zone of root dentin is devoid of cementum and covered by 166 ORAL HISTOLOGY AND EMBRYOLOGY

enamel epithelium. In other instances cementum is formed at the cemento-enamel junction for a short distance only and, following it apically, Her-twig’s epithelial root sheath remains in contact with the dentin in a limited area (Fig. 129, B). Enamel spurs, pearls or drops 1nay be formed

by such epithelium.“

7. CEMEN TO—DENTIN AL J UN GTION

The surface of the dentin upon which the cementum is deposited is normally smooth in permanent teeth. The eemento-dentinal junction,

- Dentin

Periodontal membrane ,_ 7

Intermediate cementum layer

-I--—» -- - Acellular cementum

Fig. 130.—Intermediate layer of cementum.

in deciduous teeth, however, is sometimes scalloped. The attachment of

the cementum to the dentin, in either case, is quite firm although the nature of this attachment has not been fully investigated.

Sometimes the dentin is separated from the cementum by an intermediate layer, known as the intermediate cementum layer, which does not exhibit the characteristic features of either dentin or cementum (Fig. 130). This layer contains large and irregular cells which can be regarded CEMENTUM 167

as embedded connective tissue cells. The development of this layer may be due to localized, premature disintegration of 1'-lertwig ’s epithelial sheath after its cells have induced the diflerentiation of odontoblasts, but before the production of dentinal intercellular substance. It is found mostly in the apical two-thirds of the root. Sometimes it is a continuous layer; sometimes it is found only in isolated areas.“

8. FUNCTION

The functions of cementum are, first, to anchor the tooth to the bony socket by attachment of fibers; second, to compensate by its growth for loss of tooth substance due to occlusal wear; third, to enable, by its continuous growth, the continuous vertical eruption and mesial drift of the teeth; and fourth, to make possible the continuous rearrangement of the principal fibers of the periodontal membrane.

The attachment of the fibers of the periodontal connective tissue to the surface of the tooth is the medium by which functional connection between tooth and surrounding tissues is established. Due to physiological movements of the functioning tooth, fibers have to be replaced continually. I11 order to maintain a functional relationship new cementum has to be deposited continuously on the surface of the old cementum.‘ By this continued formation of cementum new fibers of the periodontal membrane are attached to the surface of the root, and loosened or degenerated Sharpey’s fibers are thus continuously replaced. By this mechanism an adequate attachment of the tooth to the supporting tissues is maintained. The morphologic evidence of the continuous formation of cementum is shown by the presence of cementoblasts and a layer of cementoid tissue on the surface of the cementum. Cementoid tissue may be found on acellular (Figs. 121, 122, 124), as well as on cellular (Fig. 125) cementum.

The continuous deposition of cementum is of great biologic importance.“ 3' 13 In contrast to the ever alternating resorption and new formation of bone, cementum is not resorbed under normal conditions. If a layer ages or, functionally speaking, loses its vitality, the periodontal connective tissue and cementoblasts must produce a new layer of cementum on the surface to keep the attachment apparatus intact. In bone the loss of vitality can be recognized by the fact that the bone cells degenerate and the bone lacunae are empty. Lowered vitality in acellular cementum cannot be so readily ascertained but, in cellular cementum, the cells in the deepest layers may degenerate and the lacunae may be empty (Fig. 124). This indicates necrosis of the cells. On the surface, the lacunae contain normal cementocytes. The nuclei of degenerating cells in the deeper layers are pyknotic and the cells are shrunken: near the surface the cells fill the entire space of the cementum lacunae (Fig. 125) and the nuclei stain dark.“ 3 168 ORAL HISTOLOGY AND EMBRYOLOGY

9. HYPERGEIVLENTOSIS

Hypercementosis designates an abnormal thickening of the cementum. It may be difiuse or circumscribed, i.e., it may affect all teeth of the dentition, or it may be confined to a single tooth. It may even affect only certain parts of one tooth. If the overgrowth improves the functional qualities of the cementum, it is termed a cementum hypertrophy; if overgrowth occurs in nonfunctional teeth or if it is not correlated with increased function, it is termed hyperplasia.

Hypertrophic
cementum

‘i

5 ‘C Alveolar ‘bone .

Periodontal. _ _.. -.. N 73- i 1" membrane

Dentin

3»-:, 1,, ‘S1,.

1

_,,‘ I-Iypertrophic

cementum

Fig. 131.——Pronglike excementoses.

In localized hypertrophy a spur or pronglike extension of cementum may be observed (Fig. 131). This condition is frequently found in teeth which are exposed to great stress. The pronglike extensions of cementum provide a larger surface area for the attaching fibers, thus securing a firmer anchorage of the tooth to the surrounding alveolar bone.’

Localized hyperplasia of cementum may sometimes be observed in areas where enamel drops have developed on the dentin. The hyperplastic cementum, covering the enamel drops (Fig. 132), is occasionally irregular CEMENTUM 169

and sometimes contains round bodies which may be calcified epithelial rests. The same type of embedded calcified round bodies are frequently found in localized areas of hyperplastic cementum (Fig. 133). Such knoblike projections are designated as excementosis. They, too, develop around disintegrated, degenerated epithelial rests.‘

‘V 5%.; in '9. 3% 1-3,

--1;

Hyper-plastic cementum _: ~ Denun

—-—-- '- Enamel drop

Hyperplastic cementum

as

Fig. 132.—Irreg'ula.r hyperplasia or cementum on the surface or an enamel drop.

Extensive hyperplasia of the cementum of a tooth is found, occasionally, in connection with chronic periapical inflammation. Here the hyperplasia is circumscribed and surrounds the root like a cuff.

A thickening of the cementum is often observed on teeth which are not in function. The hyperplasia may extend around the entire root of the nonfunctioning teeth or may be localized in small areas (see chapter on Periodontal Membrane). Hyperplasia of cementum in nonfunctioning teeth is characterized by the absence of Sharpey’s fibers. 170 ORAL HISTOLOGY AND EMBRYOLOGY

Excementosis '

cementum

Excementosis

Alveolar bone

‘ ~«__... . . __.

Fig. 133.~—Excementoses in bifurcation of a. molar. (Gottliebfl) I71

CEMENT Ul\I

Remnants of fractured cementum Hype!-plastic cementum

._ Hyperplastic cementum

X e n. A

Fig. 134..—E:xtens1ve spikelike hyperplasia of cementum172 omu. HISTOLOGY AND EMBRYOLOGY

The cementum is thicker around the apex of all teeth and in the bifurcation of multirooted teeth than on other areas of the root. This thickening can be observed in embedded, as well as newly erupted, teeth.”

In some cases an irregular overgrowth of cementum can be found with spikelike extensions and calcification of Sharpey’s fibers, accompanied by numerous cementicles. This type of cementum hyperplasia can, occasionally, be observed on many teeth of the same dentition and is, at least in some cases, the sequelae of injuries to the cementum (Fig. 134).

10. CLINICAL CONSIDERATIONS

The fact that cementum appears to be more resistant to resorption than bone renders orthodontic treatment possible. When a tooth is moved by means of an orthodontic appliance, bone is resorbed on the side of pressure new bone is formed on the side of tension. On the side toward which the tooth is moved pressure is equal on the surfaces of bone and cementum. Resorption of bone, as well as of cementum, may be anticipated. However, in careful orthodontic treatment cementum resorption, if it occurs, is usually localized and shallow. Moreover, it is readily repaired if the intensity of pressure is reduced and the surrounding connective tissue remains intact. If resorption is extensive it may indicate a. systemic disorder, possibly of the endocrine system.‘

Excessive lateral stress may compress the periodontal connective tissue between bone and cementum and cause bleeding, thrombosis and necrosis. After resorption of the damaged tissues, accompanied by bone resorption, repair may take place.‘~ 9~ “’~ 23

It has been the aim of some investigators to determine why resorption takes place in some cases and not in others when external conditions seem to be identical. The reasons are as yet unknown. The potentiality to form new cementum does not seem to be equal in all individuals; in some, cementum forms readily; in others it does not. The latter are those cases which react unfavorably to trauma or any kind of irritation. These are the cases that develop periodontal diseases easily. The dilference in cementum formation may be explained by constitutional factors. Cementum resorption without obvious cause is called idiopathic.

Severe resorption of cementum may be followed by resorption of the dentin. After resorption has ceased the damage is usually repaired, either by formation of acellular (Fig. 135, A) or cellular (Fig. 135, B) cementum, or by alternate formation of both (Fig. 135, 0). In most cases of repair there is a tendency to re-establish the former outline of the root surface. However, if only a thin layer of cementum is deposited on the surface of a deep resorption, the root outline is not reconstructed and a baylike recess remains. In such areas sometimes the periodontal space is GEMENTUM 173

restored to its normal width by formation of new bone, so that a proper functional relationship will result. The outline of the alveolar bone, in these cases, follows that of the root surface (Fig. 136). In contrast to anatomical repair, this change is called functional repair.“

I T 4»:

JCT ' X‘

‘f5.."-‘4K

»:('si

Fig. 135.—Repair of resorbed cementum.

4. Repair by acellular cementum (a:).

B. Repair by cellular cementum (2).

0. Repair flrst by cellular (ac) and later by acellular (wz) cementum. D = Dentin; I1’. = line or resorption; P = periodontal membrane.

If teeth are subjected to acute trauma, such as a blow, smaller or larger fragments of cementum may be severed from the dentin. The tear occurs frequently at the cemento-dentinal junction, but may also be in the cementum or dentin. Transverse fractures of the root may heal by formation of new cementum uniting the fragments.

Frequently, hyperplasia of cementum is secondary to periapical inflammation or extensive occlusal stress. The fact is’ of practical significance 174 ORAL HISTOLOGY AND EMBRYOLOGY

in so far as the extraction of such teeth necessitates the removal of bone. This also applies to extensive excementoses, as shown in Fig. 133. These can anchor the tooth so tightly to the socket that the jaw or parts of it may be fractured in an attempt to extract the tooth. These facts indicate the necessity of taking roentgenograms before an extraction. Small fragments of roots, left in the jaw after extraction of vital teeth, may be surrounded by cementum, and remain in the jaw without causing

any disturbance.

" 5,

,.--' Repaired

'_;é,'_‘.:__i_uW' 1%“, resorption

---

.-I-:a..;.sa£g

. A .- New perio- dontal membrane

Perio(11:)nta.1._:. \ ‘ mem a. . ‘ ~' " r ne_rh\g,"",3_.'

Fi8- 136.—-Functional repair of cementum resorption by bone apposition. Normal width of periodontal membrane re-established.

If the cementum does not cover the cervical part of the root, recession of the gingiva will expose the highly sensitive dentin in the cervical area. When calculus is removed it is frequently impossible to avoid the removal of the thin cementum covering the cervical region of the exposed root. As the individual gets older, more cementum is gradually exposed and subject to the abrasive action of some dentifrices. Since the ceCEMENTUM 175

inentuin is the softest of the hard dental tissues, a considerable amount of cementum may be removed by these mechanical means.” The denuded dentin is then highly sensitive to thermal, chemical or mechani cal stimuli. The hypersensitivity can often be relieved with astringent chemicals which coagulate the protoplasmic odontoblastic processes.

References

. Becks, H.: Systemic Background of Paradentitis, J. A. D. A. 28: 1447, 1941.

. Black, G. V.: A Study of Histological Characters of the Periosteum and Peridental Membrane, Dental Review 1886-1887; and W. T. Keener 00., Chicago, 1887.

Box, H. K.: The Dentinal Cemental Junction (Bull. No. 3), Canad. Dent. Res. Found., May, 1922.

Coolidge, E. D.: Traumatic and Functional Injuries Occurring in the Supporting Tissues of Human Teeth, J. A. D. A. 25: 343, 1938.

Denton, G. H.: The Discovery of Cementum, J. Dent. Research 18: 239, 1939.

Gottlieb, B.: Zementexostosen, Schnielztropfen und Epithelnester (Cementexostosis, Enamel Drops and Epithelial Rests), Oesterr. Ztschr. f. Stomatol. 19: 515 1921.

. Gott1ieb’,B.: Tissue Changes in Pyorrhea, J. A. D. A. 14: 2173,1927.

. Gottlieb, B.: Biology of the Cementum, J. Periodont. 13: 13, 1942.

Gottlieb, B., and Orban, B.: Die Veriinderungen der Gewbe bei iibermiissiger Beanspruchung der Ziihne (Experimental Traumatic Occlusion), Leipzig, 1931.

10. Gottlieb, B., and Orban, B.: Biology and Pathology of the Tooth (Translated

by M. Diamond), New York, 1938, The Macmillan Co. 11. Kitchin, P. G.: ’l‘he Prevalence of Tooth Root Exposure, J. Dent. Research 20: 565 1941.

12. Kitchin,,P. 0., and Robinson, H. B. G.: The Abrasiveness of Dentifrices as Measured on the Cervical Areas of Extracted Teeth, J. Dent. Research 27: 195 19-18.

13. Kronfeld, R.: Die Zementhyperplasien an nicht funktionierenden Ziihnen (Cementum Hyperplasia on Nonfunctioning Teeth), Ztschr. f. Stomatol. 25: 1218 1927. 14. Kronfeld: R.: The Biology of Cementum, J. A. D. A. 25: 1451, 1938. 15. Malassez, M. L.: Sur le r6le des débris epitheliaux paradentaires (The Epithelial Rests Around the Root of the Teeth), Arch. de Physiol. 5: 379, 1885. Oppenheim, A.: Human Tissue Response to Orthodontic Intervention, Am. J. Orthodont. & Oral Surg. 28: 263, 1942. 17. Orban, B.: Resorption and Repair on the Surface of the Root, J. A. D. A. 15: 1768 1928.

18. Orban, B.,: Dental Histology and Embryology, Philadelphia, 1929, P. Blakiston’s Son & Co.

19. Sicher, H., and Weinmann, J. P.: Bone Growth and Physiologic Tooth Movement, Am. J. Orthodo_n_t.. Kr Oral _Surg. 30: 109, 1944.

20. Skillen, W. G.: Permeability: A Tissue_ Characteristic, _J. A. D. A. 9: 187, 1922.

21. Sorrin, S., and Miller, S. G.: The Practice of Pedodontia, New York, 1928, The Macmillan Co. _

22. Stones, H. H.: The Permeability of Cementum, Brit. D. J. 56: 273, 1934.

23. Stuteville, O. H.: Injuries Caused by Orthodontic Forces, Am. J. Oi-thpdont. 85 Oral Surg. 24: 103, 1938. _ _

24. Tainter, M. L., and Epstein, S.: A Standard Procedure for Determining Abrasion, J. Am. Coll. Dentists 9: 353, 1942.

25. Thomas, N. G., and Skillen, W. G.: Staining the Granular Layer, Dental Cosmos

26

[Old

?°°~1 9”?‘ 2"‘ 9°

IP’

62: 725, 1920. . Weinmann, J. P., and Sicher, H.: Bone and Bones. Fundamentals of Bone

Biology, St. Louis, 1947, The C. V. Mosby Co. CHAPTER VII

PERIODONTAL MEMBRANE

D1‘-I'INITION

FUNCTION

DEVELOPMENT STRUCTURAL ELELIENTS PHYSIOLOG-I0 CHANGES CLINICAL CONSIDERATIONS

9’S"'.“9°!°!"

1. DEFINITION

The periodontal membrane is the connective tissue which surrounds the root of the tooth and attaches it to the bony alveolus; it is continuous with the connective tissue of the gingivae. Various terms have been given to this tissue: peridental membrane; pericementum; dental periosteum; and alveolodental membrane. The variety of terms may be explained by the difficulty of classifying this tissue under any anatomic group. The term periodontal is derived from the Greek pert meaning around, and odous meaning tooth, thus signifying the relationship of the tissue to the tooth. This tissue is called a membrane though it does not resemble other fibrous membranes, like fasciae, capsules of organs, perichondrium, and periosteum. It has some structural and functional similarities to these tissues, but is different in that it not only serves as a pericementum for the tooth, a periosteum for the alveolar bone, but mainly as the suspensory ligament for the tooth. Therefore, the term periodontal ligament would be most appropriate.

2. FUNCTION

The functions of the periodontal membrane are formative, supportive, sensory and nutritive. The formative function is fulfilled by the cementoblasts and osteoblasts which are essential in building cementum and bone, and by the fibroblasts forming the fibers of the membrane. The supportive function is that of maintaining the relation of the tooth to the surrounding hard and soft tissues. This is achieved by connective tissue fibers which comprise the bulk of the membrane. Functions which are sensory and nutritive to the cementum and alveolar bone are carried out by the nerves and blood vessels.

3. DEVELOPMENT

The periodontal membrane is derived from the follicle, or sac which envelops the developing tooth germ. Around the tooth germ three zones can be seen: an outer zone containing fibers related to the bone; an inner zone of fibers adjacent to the tooth; and an intermediate zone of un First dratt submitted by Helmuth A. Zander. 176 rmuonommn MEMBRANE 177

orientated fibers between the other two (Fig. 137). During the formation of cementum, fibers of the inner zone are attached to the surface of the root. As the tooth moves toward the oral cavity, gradually a functional orientation of the fibers takes place.“ Instead of loose and irregularly arranged fibers, fiber bundles extend fi'om the bone to the tooth. When the tooth has reached the plane of occlusion, and the root is fully formed,

- - Dentin

- —— cementum

Bone fibers

Cemental fibers

Bone

Fig. 137.—Three zones in the periodontal membrane of a developing tooth.

this functional orientation is complete. However, due to changes in functional stresses, some changes in the structural arrangement of the periodontal membrane occur throughout life.

4. STRUCTURAL ELEMENTS

The main tissue elements in the periodontal membrane are the principal fibers, all of which are attached to the cementum?’ 3 The fiber bundles extend from the cementum to the alveolar wall, or over the alveolar wall to the cementum of the adjacent tooth, or into the gingival tissue. The principal fibers of the periodontal membrane are white collagenous connective tissue fibers and cannot be lengthened. There are no elastic fibers in the periodontal membrane. The apparent elasticity of the periodontal membrane is due to the arrangement of the principal fiber bundles. They follow a wavy course from bone to cementum, thereby allowing slight movement 178 ORAL msvronomz AND EMBRYOLOGY

of the tooth upon stress. Near the bone the fibers seem to form larger bundles before their insertion into it. Although the bundles run directly from bone to cementum, it is most probable that the single fibers do not all span the entire distance. The bundles are “spliced" together from shorter fibers and held together by a cementing substance. The principal fibers are so arranged that they can be divided into the following groups:

Gingiva.

Cementeenamel junction '_

155

«j.

E ‘L y‘, ‘\

Alveolar crest

Fig. 138.——Gingival fibers of the periodontal membrane pass from the cementum into ' the gingiva.

The fibers of the gingival group (Fig. 138) attach the gingiva to the cementum. The fiber bundles pass outward from the cementum into the free and attached gingiva. Usually they break up into a meshwork of smaller bundles and individual fibers, interlacing terminally with the fibrous tissue of the gingiva.

The fibers of the transseptal group (Fig. 139) connect adjacent teeth. The fiber bundles run mesially and distally from the cementum of one tooth, over the crest of the alveolus, to the cementum of the neighboring

tooth. The fibers of the alveolar group (Fig. 140) attach the tooth to the bone of the alveolus; they are divided into five groups: (1) Alveolar crest PERIODONTAL MEMBRANE 179

group: the fiber bundles of this group radiate from the crest of the alveolar process, and attach themselves to the cervical part of the cementum. (2) Horizontal group: these fibers run at right angles to the long axis of the tooth, directly to the bone. (3) Oblique group: the fibers run obliquely; arising from the bone, they are attached in the cementum somewhat apically from their attachment to the bone. These fibers are ‘most numerous and constitute the main support of the tooth against occlusal stress. (4) Apical group: the fibers are irregularly arranged and radiate from the apical region of the root to the surrounding bone (Fig. 1-11). (5) I ntermdicular group: From the crest of the interradicular septum fibers extend to the bifurcation of multiradicular teeth.

Enamel cuticle

Enamel cuticle Gingival papilla

Enamel

Enamel Gingival fibers

Cemento-enamel

Dentin junction

Cemento-enamel junction

cementum _

Fig 139.——Transseptal fibers of the periodontal membrane connect adjacent teeth.

The arrangement of the fibers in the different groups is Well adapted to fulfill the functions of the periodontal membrane. No matter from which direction a force is applied to the tooth, it is counteracted by some or all of the fiber groups. The principal fibers, as a whole, may be regarded as a ligament, alveolodental ligament, by which the tooth is attached to the alveolar bone. Its function is, primarily, to transform pressure exerted upon the tooth into traction on cementum and bone." The fibers 180 omu. I-IISTOLOGY AND EMBRYOLOGY

Enamel - Gingiva

Cemento-enamel junction

Alveolar crest fibers

‘ Alveolar crest

Horizontal fibers?--: , T"

‘ Bundle bone

Lamellated bone

Oblique fibers

IP12. 140.——AJveo1a.r fibers or the periodontal membrane. PERIODONTAL MEMBRANE 181

are arranged in response to functional stimuli. The structure of the periodontal membrane changes continuously to meet the requirements of the continuously moving tooth.°» 2°

Most cells of the periodontal membrane are typical fibroblasts. They are long, slender, stellate connective tissue cells whose nuclei are large and oval in shape. They lie at the surface of the fiber bundles and are, probably, active in the formation and maintenance of the principal fibers.

V.‘ 'r.‘~ ~“I “_—§‘ . ' Periodontal membrane

Fig. 141.—Apica1 fibers of the periodontal membrane.

( Orban.“ )

Bone is in a constant state of transition. As elsewhere in the body, the bone of the alveolus is constantly locally resorbed and rebuilt. Resorption of bone is brought about by the osteoclasts; formation of new bone is initiated by the activity of the osteoblasts.

Where bone formation is in progress osteoblasts are found along the surface of the wall of the bony socket, the periodontal membrane fibers passing between them. These cells are, usually, irregularly cuboid in shape, with large single nuclei containing large nucleoli and fine chromatin particles. The fibers of the periodontal membrane are secured to the

Fibroblasts

Osteoblasts and Osteo182 ORAL HISTOLOGY AND EMBRYOLOGY

bone by the formation of new bone around the ends of the fibers. Therefore, osteoblasts seem to be necessary for the attachment and reattachment

of the fibers to the alveolar bone. Osteoclasts are mostly multinucleated, and are believed to originate from undifferentiated mesenchymal cells in the periodontal membrane; they are found only during the process of active bone resorption. Presumably, the cytoplasm of the osteoclasts produces a substance which dissolves the organic components of bone, while its mineral

Epithelial ——- ———— Test —~"-——~- —"'---*-" Principal fibers

--‘-‘--2 '* Bundle bone

vessels

Cementum - I V l , ‘ ,‘ § , . - ' “ I p . Blood

i i Interstitial tissue

- —:~- - Principal i fibers

I

-. — Bundle bone

.— -W

_. .r M .

Fig. 142.—Interstitia.l spaces in the periodontal membrane consist of loose connective tissue and carry blood vessels and nerves. (0rban.=°)

contents are liberated and either removed in the tissue fluid or ingested by macrophages. Wherever their cytoplasm lies in contact with bone, hollows or grooves called “Howship’s lacunae,” or resorption lacunae, are formed. When bone resorption ceases the osteoclasts disappear. These cells are also active when resorption of the roots of teeth occurs (see chapters on Bone and Shedding). PERIODONTAL Il1EMBR.-\NE 183

Cementoblasts are connective tissue cells found on the surface of °°me’1*°b135t9 cementum betvveen the fibers. They are large cuboidal cells with spheroid or ovoid nuclei, which are active in the formation of cementum (see chapter on Cementum). The cells have irregular, fingerlike projections which fit around the fibers as they extend from the cementum.

The blood vessels, lymphatics, and nerves of the periodontal membrane Interstitial are contained in spaces between the principal fiber bundles (Fig. 142). mm‘ They are surrounded by loose connective tissue (interstitial tissue) in which fibroblasts and some histiocytes, undifferentiated niesenchymal cells and lymphocytes are found.

Blood vessels

- Dentin

- -~ —— Blood vessels

‘ — ~~ Cementum

Periodontal membrane

7 —— Alveolar bone

Blood vessels

Fig. 143.—Blood vessels enter the periodontal membrane through openings in the alveolar bone. (Orban.=‘)

The blood supply of the periodontal membrane is derived from three Blood Vessels sources: (1) blood vessels enter the periapical area together with the blood vessels for the pulp; (2) vessels branching from the inter-alveolar arteries pass into the membrane through openings in the wall of the alveolus (Fig. 143); they are the main source of supply; and (3) near the Lymphatic:

NEWS!

184 om. msronoey AND nmmzvonoor

gingivae, the vessels of the periodontal membrane anastomose with vessels passing over the alveolar crest from the gingival tissue. The capillaries form a rich network in the periodontal membrane, intertwining between the fibers.”

A network of lymphatic vessels, following the path of the blood vessels, provides the lymph drainage of the periodontal membrane. The flow is from the membrane toward and into the adjacent alveolar bone, continuing to the lymph nodes.“ 23

Epithelial rests- -— -»

" "\-s-rt

cementum I: , _.. Alveolar bone

-. at l o r

Periodontal mem- '

.. __ J1 . brane “ Q‘, ‘.17 ‘l ‘-7 ' '

Epithelial rests _

Asa:

Fig. 144.—-—Epithe!ta1 rests in the periodontal membrane.

Generally, the nerves of the periodontal membrane follow the path of the blood vessels, both from the periapical area and from the interdental and interradicular arteries through the alveolar wall. A rich plexus is formed in the periodontal membrane. Three types of nerve endings are found: one terminating in a knob-like swelling; another, forming loops or PERIODONTAL MEMBRANE 185

rings around bundles of the principal fibers; lastly, free endings of fibers branching from the main axon. These terminal branches are free of myelin sheaths. Most of the nerve endings are receptors for proprioceptive stimuli (deep sensibility). The slightest touch at the surface of the tooth is transmitted to the nerve endings through the medium of the periodontal membrane. All sense of localization is through the periodontal membrane. The sense of touch is not impaired by removal of the apical parts of the membrane, as in root resection, nor by removal of its gingival portion (gingivectomy). As elsewhere in the body, fibers from the sympathetic system supply the blood vessels of the periodontal membrane." 13

Cementnm (tangential ‘ section) ‘ '

Network of 9"" epithelial '. rests

Network of ‘ epithelial } rests -f‘

. .—N tw k t ithelial rests in the periodontal membrane. (Tangential section Fig 145 e or 0 ep almost parallel to root surface.)

In the periodontal membrane epithelial cells are found which, usually, Elgtglictfll-llm lie close to the cementum but not in contact with it (Fig. 144). They were first described by Malassez in 1885.“ Since then much research has been done as to their origin, structural arrangement and function. They 186 omu. I-IISTOLOGY AND EMBRYOLOGY

are, undoubtedly, remnants of the epithelium which forms Hertwig’s epithelial root sheath“ (see chapter on Tooth Development). At the time of formation of cementum the continuous layer of epithelium, bordering the dentin surface, breaks into strands which persist as a network parallel‘ to the surface of the root (Fig. 145). Only in a surface View, as in sections almost parallel to the root, can the true arrangement of these epithelial

Alveolar bone

Epithelial rest

’ -’ Periodontal

Cementurn membrane Dentin _. Blood vessel

Fig. 146.-—Long strand or epithelium in the periodontal membrane.

strands be seen.“ Cross or central sections through the tooth cut through the strands of the network and, thus, only isolated nests of epithelial cells appear in the sections. It is not clear whether the epithelial sheath breaks up because of degeneration of the epithelial cells, or due to active proliferation of the mesenchyme, or both. This disintegration of the epithelium enables the connective tissue to approach the outer surface of the dentin and to deposit cementum on its surface. The frequent appearane of the epithelial rests, in long strands (Fig. 146) or in tu187

PI*ZRIOD0i\'TAL MEMBRANE

bules (_Fig. 147 l, has given rise to the assumption that they may have endocrine function. Under pathologic conditions they may proliferate

and give rise to epithelial masses, associated with grannlomas, cysts, or tumors of dental origin.

Epithelial. rest ', . —.~

— Cemenmblast

Principal nbers

Fig. 1-l7.—Pseuclo-tubular structure of epithelial rest in the periodontal membrane.

Calcified bodies, cementicles, are sometimes found in the tissues of the periodontal membrane, especially in older persons. These bodies may remain free in the connective tissue; they may fuse into large calcified masses, or they may be joined with the cementum (Fig. 148). As the cementum thickens with advancing age, it may envelop these bodies in which event the cemcnticles become interstitial in location. When they are adherent to the cementum they form excementoses. The origin of

these calcified bodies is not established; it IS presumed that degenerated cells, usually epithelial, form the nidus for their calcification.

5. PEYSIOLOGIG CHANGES

Several studies of the width of the periodontal membrane, in“human specimens, have been reportecl.“ 3- “r 12 All reports agree that the thickness of the periodontal membrane varies in different individuals, in dif cementicles

Measurements and changes in Dimensions During 188 ORAL HISTOLOGY AND EMBRYOLOGY

ferent teeth in the same person, and in different locations on the same tooth as is illustrated in Tables III to V1.5

TABLE III THICKNESS or PERIODONTAL MEMBRANE or 172 TEETH FROM 15 HUMAN JAWS

AVERAGE AT AVERAGE AT AVERAGE AT AVERAGE OF‘

ALV. CREST MIDROOT APEX TOOTH

14:); MM MM MM A es 11-10 83 teeth from 4 jaws 0 23 0 17 0 24 0 21 Ages 32-50 36 teeth from 5 jaws 0.20 0.14 0.19 0.18 Ages 51457 [ _ 35 teeth from 5 jaws 0.17 0.12 0.16 0.1::

Table III shows that the width of the periodontal membrane decreases with age, and that it is wider at the crest and apex than at the midroot. (Coo1idge.8)

TABLE IV

THICKNESS or PE1uoBoNTAL Trssuns IN VARYING CoNmTxoNs or FUNcTIoN

ALV. CREST MIDROOT APEX AVERAGE

MM. MM. MM. MM. Teeth in heavy function 44 teeth from 8 jaws 0.20 0.14 0.19 0.18 Teeth not in function 20 teeth from 12 jaws 0.1-1 0.11 0.15 0.13 Embedded teeth 5 teeth 0.09 0.07 0.08 0.08

_Table IV shows that the width of the periodontal membrane is greater around teeth which are subjected to heavy stress and decreases with loss of function. (Coolidgefi)

TABLE V

COMPARISON or THICKNESS or PERIODONTAL MEMBRANE or Foua INGISORS AND FOUR MoLABs (SUBJECT AGED 11 YEARS)

ALv. CREST MIDROOT APEX AVERAGE MM. MM. MM. MM. 4 incisors 0.33 0.25 0.28 0.29 4 molars 0.22 0.15 0.26 0.21

Table V demonstrates that there is a difierenee in the width of the membrane in different teeth in the same individual. (Coolidge!)

TABLE VI

COMPARISON or PERIODONTAL MEMBRANE IN DIFFERENT LocAT1oNs AROUND THE SAME '1‘ooTH (SUBJECT AGED 11 YEARS)

MESIAL DISTAL LABIAL LINGUAL MM. MM. MM. MM. Upper ri ht central incisor, mesial and bial drift 0.12 0.24 0.12 _ 0.22 Upper left central incisor, no drift 0.21 0.19 0.24 0.24 Upper right lateral incisor, distal and labial drift 0.27 0.17 0.11 0.15

Table VI shows the variation in width of the mesial, distal, labial, and lingual sides of the same tooth. (Coolidge!) PERIODONTAL MEMBRANE 189

The measurements shown in the tables indicate that it is not feasible

to refer to an average figure of normal width of the periodontal membrane. Measurements of large number of cases range from 0.15 to 0.38

mm. The ‘fact that the periodontal membrane is the thilmest in the m1ddle region of the root shows that the fulcrum of physiologic movement Is in this reglon. The thickness of the periodontal membrane seems

‘ Free cementicle

Alveolar bone

W’ i '_ Attached cementicle

' Periodontal membrane

Embedded cementicle

Fig. 148.—Cementicles in the periodontal membrane.

to be maintained by the ftmctional movements of the tooth. It is thinner in flmctionless and embedded teeth. The fact that cementum and bone do not fuse even in functionless teeth might be due to the fact that both lose their growth potential if function is lost.

Physiologic movement of human teeth is characterized by their tendency to migrate mesially in compensation for the wear at their contact points.” In mesial migration a difference can be observed in the periodontal mem Physiologic Changes Marrow space

190 om. nrsronoor mo nmsmzonoer

brane in the distal and mesial areas (Fig. 149, A and B). On the distal side of the tooth, the interstitial spaces with their blood vessels, lymph spaces and nerves, appear in sections elliptic in contrast to those on the mesial side that appear round.” Bone resorption on the mesial side of the tooth sometimes opens marrow spaces which become continuous with the periodontal membrane (Fig. 149, A). Frequently, however, the drift is so gradual that bone formation in the marrow spaces keeps pace with the resorption on the periodontal membrane side, and the thickness of the alveolar bone is maintained. Due to the shift of the tooth, epithelial rests may become incorporated in the bone on the side from which the tooth is shifting.“

Alveolar - ' "

bone

Interstitial space

Principal fibers

Fig. 149.—Interstitie.1 spaces between the principal fiber bundles are round on the pressure side (A) and elliptic on the tension side (3). Marrow spaces open up on the pressure side and become interstitial spaces.

C : Cementum. D : Dentin.

6. CLINICAL CONSIDERATIONS

The complex functional relationship between the teeth and their supporting tissues brings about continuous structural changes during life. Between the two extremes of occlusal trauma and loss of function there

“ i‘ Lamellated

bone

Bundle bone l’l<}RIODON'l‘AL MEMBRANE 191

are many intermediate stages. In loss of function the periodontal membrane becomes narrower, due to decreased use of that particular tooth.‘ 1°’ 1‘ The regular arrangement of the principal fibers is lost and the periodontal membrane appears as an irregularly arranged connective tissue. The cementum becomes thicker but finally aplastic; it contains no Sharpey’s fibers. Also, the alveolar bone is in an aplastic (inactive) state and lacks Sharpey’s fibers (Fig. 150, B).

Bundle — bone ~ lAlveola.r bone _ ] (lamellated) 1;. } - K Periodontal I‘ . . membrane .1 g , .:l§ Bundle —--—---— . _ bone E P H do tal ‘ e o 11 membrane Lamellated —— '5 . Haversian “, bone 1

59' we

Fig‘. 150.—~Periodontal membrane or a. functioning (A) and nontunctioning (B) tooth. In the functioning tooth the periodontal membrane is wide, principal fibers are present. cementum (C) is thin; bundle bone with Sharpey's fibers. In the nonfunctioning tooth the periodontal membrane is narrow, no principal fiber bundles are present. Cementu_m is thick (0 and 0') ; alveolar bone is lamellated with no Shar-pey's fibers. D = Dentin.

For restorative dentistry the importance of these changes in structure is obvious.” The supporting tissues of a tooth long out of function are unable to carry the load suddenly placed upon the tooth by restoration. This applies to bridge abutments, teeth opposing bridges or dentures, and teeth used as anchorage for removable bridges. This may account for the 192 ORAL HISTOLOGY AND EMBRYOLOGY

inability of a patient to use a restoration immediately following its placement. Some time must elapse before the supporting tissues are again rearranged in response to the new functional demands. This may be termed an adjustment period which, likewise, must be permitted to follow orthodontic treatment.

The stress, especially of a lateral type, often placed upon the supporting apparatus may be more than the tissue can tolerate. Sudden trauma of the periodontal membrane, such as in accidental blows, condensing of foil, rapid mechanical separation, may produce pathologic changes: fractures or resorption of the cementum, tears of the fibers, hemorrhage and necrosis. The adjacent alveolar bone is resorbed and the periodontal membrane thickened; the tooth becomes loose. When trauma is eliminated repair may take place. For practical purposes it is important that, in the construction of fillings and bridges, the occlusion be carefully considered, and interference in lateral movements (cusp interference) avoided or eliminated. It is also important that missing teeth be immediately replaced to avoid tipping and migration of remaining teeth; failure to do so may result in loss of function and traumatism.

Orthodontic tooth movement depends upon bone resorption and bone formation stimulated by properly regulated pressure and tension." These stimuli are transmitted through the medium of the periodontal membrane. If the movement of teeth is within physiologic limits (Which may vary with the individual) the initial thinning of the periodontal membrane on the pressure side, is compensated for by bone resorption, whereas the thickening of the periodontal membrane, on the tension side, is balanced by bone apposition. If new bone formation is impaired by faulty manipulation or disease, the periodontal membrane may become wider and the tooth may loosen, or even be completely lost. Under the stimulus of inflammation such as occurs in a dental granuloma the epithelial rests of the periodontal membrane may proliferate to form a periodontal cyst around the root end of the tooth. The dental granulomas are found frequently, and very careful studies“: 9“ have shown that 100 per cent of dental granulomas have either proliferating or resting epithelium. Since all dental granulomas contain this material, they must" all be considered as potential periodontal cysts.

References

1. Berkelbach van der Sprenkel, H.: Zur Neurologie des Zahnes (Neurology of the Tooth), Ztschr. f. mikr.- anat. Forsch. 38: 1, 1935.

2. Black, G. V.: A Study of the Histological Characters of the Periosteum and Peridental Membrane, Chicago, 1887, W. T. Keener Co.

3. Black, G. V.: The Fibers and Glands of the Peridental Membrane, Dental Cosmos 41: 101, 1899.

4. Box, K. F.: Evidence of Lymphatics in the Periodontium, J. Canad. D. A. 15: 8, 194.9.

5. Brunn, A. v.: Ueber die Ausdehnung des Schmelzorganes und seine Bedentung fur die Zahnbildung (The Extension of the Enamel Organ and Its Significance in Tooth Development), Arch. f. mikr. Anat. 29: 367, 1887. PERIODONTAL MEMBRANE 193

6. Bruszt, P.: Ueber die netzartige Anordnung des paradentalen Epithels (The Network Arrangement of the Epithelium in the Periodontal Membrane), Ztschr. f. Stomatol. 30: 679, 1932.

7. Coolidge, E. D.: Clinical Pathology and Treatment of the Dental Pulp and _Periodontal Tissues, Philadelphia, 1939, Les. & Febiger.

8. Cool1g§e,11;3éi93'17‘he Thickness of the Human Periodontal Membrane, J. A. D. A.

. , .

9. Gottlieb, B.: Paradental Pyorrhoe und Alveolar atrophie (Paradental Pyorrhea and Alveolar Atrophy), Fortschr. d. Zahnheilk. 2: 363, 1926.

9a. Hilli J.: The Epithelium in Dental Granulomata, J. Dent. Research 10: 323,

10. Kellner, Histologische Befunde an antagonistenlosen Ziihnen (Histologic Findings on Teeth Without Antagonists), Ztschr. f. Stomatol. 26: 271, 1928.

11. Klein, A.: Systematische Untersuchungen iiber die Periodontalbreite (Systematic Investigations on the Width of the Periodontal Membrane), Ztschr. f. Stomatol. 26: 417, 1928.

12. Kronfeld, R.: A Case of Tooth Fracture, With Special Emphasis on Tissue Repair and Adaptation Following Traumatic Injury, J. Dent. Research 15: 429, 1935/6.

13. Lehner, J., and Plenk, H.: Die Ziihne (The Teeth), Moellendorfs Handbuch. d. mikrosk. Anat. vol. 3, Berlin, 1936, J. Springer, p. 449.

14. Malassez, M. L.: Sur l’existence de masses epithéliales dans le ligament alveolodentaire (On the Existence of Epithelial Masses in the Periodontal Membrane), Compt. rend. Soc. de biol. 36: 241, 1884.

15. McCrea, M. W.: Histologic Studies on the Occurrence of Epithelium in Dental Granulomata, J. A. D. A. 24: 1133, 1937.

16. Noyes, F. B.: A Review of Work on the Lyniphatics of Dental Origin, J. A. D. A. 14: 714, 1927.

17. Oppenheim, A.: Human Tissue Response to Orthodontic Intervention of Short and Long Duration, Am. J. Orthodont. & Oral Surg. 28: 263, 1942.

18. Orban, B.: Entwicklungsgeschichte und Histogenese (Embryology and Histogenesis), Fortschr. d. Zahnheilk. 3: 749, 1927.

19. Orban, B.: Biologic Considerations in Restorative Dentistry, J. A. D. A. 28: 1069 1941.

20. Orban, B’: A Contribution to the Knowledge of the Physiologic Changes in the Periodontal Membrane, J. A. D. A. 16: 405, 1929.

21. Orban, B.: Dental Histology and Embryology, Philadelphia, 1929, P. Blakiston’s Son & Co.

22. Robinson, H. B. G.: Some Clinical Aspects of Intra-Oral Age Changes, Geriatrics 2: 9 1947.

23. Schweitzer, G.: Die Lymphgeflisse des Zahnfieisches und der Ziihne (Lymph Vessels of the Gingivae and Teeth), Arch. 1:‘. mikr. Anat. 69: 807, 1907; '74: 927, 1909.

24. Sicher, H.: Ban und Funktion des Fixationsapparates der Meerschweinchenmolaren ( tructure and Function of the Supporting Apparatus in the Teeth of Guinea Pigs), Ztschr. f. Z. Stomatol. 21: 580,.1923. .

25. Weinmann, J. P.: Progress of Gingival Inflammation into the Supporting Structures of the Teeth, J. Periodont. 12: 71. 1941. _

26. Weinmann, J. P.: Bone Changes Related to Eruption of the Teeth, Angle

Orthodontist 11: 83, 1941. CHAPTER VIII

MAXILLA AND MANDIBLE (ALVEOLAR PROCESS)

1. DEVELOPIMEENT OI‘ MAXJILA AND MANDIBLE

2. DEVELOPMENT 01' ALVEOLAB PROCESS

3. STRUCTURE OI’ AINEOLAR PROCESS

4. PHYSIOLOGIC CHANGES DI '1‘H.'.l':‘. ALVEOLAR PROCESS 5. I'N'TE.'R.N.A.L RECONSTRUCTION OF BONE

6. CLINICAL CONSIDERATIONS

1. DEVELOPMENT OF MAXILLA AND MANDIBLE

In the beginning of the second month of fetal life the skull consists of three parts: The chondrocranium, which is cartilaginous, comprises the base of the skull with the otic and nasal capsules; the desmocranium, which is ‘membranous, forms the lateral walls and roof of the brain case; the appendicular or visceral part of the skull consists of the cartilaginous skeletal rods of the branehial arches.

The bones of the skull develop either by endochondral ossification, replacing the cartilage, or by intramembranous ossification in the mesenchyme. Intramembranous bone may develop in close proximity to cartilaginous parts of the skull, or directly in the desmocranium, the membranous capsule of the brain (Fig. 151).

The endochondral bones are the bones of the base of the skull: ethmoidal bone; inferior concha (turbinate bone); body, lesser wings, basal part of greater wings, and lateral lamella of pterygoid process of the sphenoid bone; petrosal part of temporal bone; basilar, lateral, and lower part of squamous portion of occipital bone. The following bones develop in the desmocranium: frontal bones; parietal bones; squamous and tympanic parts of temporal bone; parts of the greater wings, and medial lamina of pterygoid process of sphenoid bone; upper part of squamous portion of occipital bone. All the bones of the upper face develop by intramembranous ossification; most of them close to the cartilage of the nasal capsule. The mandible develops as intramembranous bone, lateral to the cartilage of the mandibular arch. This cartilage, Mecke1’s cartilage, is in its proximal parts the primordium for two of the auditory ossicles: incus (anvil) and malleus (hammer). The third auditory ossicle, the stapes (stirrup), develops from the proximal part of the skeleton in the second branchial arch which then gives rise to the styloid process, stylohyoid ligament and part of the hyoid bone which is completed by the derivatives of the third arch. The fourth and fifth arches form the skeleton of the larynx.

First draft submitted by Harry Sicher and Joseph P. Welnmanu. 194 — — ~ - — — — — Greater win of F ' sphenoid bgone Medial plate of pterygoid A _ process ' 1 Frontal bone I Parietal bone 1"‘

i

5

3 xi ‘,2

i v _/— Nasal capsule

3 1 _— Nasal bone

1 _ 4' .7 _ —_ Lacrlmal bone l ‘ \ -ll ' es .

~ ‘ “rs .\ «<T'« . = ~; Maxilla

• . _ A.» ‘ was... —

E j (4 LT zygomatic bone Occipitai —————.—- _ suuama I 0 k ‘ l - 7 ‘.__ Mandible \ ‘Ir Lateral part of ;’ \ \ occipital bone . \ Tympanic bone Petrosal bone '——-é-—-?———’ \ Sm ‘d 0: process Squama of ' ' temporal bone . Medial plate or‘ _ Water Wins 0‘ pm-ygoid - sphenoid bone process Frontal bone Parietal bone 4 I ‘ ' Nasal bone L... ‘ / Nasal capsule — 'A Lacrimal bone — _ ‘ ' W‘ . Maxilla ‘——— _.__;__ ",. j' . , ‘H Palatine bone _ l - ' Occipltul Mandible squama " ‘Ui. I Meckel's ‘ I cartilage . ‘ / v p , ‘ ,' Hammer. , [ " . Pel;osa.l bone ‘ » Min 1 Styloid process ' ~ -— -—— --—--—‘--*-‘

Fig. 151.—Reconstruction of the sl_£u1l ot a. human embryo 80 mm. long. gtarfilagez green. Intramembranous bones: punk. Endochondral bones: white. (Sxeher and

Tandlerfl)

A. Right lateral view. B. Left lateral view after removal of left int:-amernbranous bones.

MAXILLA. AND MANDIBLE 195

The human maxillary bone is formed, on either side, from the union of two bones, premaxilla and maxilla, which remain separate in most other mammals. In man the two bones begin to fuse at the end of the second month of fetal life. The line of fusion is indicated in young individuals by the intermaxillary (incisive) suture on the hard palate.

Developing tooth

Inferior Bone alveolar (mandible) nerve

Meckel’s cartilage man 1 e g I(Bone d_bI )

Fig. 152.——Deve1opment of the mandible as intramembranous hone lateral to Meckers cartilage (human embryo 45 mm. long).

The maxilla proper develops from ‘one center of ossification which

appears in the sixth week. The bone is then‘ situated on the lateral side of the cartilaginous nasal capsule and forms the wall of the nasal cavity when the cartilage has disappeared. The prernaxilla, or os incisivum, has two independent centers of ossification. Ultimately, it forms that part of the maxilla which icarriesthe two incisors, the anterior part of the palatine process, the rim of the piriform aperture, and part of the frontal processfi“

Maxilla. 196 ORAL HISTOLOGY AND EMBRYOLOGY

' Connective tissue

‘ Cartilage

Fig. 153.—Deve1opment of mandibular symphysis.

A. Newborn infant: symphysis wide open: mental ossicle (roentgenogram).

B. Child 9 months: symphysis partly closed; mental ossicies fused to mandible (roentgenogram).

0. Frontal section through mandibular symphysis of newborn infant. Connective tissue in midline is transformed into cartilage on either side which is later replaced

by bone. MAXJLLA AND MANDBLE 197

The mandible makes its appearance as a bilateral structure in the sixth week of fetal life and is a thin plate of bone lateral to, and at some distance from, Meckel’s cartilage (Fig. 152). The latter is a cylindrical rod of cartilage; its proximal end (close to the base of the skull) is continuous with the hammer, and is in contact with the anvil. Its distal end (at the midline) is bent upwards and is in contact with the cartilage of the other side (Fig. 151). The greater part of Meckel’s cartilage disappears without contributing to the formation of the bone of the mandible. Only a small part of the cartilage, some distance from the midline, is the site of endochondral ossification. Here, it calcifies and is invaded and destroyed by connective tissue and replaced by bone. Throughout fetal life the mandible is a paired bone the two halves of which are joined in the midline by fibrocartilage. This synchondrosis is called mandibular symphysis. The cartilage at the symphysis is not derived from Meckel’s cartilage but differentiates from the connective tissue in the midline. In it small irregular bones, known as the mental ossicles, develop and, at the end of the first year, fuse with the mandibular body. At the same time the two halves of the mandible unite by ossification of the symphysial fibrocartilage (Fig. 153).

2. DEVELOPMENT OF THE ALVEOLAB. PROCESS

Near the end of the second month of fetal life, the bones of maxilla and mandible form a groove which is open towards the surface of the oral cavity (Fig. 152). In a later stage the tooth germs are contained in this groove which also includes the dental nerves and vessels. Gradually, bony septa develop between the adjacent tooth germs, and much later the primitive mandibular canal is separated from the dental crypts by a horizontal plate of bone.

An alveolar process in the strict sense of the word develops only during the eruption of the teeth. It is important to realize that during growth part of the alveolar process is gradually incorporated into the maxillary or mandibular body while it grows at a fairly rapid rate at its free borders. During the period of rapid growth, a special tissue may develop at the alveolar crest. Since this tissue combines characteristics of cartilage and bone, it is called ch/(android bone (Fig. 154).

3. STRUCTURE OF THE ALVEOLAB. PROCESS

The alveolar process may be defined as that part of the maxilla and mandible which forms and supports the sockets of the teeth (Fig. 155). Anatomically, no distinct boundary exists between the body of the maxilla or mandible and their respective alveolar processes. In some places the alveolar process is fused with and partly masked by bone which is not functionally related to the teeth. In the anterior part of the maxilla the palatine process fuses with the alveolar process. In the pos Mandible 198 ORAL HISTOLOGY AND EMBRYOLOGY

terior part of the mandible the oblique line is superimposed upon the bone of the alveolar process (Figs. 155, D and E’ ) . As a result of its adaptation to function, two parts of the alveolar process

can be distinguished. The first consists of a thin lamella of bone which surrounds the root of the tooth and gives attachment to principal fibers

of the periodontal membrane. This is the alveolar bone proper. The

v'.>--—'‘ “-4

Proliferation zone at alveolar crest

Chondroid — bone in

• -vie,

Chondroid *--—' bone - .

Uhwl 11 so 1;‘? V

‘ Resorptlon

ii

Fig‘. 154.—Vex-tical growth of mandible at alveolar crest. Formation of chontlrold bone which is replaced by typical bone.

second part is the bone which surrounds the alveolar bone and gives support to the socket. This has been called supporting bone.” The latter, in turn, consists of two parts: the compact bone (cortical plate) forming the vestibular and oral plates of the alveolar processes, and the spongy bone between these plates and the alveolar bone proper (Fig. 155). The cortical plates, continuous with the compact layers of maxillary and mandibular body, are generally much thinner in the maxilla than in the mandible. They are thickest in the bicuspid and molar region of the MAXILLA AND MANDIBLE 199

Fig. 155.—Gross relations of alveolar processes:

A. Horizontal section through upper alveolar process. _,.

B. Labiollngual section through upper lateral incisor.

0. Labiolingual section through lower cuspid.

D. Labiolingual section through lower second molar.

E. Labiolingual section through lower third molar. (Sicher and Tandlerfl)

Fig. 156.—Dia.gra.mma.tic illustration of the relation between the cemento-enamel junction of adjacent teeth and the shape of the crests of the alveolar septa. (Ritchey, B., and Orban, B.“".) 200 ORAL HISTOLOGY AND EMBRYOLOGY

lower jaw, especially on the buccal side. In the maxilla the outer cortical plate is perforated by many small openings through which blood and lymph vessels pass. In the lower jaw the cortical bone of the alveolar process is dense and, occasionally, shows small foramina. In the region of the anterior teeth of both jaws the supporting bone is, usually, very thin. No spongy bone is found here and the cortical plate is fused with the alveolar bone proper (Figs. 155, B and C).

Circumferential lamel lae

Reversal line

Haversian sytem

Interstitial -— lamellae

g Resting line

Fig. 157A.-—Appositiona.1 growth of mandible by formation of circumferential lamellae.

Ehetshe are replaced by Haversian bone; remnants of circumferential lamellae in the ep .

The outline of the crest of the intraalveolar septa, as they appear in the roentgenogram, are dependent upon the position of the adjacent teeth. In a healthy mouth the distance between the cemento-enamel junction and the free border of the alveolar bone proper is fairly constant. In consequence the alveolar crest is often oblique if the neighboring teeth are inclined. In the majority of individuals the inclination is most pronounced in the premolar and molar region, the teeth being MAXILLA AND MANDIBLE 201

tipped mesially. Then, the ceniento-enamel junction of the mesial tooth is situated in a more occlusal plane than that of the distal tooth and the alveolar crest, therefore, slopes distally (Fig. 156).

The interdental and interradicular septa contain the perforating canals of Zuckerkandl and Hiischfeld, which house the interdental and interradicular arteries, veins, lymph vessels and nerves.

PrinclpaJ flgyers o perio- -I Lgmellated ' one \. BK ' "" Haversian system

Fig. 157B.—Bundle bone and I-Iaversian bone on the distal alveolar wall (silver impregnation).

Histologically, the cortical plates consist of longitudinal lamellae and Haversian systems (Fig. 157A) . In the lower jaw circumferential or basic lamellae reach from the body of the mandible into the cortical plates. The trabeculae of the spongy bone of the alveolar process are placed in the direction of the stresses to which it is subjected as a result

of mastication (Fig. 158). The functional adaptation of this spongy bone is particularly evident between the alveoli of molars where the 202 ORAL HISTOLOGY AND EMBRYOLOGY

trabeculae show a parallel horizontal arrangement. From the apical part of the socket of lower molars trabeculae are, sometimes, seen radiating in a slightly distal direction. These trabeculae are less prominent in the upper jaw, because of the proximity of the nasal cavity and maxillary

Fig. 158.—Suppox-ting trabeculae between alveoli. A. Roentgenogram or a. mandible.

B. Meslodistal section through mandibular molars showing alveolar bone proper and supporting bone.

sinus. The marrow spaces in the alveolar process may contain hemopoietic, but, usually, contain fatty marrow. In the condyloid process,

angle of mandible, maxillary tuberosity, and other foci cellular marrow is frequently found, even in adults." 1‘ MAXILLA AND MANDIBLE 203

The alveolar bone proper which forms the inner wall of the socket (Fig. 158) is perforated by many openings which carry branches of the interalveolar nerves and blood vessels into the periodontal membrane (see chapter on Periodontal Membrane). It is called cribriform plate or lamina dura ; the latter term refers to the dense appearance of the alveolar bone proper in roentgenograms. The alveolar bone proper consists partly of lamellated, partly of bundle bone. The lamellae of the lamellated bone are arranged roughly parallel to the surface of the adjacent marrow spaces, others form Haversian systems. Bundle bone is that bone to which the principal fibers of the periodontal membrane are anchored. The term bundle bone was chosen because the bundles of the principal fibers continue into the bone as Sharpey’s fibers. The bundle bone is characterized by the scarcity of the fibrils in the intercellular substance. These fibrils, moreover, are all arranged at right angles to the Sharpey’s fibers. The bundle bone appears much lighter in preparations stained with silver than lamellated bone because of the reduced number of fibrils (Fig. 157B). Because all the fibrils run in the same direction, the bundle bone is not lamellated.

4. PHYSIOLOGIG CHANGES IN THE ALVEOLAR PROCESS

The internal structure of bone is adapted to mechanical stresses. It changes continuously during growth and alteration of functional stresses. In the jaws this change takes place according to the growth, eruption, wear and loss of teeth. With advancing age parts of the bone and the osteocytes lose their vitality, and regeneration has to follow. All these processes are made possible only by a coordination of destructive and formative activities. Specialized cells, the osteoclasts, have the function of eliminating overaged bony tissue or bone which is no longer adapted to mechanical stresses.

Osteoclasts are multinucleated giant cells (Fig. 159, A). The number of nuclei in one cell may rise to a dozen or more. However, it is to be noted that, occasionally, uninuclear osteoclasts are found. The nuclei are vesicular, showing a prominent nucleolus and little chromatin. The cell body is irregularly oval or club-shaped and may show many branching processes. In general, osteoclasts are found in bay-like grooves in the bone which are called Howship’s lacunae; they are hollowed out by the activity of the osteoclasts. The cytoplasm which is in contact with the bone is distinctly striated. These striations have been explained as the expression of resorptive activity of these cells. The osteoclasts seem to produce a proteolytic enzyme which destroys or dissolves the organic constituents of the bone matrix. The mineral salts thus liberated are removed in the tissue fluid or ingested by macrophages. A decaleification of bone during life has often been claimed but has never been demonstrated.

Osteoclasts differentiate from young fibroblasts or undifferentiated mescnchymal cells probably by division of nuclei without the usual division of 204 ORAL msronoev AND EMBRYOLOGY

the cytoplasm. Some investigators believe that the osteoclasts may arise by fusion of osteoblasts, others believe that they difierentiate from endothelial cells of capillaries. The stimulus which leads to the diiferentiation of mesenchymal cells into osteoblasts or osteoclasts is not known. Osteoclastic resorption of bone is partly genetically patterned, partly functionally determined. Also overaged bone seems to stimulate the differentiation of osteoclasts‘ possibly by chemical changes that are the consequence of degeneration and final necrosis of the osteocytes.

New bone is produced by the activity of osteoblasts (Fig. 159, B). These cells also difierentiate from fibroblasts or the undifferentiated mesenchymal

.i.«r~$

-u.0m

E

as

an’

Fig. 159.—Resorption and apposition of bone. A. Osteoclasts in Howship’s lacunae

B. Osteoblasts al 11 a ho tr b la. La. 1 1 fomafion (high magngflmflolxbe. a ecu yer o osteo 1! tissue as a sign of bone

- cells of the connective tissue. Functioning osteoblasts are arranged along

the surface of the growing bone in a continuous layer, similar in appearance to a cuboidal epithelium.

The osteoblasts are said to produce the bone matrix by secretion. The matrix is at first devoid of mineral salts. At this stage, it is termed

—--———-up-‘ I. ‘ , ‘ Osteoblas MAXJLLA AND MANDIBLE 205

osteoid tissue. It is still undecided Whether the fibrils of the matrix are connective tissue fibrils which become embedded in the substance of the matrix, or whether the fibrils difierentiate in the primarily amorphous matrix. If a certain amount of matrix is produced some of the osteoblasts become embedded in the matrix, and are known as osteocytes. Normally, the organic matrix calcifies immediately after formation?’ 1‘ The ratio of organic and inorganic substance in dry bone is approximately 1 :2. (See Table in chapter on Enamel for complete data.)

5. INTERNAL RECONSTRUCTION OF BONE

The bone in the alveolar process is identical to bone elsewhere in the body and is in a constant state of flux. During the growth of jaw bones, bone is deposited on the outer surfaces of the cortical plates.. The changes are most readily observed in the mandible, with its thick cortical layer of compact bone. Here bone is deposited in the shape of basic or circumferential lamellae (Fig. 157A). When the lamellae reach a certain thickness they are replaced from the inside by Haversian bone. This is a reconstruction in accordance with the functional and nutritional demands of the bone. In the Haversian canals, closest to the surface, osteoclasts differentiate and resorb the Haversian lamellae, and part of the circumferential lamellae. After a time the resorption ceases and new bone is apposed onto the old. The scalloped outline of Howsh:1p’s lacunae which turn their convexity toward the old bone remains visible as a darkly stained cementing line, sometimes called the “reversal” line. This is in contrast to those cementing lines which seem to correspond to a rest period in an otherwise continuous process of bone apposition; they are called resting lines (Fig. 157A). Resting and reversal lines are found between layers of bone of varying age.

Another type of internal reconstruction is the replacement of compact bone by spongy bone. This can be observed following the growth of the bone when the compact outer layer has expanded to a certain extent. The process of destruction can be observed from a section through bone, by noting the remnants of partially destroyed Haversian systems, or partially destroyed basic lamellae which form the interstitial lamellae of the compact bone.

Wherever a muscle, tendon, ligament, or periodontal membrane is attached to the surface of bone, Sharpey’s fibers can be seen penetrating the basic lamellae. During replacement of the latter by Haversian systems fragments of bone containing Sharpey’s fibers remain in the deeper layers. Thus, the presence of interstitial lamellae containing Sharpey’s fibers indicates the former level of the surface.“

Alterations in the structure of the alveolar bone are of great importance in connection with the physiologic movements of the teeth. Thee movements are directed mesio-occlusally. At the alveolar fundus the con206 ow. HISTOLOGY AND nnmzvonoer

tinual apposition of bone can be recognized by resting lines separating parallel lavers of bundle bone; when the bundle bone has reached a cer tain thickness it is partly resorbed from the marrow spaces and then replaced by Haversian bone or trabeculae. The presence of bundle bone indicates the level at which the alveolar fundus was previously situated. During the mesial drift of a tooth, bone is apposed on the distal, and resorbed

4; .

. - ii‘ , ' "i L ‘I

‘ I

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‘ *‘ R ‘ " ‘. i. ‘ _ t l ‘

‘ v —- ._.- ———1>-'--—-L Resorptlon

R‘-' L .,z' a

' ; ‘ :t:-‘; v  ,1??  ~-  Lamellated
 ‘ ‘F bone

, is _ lg i_ -‘_ - _- —— -~—-—. Periodontal 3". membrane

3. «

sat: lg)!’ ‘/ ‘ _ 9 Resorptlon __‘__-_ _ _ _ _ *9 A B.

Fig. 160.-—-Meslel drift. .4. Appositlon of bundle bone on the distal alveolar wall. 3. Resorption of bone on the mesial alveolar wall. (Weinmann.”)

on the mesial, alveolar wall (Fig. 160). The distal Wall is made up almost entirely of bundle bone. However, the osteoclasts in the adjacent marrow

spaces remove part of the bundle bone when it reaches a certain thickness. In its place lamellated bone is laid down (Fig. 157B).

On the mesial alveolar wall of a drifting tooth signs of active resorption are observed by the presence of Ho\vship’s lacunae containing osteoclasts (Fig. 160). Bundle bone on this side is present in relatively few areas. When found, it usually forms merely a thin layer (Fig. 161). This is due to the fact that the mesial drift of a tooth occurs in a rocking moMAXILLA AND MANDIBLE 207

tion. Thus, resorption does not involve the entire mesial surface of the alveolus at one and the same time. Moreover, periods of resorption alternate with periods of rest and repair. It is during these rest periods that bundle bone is formed, and detached periodontal membrane fibers are again secured. It is this alternating action that stabilizes the periodontal membrane attachment on that side of the tooth. Islands of bundle bone are separated from the lamellated bone by reversal lines which turn their convexities toward the lamellated bone (Fig. 161).

Bundle bone

Dentin 1 ' ~ ‘ —~——- Reversal line

Lamellated bone

Periodontal membrane

' " *" Reversal line

Bundle bone

’,1

__ - wan istin fly or simple lamellated bone; islands of Fig‘ 161 bfiilhslglbghgecfigghoringcggisnd giuoé-s of the periodontal membrane.

6. CLINICAL CONSIDERATIONS

Bone is one of the hardest tissues of the human body. Nevertheless, bone is, biologically, a highly plastic tissue. Where bone is covered by a vascularized connective tissue, it is exceedingly sensitive to pressure whereas tension acts, generally, as a stimulus to the production of new bone. It is this biologic plasticity which enables the orthodontist to move 208 ORAL HISTOLOGY AND EMBRYOLOGY

teeth Without disrupting their relations to the alveolar bone. Bone is resorbed on the side of pressure, and apposed on the side of 1361131011; thus allowing the entire alveolus to shift with the tooth.

The adaptation of bone structure to functional stresses is quantitative as Well as qualitative, namely, decreased function leads to a decrease in the bulk of the bone substance. This can be observed in the supporting bone of teeth which have lost their antagonists.’ Here, the spongy bone around the alveolus shows marked rarefication: the bone trabeculae are

> ;_=; '- _ :75-;_"' '_“."t’: . A. ' B. Fig. 162.-—Osteoporosis of alveolar process caused by inactivity or the tooth _which has no antagonist Labiolingual sections through upper molars of the same individual:

4. Disappearance of bony trabeculae after loss of function; plane or mesiobuccal root; alveolar bone proper remains intact.

3. Normal spongy bone in the plane of mesiobuccal root or functioning tooth.

less numerous and very thin (Fig. 162). The alveolar bone proper, however, is generally well preserved because it continues to receive some stimuli by the tension exerted upon it via principal fibers of the periodontal membrane. A similar distinction in the behavior of alveolar and supporting bone can be seen in certain endocrine disturbances and vitamin deficienciesli 2 (Fig. 163).

The independence of the growth mechanisms of the upper and lower jaws accounts for their frequent variations in relative size. Trauma or inflammatory processes can destroy the condylar growth center of the MAXILLA AND MANDIBLE 209

mandible on one or both sides. I-Iyperfunction of the hypophysis, leading to acromegaly, causes a characteristic overgrowth of the mandible, even at a time when sutural growth has ceased.“ The maxillary growth in such cases is confined to bone apposition on the surfaces, because a general enlargement of the upper face is impossible.

During healing of fractures or extraction wounds, an embryonic type of bone is formed which only later is replaced by mature bone. The embryonic bone, immature or coarse fibrillar bone, is characterized by

Fig. 163.—Dlflerence in reaction of alveolar bone and supporting bone: 4. Normal bone structure in bifurcation of dog's tooth.

B. Osteoporosis of supporting bone in bifurcation ot dog’s tooth. Dog fed on diet deficient in nicotinic acid. Alveolar bone proper intact. (Similar conditions could be produced by other dietary deficiencies.) (Courtesy H. Becks,’ University of California.)

the great number, great size, and irregular arrangement of the osteocytes and the irregular course of its fibrils. The greater number of cells and the reduced volume of calcified intercellular substance renders this immature bone more radiolucent than mature bone. This explains why bony callus cannot be seen in roentgenograms at a time when histologic examination of a fracture reveals a well-developed union between the 210 omu. HISTOLOGY AND EMBRYOLOGY

fragments and why a socket after an extraction wound appears to be empty at a time when it is almost filled with immature bone. The visibility in radiograms lags two to three weeks behind actual formation of new bone.

References

1. Becks, H.: Dangerous Consequences of Vitamin D Overdoage on Dental and Paradental Structures, J . A. D. A. 29: 1947, 1942. _ _ 2. Becks, H.: The Efiect of Deficiencies of the Filtrate Fraction of the Vitamin B C0mp1eX42 and Nicotinic Acid on Teeth and Oral Structures, J . Periodont. 13: 18 19 . 3. Bloom, W.: and Bloom, M. A.: Calcification and Ossification. Calcification of Developing Bones in Embryonic and Newborn Rats, Anat. Rec. 78: 497, 1940. 4. Box, H. K.: Red Bone Marrow in Human Jaws, Toronto, 1933, University of Toronto Press. 5. Breitner, C.: Bone Changes Resulting From Experimental Orthodontic Treatment, Am. J. Orthodont. & Oral Surg. 26: 521, 1940. 6. Brodie, A. G.: Some Recent Observations on the Growth of the Mandible, Angle Orthodontist 10: 63, 1940. 7. Brodie, A. G.: On the Growth Pattern of the Human Head From the Third Month to the Eighth Year of Life, Am. J. Anat. 68: 209, 194]. 8. Gottlieb, B.: Zur Aetiologie und Therapie der Alveolarpyorrhoe (Etiology and Therapy of Alveolar Pyorrhea), Oesterr. Ztschr. f. Stomatol. 18: 59, 1920. 9. Kellner, E.: Histologische Befunde an antagonistenlosen Zfihnen (Histological Findings on Teeth Without Antagonists), Ztschr. f. Stomatol. 26: 271, 1928. 10. Lehner, J., and Plenk, H.: Die Ziihne (The Teeth), Moellendorfis Handbueh d. mikrosk. Anat., vol. 3, Berlin, 1936, Julius Springer. 11. McLean, F. 0., and Bloom, W.: Calcification and Ossification. Calcification in , Normal Growing Bone, Anat. Rec. 78: 333, 1940. 12. Orban, B.: Dental Histology and Embryology, ed. 1, Chicago, 1928, Rogers Printing Co. 13. Orban, B.: A Contribution to the Knowledge of the Physiologic Changes in the Periodontal Membrane, J. A. D. A. 16: 405, 1929. 139.. Ritchey, B., and Orban, B.: The Crests of the Interdental Alveolar Septa, J. Period. 1953 (in print). 14. Sclmfier, J .: Die Verkniicherimg des Unterkiefers (0ssification of the Mandible), Arch. f. mikr. Anat. 32: 266, 1888. 15. Schoenbaner, F.: Histologische Befunde bei Kieferosteomyelitis (Histologic Findings in Osteomyehtis of the Jaw), Ztschr. f. Stomatol. 35: 820, 1937. 16. Schour, I., and Massler, M.: Endocrines and Dentistry, J. A. D. A. 30: 595, 763, 943, 194.3. 17. Sicher, EL, and Tandler, J.: Anatomie fiir Zahniirzte (Anatomy for Dentists), Vienna, 1928, Julius Springer. 18. Weinmann, J. P.: Das Knochenbild bei Stiirungen der physiologischen Wanderung der Z§.hne (Bone in Disturbances of the Physiologic Mesial Drift), Ztschr. f. Stomatol. 24: 397, 1926. 19. Weinmann, J. P.: Bone Changes Related to Eruption of the Teeth, Angle Orthodentist 11: 83, 1941. 19a. Woo, Fu-Kang: Ossification on Growth of the Human Maxilla, Premaxilla and Palate Bone, Anat. Rec. 105: 737, 1949. 20. Zawisch-Ossenitz, C. v.: Die basophilen Inseln und andere basophile Elemente im menschlichen Knochen (Basophilic Islands and Other Basophilic Elements in Human Bone), Ztschr. f. mikr.-Anat. Forsch. 18: 393, 1929. CHAPTER IX

THE ORAL MUCOUS MEMBRANE

1. GENERAL CHARACTERISTICS

2. TRANSITION BETWEEN SKIN AND MUCOUS MEMBRANE

3. SUBDIVISIONS 01‘ THE ORAL MUCOSA

A. Mastlcatory Mucosa a. Gingiva b. Epithelial Attachment and Gingival Sulcus c. Hard Palate

B. Lining mucosa. a. Lip and Cheek b. Vestibular Fornix and Alveolar Mucosa

c. Sublingual Mucosa and Mucous Membrane of the Interior Surface of the Tongue (1. Soft Palate

C. Specialized Mucosa or Dorsal Lingual Mucosa 4. CLINICAL CONSIDERATIONS

1. GENERAL CHARACTERISTICS

The oral cavity, as the first part of the digestive tract, serves a variety of functions. It is both the portal of entry and the place of mastication of food. It contains the taste organs. Entering it is the fluid saliva which not only lubricates the food to facilitate swallowing, but also contains enzymes which initiate digestion. The oral cavity is lined throughout by a mucous membrane. This term designates the lining of any body cavity which communicates with the outside.

The morphologic structure of the mucous membrane varies in the different areas of the oral cavity in accordance with the functions of specific zones and the mechanical influences which bear upon them. Around the teeth and on the hard palate, for example, the mucous membrane is exposed to mechanical influences in the mastication of rough and hard food, whereas, on the floor of the mouth, it is largely protected by the tongue. This is the reason why the mucous membrane around the teeth and on the hard palate varies in structure from that of the floor of the mouth, cheeks, and lips.

The mucous membrane is attached to the underlying structures by a layer of connective tissue, the submucosa, which varies in character in different areas. The oral mucous membrane is composed of two layers; the surface epithelium and the lamina propria (Fig. 164). A basement membrane separates the lamina propria from the stratified squamous

First dratt submitted by Balint Orban and Harry slcher. 211 212 om rusronoer AND EMBRYOLOGY

epithelium. The epithelium consists of several layers of cells which flatten out as they approach the surface. All these cells are connected with each ‘other by intercellular bridges. The innermost is the basal layer, consisting of cuboid cells which effect the attachment of the epithelium to the basement membrane of the connective tissue by numerous short basal processes that fit into grooves of the lamina propria. The more superficial cells form the so-called “prickle-cell” layer which consists of several layers of polyhedral cells. The term is derived from the fact

Keratlnous layer

Granular layer Opening 0! duct

Prickle cell layer

Basal layer Basement membrane ‘ — Subepithelial Capillaries M’-We Plexus Lamina propria. Nerve

Submucous layer

Artery Vein

Periosteum

Bone

Fig. 164.-—Diagra.mmatic drawing of oral mucous membrane (epithelium and lamina propria. and submucosa).

that the intercellular spaces are wide and the intercellular bridges prominent, thus giving the isolated cell a spinous appearance. Basal and prickle-cell layers are sometimes referred to as germinative layers. Regeneration of epithelial cells, lost at the surface, occurs by mitotic division of cells in the deepest layers.

The cells of the prickle-cell layer flatten and pass into first the granular layer and then the keratinous layer as they move toward the surface. The cells of the granular layer contain fine kerato-hyalin granules which are basophil and stain blue in hematoxylin-eosin preparation. The nuclei ORAL MUGOUS MEMBRANE 213

of the flattened cells are pyknotic. The keratinous layer is characterized by its acidophil nature; here the nuclei have mostly disappeared. The structure of the granular and keratinous layers varies in the diiferent regions of the oral cavity. A stratum lucidum, such as is seen in regions of the skin where hornification is abundant, is, as a rule, missing in the oral mucosa.

The lamina propria is a dense connective tissue layer of variable thickness. Its papillae, which indent the epithelium, carry both blood vessels and nerves. Some of the latter actually pass into the epithelium. The papillae of the lamina propria vary considerably in length and width in different areas. The inward epithelial projections between the papillae are described as epithelial pegs, because of their appearance in sections. They are in reality, however, a continuous network of epithelial ridges. The arrangement of the papillae increases the area of contact between lamina propria and epithelium, and facilitates the exchange of material between blood vessels and epithelium. The presence of papillae permits the subdivision of the lamina propria into the outer papillary, and the deeper reticular layer.

The submucosa consists of connective tissue of varying thickness and density. It attaches the mucous membrane to the underlying structures. Whether this attachment is loose or firm depends upon the character of the submucosa. Glands, blood vessels, nerves, and also adipose tissue are present in this layer. It is in the submucosa that the larger arteries divide into smaller branches which enter the lamina propria. Here they again divide, to form a subepithelial capillary network in the papillae. The veins originating from the capillary network follow the course of the arteries. The blood vessels are accompanied by a rich network of lymph vessels which play an important part in the drainage of the mucous membranes. The sensory nerves of the mucous membrane traverse the submucosa. These nerve fibers are myelinated but lose their myelin sheath in the mucous membrane before splitting into their end arborizations. Sensory nerve endings of various types are found in the papillae; some of the fibers enter the epithelium where they terminate in contact with the epithelial cells as free nerve endings. The blood vessels are accompanied by nonmyelinated visceral nerve fibers which supply their smooth muscles; other visceral fibers supply the glands.

The oral cavity can be divided into two parts: the vestibulum oris* (vestibule) and the cavum oris proprium (oral cavity proper). The vestibule is that part of the oral cavity proper which is bounded by the lips and cheeks on the outer side, and by the teeth and alveolar ridges on the inner. The oral cavity lies within the dental arches and bones of the

jaw, being limited posteriorly toward the pharynx by the anterior pillars of the fauces.

‘The use of the terms vestibular instead of labial and buccal, and oral instead of lingual or palatal, is suggested. 214 ORAL HISTOLOGY AND EMBRYOLOGY

2. TRANSITION BETWEEN SKIN AND MUCOUS MEMBRANE

The transitional zone between the skin covering the outer surface of the lip and the true mucous membrane lining the inner surface, is the red area or Vermilion border of the lip. It is present in man only (Fig. 165). The skin of the lip is covered by a hornified epithelium of moderate thickness; the papillae of the connective tissue are few and short. Many sebaceous glands are‘ found in connection with the hairs; sweat glands occur between them. The epithelium is typically stratified and squamous with a rather thick hornified layer. The transitional region

.

4 t.‘» , ‘T’ Red zone of

3*‘ _ lip Mucous mem- —— » brane of lip

Skin of lip

Labial glands

‘ orbiculafis ~ " ' oris muscle

Fig. 165.—Section through lip.

is characterized by numerous densely arranged long papillae of the lamina propria, reaching deep into the epithelium and carrying large capillary loops close to the surface. Eleidin in the epithelialcells renders them translucent. Thus, blood is visible through the thin parts of the transparent epithelium covering the papillae; hence the red color of the lips. Because this transitional zone contains only occasional single sebaceous glands, it is particularly subject to drying if not moistened by the tongue. ORAL MUCOUS MEMBRANE 215

The boundary between the red zone of the lip and the mucous membrane is found where hornification of the transitional zone ends. The epithelium of the mucous membrane of the lip is not hornified.

3. SUBDIVISIONS OF THE ORAL MUGOSA

In studying any mucous membrane the following features should be considered: (1) type of covering epithelium; (2) structure of lamina propria, especially as to its density, thickness, and presence or lack of elasticity; and (3) its fixation to the underlying structures, in other words, the submucous layer. A submucosa may be present or absent as a separate and well-defined layer. Looseness or density of its texture determines whether the mucous membrane is movably or immovably attached to the deeper layers. Presence or absence and location of adipose tissue or glands should also be noted.

The oral mucosa may be divided primarily into three different types. During mastication some parts are subjected to strong forces of pressure and friction. These parts, gingiva and covering of the hard palate, may be termed masticatory mucosa. The second type of oral mucosa is that which is merely the protective lining of the oral cavity. These areas may be termed lining mucosa. They comprise the mucosa of lips and checks; the mucosa of the vestibular fornix and that of the upper and lower alveolar process peripheral to the gingiva proper; the mucosa of the floor of the mouth extending to the inner surface of the lower alveolar process; the mucosa of the inferior surface of the tongue; and finally, the mucous membrane of the soft palate. The third type of mucosa is represented by the covering of the dorsal surface of the tongue and is highly specialized; hence, the term specialized mucosa.

A. Masticatory Mucosa

Gingiva and covering of the hard palate have in common the thickness and hornification of the epithelium, the thickness, density, and firmness of the lamina propria, and, finally, their immovable attachment to the deep structures. Hornification is absent or replaced by parakeratinization in some individuals whose gingiva otherwise has to be regarded as normal. As to the structure of the submucosa, these two areas differ markedly. In the gingiva, a well-differentiated submucous layer cannot be recognized; instead, the dense and inelastic connective tissue of the lamina propria continues into the depth to fuse with the periosteum of the alveolar process or to be attached to the cervical region of the tooth.

In contrast to this, the covering of the hard palate has, with the exception of narrow areas, a distinct submucous layer. It is absent only in the peripheral zone where the tissue is identical with the gingiva, and in a narrow zone along the midline, starting in front with the palatine or incisal papilla and continuing as the palatine raphe over the entire length of the hard palate. In spite of the presence of a well-defined 216 ORAL HISTOLOGY AND EMBRYOLOGY

submucous layer in the wide lateral fields of the hard palate between palatine raphe and palatine gingiva, the mucous membrane is immovably attached to the periosteum of maxillary and palatine bones. This attachment is accomplished by dense bands and trabeculae of fibrous connective tissue Which join the lamina propria of the mucous membrane to the periosteum. The submucous space is thus subdivided into irregular intercommunicating compartments of various sizes. These are filled with adipose tissue in the anterior part and with glands in the posterior part of the hard palate. The presence of fat or glands in the submucous layer acts as a hydraulic cushion comparable to that which We find in the subcutaneous tissue of the palm of the hand and the sole of the foot.

The presence or absence of a distinct submucous layer permits the subdivision of the masticatory oral mucosa into the non—cushioned and the cushioned zones. The non-cushioned zone consists of the gingiva and the palatine raphe, the cushioned zone consists of the remainder of the mucosa covering the hard palate.

A. GINGIVA

The mucous membrane surrounding the teeth, the gingiva, is subjected to forces of friction and pressure in the process of mastication. The character of this tissue shows that it is adapted to meet these

.7. 7 .. . T.‘ Alveolar R

mucosa. -- “T Mucoginglval

Junction

Att hed —— —— ' ‘ {if in « -.,A r, F”? Interdental g g .— ,_“,~-~, papilla. P Free g'ing'lva.1 Attifilcéligi g’°°"° Migicogingival 1 * _ junction Alveo ar 1-vi" .. mag. mucosa 9. A \ _ * __ — _

Fig. 166.—Sur1‘a.ce of the gingivu of a young adult.

stresses. The gingiva is sharply limited on the outer surface of both jaws by a scalloped line (mucogingival junction) which separates it from the alveolar mucosa (Fig. 166). The gingiva is normally pink, sometimes With a grayish tinge, a variation which is partly caused by differences in the thickness of the stratum corneum. The alveolar mucosa is red, showing numerous small vessels close to the surface. A similar line of demarcation -‘M. ‘.g;-.;, 7,

Keratinous layer:jg__*,.:£, M '

cells

Flattened surface P v w ' , V

Parakeratotic "> layer 3

g > .

3, ’ ._ ‘ ’f‘i

' in ‘ '

Prickle ce11s_" '*‘ 4%

3...

4

' 1’ ""4" *‘ ’ " ' ' ‘——, ’=' Basal layer

Fig. 167.——Varia.tions of glnglval epithelium. A. Hornmcatlon.

B. No hornmcation.

0'. Paxakeratonia. 218 ORAL HISTOLOGY AND EMBRYOLOGY

is found on the inner surface of the lower jaw between gingiva and the mucosa on the floor of the mouth. In the palate, there is no sharp dividing line because of the dense structure and firm attachment of the entire palatal mucosa.

Normally, the epithelium of the gingiva is hornified on its surface (Fig. 167, A) and contains a granular layer. In the absence of hornification (Fig. 167, B) there is no granular layer and the flat surface cells contain nuclei which are, frequently, pyknotic. Other cases show a partial or incomplete hornification (Fig. 167, 0) characterized by a well-defined

Epithelium? — . f X ' ' H {Q t," -Pngarggrlxted

I layer ‘ V i. If " ‘ . "~

I Connective tissue

Fig. 168A..—Pig'ment in basal cells of gingiva. of a. Negro.

surface layer containing flat cells which have lost their boundaries. Nuclei are present but are extremely flat and pylmotic; this condition is termed parakeratosis. All transitions from nonhornified to parakeratotic and hornified epithelium of the gingiva should be considered as Within the range of normal.

The epithelium covers the margin of the gingiva and continues into the epithelial lining of the gingival sulcus to terminate on the surface of the

tooth as the epithelial attachment (see section on Epithelial Attachment). ORAL MUCOUS MEMBRANE 219

The cells of the basal layer may contain pigment granules (melanin)

(Fig. 168:1). While pigmentation is a normal occurrence in Negroes, it is often found, too, in the white race, especially in people with dark complexion. When found, it is most abundant in the bases of the interdental papillae. It may increase considerably in cases of Addison’s

u— -*‘—"—*“‘ a 

Fig. 168B.——Dendritic melanoblasts in the basal layer of the epithelium. Biopsy of normal gingiva. (x1000.) (Courtesy Esther Carames de Aprile, Buenos Aires.)

1..

'5'-i:..

Fig. 1680.—Macropha.ges in the normal gingiva.._ Rio I-Iortega. stain. ()(1000.) (Courtesy Esther Carames de Aprile, Buenos Aires.)

disease (destruction of the adrenal cortex). The melanin pigment is stored by the basal cells of the epithelium, but these cells do not produce the pigment. The melanin is elaborated by specific cells, melanoblasts, situated in the basal layer of the epithelium (Fig. 168, B). These cells have long processes and are also termed “dendritic” cells. In the usual hematoxylin-eosin specimen, these cells appear with a clear cytoplasm and are also known as “clear cells.” 220 ORAL I-1I§'l‘0LOGY AND EMBRYOLOGY

The lamina propria of the gingiva consists of dense connective tissue Which is not highly vascular. Macrophages are present in the normal ging-iva (Fig. 168, C). These cells play an important function in the defense mechanism of the body. The papillae are characteristically long, slender, and numerous. The presence of these high papillae permits the sharp demarcation of the gingiva and alveolar mucosa in which the papillae are quite low (Fig. 169). The tissue of the lamina propria contains only few elastic fibers which are, for the most part, confined to the walls of the

Hard palate

—h—- Alveolar mucosa.

, .- .’ ‘ w.a,~;L.i' 1 Emu .

Fig. 169.—Structura1 dlflferences between glngiva. and alveolar mucosa. Region of - upper bicuspid.

blood vessels. The gingival fibers of the Pariodontal membrane enter into the lamina propria, attaching the gingiva firmly to the teeth (see chapter on Periodontal Membrane). The gingiva is also immovably and firmly attached to the periosteum of the alveolar bone; here, a very dense connective tissue, consisting of coarse collagenous bundles (Fig. 170, A) extends from the lamina propria to the bone. In contrast, the submucosa underlying the alveolar mucous membrane is loosely textured (Fig. 170, B). The fiber bundles of the lamina propria are here thin and regularly interwoven. The alveolar mucosa and the submucosa contain numerous elastic fibers which are thin in the lamina propria and thick in the submucosa. omu. MUCOUS MEMBRANE 221

The gingiva. is well innervated.“ Difierent types of nerve endings can be observed, such as the Meissner 01- Krause eorpuscles, end bulbs, loops or fine fibers. Fine fibers enter the epithelium as “ultra-terminal” fibers. (Figs. 171A and B.)

, S. , Lamlna propria L "

Submucosa

Epithelium

Lamina proprla.

Submucosa.

Fig. 170.—Differences between ging-Iva. (A) and alveolar mucosa (8). Silver impregnation ot collagenous fibers. Note the coarse bundles of fibers in glngiva. and finer fibers in alveolar mucosa.

The gingiva can be divided into the free gingiva and attached gingiva (Figs. 172A and 172B).” The dividing line between these two parts of the gingiva is the free gingival groove which runs parallel to the margin of the gingiva at a. distance of 0.5 to 1.5 mm. The free 222 omu. HISTOLOGY AND EMBRYOLOGY

0».

Fig. 171A.—Meissner tactile corpuscle in the human gingiva. S_i1veg- impregnation after Bielschowsky-Gros. (Courtesy F. VV. Gan-ns and J. AltchlS0n.3“)

. 1:

Fig. 171B.——-Intraepithelial “uli:raterminal" extensions and nerve endings in the human

gingiva. Silver impregnation after Bielschowsky-Gros. (Courtesy F. W. Gaitns and J. A.itchiaon.'-) ORAL MUCOUS MEMBRANE 223

Marginal

Inter —'—‘ glngiva dental Fr” pagirlla. / gingiva

. 93 Margin of gigrgoggé the gingiva.

Inter- ‘' ° ° ° ' ° ‘’ Fr.“ dental o , ° I ,, ° 6 0 II‘ o 0 _ ‘’ H 0 ° ° gmgival ‘°‘‘‘s -» ., ~ ‘’ ., ,° ° ,, ° . " .. ,° . "—_.._._° A‘?'t2‘3’.§a ., ° ' 0 glngive.

3 6 _Muco- ° ” G (stippled)

gmgwal junction Alveolar mucosa

Fig. 172A.—Diag'ram illustrating the surface characteristics of the gingiva.

Margin of the glngiva.

Free ginglva.

Free gingival groove

Attached gingiva ( stlppl ed )

Mucogingival Junction

Alveolar mucosa.

-¢_—.r‘.—"‘..

— .4.1‘

Fig. 172B.—Diag-ram illustrating the diflerence between the tree ginglva. attached glnglva, and alveolar mucosa. 224 ORAL HISTOLOGY AND EMBRYOLOGY

gingival groove is, on histologic section (Fig. 173), a shallow V-shaped groove corresponding to the heavy epithelial ridge which divides the free and the attached gingiva. The free gingival groove develops at the level of, or somewhat apical to, the bottom of the gingival sulcus. In

' 9 ’../,2",-I 'j}r""‘_

1 .

——.-- Free ginglval groove

- »»»» ——»-—— . —— . A .-«r‘x".‘.&=;

Fi§- 173-—Bi0Dsy specimen of gingiva. showing_ tree gingival groove and stippled at. tached ging-Ava.

501119 03868, the free gingival groove is not as Well defined as in others, and then the division between the free and attached gingiva is not clear. The tree gingival groove and the epithelial ridge are brought about by functional impacts upon the free gingiva, folding the movable free part back upon the attached and immovable zone. ORAL MUCOUS MEMBRANE 225

The attached gingiva is characterized by high connective tissue papillae elevating the epithelium, the surface of which appears stippled (Fig. 173). Between the elevations there are small depressions which correspond to the center of heavier epithelial ridges and show signs of degeneration and hornification at their depth. The stippling is most probably an expression of functional adaptation to mechanical impacts. The degree of

.,-.,.,3,..,

 ' ‘Oral epithelium

«- K . ~ /, : ‘ Reduced enamel “ g _ ' " ‘ epithelium

Enamel

Reduced enamel epithelium

Pulp

.1 ‘ -’

Cemento-enamel

. junction

iii;

l » ,

-.I----=- :9: _Periodonta.l mem ., ‘; ‘E brane

sea

3, ' ,‘»". T’ *1

1 .

Undeveloped apical

Fig. 174.—I-Iuman permanent incisor. The entire surface of the enamel is covered léybrediiced enamel epithelium. Mature enamel is lost by decalciflcation. (Gottlieb and 1- an. )

stippling varies with different individuals. The disappearance of stippling is an indication of edema, an expression of an involvement of the attached gingiva in a progressing gingivitis.

The attached gingiva appears slightly depressed between adjacent teeth, corresponding to the depression on the alveolar bone process between eminences of the sockets. In these depresssions, the attached gingiva often forms slight vertical folds. 226 ORAL I-IISTOLOGY AND EMBRYOLOGY The interdental papilla is that part of the gingiva that fills the space

between two adjoining teeth and is limited at its base by a line connecting the margin of the gingiva at the center of one tooth and the center

Ora.l——— -—-— 2. .' epithelium , Q "K;

Fusion oi’ oral

and enamel "3 .,g epithelium , , f V.‘ ._ .

I ‘~ _ ""”'—“—'.‘1{e(luced enamel

~ ._ ' __ epithelium ( ,, an Reduced enamel :15,’ <-‘J epithelium § 93;‘? . .5‘.

Fusion of oral and enamel epithelium X

Oral epithelium

Cemento-enamel junction

cementum

Fig. 175.—Rednce_d enamel epithelium fuses with oral epithelium. X in the diagram indicates area from which the photomlcrograph was taken.

of the next. The interdental papilla is composed of free gingiva and attached gingiva in various relations, depending largely upon the relationship of the neighboring teeth. ORAL MUCOUS MEMBRANE 227

B. EPITHELIAL ATTACHMENT AND GI.\‘GIVAL SULcus*

At the conclusion of enamel matrix formation the ameloblasts pro- De"91°Pm°nt

duce a thin membrane on the surface of the enamel: the primary enamel cutwle. It is a. limiting membrane, connected with the intei-prismatic

L our ll - -- “ oral epithelium ' " - epithelium .' F. 4-Gr * . . in

Enamel ’ "‘-—“ J‘ ".73" cuticle ‘r. .-9.

- "3' Y‘

5* -it

” Epithelial Enamel , attachment

.1: , Epithelial ‘I

attachment _.

Reduced enamel epithelium (now epithelial attachment)

Dentin

Pulp

Cemento-enamel junction

Cementum

Fig. 176.—'I‘ooth emerges through a perforation in the fused epithelial. X in the diagram indicates area from which the photomicrograph was taken.

enamel substance. The ameloblasts shorte11 after the enamel cuticle is formed, and the epithelial cells comprising the enamel organ are reduced to a few layers of cuboidal cells which are then called reduced

‘First draft of this section submitted by Bemliard Gottlieb. 228 ORAL HISTOLOGY AND EMBRYOLOGY

enamel epitheliunt. Under normal conditions it covers the entire enamel surface extending to the cemento-enamel junction (Fig. 174) and remains attached to the primary enamel cuticle. During eruption the tip of the tooth approaches the oral mucosa and the reduced enamel epithelium fuses with the oral epithelium (Fig. 175).

The epithelium which covers the tip of the crown degenerates in its center, and the crown emerges through this perforation into the oral cavity (Fig. 176). The reduced enamel epithelium remains organically attached to that part of the enamel which has not yet erupted. Once the tip of the crown has emerged, the reduced enamel epithelium is termed the epithelial attachment.‘ At the marginal gingiva the epithelial attachment continues into the oral epithelium (Fig. 177). As the tooth

Erupted enamel Glngival sulcus Free gingiva

Oral epithelium

Epithelial attachment

Enamel

Cemento-enamel junction

Dentin

Pulp

Fig 177.—Diagramma.tic illustration of epithelial attachment and gingival sulcus at an early stage of tooth eruption. Bottom of the sulcus at x.

erupts, the epithelial attachment is gradually separated from its surface. The shallow groove which develops between the gingiva and the surface of the tooth and extends around its circumference is the gingival sulcus (Fig. 177). It is bounded by the surface of the tooth on one side, and by the gingiva on the other. The bottom of the sulcus is found where the epithelial attachment (formerly reduced enamel epithelium) separates from the surface of the tooth. The part of the gingiva which is coronal to the bottom of the sulcus is the marginal gingiva. While the epithelial attachment is separated from the surface of the enamel, it produces often the secondary enamel cuticle} This is a hornified layer, 2 to 10 microns in thickness. ORAL MUCOUS MEMBRANE

A. B. 0.

Fig. 178.-—Three sections oi.’ the same tooth showing different relations of tissues at cemento-enamel junction. 4. Epithelial attachment reaching to cemento-enamel Junction.

B. Epithelial attachment leaves the enamel free at cemento-enamel junction.

0. Epithelial attachment covers part or the cementum. cementum overlaps the end of the enamel.

EA = epithelial attachment; E = enamel (lost in decaiciflcetion); 0 = cementum: X = end of epithelial attachment. (Or-ba.n.")

229 $5

230 omu. HISTOLOGY AND EMBRYOLOGY

In erupting teeth the epithelial attachment extends to the cementeenamel junction (Fig. 177). Occasionally, the epithelium degenerates in the cervical areas of the enamel; then the surrounding connective tissue frequently deposits cementum upon the enamel. This does not always occur aI'Ol111(l the entire surface of a tooth. Different sections of the same tooth may, and frequently do, show varying relationships in the area Where enamel and cementum meet (Fig. 178).

Enamel

Cuboidal cells of epithelial attachment

Flattened cells in epithelial attachment

Dentin

Basal cells of

epithelial attachment

Cemento-enamel junction

Fig. 179.——Arra.ngement of cells in the epithelial attachment indicate functional influences. (Orban.“')

The epithelial attachment is the derivative of the reduced enamel epithelium. In some cases, ameloblasts may still function at the apical end of the attachment when the tip of the crown has already emerged through the oral mucosa. The ameloblasts flatten out rapidly and then the reduced enamel epithelium forms the epithelial attachment. This is thin at first and consists of 3 to 4 layers of cells (Figs. 181, 182) but thickens gradually with advancing age to about 10 to 20 rows of cells, or more (Figs. 183, 184).

The epithelium which forms the attachment is stratified squamous epithelium. As a rule, the junction between epithelial attachment an_d connective tissue is smooth. It may be considered as a sign of irritation if the epithelial attachment sends fingerlike projections, epithelial pegs, into the conective tissue. The cells within the epithelial attachORAL MUCOUS MEMBRANE 231

ment are elongated, and are arranged more or less parallel to the surface of the tooth (Fig. 179). There is a distinct pattern in the direction of these flattened cells which may be the result of functional influences upon the attachment.“ The cells at the surface of the epithelial attachment are firmly fastened to the tooth and must follow all its movements. The basal layer of the epithelial attachment, on the other hand, is anchored to the surrounding connective tissue and must follow all the movements to which the gingival margin is subjected. The cells within the epithelial attachment are exposed to these different stresses. The

-. Epithelial bridge cross» ing tear in attachment

Epithelial cells attached to cementum

p Epithelial bridge crossing tear in attachment

‘ Epithelial attachment torn from cementum

Epithelial cells attached

‘ ‘Q to cementum ¥

Fig. 180.—Artitlcia1 tear in epithelial attachment. Some cells are attached to the ‘ cementum, others bridge the tear. (Orban and Muellenl‘)

attachment of the surface cells to enamel or cementum seems to be more firm than the connection of these cells to the deeper layers of the epithelium. For this reason tears occur frequently between the cuboidal cells attached to the tooth and the rest of the epithelial attachment. Such tears are found as artifacts in microscopic specimens (Fig. 180) but

may also occur during life.“ shift of Epithelial Attachment

First Stage

232 omu. HISTOLOGY AND EMBRYOLOGY

The relation between epithelial attachments and the surface of the tooth changes constantly. When the tip of the enamel first emerges through the mucous membrane of the oral cavity, the attachment covers almost the entire enamel (Fig. 181). Tooth eruption is relatively fast (see chapter on Tooth Eruption) until the tooth reaches the plane of occlusion. This causes the epithelial attachment to separate from the enamel surface, gradually exposing the crown. When the tooth reaches the plane of occlusion, one-third to one-fourth of the enamel is still covered by the epithelial attachment (Fig. 182). The gradual ex

I I I I /I ‘ I \ rll II \ I \ I \ F ’ I \ ree(gnn§:;:i \\ Free gingiva sulcus) \ - ' ’ ' ""‘ Gingival sulcus Enamel Dentin - —- - ‘ Enamel Epithelial —-' E lth ll l tta attachment Bnelfta 8' ch _ " *"»-"' Pulp Cementmenamel —— . junction _

" '—'- Cemento-enamel Junction

Fig. 181.—Epithelial attachment and glngival sulcus in an erupt‘ t th. of enamel is indicated by dotted line. Enamel lost in decalcifllgagtloii? (K1:-J¢!:'ii.i!)etl%1.1°‘))ut

posure of the crown by separation of the epithelial attachment from the enamel is known as passive eruption. The simultaneous elevation of the teeth, toward the occlusal plane, is termed active eruption (see chapter on Tooth Eruption).

The bottom of the gingival sulcus remains in the region of the enamelcovered crown for some time, and the apical end of the epithelial attachment stays at the cemento-enamel junction. This relationship of the epithelial attachment to the tooth characterizes the first stage in passive omu. MUCOUS MEMBRANE 233

eruption (Fig. 183). It persists in primary teeth almost up to one year before shedding and, in permanent teeth, usually to the age of about twenty or thirty; however, this is subject to great variations.

The epithelial attachment forms, at first, a wide band around the cervical part of the crown which becomes gradually narrower as the separation of epithelium from the enamel surface proceeds. Long before the bottom of the sulcus reaches the cemento—enamel junction, the epithelium proliferates along the surface of the cementum and the apical end of the

=‘ as

Enamel T ‘I 9 Dentin *'“" '* -: V \ Gingival sulcus .. _, ,3,‘ -4 p ’_ Free gingiva.

.

g“‘“ " —. Epithelial attachment Cemento-enamel '— "" junction

' 4' 4 Alveolar crest

Fig. 182.—Tooth in occlusion. One-fourth of the enamel is still covered by the epithelial attachment. (Kr-onfeld."')

epithelial attachment is then found in the cervical part of the root, on the cementum. This is the second stage in the passive eruption of teeth. In this phase the bottom of the gingival sulcus is still on the enamel; the apical end of the epithelial attachment has shifted to the surface of the cementum (Fig. 184).

The downgrowth of the epithelial attachment along the cementum is impossible as long as the gingival and transseptal fibers are still intact. It is not yet understood whether the degeneration of the fibers is

Second stage Third Stage

234 omu. msronoev AND EMBRYOLOGY

primary or secondary to the proliferation of the epithelium.“ Recent findings indicate that destruction of the fibers is secondary, the proliferating epithelial cells actively dissolving the principal fibers byenzymc action (desmolysis). A primary destruction of the principal fibers had been explained by the action of bacterial toxins from the gingival sulcus. The second stage of passive tooth eruption may persist to the age of forty or

Enamel cuticle

Bottom 01 glnglval snlcus

Enamel

Epithelial attachment

Cemento-enamel junction

Cementum

Fig. 183.—-Epithelial attachment on the enamel. First stage in passive tooth eruption. (Gotflieb and Orbanfi)

later. With advancing age the epithelial attachment further separates from the enamel surface, and the apical end of the epithelium continues to grow down along the cementum.

For a short time, the bottom of the gingival sulcus is just at the cementeenamel junction, the epithelial attachment is entirely on the cementum, and the enamel-covered crown is exposed (Fig. 185). This is the third stage in passive tooth eruption. Because of the continuous active and 235

ORAL MUCOUS MEMBRANE

Fre_e gmgiva

gingival sulcus

0-. 0 m o t t o B

Epithelial attachment to enamel

Cemento-enamel

junction

cementum

Epithelial , . _ attachmentn -‘«‘ to cementum .

End of epithelial attachment

Second

Fig. 184.—EpitheIia.l attachment partly 01.1 the enamel, partly on the cementum. stage in passive tooth eruption. (Gottiieb and Oz-ba.n.') E‘ourth Stage

236 ORAL HISTOLOGY AND EMBRYOLOGY

passive eruption of the teeth, the epithelium shifts gradually along the surface of the tooth and the attachment does not remain at the linear cemento-enamel junction for any length of time. The third stage in passive eruption marks only a moment in a more or less continuous process. If a part of the cementum is already exposed by separation of the

Enamel

1 E

,’ . Bottom of Einglval . I sulcus

I ‘ ! , .

Cemento-enamel junction

Oral epithelium

Epithelial attachment ;

End of epithelial - j ' _ "L _ ' attachment , .

Fig. 185.—Epithelial attachment on the cementum; bottom of the gingival sulcus at the cemento-enamel junction. Third stage in passive tooth eruption. (Gottlieb.')

epithelial attachment from the tooth surface, the fourth stage of passive eruption is reached. The epithelium is entirely attached to the cementum (Fig. 186).

It would appear that the epithelial attachment has to maintain a certain Width* to assure normal function of the tooth. Therefore, this proliferation along the cementum should be considered a physiological

'The width of the epithelial attachment varies from 0.25 to 6 mm.“ ORAL MUCOUS MEMBRANE 237

process, if it is in correlation to active eruption and attrition. If it progresses too rapidly or precociously and loses, therefore, correlation to active eruption, it must be considered as a pathologic process.

An atrophy of the gingiva. is correlated with the apical shift of the epithelial attachment, exposing more and more of the crown, and, later, of the root, to the oral cavity. The recession of the gingiva is therefore a physiologic process if it is correlated both to the occlusal wear and to the compensatory active eruption.

.*"*r.--vj _"“'*'~""""" '

x 1-: - ‘ .» - ,, . a

Enamel

‘ .

Cemento~ena.mel junction

Free gingiva.

Cementum (exposed)

Bottom of gingival sulcus

Free gingival groove -, V‘

cementum

Oral epithelium " —'

'7 End of epithelial attachment

Fig. 186.—Epithelial attachment on the cementum; bottom of_the ginglva-1 sulcns also on the cementum Fourth stage in passive tooth eruption. (Gott1ieb_6)

The rate of passive tooth eruption varies in difierent persons, and in different teeth of the same individual, as well as on different surfaces of the same tooth. In some cases, the fourth stage of passive tooth eruption is observed in persons during their twenties; in others, even at the age of fifty or later, the teeth are still in the first or second stage of eruption. The rate varies also in diflerent teeth of the same jaw: the earlier ,-,.,,_ __ _ K

88%

l'.‘)O'l0.\lI9I-\I(E[ (INV ;\’9()’I0£|LSIl-I 'IV}IO

A. B. C.

Fig. 187.—-Three sections of the same tooth showing different relationship of soft to hard tissues. A. Bottom of the sulcua on the enamel (second stage).

B. Bottom of the sulcus at cemento-enamel junction (third stage).

0. Bottom of the aulcua on cementum (fourth stage).

E = enamel lost in decalciflcation—outline indicated by dotted line; EA = epithelial attachment; 5: - bottom of

gingival sulcus: mm = and of epithelial attachment. ’ Mode of Attachment of Epithelium

ORAL MUCOUS MEMBRANE 239

a tooth erupts, the more advanced can be its passive eruption. Even around the same tooth there is a variation; one side may be in the first stage, the other in the second or even the fourth stage (Fig. 187). At no time are all parts of the bot_tom of the gingival sulcus in the same relation to the tooth.

Gradual exposure of the tooth to the oral cavity makes it possible to distinguish between the anatomical and clinical crowns of the tooth (Fig. 188). That part of the tooth which is covered by enamel is the anatomical crown; the clinical crown is that part of the tooth exposed in the oral cavity.“ In the first and second stages, the clinical crown

II III IV

Fig. 188.—Diagrammatie illustration of the four stages in passive tooth eruption: in Stages I and 11 the anatomic crown is larger than the clinical; in Stage III anatomic and inical crowns are equal; in Stage IV the clinical crown is larger than the anatomic. The arrow in the small diagram indicates the area from which the drawings were made.

E = enamel; E4 = epithelial attachment; 0 = cemento-enamel junction; 5.‘ = bottom of gingival sulcus.

is smaller than the anatomical. In the third stage, the enamel-covered part of the tooth is exposed and the clinical crown is equal to the anatomical. It should be emphasized that this condition is not actually encountered, because the bottom of the gingival sulcus is never at the same level all around the tooth. In the fourth stage the clinical crown is larger than the anatomical because parts of the root have been exposed.

The means by which the epithelium is attached to the enamel is not as yet fully understood. Several explanations have been advanced. Formerly it was claimed that the epithelium is not organically attached to the tooth but is kept in place by tissue tone and elasticity of the con240 ORAL HISTOLOGY AND EMBRYOLOGY

nective tissue of the gingiva pressing the epithelium against the tooth surface. This concept has been disproved by microscopic evidence, which shows that there is an organic union between the epithelium and the tooth surface. The strength of the attachment was demonstrated by the following experiment: The teeth and surrounding tissues in young dogs were frozen and ground into relatively thin sections. These were placed under the dissecting microscope, and the free margin of the giiigiva was pulled away from the tooth with a needle. By this method it was possible to demonstrate that the attachment can be severed from

Epithelial attachment

Epithelial

'3. attachment

to 189.—e-LG:-ound section of hard and soft tissues of teeth. Epithelial attachment

A. General view of inter-dental papilla. 3- Higher ma.g'nifl<‘£ti011 01 Elnsival sulcus and epithelial attachment

1. 4: ‘L fnaettnzfliafiaf a‘l€.?;‘l,‘;.§e.§iP($m‘;%‘:.Ef€.Ea?;:’éi“ji..f‘cu‘:‘n ,‘t°*‘€§3,d:£k§‘:z‘;,;Lb:‘:§g:;

the tooth only to a certain depth; from there on it tears instead of separating from the tooth.” The firmness of the attachment may be further shown by studying ground sections prepared by a. special method of investing soft and hard tissues (Fig. 189). In such specimens the enamel. is not lost as in decalcified sections, and the relations between epithelium and enamel are undisturbed. Another confirmation of the organic connection between tooth surface and epithelium is the fact that, omar. MUCOUS MEMBRANE 241

after extraction of teeth, epithelium is often found adherent to the extracted tooth,’ The firm connection between epithelium and enamel is a primary 11111011, the enamel being a cuticular product of the ameloblasts.

The layer of the epithelial attachment that is attached to the surface of the enamel is the regressed ameloblast layer.

It has also been claimed that the secondary cuticle plays an important role in cementing the epithelium to the surface of the tooth. This cuticle‘ is a hornified structure, homogenous and brittle. It lies outside the primary enamel cuticle (see chapter on Enamel) and stains bright yellowishred in hematoxylin-eosin preparations. It is resistant to acids and

Secondary '< ' l enamel cuticle

Epithelial . .

attachment a l

‘ .

Cemento- —— -enamel junction

Cements.) cuticle ; (dental .’

cuticle)’ fl “j s §:}is._.

31 

Fig. 190.—Seconda.ry enamel cuticle follows epithelial attachment to the cementum forming the “dental cuticle." Arrow in diagram indicates area. from which the photomicrograph was taken.

alkalies and may act as a protective layer on the tooth surface. Even yet its method of formation is not quite clear: some investigators claim‘ that it develops by transformation of the cells which are adjacent to the tooth surface in a manner similar to normal hornification. Others contend that this cuticle is a secretory product of the epithelial cells.“ The secondary cuticle is not limited to the surface of the enamel, as is the primary cuticle, but follows the epithelial attachment when it shifts along the cementum; hence it is designated by the term cuticula. dentis The Gtngival suleus

242 ORAL msronocv AND EMBRYOLOGY

(dental cuticle) (Fig. 190). The formation of the dental cuticle by the epithelial attachment is believed to be a reaction of the epithelium to its contact with a hard structure. It is further assumed that formation of the cuticle is the first phase of a process which, ultimately, leads to separation of the epithelium from the tooth. However, some investigators claim that this cuticle is a pathologic structure, induced by inflammation of the gingiva."

~7
Cuticle

l'l‘

F." cementum ' xx’, ‘.1:

5'3: ' Extension or cuticle Into _ ' space in cementum Dentin _ "

Fig. 191.—Horny substance of the dental cuticle extends into the spaces of the cementum. (Gottlieb and Orbanfi)

The mechanism of attachment of the epithelium to the enamel is still open to further investigation. The attachment of the epithelium to the cementum is accomplished by fine processes of the epithelial cells, extending into minute spaces of the cementum where Sharpey’s fibers were previously located. This mode of attachment can be likened to the attachment of the basal cells of an epithelium to the underlying basement membrane. When the dental cuticle is formed on the surface of the cementum,-the horny substance extends into these spaces (Fig. 191).

The erupting crown is surrounded by a tissue formed by the fusion of the oral and reduced enamel epithelium. The gingival suleus forms when the tip of the crown emerges through the oral mucosa. It deepens as a result of separation of the reduced enamel epithelium from the actively erupting tooth. Shortly after the tip of the crown has appeared in the oral cavity the tooth establishes occlusion with its antagonist. otm. MUCOUS MEMBRANE 243

During this interval the epithelium separates rapidly from the surface of the tooth. Later, when the tooth reaches its occlusion, separation of the epithelial attachment from the surface of the tooth slows down.

Actual movement of the tooth (active eruption) and peeling off of the epithelial attachment (passive eruption) are the two integral factors of tooth eruption. The normal correlation between the two may be broken. In accelerated active eruption (teeth Without antagonists), the rate of passive eruption does not necessarily increase. On the other hand, in the case of a pathologic recession of gingiva, the peeling off of the epithelial attachment may be accelerated without appreciable change in the rate of active eruption.

E E E

EA EA

II III IV

_ Fig. 192.—Dia.grarnmatic illustration of diflerent views on the formation of the gmgival sulcus as discussed in the text. Arrow in the small diagram indicates area. from which the drawings were made.

The formation and relative depth of the gingival sulcus, at different ages, has proved an extremely controversial subject. Until the epithelial attachment was recognized, it was believed that the gingival sulcus extended to the cemento—enamel junction, immediately after the tip of the crown pierced the oral mucosa (I in Fig. 192). It was assumed that the attachment of the gingival epithelium to the tooth was linear and existed only at the cemento—enamel junction. Since the epithelial attachment has been first described, it has been recognized that no cleft exists between epithelium and enamel, but that enamel and epithelium are in firm organic connection. The gingival sulcus is merely a shallow groove, the bottom of which is at the point of separation of the attachment from the tooth (II in Fig. 192) . The separation of the epithelium from the tooth is now considered a physiologic process. 244 ORAL HISTOLOGY AND EMBRYOLOGY

Some investigators contend that the deepening of the gingival sulcus is due to a tear in the epithelial attachment itself (III in Fig. 192). Tears may deepen the gingival sulcus when the free margin of the gingiva is exposed to excessive mechanical trauma.

Others claim‘, 22 that the gingival sulcus forms at the line of fusion between the enamel epithelium attached to the surface of the enamel, and the oral epithelium (IV in Fig. 192). Accordingly, the oral epithelium proliferates at the connective tissue side of the epithelial attachment and replaces the former enamel epithelium which degenerates progressively.

The depth of the normal gingival sulcus has been a frequent cause of disagreement, investigations, and measurements.“ Under normal conditions, the depth of the sulcus varies from zero to six millimeters; 45 per cent of all measured sulci were below 0.5 mm., the average being about 1.8 mm. It can be stated that the more shallow the sulcus, the more favorable are the conditions at the gingival margin. Every sulcus may be termed “normal,” regardless of its depth, if there are no signs of a pathologic condition in the investing tissues.

The presence of leucocytes and plasma cells in the connective tissue at the bottom of the gingival sulcus should not, in itself, be considered a pathologic condition. It is evidence, rather, of a defense reaction in response to the constant presence of bacteria in the gingival sulcus. These cells form a barrier against the invasion of bacteria and the penetration of their toxins.“

The blood supply of the gingiva is derived chiefly from the branches of the alveolar arteries which penetrate the alveolar septum,” and from arteries lying on the outside of the alveolus and jawbones. The blood vessels of the gingiva anastomose with those of the peridontal membrane. There is a rich network of lymph vessels in the gingiva along the blood vessels leading to the submental and submaxillary lymph nodes. There is also a rich plexus of nerve fibers and numerous nerve endings in the gingiva.

C. HARD PALATE

The mucous membrane of the hard palate is tightly fixed to the underlying periosteum and, therefore, immovable. Its color is pink, like that of the gingiva. The epithelium is uniform in character throughout the hard palate, with a rather thick hornified layer and numerous long pegs. The lamina propria, a layer of dense connective tissue, is thicker in the anterior than in the posterior parts of the palate. Various regions in the hard palate differ because of the varying structure of the submucous layer. The following zones can be distinguished (Fig. 193): (1) the gingival region, adjacent to the teeth; (2) the palatine raphe, also known as the median area, extending from the incisive (palatine) papilla

posteriorly; (3) the anterolateral area, or fatty zone between raphe and.

gingiva, (4) -the posterolateral zone or glandular zone, between raphe and gingiva. om. MUCOUS MEMBRANE 245

E Palatine papilla

Gmgiva

Raphe

Soft palate

.... ..

._.., _

Alveolar crest _

Fig. 194.—Structura.l differences between gglngivs. and palatine mucosa. Region or first m a.r. 246 ORAL rnsronocv AND EMBRYOLOGY

The marginal area shows the same structure as the other regions of the gingiva. Therefore, in this zone, a submucous layer cannot be differentiated from the lamina propria or periosteum (Fig. 194). Similarly, the layers of the lamina propria, submucosa, and periosteum cannot be distinguished in the palatine raphe, or median area (Fig. 195). If a palatine torus is present, the mucous membrane is noticeably thin and the otherwise narrow raphe spreads over the entire torus.

In the lateral areas of the hard palate (Fig. 196), in both fatty and glandular zones, the lamina propria is fixed to the periosteum by strands of dense fibrous connective tissue which are at right angles to the surface and divide the submucous layer into irregularly shaped spaces. The distance between lamina propria and periosteum is smaller in the anterior than in the posterior parts. In the anterior zone the connective tissue

‘. Nasal septum

Median palatine suture

‘-'Connective tissue ' ‘i. strands

Fig. 195.—'1‘r-ansverse section through hard palate. Palatine raphe; fibrous strands connecting mucosa and periosteum; palatlne vessels. (E. C. Pendletonfi)

spaces contain fat (Fig. 195) while in the posterior part lobules of mucous glands are packed into the spaces (Fig. 196). The glandular layer of the hard palate extends posteriorly into the soft palate.

In the sulcus between alveolar process and hard palate, the anterior palatine vessels and nerves are found surrounded by loose connective tissue. This area being wedge-shaped in cross section (Fig. 197) is relatively large in the posterior parts of the palate and gradually diminishes in size anteriorly.

The pear-shaped or oval incisive (palatine) papilla is formed of dense 1“°i‘iY° connective tissue. It contains the oral parts of the vestigial nasopalatine mun‘ ducts. These are blind epithelial ducts of varying lengths. They are lined by a simple or pseudostratified columnar epithelium, rich in goblet cells; small mucous glands open into the lumen of the ducts. Frequently, ORAL mucous MEMBRANE 247

the ducts are bordered by small irregular islands of hyalin cartilage, vestigial extensions of the paraseptal cartilages. The nasopalatine ducts are patent in most mammals a11d, together with Jacobson ’s organ, are considered as auxiliary olfactory sense organs. The cartilage is sometimes found in the anterior parts of the papilla; it then shows no apparent relation to nasopalatine ducts (Fig. 198).

The transverse palatine ridges (palatine rugae), irregular and often asymmetric in man, are ridges of mucous membrane -extending laterally from the incisive papilla and the anterior part of the raphe. Their core is a dense connective tissue layer with finely interwoven fibers.

In the midline, especially in the region of the palatine papilla, epithelial pearls may be found in the lamina propria. They consist of concentrically arranged epithelial cells which are frequently hornified. They are remnants of the epithelium in the line of fusion between the palatine processes (see chapter on Development of the Face).

B. Lining Mucosa

All the zones of the lining mucosa are characterized by a relatively thin, nonhornified epithelium and by the thinness of the lamina propria. They differ from one another in the structure of their submucosa. Where the lining mucosa reflects from the movable lips, cheeks and tongue to the alveolar bone, the submucosa is loosely textured. In regions where the lining mucosa covers muscles, as on the lips, cheeks, and underside of the tongue, it is immovably fixed to the epimysium or fascia of the respective muscle. In these regions the mucosa is also highly elastic. These two characteristics safeguard the smoothness of the mucous lining in any functional phase of the muscle and prevent a folding which would interfere with the function; for instance, the teeth might injure the lips or cheeks if such folds protruded between the teeth. The mucosa of the soft palate is a transition between this type of lining mucosa and that which is found in the fornix vestibuli and in the sublingual sulcus at the floor of the oral cavity. In the latter zones, the submucosa is loose and of considerable volume. The mucous membrane is loosely and movably attached to the deep structures which allows for a free movement of lips and checks and also tongue.

Thus, it is possible to subdivide the lining mucosa into the two main types of tightly and loosely attached zones; the tightly fixed area, however, should be subdivided once more on the basis of the absence or presence of a distinct submucous layer. This layer is lacking on the underside of the tongue but is present in the lips, cheeks, and soft palate. In the latter areas, the mucous membrane is fixed to the fascia of the muscles, or to their epimysium, by bands of dense connective tissue between which either fat lobules or glands are situated.

A. Ln> AND CHEEK

The epithelium of the mucosa on the lips (Fig. 165) and the cheek (Fig. 199) is typically stratified and squamous, Without hornification.

Palatine Eugae (transverse palatine ridges)

Epithelial Pearls Soft palate End of hard palate Lamlna. propria.

Musculua inclslvus

Alveolar crest

Fig. 196.—Longltudlna.l section through hard and soft palate lateral to mldllne. Fatty and glandular zones of hard palate. Palatine vessels ' . and nerves

Alveolar crest

Fig‘. 197.—'1‘z-ansverse section through posterior part of hard palate, region or second molar. Loose connective tissue in the furrow between alveolar process and hard palate around palatine vessels and nerves.

, Incisal canal

Cystic remnant of

nasopalatine duct

Central lncior—

Fig. 198.—Sa.gitta.l section through palagne pai1l>lll.la and anterior palatine canal. Cartilage Dan 250 ORAL HISTOLOGY AND EMBRYOLOGY

The surface layer consists of very flat cells containing pyknotic nuclei. These superficial cells are continuously shed and replaced.

The lamina propria of the labial and buccal mucosa consists of dense connective tissue which sends irregular papillae of moderate length into the epithelium.

"The submucous layer connects the lamina propria to the thin fascia of the muscles and consists of strands of densely grouped collagenous fibers. Between these strands loose connective tissue containing fat and small mixed glands is found. The strands of dense connective tissue limit the mobility of the mucous membrane against the musculature and prevent its elevation into folds. Small Wrinkles appear in the mucosa during the contraction of the muscles, thus preventing the mucous membrane of the lips and cheeks from lodging between the biting surfaces of the teeth during mastication. The mixed glands of the lips are situated in the submucosa, While in the check the larger glands are usually found between the bundles of the buccinator muscle, and sometimes on its outer surface. A horizontal middle zone on the cheek, lateral to the corner of the mouth, may contain isolated sebaceous glands (“Fordyce spots”). These occur in the zone of embryonic fusion between the lateral parts of the primary lips during the development of the cheek (see Chapter I).

The epithelium and lamina propria of the mucous membrane in the vestibular fornix do not differ from those of the lips and cheeks. However, the submucosa here consists of loose connective tissue, which often contains a considerable amount of fat. This layer of loose connective tissue is thickest at the depth of the fornix. The labial and buccal frenula are folds of the mucous membrane, containing loose connective tissue. No muscle fibers are found in these folds.

B. VESTIBULAR FORNIX AND ALVEOLAR MUCOSA

The vestibular fornix is the area where the mucosa of lips and checks reflects to become the mucosa covering the jaws. The mucous membrane of the cheeks and lips is firmly attached to the buccinator muscle in the cheeks and the orbicularis oris muscle in the lips. In the fornix, the mucosa is loosely tonnected to the underlying structures and thus permits the necessary movements of lips and cheeks. The mucous membrane covering the outer surface of the alveolar process is loosely attached to the periosteum in the area close to the fornix. It continues into, but is sharply limited from, the gingiva, which is firmly attached to the periosteum of the alveolar crest and to the teeth.

Gingival and alveolar mucosae are separated by a scalloped line, muco-gingival junction. The altered appearance of tissues on either side of this line is due to a difference in their structures. The attached gingiva is stippled, firm, thick, lacks a separate submucous layer, is immovably attached to the bone, and has no glands. The gingival epithelium is thick and hornified; the epithelial ridges and the papillae omu. MUGOUS MEMBRANE 251

of the lamina propria are high. The alveolar mucosa is thin and loosely attached to the periosteum by a well-defined submucous layer of loose connective tissue and may contain small mixed glands. The epithelium is thin, not hornified, and the epithelial ridges and papillae are low and: are often entirely missing. Structural differences also cause the difference in color between the pale pink gingiva and the dark red lining mucosa.

Epithelium

Dense connectlve tissue strands

Submucosa

Buccinator _ , . _ _. muscle _ —; » . pi

Fig. 199.—Section through mucous membrane of check. Note the strands ot dense connective tissue attaching the mucous membrane to the buccinator muscle.

0. Mucous IVIEMBRANE or TI-IE INFERIOR SURFACE on THE TONGUE AND on THE FLOOR on‘ THE ORAL CAVITY

The mucous membrane on the floor of the oral cavity is thin and loosely attached to the underlying structures to allow for the free mobility of the tongue. The epithelium is not hornified and the papillae of the 252 ORAL msvronoev AND EMBRYOLOGY

Epithelium

Lamina propria

Submucosa

Submucosa

Lamina. propria :

Fig. 201.—Mucous membrane on interior surface of tongue. can. MUCOUS MEMBRANE 253

lamina propria are short (Fig. 200). The submucosa contains adipose tissue. The sublingual glands lie close to the covering mucosa in the sublingual fold. The sublingual mucosa joins the lingual gingiva in a sharp line that corresponds to the mucogingival line on the vestibular surface of both jaws. At the inner border of the horseshoe-shaped sublingual sulcus, the sublingual mucosa reflects onto the lower surface of the tongue and continues as the ventral lingual mucosa.

The mucous membrane of the inferior surface of the tongue is smooth and relatively thin (Fig. 201). The epithelium is not hornified; the papillae of the connective tissue are numerous but short. Here, the submucosa cannot be identified as a separate layer; it binds the mucous membrane tightly to the connective tissue surrounding the bundles of the striated muscles of the tongue.

D. SOFT PALATE

The mucous membrane on the oral surface of the soft palate is highly vascularized and of reddish color, noticeably differing from the pale color of the hard palate. The papillae of the connective tissue are few and short. The stratified squamous epithelium is not hornified (Fig. 202).

Fig. 202.—Mucous membrane from oral surface of soft palate. 254 ORAL HISTOLOGY AND EMBRYOLOGY

The lamina propria shows a distinct layer of elastic fibers separating it from the submucosa. The latter is relatively loose and contains an almost continuous Iayer of mucous glands. Typical oral mucosa continues around the free border of the velum palatinum and is replaced, at a variable distance, by nasal mucosa with a pseudostratified, ciliated, col umnar epithelium.

G. Specialized Mucosa or Dorsal Lingual Mucosa

The superior surface of the tongue is rough and irregular (Fig. 203). A V-shaped line divides it into an anterior part, or body, and a posterior part, or base of the tongue. The former comprises about two-thirds of the length of the organ, the latter forming the posterior one-third. The fact that these two parts develop from different areas of the branchial region (see chapter on Development of the Face) accounts for the different source of nerves of general sense: the anterior twothirds is supplied by the trigeminal nerve through its lingual branch; the posterior one-third by the glossopharyngeal nerve. '

The body and base of the tongue differ widely in the structure of their covering mucous membrane. On the anterior part are found numerous fine-pointed, cone-shaped papillae which give it a velvet-like appearance. These projections, the filiform papillae (thread-shaped) are built of a core of connective tissue which carries secondary papillae (Fig. 204, A). The covering epithelium is hornified, especially at the apex of the papillae. This epithelium forms hairlike tufts over the secondary papillae of the connective tissue.

Interspersed between the filiform papillae are the isolated mushroomshaped or fungiform papillae (Fig. 204, B) which are round, reddish prominences. Their color is derived from a rich blood supply visible through the relatively thinner epithelium. Some fungiform papillae contain a few taste buds.

In front of the dividing V-shaped line, between the body and base of the tongue, are found the vallate or circumvallate (walled—in) papillae (Fig. 205) ; they are 8 to 10 in number. They do not protrude above the surface of the tongue, but are bounded rather by a deep and circular furrow which seems to cut them out of the substance of the tongue. They are slightly narrower at their base. Their free surface shows numerous secondary papillae which are covered by a thin and smooth epithelium. On the lateral surface of the vallate papillae and occasionally on the walls surrounding them, the epithelium contains numerous taste buds. Into the trough open the ducts of small albuminous glands (von Ebner’s glands) which serve to Wash out the furrows into which the soluble elements of food penetrate to stimulate the taste buds.

At the angle of the V-shaped line on the tongue is found the foramen I

cecum which is a .remnant of the thyroglossal duct (see chapter on Development of the Face). Posterior to the vallate papillae, the surface of ORAL MUCOUS MEMBR.-XNE 255

the tongue is irregularly studded with round or oval pron1inences known as the lingual follicles. Each of the latter show one or more lymph nodules, sometimes containing a germinal center (Fio-. 206). Most of these prommences have a small pit at the center, the lingual crypt, which is lined with stratified squamous epithelium. Innumerable lymphocytes migrate into the crypts through the epithelium. The ducts of the medium—sized posterior lingual mucous glands open into the crypts. Together the lingual follicles form the lingual tonsil.

Filiform papillae

Fungitorni - - - — — — — _ papilla Foliate papillae Vallate D9-Dilla. z’ Foramen cecum 335' 2)-r’ Lingual tonsil hr» Entrance to larynx , , Pha.ryngo_ _ . 1 .' . , epiglottic Eplglottis“ "‘ p, " _ * . I -‘ : fold " L‘ ' .‘,,—' Cuneiform ~ tubercle . _ P’?

§«:,...— Fold of supe‘ I, rlor laryn"" geal nerve

i‘_' " ‘ ' Corniculate

' tubercle

c. ,7 “~ Piriform sinus Interarytenoid - * — — - -* ‘ notch

Fig. 203.—Surtace view of human tongue. (Sicher and Tandler.)

On the lateral border of the posterior parts of the tongue sharp parallel furrows of varying length can often be observed. They bound narrow folds of the mucous membrane and are the vestiges of the large foliate papillae found in many mammals. They may contain taste buds. Taste Buds

256 ORAL ELISTOLOGY AND EMBRYOLOGY

The taste buds are small ovoid or barrel-shaped intra-epithelial organs of about 80 microns in height and 40 microns thickness (Fig. 207). They touch with their broader base the basement membrane while their narrower tip almost reaches the surface of the epithelium. The tip is cov wefcfl 4 395

Fig. 204.——-Filiform (A) and fungiform (B) papillae.

ered by a. few flat epithelial cells, which surround a small opening, the taste pore. It leads into a narrow space between the peripheral ends of the sustentacular (supporting) cells of the taste bud. The outer supporting cells are arranged like the staves of a barrel, the inner and shorter ones ow. MUOOUS mmmmm 257

,5-5 Taste bud

5 3%:

“ of v. Ebnel-'5

{——— _..._’ Opening of duct ' " ' gland

zland

Lymph nodule with germinal _ center

Fig. 206.—L1ng'u8.l follicle. 258 ORAL HISTOLOGY AND EMBRYOLOGY

are spindle-shaped. Between the latter are arranged 10 to 12 neuroepithelial cells, the receptors of taste stimuli. They are thin, dark-staining cells that carry a stiff hairlike process at each superficial end. This hair reaches into the space beneath the taste pore.

A rich plexus of nerves is found below the taste buds. Some fibers enter the taste bud from the base and end in contact with the taste cells. Others end in the epithelium between the taste buds.

Taste buds are numerous on the inner wall of the trough surrounding the vallate papillae, in the folds of the foliate papillae, on the posterior surface of the epiglottis and on some of the fungiform papillae at the tip and the lateral borders of the tongue.

Stratified squamous epithelium Taste pore Taste cells Supporting cells

Connective tissue

Supporting cells

Fig. 20'l'.—Taste buds from the slope of a. vallate papilla. (From .1’. Schafter.)

The primary taste sensations, namely, sweet, salty, bitter, and sour, are not perceived in all regions of the tongue. Sweet is tasted at the tip, salty at the lateral border of the body of the tongue. Bitter and sour are recognized in the posterior part of the tongue, bitter in the middle, sour in the lateral areas. The distribution of the receptors for primary taste qualities can, diagrammatically, be correlated to the different types of papillae. They are mediated by different nerves. The vallate papillae recognize bitter, the foliate papillae sour, taste. The ORAL MUCOUS MEMBRANE 259

taste buds on the fungiform papillae at the tip of the tongue are receptors for sweet, those at the borders for salty, taste. Bitter and acid (sour) taste are mediated by the glossopharyngeal, sweet and salty taste by the intermediofacial nerve via chorda tympani.

4. CLINICAL CONSIDERATIONS

To understand the pathogenesis of periodontal diseases and the pathologic involvements of the difierent structures, it is essential to be thoroughly familiar with the structure of cementum, periodontal membrane, alveolar bone, and the structure of the marginal gingiva, gingival sulcus, and epithelial attachment, as Well as their biologic relation to each other. Periodontal disturbances, frequently, have their origin in the gingival sulcus and marginal gingiva, leading to the formation of a deep gingival pocket.‘ Moreover, the safe and speedy reduction of the depth of the gingival pocket is the primary objective of treatment. The superiority of any given method of treatment should be judged by its ability to accomplish this end whether the method be surgical, chemical, or electrical.

In restorative dentistry, the extent of the epithelial attachment plays an important role. In young persons, this attachment of the epithelium to the enamel is of considerable length and the clinical crown is smaller than the anatomical. The enamel cannot be removed entirely without destroying the epithelial attachment. It is, therefore, very difficult to prepare a tooth properly for an abutment or crown in young individuals. On the other hand, the preparation may be mechanically inadequate when it is extended only to the bottom of the gingival sulcus. It should be understood, therefore, that, in young persons, a restoration may serve merely as a temporary measure and require ultimate replacement.

When large areas of the root are exposed, and a restoration is to be placed, the preparation need not cover the entire clinical crown. The first requirement is that the restoration be adapted to mechanical needs.

In extending the gingival margin of any restoration in the direction of the bottom of the gingival sulcus, the following rules should be observed: If the epithelial attachment is still on the enamel, and the gingival papilla fills the entire proximal space, the gingival margin of a cavity should be placed below the marginal gingiva. Special care should be taken to avoid injury to the gingiva and epithelial attachment, to prevent premature recession of the gingiva. When the gingiva is pathologically affected, treatment should precede the placing of a filling. If the gingiva has receded from the enamel, if the gingival papilla does not fill the interproximal space and if the gingival sulcus is very shallow, the margin of a cavity need not necessarily be carried below the free margin of the gingiva. The gingival margin of a cavity should be placed far enough from the contact poi11t to permit proper cleansing.

‘The term gingival pocket designates the pathologic condition of the gingival sulcus. 260 ORAL msrronocv AND EMBRYOLOGY

When the anatomical root is exposed, a predisposition to cemental caries and abrasion exists. Improperly constructed clasps, overzealous scaling, and too abrasive dentifrices may result in marked abrasion. After loss of the cementum the dentin may be extremely sensitive to thermal or chemical stimuli. Drugs, judiciously applied, may be used to accelerate sclerosis of the tubules and secondary dentin formation.

It is desirable to keep the depth of the gingival sulcus at a minimum. The more shallow the sulcus, the less opportunity for irritating material to be deposited. This can be done in part by proper massage and brushing.

The diflerence in the structure of the submucosa in various regions of the oral cavity is of great practical importance. Wherever the submucosa consists of a layer of loose connective tissue, edema or hemorrhage causes much swelling and infections spread speedily and extensively. Generally, inflammatory infiltrations in such parts are not very painful. If possible, injections should be made into loose submucous connective tissue. Such areas are the region of the fornix and the neighboring parts of the vestibular mucosa. The only place in the palate where larger amounts of fluid can be injected without damaging the tissues is the furrow between the palate proper and alveolar process (Fig. 197). Also, it will be found that in the areas where the mucosa is loosely fixed to the underlying structures, it is easier to suture surgical wounds than in those places where the mucous membrane is immovably attached.

The gingiva is exposed to heavy mechanical stresses during mastication. Moreover, the epithelial attachment to the tooth is relatively weak, and injuries or infections can cause permanent damage here. Strong hornification of the gingiva may afford relative protection. Therefore, measures to increase hornification can be considered a prevention against injuries. One of the methods of inducing hornification is mechanical stimulation, such as massage or brushing.

Unfavorable mechanical irritations of the gingivae may ensue from sharp edges of carious cavities, overhanging fillings or crowns, and accumulation of calculus. These may cause chronic inflammation of the gingival tissue.

Many diseases show their symptoms, initial and otherwise, in the oral mucosa. For instance, metal poisoning (lead, bismuth) causes characteristic discoloration of the gingiva margin. Leukemia, pernicious anemia, and other blood dyscrasias can be, and often have been, diagnosed by characteristic infiltrations of the oral mucosa. In the first stages of measles, small red spots with bluish-white centers can be seen in the mucous membrane of the cheeks, even before the skin rash appears; these spots are known as Koplik’s spots. Endocrine disturbances, including those of the estrogenic and gonadotropic hormones and of the pancreas may be reflected in the oral mucosa. ORAL MUCOUS MEMBRANE 261

In denture construction it is important to observe the firmness or looseness of attachment of the mucous membrane to the underlying bone. Denture—bearing areas should be those where the attachment of the mucosa is firm. The margin of dentures should not reach into areas where the loose mucous membrane is moved by muscle action.“’v 2°

In old age, the mucous membrane of the mouth may atrophy in the cheeks and lips; it is then thin and parchment-like. The atrophy of the lingual papillae leaves the upper surface of the tongue smooth, shiny and varnished in appearance. A senile atrophy of major and minor salivary glands may lead to xerostomia and sometimes an accompanying atrophy of the mucous membrane. In a large percentage of individuals, the sebaceous glands of the cheek may appear as fairly large, yellowish patches. Such a condition is known as Fordyce’s disease, but does not represent a pathologic change.

References

1. Aprile, E. C. de: Contribucion al estudio de los elementos reticulo endoteliales de la mucosa gingival, Arch. Hist. normal y Pat. 3: 473, 1947. la. Becks, H.: Normal and Pathological Pocket Formation, J. A. D. A. 16: 2167, 1929. 2. Bodecker, C. F., and Applebaum, E.: The Clinical Importance of the Gingival Crevice, Dental Cosmos 176: 1127, 1934. 3. Fish, E. W.: Bone Infection, J. A. D. A. 26: 691, 1939. 3a. Gairns, F. W., and Aitchison, J. A.: A Preliminary Study of the Multiplicity of Nerve Endings in the Human Gum, The Dental Record 70: 180, 1950. 4. Gottlieb, B.: Der Epithelansatz am Zahne (The Epithelial Attachment), Deutsche Monatschr. f. Zahnh. 39: 142, 1921. 5. Gottlieb, B.: Aetiologie und Prophylaxe der Zahnkaries (Etiology and Prophylaxis of Caries), Ztschr. f. Stomatol. 19: 129, 1921. 6. Gottlieb, B.: Tissue Changes in Pyorrhea, J. A. D. A. 14: 2178, 1927. 7. Gottlieb, B., and Orban, B.: Biology of the Investing Structures of the Teeth, Gordon ’s Dental Science and Dental Art, Philadelphia, 1938, Lea av Febiger. 8. Gottlieb, B., and Orban, B.: Biology and Pathology of the Tooth (Translated by M’. Diamond), New York, 1938, The Macmillan Co. 9. Kronfeld, B.: The Epithelial Attachment and So-Called Nasmyth’s Membrane, J. A. D. A. 17: 1889, 1930. 10. Kronfeld, 3.: Increase in Size of the Clinical Crown of Human Teeth With Advancing Age, J . A. D. A. 18: 382, 1936. 11. Lehner, J.: Ein Beitrag zur Kenntniss vom Schmelzoberhiiutchen (Contribution to the Knowledge of the Dental Cuticle), Ztschr. f. mikr.-anat. Forsch. 27: 613, 1931. 12. Meyer, W.: Ueber strittige Fragen in der Histologie des Schmelzoberhiiutchens (Controversial Questions in the Histology of the Enamel Cuticle), Vrtljsschr. f. Zahnh. 46: 42, 1930. 13. Orban, B., and Kohler, J.: Die physiologisiche Zahnfleischtasche, Epithelansatz und Epitheltlefenwucherung (The Physiologic Gingival Sulcus), Ztschr. f. Stomatol. 22: 353, 1924. 14. Orban, B., and Mueller, E.: The Gingival Crevice, J. A. D. A. 16: 1206, 1929. 15. Orban, B.: Hornification of the Gums, J . A. D. A. 17: 1977, 1930. 16. Orban, B.: Zahnfleischtasche und Epithelansatz (Gingival Snlcus and Epithelial Attachment), Ztschr. f. Stomatol. 22: 353, 1924. 17. Orban, B.: Clinical and Histologic Study of the Surface Characteristics of the Gingiva, J . Oral Surg., Oral Med., Oral Path. 1: 827, 1948. 18. Orban, B., and Sicher, 11.: The Oral Mucosa, J. Dent. Educ. 10: 94-103, 163-164, 1946. 19. I-‘endleton, E. 0.: The Minute Anatomy of the Denture Bearing Area, .1’. A. D. A. 21: 488, 1934. _ _ 20. Pendleton, E. 0., and Glupker, 11.: Research on the Reaction of Tissues Supporting Full Dentures, J. A. D. A. 222 76, 1935262 ORAL HISTOLOGY AND EMBRYOLOGY

21. Robinson, H. B. G., and Kitchin, P. 0.: The Effect of Massage With the Tooth brush on Keratinization of the Gingivae, Oral Surg., Oral Med., Oral Path. 1: 1042, 1948.

22. Skillen, W. G.: The Morphology of the Gringivae of the Rat Molar, J. A. D. A. 17: 645, 1930.

23. Toller, J. R.: Studies of the Epithelial Attachment on Young Dogs, Northwestern U. Bull. 11: 13, 1940.

24. Wassermann, F.: Personal communication.

25. Weinmann, J. P.: Progress of Gingival Inflammation Into the Supporting Structures of the Teeth, J. Periodont. 12: 71, 1941.

26. Weinmann, J. P.: The Keratinization of the Human Oral Mucosa, J. Dent. Research 19: 57, 1940.

27. Wermuth, J.: Beitrag zur Histologie der Gregend seitlich Von der Papilla palatina (Histology of the Region Lateral to the Incisive Papilla), Deutsche Monatschr. f. Zahnh. 45: 203, 1927. CHAPTER X GLANDS OF THE ORAL CAVITY

INTRODUCTION; SALIVA

EISTOGENESIS

CLASSIIPICATION OF SALIVARY G-LANDS SEGRETORY CELLS OI‘ THE SALIVARY G-LANDS MYOEPITHELIAL CELLS

DUCT ELEMENTS

INTERSTITIAL TISSUE

SAI.-IVARY G-LAITDS OI‘ MAJOR SECRETION SALIVABY G-LANDS O1‘ MINOR SECRETION

. CLINICAL CONSIDERATIONS

H °S°9°.“.°°9‘!*“."°!°!"

1. INTRODUCTION

The salivary glands of man are exocrine glands, the primary function of which is to transform and secrete materials brought to them via the circulating fluids of the body. This function represents active Work in producing and discharging complex substances, such as mucin and ptyalin, which are not found in the circulating blood and lymph. The cells give morphologic evidence of their secretory function, and because they remain intact throughout a cyclic process of formation and discharge, these glands are classified as merocrine in type.

A secondary function of the salivary glands is to excrete certain substances. Evidence of this may be seen in comparing the constancy of the ratio between salivary and blood urea, nitrogen and creatinine.”

Saliva is the term applied to the accumulated secretory and excretory products discharged by the salivary glands into the oral cavity. The saliva is the first of many digestive fluids to act upon the food elements in the diet, its main actions being to assist in the mastication of food and to act as a solvent for bringing components into solution, thus facilitating the stimulation of the taste organs. Albuminous or serous cells of the glands liberate the enzyme ptyalin or amylase which causes a preliminary breakdown of carbohydrates. The mucous celLs liberate mucin which counteracts tendencies to desiccation of the oral membranes and dental hard structures, and aids in the lubrication of the bolus of food for deglutition. The proteins and salts of saliva act as bufiers which tend to counteract the acids and alkalies in the oral cavity. Saliva is mechanically protective inasmuch as it serves to flush the sur Flrst draft submitted by Virgil D. Cheyne. 263 264 emu. HISTOLOGY AND ammevocoev faces of the teeth and mucous membranes of food and debris. Its action of removing bacteria from ducts and surfaces is a safeguard against infection.

There is some indication that saliva, normally, contains an antibacterial factor which inhibits the growth and activity of aciduric bacteria in the oral cavity, and may act to prevent dental caries.‘ 1° There is also evidence, however, that the saliva of some individuals may supply the proper culture medium needed for the bacteria found in the mouth. Because of these contradictions the role of saliva in dental caries is as yet unsettled and requires further investigation.

The total daily amount of saliva secreted by man is approximately 1,500 c.c. This quantity is subject to great variation, depending upon age, exercise, and diet. It is materially influenced by physical and psychologic stimulation and varies Widely in different individuals. Of the total amount secreted, the large salivary glands (parotid, submaxillary, and sublingual) contribute by far the greatest amount. The quality is directly dependent upon the type of glands which participate in its formation.

The methods of collection and the type of stimulus have an important influence upon the composition of saliva. In man, the mixed excretions from the glands may be collected in the unstimulated or resting state by simply cxpectorating into a receptacle or, in the stimulated or active state, by chewing parafiin. Pure secretions from the individual glands may be collected by the use of Lashley’s double metal cup instrument which can be applied to the mucous membrane surrounding the papillae of the salivary ducts,” or by direct canalization of the ducts of the parotid, submaxillary, or sublingual glands. Saliva obtained in this manner is a clear, colorless fluid. The function of certain glands or groups of glands in animals has been clarified by selectively removing salivary tissue,‘ or by the experimental production of a fistula, the duct being diverted to the outside of the oral cavity.

Mixed saliva is a frothy, slightly opalescent fluid containing water, proteins, mineral salts, ptyalin, mucin, food particles, desquamated epithelial cells and salivary corpuscles. Its viscosity is dependent upon the predominating type of saliva secreted. Serous saliva imparts the Watery characteristics to the fluid; mucin in the saliva renders it thick and ropy.

The specific gravity of mixed saliva varies from 1.000 to 1.020, the freezing point being lower than for the other secretions of the digestive glands. Results of hydrogen-ion determinations (pH) of saliva vary greatly, owing to individual variation, time of day, and difierence in methods used for its determination. The mean or average pH of resting saliva is approximately 6.8, ranging from 5.6 to 7.6 and being highest just before meals.‘ Undoubtedly, oral hygiene and the nature of the oral flora are also influencing factors.

Chemically, human, mixed saliva is a dilute solution containing about 0.2 per cent inorganic solutes and 0.5 per cent organic matter. The bulk of the inorganic portion consists of potassium and phosphate ions. The following

Quantity

Methods of Study

characteristics GLANDS on THE ORAL CAVITY 265

elements, however, are found in appreciable amounts: Cl, P. Na, K, Mg, Ca, and S. The amount of NaCl is approximately 90 mg. per 100 c.c.; the amount of carbonate, as C0,, 13.0 mg. The C0._., Ca, and K present in the saliva exceed the concentration in the blood, While the sodium chloride concentration is lower in saliva. Oxygen is present in the human parotid saliva in amounts varying from 0.84 to 1.46 c.c. per 100 c.c.

Leucocytes

Epithelial

Leucocytes

Fig. 208.—Smear of human saliva (Wright's stain). (Orban and Weinmannfl)

A large portion (0.4 per cent) of the organic matter in mixed secretions is mucin. With the exception of mucin, the principal organic constituents of saliva are albumin, globulin, amylase, and cholesterol. Urea, uric acid, creatinine, maltase, and ammonia are found in varying amounts. The ammonia originates largely from the decomposition of urea. In normal subjects values range from 1.28 to 13.66 mg. of ammonia nitrogen per 100 c.c. of saliva.” Total nonprotein nitrogen, urea plus ammonia, nitrogen, and uric acid average 37 per cent and 40 per cent, respectively, of the corresponding constituents of blood.” Blood amino-acids and polypeptides are not found in appreciable amounts in the saliva. Histology

266 can. msronocr AND snnsronoer

Sulfocyanate is generally present in the saliva to the extent of several milligrams per cubic centimeter. It is greatest in habitual smokers. The significance of sulfocyanate in the saliva is not known, but it probably comes from ingested cyanides present in certain fruits, tobacco, and from the disintegration of protein material. It is, apparently, not related to tooth decay.”

The opacity of saliva is attributed mainly to the presence of desquamated epithelial cells and salivary corpuscles (Fig. 208), the latter consisting of polymorphonuclear leucocytes and lymphocytes. The epithelial cells are large and flat with oval nuclei. They may be round or roughly irregular, with a granular cytoplasm. The salivary corpuscles are derived from the mucous membrane of the mouth, the tonsils and salivary glands. The average number of salivary corpuscles is, usually, less than 25 cells per cubic mm. of saliva, but higher counts (500 to 1,000) have been reported.” Lymphocytes constitute a relatively minor proportion of this number. Corpuscle counts are high after a night’s rest, low after meals. Their role is as yet imperfectly understood but it is the opinion of some investigators that they are phagocytic, reducing the bacterial flora of the mouth.

2. HISTOGENESIS

The salivary glands are formed during fetal life as solid buds of oral epithelium with club-shaped ends pushing into the subjacent mesoderm. As the bud or anlage grows it proliferates distally, forming a cord of cells. The most distal portion forms the alveoli or fimctional elements of the gland. Cords and buds are at first solid and are later hollowed out to form ducts and alveoli.

The bud of the parotid salivary gland appears as a shelflike outgrowth of epithelium during the fourth week of fetal life at the angle of the maxillary process and the mandibular arch (sulcus buccalis) ; the bud of the submaxillary appears in the sixth week, and that of the major sublingual (Bartholinian) during the eighth to ninth week from similar outgrowths located at the medial angle of the hollow between the tongue and mandibular arch (sulcus lingualis). The minor sublingual glands (Rivinian) arise as independent proliferations in the alveolingual region associated with the sulcus lingualis at the lateral margin of the plica sublingualis. Accessory and secondary lobes of the parotid and submaxillary glands become visible during the eighth to ninth weeks, as outgrowths arising from the cords of their respective glands. All the elements of the smaller sublingual, glossopalatine and palatine groups develop from the primitive oral epithelium. The anterior lingual glands are noticeable for the first time at ten weeks. They start as epithelial proliferations located on the ventral surface near the tip of the tongue on both sides of the median line. Development of the labial glands takes place simultaneously with the anterior lingual glands. Lymphoid tissue GLANDS on THE ORAL CAVITY 267

is, frequently, found in the fetal salivary glands; this is especially common in the parotid. Occasionally, remnants of lymphatic tissue are found in the adult.

3. CLASSIFICATION OF THE SALIVARY GLANDS

The human salivary glands are usually classified either according to the type of cells or according to the location of the gland. Cells which liberate mucin are named mucous cells, and those Which secrete some form of protein (enzyme) are called albuminous or serous cells, but it is now quite evident that all mucous cells, as Well as all albuminous cells, do not produce identical products. In many cases the secretory granules of albuminous cells give a distinct reaction for mucin with mucicarmine stain. This would indicate that it is possible for these cells to secrete both mucin and protein substances. Although a simple classification of the glands according to the chemical qualities of their secretion remains unsatisfactory, the glands are best classified as albuminous, mixed and mucous glands. The parotid gland of the adult is a pure albuminous gland. Glands with very few or no mucous cells are those of the vallate papillae. Glands in which both serous and mucous cells are present (true mixed glands) are referred to as predominantly serous or predominantly mucous, depending upon the ratio of the cell types. Those with a few mucous cells include the submaxillary gland (and the parotid gland of the newborn). Those predominantly of mucous character include the labial glands, small buccal glands, anterior lingual glands, and the sublingual gland. In man pure mucous glands are those at the base and border of the tongue, the glossopalatine glands and the palatine glands.

Classification of the Oral Glands According to Location?‘

A. Glands of the vestibule: 1. labial glands: a. superior labial glands b. inferior labial glands

2. buccal glands: a. minor buccal glands b. parotid gland

B. Glands of the oral cavity proper: 1. glands of the floor of the mouth (alveolingual complex)

a. submaxillary (submandibular) gland

b. major sublingual gland

c. minor sublingual glands

d. glossopalatine glands The Albuminous Cell

means

268 ORAL msronoov AND nmnnvonoev

2. glands of the tongue:

a. anterior lingual glands b. posterior lingual glands

(1) glands of the vallate papillae (2) glands of the base of the tongue

3. palatine glands

4. SECRETORY CELLS OF THE SALIVARY GLANDS

Both albuminous and mucous cells vary in appearance with the flinctional changes of the gland.

The albuminous or serous cells of the parotid gland and other glands of the mouth probably do not perform an identical function; the cells, however, resemble each other closely. Their secretion is a thin watery fluid containing a high percentage of organic and inorganic substances.

Albuminous cells are roughly pyramidal or polyhedral in shape, and form globular alveoli, the lumina of which are very narrow. The cells drain, for the most part, by intercellular secretory capillaries or canaliculi. In resting cells of a fixed specimen the small highly refractive secretory granules, embedded in a closely reticulated cytoplasm, obscure the cell boundaries. These zymogen granules are the antecedents of the enzyme ptyalin. They accumulate between the nucleus and the free end of the cell. They are easily dissolved by chemical agents, but are more stable than the granules in the mucous cell. Following stimulation they diminish in number (Fig. 210).

In addition to the secretory granules the cytoplasm contains rod-shaped mitochondria, a Golgi net, and a cytocentrum which can be demonstrated only by special staining methods (Fig. 210). Intracellular fat droplets are common. The nucleus of the albuminous cell is large, spheroidal, and filled with abundant chromatin substance. Its size and location are somewhat dependent upon the stage of activity of the cell.

The mucous cell of the salivary glands secretes mucin, a glycoprotcin which, dissolved in water, becomes a lubricating solution called mucus. It makes the saliva highly viscid. In man, mucous cells are studied best in sublingual glands, the mucous glands of the tongue, the glossopalatine and palatine glands. They are also found in small mixed glands where they make up the greater number of alveoli; in the submaxillary gland they are few in number.

The mucous cells are irregularly cuboidal in form and aligned against a basement membrane (Fig. 211). Mucous alveoli vary from globular to long branching masses, their lumina forming large ovals or elongated tubules. In the fixed preparation the nucleus is often deformed, shrunken; it is located at the base of the cell. The accumulation and removal of ‘,'.~

Buccal mt pad ". . “K, ‘In...

Parofid gland -"""" 3’~‘“ I

Minor sublingual --.-/‘V g’ ':-4-_..,m».“‘ ducts »

Sublingual gland ———— —— Ii‘ '

V Submaxillary duct — — — — ~ — — - J

Submaxillary _. L _' ______ .../ gland

Fig. 209.-Salivary glands of mad 1:1 muscle mug: ed.5°°?esi:11l1(-er a1;3&flT:‘f1dlt:1:P;nudib1e and mylohyold

5 _—: .3.

‘a

Different functional stages at (zknmermannfi)

Fig. 210.——A1buminoua gland. cycle is indicated by the letters 9. to g.

0" - Mucous cell Arrangement o1'_ cells in

Glands

Intercellular secre 270 ORAL HISTOLOGY AND EMBRYOLOGY

mucigen can be studied under favorable conditions. As the stimulated cell liberates its contents, the nucleus rises from the base and assumes an ovoid shape.

Mucigen granules cannot be observed because of their labile character except in fresh condition or by special methods of fixing and staining, whereby they can be stained specifically with mucicarmine and mucihematin. Mucous cells which have lost their granules have an empty appearance and the remaining cytoplasm takes a faintly blue stain with hematoxylin. In properly prepared specimens a few irregular mitochondria, a Golgi net and a cytocentrum can be demonstrated; fat glob ules are a constant feature.

Albuminous cell of demllune

Lumen of alveolus

— Mucous cell tory capillary

Fig. 212.-7Semidiagr-ammatic drawing or a. section through a mixed alveolus in the submaxillary gland. Serous cells forming a. demllune around the mucous cells.

In mixed glands mucous and serous cells are combined in such a Way that either all the cells of some alveoli are serous, and all the cells of others mucous; or that within the same alveolus both serous and mucous cells are present. In a mixed alveolus the albuminous cells occupy a position at the terminal or peripheral region. They are found as small crescent-shaped clumps which cap the mucous cells: crescents or demilunes of Gianuzzi (Figs. 212 and 215, a). Crescent cells are somewhat smaller, more finely granular, and darker staining than mucous cells in ordinary preparations. Albuminous cell

Process of myoepithelial cell

GLANDS or run om. cmrr 271

The secretory surfaces of the mucous cells form the lumen of a mixed alveolus. The cells of the crescents do not reach the lumen and discharge

their secretion through fine secretory capillaries which pass between the mucous cells (Fig. 212).

5. MYOEPITHELIAI. CELLS

In all salivary glands a syncytium of branching stellate cells surrounds the ducts and cells of the terminal secretory portions. They are in close

contact with the bases of the glandular cells and lie between them and the basement membrane. They lie in a similar location in the ducts. Viewed

cell Fibroblast

Fat

Fibroblast

s

2 .‘ Basement Blood vessel duct

Fig. 213.—A1buminous alveoli and striated duct or subma.xilla.ry gland with myoepithelial cells. (Modified after Zimmennannfi)

from the periphery, they appear as spider—like structures embracing the alveoli (Fig. 213). Although probably of epithelial origin, these cells function as a part of the supporting structure of the glandular elements and are called basal or basket cells, or myoepithelial cells. The body of the myoepithelial cell is made up of a dark, angular nucleus with a scanty amount of cytoplasm containing fine, straight fibrils which continue into many tentacle-like processes that encircle the basal portion of the alveolar cells. In cross section only their nuclei are visible. The cells become especially prominent after treating fresh glandular tissue in the state of active secretion with osmic acid or by teasing fresh glandular substance in water.“

It is generally believed that myoepithelial cells are contractile cells

which facilitate the movement of the secretion into and through the ducts. The phenomenon which is known as motor effect of the sympathetic

Myoepithelial

membrane

Lumen of striated

Location

Albumlnous cell

' ‘ Myoepithelial cell .— Striated cell _._ __. Excretory duct

4. .1 _._ Striated duct __ Intercalated duct Secretory alveoll __ Excretory duct B.

———. — Striated duct Intercalated duct

Secretory alveoll

.__ ;._ Excretory duct

__ __ Striated duct

0.

8] 214.——Dia.g-rams of the duct system and terminal‘ secretory portions or salivary

A. Parotid. B. Subma.xil.Ia.ry. G’. Sublzlngual. (Modified after Brauafi) GLANDS on THE ORAL CAVITY 273

nerves on the large salivary glands is probably caused by contraction of these cells under nervous stimulation.“ True muscular tissue is absent in the salivary glands.

6. DUCT ELEMENTS

The duct system of the salivary glands is complex and branching (Fig. 216). The smallest excretory channels are the intercalated ducts or the so-called necks or isthmuses. These connect the terminal alveoli with the

Albumlnous cell - Myoepithelial

_, . cell

, . I’

serous alveolus I’-ll’-31'¢°11“18!‘ secretory

capillary

Demllune

Myoeplthelial cell Basement membrane Mucous cells

Intercalated duct

Striated duct

Fi . 216.—Reconstruc1:ion of a terminal portion and its duct or a salivary gland (a). (b) ross section through serous alveolus. (0) Cross section through mucous alveolus. (d) Qross section through lntercalated duct. (a) Cross section through striated duct. (Maximow and Bloom“)

excretory system. An outstanding characteristic of the intercalated ducts is their thin Wall and relatively small diameter. They are always surrounded by moyepithelial cells ‘(Fig 213). The cells are simple, low cuboidal in type, remain relatively undifferentiated, and take ordinary stains very poorly. They are of variable length depending on the type of gland which they drain. The parotid gland has long intercalated very short and inconspicuous (Fig. 214). In pure mucous glands the cells abut directly upon the distal tubules of the larger excretory ducts.

In the parotid and submaxillary glands striated ducts (secretory ducts, salivary tubules) intervene between the intercalated ducts and the larger excretory ducts. These ducts are believed to secrete water and inorganic salts which act to dissolve the antecedents secreted by the alveolar cells. In the striated ducts the epithelial cells are regular and columnar in form 274 ORAL HISTOLOGY AND EMBRYOLOGY

and arranged in a single layer. The cytoplasm is finely granular and contains a nucleus which is centrally placed. The perpendicular striations from which the cells derive their name are confined to the outer or basal zone near the basement membrane (Figs. 215, 217). In the larger ducts (parotid, submaxillary, major sublingual) the epithelium is columnar and pseudo-stratified; a basement membrane is distinct between epithelium and connective tissue wall. Where the ducts open into the oral cavity the walls fuse with the mucous membrane.

A common feature of compound glands in general is the presence of secretory capillaries or canaliculi which arise from the smallest excretory ducts and penetrate between the functional cells at their boundaries (Figs. 212, 215). The purpose of secretory capillaries is to increase the drainage capacity of alveoli composed of multiple layers of cells and, for that reason secretory capillaries are a constant feature of mixed alveoli. The capillaries are most effectively demonstrated with silver impregnation.

7. INTERSTITIAI. GONNECTIVE TISSUE; BLOOD, LYMPH AND NERVE SUPPLY

The interstitial substance of the salivary glands is loose connective tissue made up of a large number of fibers. The fibers run in all directions to form networks which surround and support the various elements. In it are fibroblasts, macrophages, plasma and fat cells which vary in relative number with the type of gland. Around the terminal alveoli and ducts, located peripherally to the myoepithelial cells, the connective tissue forms a basement membrane.

The salivary glands possess a rich blood supply. The larger arteries follow the course of the excretory ducts, giving off branches which accompany the divisions of the ducts to the lobules; the capillaries form dense networks on the outer surface of the basement membrane of alveoli and ducts. The veins and lymph vessels follow the arteries in reverse order to drain the gland. The main branches of the nerves supplying the salivary glands also follow the course of the vessels to break up into terminal plexuses in the connective tissue adjacent to the alveoli. Both sympathetic and parasympathetic fibers pass through the basement membrane and end in varicose filaments and budlike expansions between the secretory cells.

8. MAJOR SALIVARY GLANDS

The parotid, submaxillary and sublingual glands are often classified as the salivary glands proper. Because of their size and the volume of saliva which they contribute they deserve special consideration. Physiologic investigations have been, for the most part, carried out on these glands but conclusions which have been drawn from their study can probGL.-LNDS or THE ORAL oavrrr 275

ably be applied with little change to the numerous smaller glands of the oral cavity. A comparison of the anatomic features of the three large salivary glands is presented in the accompanying table.

Tasnn IX

COMPARISON or rm: MAJOR Sanrvucr GLANDS (Amen Cownnv)

SUBMAXILLARY SUBLINGUAL

Size and Largest; main and ac- Intermediate; well lim-Smallest; major gland

shape cessory parts both en- ited and encapsulated; and several minor

capsulated; compound, compound, branched, ones; no capsule; com branched, alveolar alveolar, partly tubular poxmd, b ranch e d, tubnlo-alveolar

Posifion A r ound mandibular Beneath mandible (also In floor of mouth ramus anterior to ear called submandibular

gland)

Ducts Parotid (Stenson’s)ductSubma.xi1lary (Whar- Major sublingual (Baropens opposite second ton’s) duct opens on tholin’s) duct opens upper molar; double either side of frenu- near submaxillary layer columnar cells on lum of tongue; struc- sometimes by common in a r k e d basement ture same aperture, also several membrane minor sublingual

(Rivinian) ducts; structure same

Secretory Single layer very con- Same but somewhat Rare or absent

ducts spicuously striated longer and may coneolumnar cells tain yellow pigment

Inter- Long, narrow, brancl1- Much shorter but similar Absent

calated ing made of single structure ducts layer of flattened cells

59°79“?! 5610115 8-1V601i, 1111160115 Serons alveoli predom-Major gland: mucous

e_pithe- alveoli rare (in new- inate, some mucous al- alveoli predominate, hum born) veoli have serous cres- many serous crescents cents and alveoli. Minor glands all mucous Interstitial Fat cells most abundant Connective tissue septa ‘$188118 most abundant Ni’-"73 Sensory: fifth nerve. Sens fifth nerve. Sensory: fifth nerve WPP1)’ Secretary: (1) sympa- Secretory: (1) sympa-Secretory: same as subthetic, superior cer- thetic, same; (2) maxillary gland

vical ganglion (vaso- parasympathetic, constriction); seventh‘ nerve, chords (2) parasympathetic, tympam, subrnamllary ninth nerve, fitic gan- ganglion (vasod1laglion (vasodilation) tion)

The parotid gland (glandula parotis) is the largest of the salivary glands. Its superficial portion is located in front of the external car on the lateral surface of the masseter muscle and extends slightly backward below the external auditory meatus. Its upper corner never transgresses the zygomatic arch, the lower corner reaches into the neck as cervical lobe (Fig. 209). The deep part of the parotid gland fills the retromandibular fossa. The gland is enclosed within a strong capsule which is tightly adherent and continuous with the connective tissue separating lobes and lobules. Accessory parotid glands are often found alongside

the parotid duct.‘

Parotid Gland 276 our. HISTOLOGY mu mmnmzonoey

The parotld gland empties by the parotid duct (ductus parotideus, Stenson’s duct) which is given off at the anterior corner of the gland, continues forward, turns around the anterior border of the masseter muscle, pierces the buccinator muscle and mucous membrane of the cheek to open opposite the upper second molar. Usually a small papilla marks the opening.

. 1:, yrs ‘;f'::.&v:h ‘,. ‘ ‘xi an

Branching duct

'$;':‘I".‘;‘3|. ’ - ;’V

Fig. 216.—Section through a human parotid gland. Intercalated ' ~ *~-~—v~— duct Striated duct ,, new W4, A *-W’-r—‘ ' - - --— striated duct

Fig. 217.—I-Iigher magnification of field X in Fig. 216. GLANDS on THE omu. csvrrr 277

- Albuminous

alveoll 3-Mucous alveoli 5 ‘i id 57>‘ i« I‘ ./ .:"‘- ‘ii. . .‘:- ’ ‘Zn :1" i

Fig. 218.—Section through a human submaxillary gland.

7)" Albuminous

Demilune _* ‘mean

Mixed -alveolus

Interlobulsr septum

Fig. 219.—Higher magnification or fleld X in Fig. 218.

The parotid gland of the adult is made up entirely of albuminous cells (Fig. 216). The alveoli which form small tightly packed oval masses are drained by long thin branching intercalated ducts; striated tubules are conspicuous (Fig. 217).

The parotid gland produces a thin and watery saliva which serves for the moistening and cleansing of the mouth cavity. It contains, besides 278 ORAL HISTOLOGY AND EMBRYOLOGY

Interlobular ‘ septum

Fig. 220.—-Section through a. human major sublingual gland.

Fig. 221.-—Higher magnification of field X in Fig. 220. GLANDS or THE osar. oavrrr 279

salts and proteins, the enzyme ptyalin (amylase) which acts chemically to hydrolize starch into simpler compounds.

The submaxillary gland (submandibular gland; glandula submaxillaris) of man comprises one component of the group of glands in the floor of the mouth sometimes designated as the alveolingual complex.‘ It is ovoid in form, loosely encapsulated and about the size of a walnut. The greater part of the gland is located in the submaxillary triangle behind and below the free border of the mylohyoid muscle (Fig. 209). It is usually divided into several large lobes by deep incisures penetrating to the hylus. A tongue—like extension of the gland usually lies above the mylohyoid muscle close to the sublingual glands. It, occasionally, extends forward under cover of the lesser sublingual gland, nearly to the midline, and is designated as the secondary submaxillary gland proper.

The submaxillary gland including its accessory portions drains by the submaxillary duct (Wharton’s duct) which is composed of many smaller ducts arising in the lobules of the gland. The submaxillary duct is much thinner than the parotid duct. The supporting stroma contains a few longitudinal smooth muscle cells. It opens by a narrow orifice on the summit of a small papilla, caruncula sublingualis, at the side of the lingual frenulum at the floor of the mouth.

In man, the submaxillary gland is of the mixed type with albuminous elements predominating (Fig. 218). Many purely serous alveoli are present; infrequently occurring mucous alveoli are usually capped by demilunes of serous cells. The intercalated ducts of the submaxillary gland are relatively short (Fig. 214), but similar in structure to those of the parotid gland (Fig. 219). The striated tubules are also structurally similar to those of the parotid but are somewhat longer (Fig. 214).

The secretion of the submaxillary gland contains mucin and is, consequently, more viscid than that of the parotid gland. It is described as clear and abundant. It varies, however, both in quantity and quality with the type of stimuli.

The sublingual glands form a composite of one larger and several smaller glands which open independently into the oral cavity. The larger or major sublingual gland (Bartholinian gland) is drained by a single duct, major sublingual duct, Bartholin’s duct. The smaller glands, Rivinian glands, are usually 8 to 20 in number and drain by separate openings, Rivinian ducts. The greater and lesser sublingual glands plus the supramylohyoid submaxillary gland sometimes carry the inclusive designation of “massa sublingualis.”‘

The sublingual gland or glands of the adult are the smallest of the units

comprising the salivary glands proper. The greater sublingual is narrow, flattened and elongated; it is situated in the floor of the mouth in

the sublingual fold (Fig. 209). The course of the duct which drains it is roughly parallel to and a little lateral to the submaxillary duct. It opens into the mouth at the side of the frenulum of the tongue on the

submaxillary Gland

sublinguai tion

Tubulo-alveolar : terminal por- _ A Albumlnous alveolus septum Demllune Mucous alveoli

fiiual Glands

Minor Buccal Glands

Demllune .7

280 out HISTOLOGY AND EMBRYOLOGY

salivary caruncle with Wharton’s Qluct, in most cases; occasionally, however, the duct opens independently into the oral cavity near the submaxillary duct.

Some of the ducts of Rivini which do not take part in the formation of the larger sublingual duct, join the submaxillary duct, others open separately into the mouth on an elevated crest of the mucous membrane, plica sublingualis.

The large sublingual gland in man is a mixed gland in which the mucous elements predominate (Figs. 220, 221, 222). Most alveoli are purely mucous, the albuminous cells are mostly found as demilunes in mixed alveoli. Purely serous alveoli are rare. The smaller sublingual glands are, for the most part, mucous glands.

Fig. 222.--Section thro h a human sublingual gland with long tubulo-alveolar terminal no ons. (Courtesy Army Medical Museum.)

10. MINOR SALIVARY GLANDS

The labial glands, which are located in the inner surface of the lips, are of the mixed type. They are variable in size and closely packed in the submuoosa where they may be easily palpated. They are not encapsulated. The secretory portions may contain both serous and mucous cells lining the same lumen but more often typical demilunes are formed. A considerable number may contain only mucous cells (Fig. 223). The cells have a distinct muco-albuminous character, the intercalated ducts are short.

The buccal glands, which are a continuation of the labial glands, bear a marked resemblance to those of the lips. The glands which lie in the immediate vicinity of the parotid duct opening, and drain in the third molar region, are frequently designated as the molar glands (Fig. 224). GLANDS or THE ORAL CAVITY 281

The glossopalatine (isthmian or faucial) glands are pure mucous glands; G1‘(’}*:;P;:‘”"° they are located in the isthmus region and are a continuation, posteriorly, of the lesser sublingual glands. They ascend in the mucosa of the glosse Fig. 224.—Section through a human retromolar gland. Palatine Glands

Glands of the Tongue

282 ORAL HISTOLOGY AND EMBRYOLOGY

palatine fold. They may be confined to the anterior faucial pillar or extend into the soft palate to fuse with the palatine glands pI‘0PeI‘- They may also be seen on the lingual side of the retromolar area of the mandible. The palatine glands which occupy the roof of the oral cavity can be topographically divided into ( 1) glands of the hard palate; (2) glands of the soft palate and uvula. They are composed of independent glandular aggregates numbering approximately 250 in the hard palate, 100 in the soft palate, and 12 in the uvula. In the posterior area of the hard palate the glands lie between the mucous membrane and bone supported by a

Fig. 225.——'.l.‘he palatine glands. (Sicher and Tandlerfi)

dense framework of connective tissue characteristic of this region. Continuing backward, the lateral groups become arranged into compact rows and take on considerable size (Fig. 225). They merge with those of the soft palate and form a thick layer between the mucous membrane and palatal musculature (see chapter on Mucous Membrane).

The structure of the palatine glands is that of long branched tubulo~

alveoli connecting with single ducts. The predominating cell produces only mucus. Cells of the so-called intercalated ducts are converted into

mucous cells in the palatal glands, and function as part of the elongated alveoli.

The glands of the tongue are of three types: serous, mucous, and mixed, the mucous being the most numerous. The anterior lingual gland (gland GLANDS or ran oaar. cavrrx 283

of Blandin-Nuhn) is located close to the inferior surface of the tongue, one on each side of the frenulum near the apex. The structure is composed of a group of raccmose glands embedded deeply Within the structure of the tongue (Fig. 226). Approximately five small ducts open Imder the tongue on the plica fimbriata. The gland is of the mixed type although chiefly mucous in its anterior part. In its posterior part are found mucous alveoli capped with delicate demilunes, with a distinctly serous character.

The glands of the base and border of the tongue are of the pure mucous variety. The glands which are located on the surface of the tongue -bear long mucous tubular alveoli and ill-defined ducts. In the immediate region of the vallate and foliate papillae they are replaced by the serous glands of the gustatory papillae (glands of v. Ebner). These glands pour a watery secretion into and serve to wash out the furrows of the circumvallate papillae. (See chapter on Mucous Membrane.)

Anterior lingual gland ,’

Fig. 226.-Longitudinal section through the tip of the tongue of a. newborn child. Anterior lingual gland.

11. GLINIGAL CONSIDERATIONS

Pathologic disturbances of the salivary glands are relatively infrequent. When they do occur the result may be either an increase in the flow of saliva (sialism) or a decrease (xerostomia). Secretion is increased in mental and nervous affections, occasionally in acute fever and during attacks of generalized stomatitis. Injections of certain drugs, particularly mercury and iodine compounds, are likely to produce an abundance of saliva. Other than the discomfort. an abundance of saliva results in no known harm. Disturbances that cause a reduction of saliva, however. bring about loss of the protective action which this fluid exerts upon 284 ORAL I-IISTOLOGY AND EMBRYOLOGY

the teeth and oral tissues. Atrophy of the secretory elements and their replacement by adipose tissue occurs in old age. The resulting xerostomia may cause discomfort to a. patient wearing artificial dentures. Through its loss the lubricating, cleansing and neutralizing power of the saliva is forfeited. Moreover, a normal flow of saliva is a mechanical guard against infection.

Inflammation is frequently the cause of disturbances in the flow of saliva. It is common in the parotid gland, less common in the submaxillary, sublingual and smaller glands. Pyogenic organisms are the chief offenders in acute infections. Most frequently in debilitated individuals suffering from infectious fever or general postoperative complications, the infection may be confined to the ducts (sialodochitis) or, less frequently, spread through the parenchyma of the gland (sialadenitis). Inflammation of the glandular substance itself, when it occurs, is usually severe. When it progresses to suppuration, surgery is indicated.

Glass blowers and players of wind instruments are especially subject to infection of the salivary ducts. The heightened intraoral pressure tends to dilate the ducts, counteract the normal outflow of saliva, and bacteria are forced into the ducts.

Infection of the ducts of a salivary gland may cause a mass of dead cells or bacterial debris to become lodged in a constricted area of the ducts. If allowed to remain, such a mass acts as a nidus in which calcium salts are deposited. This leads to the formation of a salivary calculus. Salivary calculi occur most often in the submaxillary duct (90 per cent) where they vary in size from minute particles to deposits several centimeters in length. If they are retained their obstructive influence invites inflammatory exacerbations afiecting the parenchymatous tissues; or, if saliva is retained under pressure for any length of time, atrophy and fibrosis of the gland may result. Salivary duct calculi are easily

detected by palpation or roentgenologic examination, and are removed by gentle pressure or by excision. When calculi involve the glandular sub stance proper, total extirpation of the gland may be advisable.

Infectious parotitis (mumps) is the most common example of a virus infection of the salivary glands. This disease shows tender swelling of the parotid region, usually bilateral, with mild fever but no leukocytosis. Tuberculosis, syphilis, and actinomycosis may occasionally affect the salivary glands. The etiologic agents may be hematogenous or carried to the glandular substance through the ducts.

Mikulicz’ disease is a type of granulomatous inflammation, rare in occurrence, which affects both the salivary and lacrimal glands, and occasionally, the lips and eyelids. It makes its appearance as a symmetrical, indolent enlargement which may last several years. A dry mouth is one of the accompanying symptoms. Histologically, there is a lymphocytic infiltration of the interstitial connective tissue and, if persistent, ultimate GLANDS or THE omu. CAVITY 285

destruction of the parenchymatous elements.“ The blood picture remains normal. It must be diflerentiated from Mikulicz’ syndrome which is associated with such general processes as leukemia, Hodgkin’s disease, and syphilis. A variety of tumors have been described in connection with the salivary glands: mixed tumors, carcinoma, sarcoma, and several other types are found of which about 75 per cent occur in the parotid. Of this number about 95 per cent are of the mixed variety.’

Congenital malformations of the salivary glands may vary from atresia of the ducts to complete aplasia of the gland. Such disturbances are more common in the floor of the mouth in connection with the alveolingual complex, but they are not uncommon in the parotid area. Atresia is less common than aplasia, but when present causes disfiguring cysts or tumorlike growths. The large sublingual gland is most frequently afiected, giving rise to the so-called ranula, in the floor of the mouth. The glands of Blandin-Nuhn, located in the anterior part of the tongue, are susceptible to cystic involvement as a result of closure of their ducts. These cysts are designated as mucous cysts or mucoceles. Mucoceles are quite commonly found in connection with the smaller glands of the oral cavity, where they probably result from trauma, a mild infection of the duets with consequent closure. They are, however, of little concern and usually disappear after rupture and discharge of their contents.

Aberrant glands are encountered occasionally in the alveolingual area. They are accessory glands which have become detached from the duct system. These glands remain functional but because they-lack an excretory duct, the secretion accumulates within their structure and causes distention with cyst formation.

The use of rubber dam or prolonged pressure by cotton rolls can occlude the opening of one of the salivary ducts. The resulting swelling occurs at the time the work is in progress, and disappears soon after the obstruction is removed and the saliva has an opportunity to discharge.

References

1. Appleton, J. L. T.: Bacterial Infection, Philadelphia, 1925, Lea &; Febiger.

2. Babkin, B. P.: The Physiology of the Salivary Glands, in Gordon, S. M.: Dental Science and Dental Art, Philadelphia 1938, Lea & Febige .

3. Braus, H.: Anatomic des Menschen (Human Anatomy), Book 2, ed. 2, Berlin, 1934, Julius Springer.

4. Brawley, R. E.: Studies of pH of Normal Resting Saliva: Variations With Age and Sex; Diurnal Variation, J. Dent. Research 15: 55, 79, 1935.

5. Car-malt, Churchill: Contribution to the Anatomy of the Adult Human Salivary Glands, IV, Part 1, Geo. Cracker Special Research Fund, 1913.

6. Cheyne, V. D.: Efiects of Selective Salivary Gland Extirpation Upon Experimental Dental Caries in Rat, Proc. Soc. Exper. Biol. & Med. 42: 587, 1939.

7. Cheyne, Virgil D., Tiecke, Richard W., and Home, Eleanor V.: A Review of So-Called Mixed Tumors of the Salivary Glands Including an Analysis of Fifty Additional Cases, Oral Surg., Oral Med., Oral Path. 1: 359, 1948.

8. Gies, W. J., and Kahn, M.: An Inquiry Into the Possible Relation of Sulfacyanate to Dental Caries, Dental Cosmos 55: 40, 1913.

9. Hill, T. J .: Salivary Factor Which Influences Growth of L. Acidophilus and Is an Expression of Susceptibility or Resistance to Dental Caries, J. A. D. A. 26:

239, 1939. 286

10. 1 1. 12. 13. 14.

15. 16.

17. 18.

19. 20. 21.

22. 23. 24.

ORAL I-IISTOLOGY AND EMBRYOLOGY

Hill, '1‘. J.: The Influence of Saliva Upon the Growth of Oral Bacteria, J . Dent. Research 18: 214, 1939.

Inouye, J. M.: Biochemical Studies of Salivary Mucin, J. Dent. Research 10: 7, 1930. Langley, J . N .:

261, 1379.

Lashley, K. S.: Reflex Secretion of the Human Parotid Gland, J . Exper. Psychol. 1: 461, 1916.

Lehman, J. A., and Leaman, W. G.: 1940.

Mathews: The Physiology Maximow, A. A., and Bloom, W.: 1942, W. B. Saunders Co. Orban, B., and Weinmann, J. P.: Cellular Elements of Saliva and Their Possible

Role in Caries J. A. D. A. 26: 2008, 1939.

Rosemann, B.: Iihysikalische Eigenschaften und chemische Zusammenstezung der Verdauungssiifte unter normalen und abnormen Bedingungen. Handb. der normalen und pathologischen Physiologic (Physical Properties and Chemical Constitution of the Digestive Juices Under Normal and Abnormal Conditions. I. Saliva, Handbook of Normal and Pathologic Physiology), Berlin, 1927, Julius Springer, vol. 3, p. 819.

Sicher, H., and Tandler, J .: Anatomie fiir Zahniirzte (Anatomy for Dentists), Berlin, 1928 Julius Springer.

Stephens, D. J.,’and Jones, E.: Leukocytes in the Saliva in Normal and Abnormal Subjects, Proc. Soc. Exper. Biol. & Med. 31: 879, 1934.

Thoma, K. E.: A Contribution to the Knowledge of the Development of the Snbmaxillary and Sublingual Salivary Glands in Human Embroys, J . Dent. Research 1: 95, 1919.

Updegrafi, H., and Lewis, H. B.: A Quantitative Study stituents of Saliva, J. Biol. Chem. 61: 633, 1924. Youngberg, G. E.: Salivary Ammonia and Its Relation to Dental Caries, J . Dent.

Research 15: 247, 1936.

Zimmermann, K. W.: Die Speicheldriisen der Mundhiihle und die Bauchspeicheldriise. Handb. der mikr. Anat. des Menschen (The Salivary Glands and the Pancreas. Handbook of Human Microscopic Anatomy), Book 5, Part 1, Berlin, 1927, Julius Springer.

On the Changes in Serous Cells During Secretion, J. Physiol. 2:

Mikulicz’s Disease, Internat. Clin. 3: 105,

of Secretion, Ann. New York Acad. Sc. 11: 293, 1898. A Textbook of Histology, ed. 4, Philadelphia,

of Some Organic ConCHAPTER XI

ERUPTION OF THE TEETH

1. INTRODUCTION 2. EISTOLOGY OI‘ ERUTTION

a. Preemptive Phase 1:. Pre1'uncti.ona.1 Phase c. Functional Phase

3. MEGEANISM OF ERUPTION 4. CLINICAL CONSIDERATIONS

1. INTRODUCTION

The human teeth develop in the jaws and do not enter the oral cavity until the crown has matured. In the past, the term eruption was generally applied only to the appearance of the teeth in the oral cavity. It is, however, known that the movements of the teeth do not cease when the teeth meet their antagonists.“ 7 Movements of eruption begin at the time of root formation and continue throughout the life span of a tooth. The emergence through the gingiva is merely an incident in the process of eruption. The eruption of deciduous as well as permanent teeth can be divided into the prefunctional and functional phases. At the end of the prefunctional phase the teeth come into occlusion. In the functional phase the teeth continue to move to maintain a proper relation to the jaw and to each other.

Eruption is preceded by a period in which the developing and growing teeth move to adjust their position in the growing jaw.’ A knowledge of the movements of the teeth during this preeruptive phase is necessary for a complete understanding of eruption. Thus, the movements of the! teeth can be divided into three phases: (1) preeruptive phase; (2) prefunctional phase; (3) functional phase.

During these phases the teeth move in difierent directions.” These movements can be termed: ( 1) axial: occlusal movement in the direction of the long axis of the teeth; (2) drifting: bodily movement in a distal, mesial, lingual or buccal direction; (3) tilting: movement around a transverse axis; (4) rotating: movement around a longitudinal axis.

2. HISTOLOGY OF ERUPTION

During the first, preeruptive phase the enamel organ develops to its Preemptive full size, and formation of the hard substances of the crown takes place. Pm“

First draft submitted by Joseph P. Weinmann. 287 288 ORAL HISTOLOGY AND EMBRYOLOGY

At this time the tooth germs are surrounded by the loose connective tissue of the dental sac and by the bone of the tooth crypt.

The development of the teeth and the growth of the jaw are simultaneous and interdependent processes. The microscopic picture of the growing jaw indicates that extensive growth takes place in that area of the jaws where the alveolar crest ultimately develops (Fig. 227). The tooth germs maintain their relationship to the growing alveolar margin by moving occlusally and buccally.‘

. fxi

. Anlage of . permanent

tooth

Fig. 227.—-Cross section through lower jaw and deciduous molar or human fetus (4th month). Tooth germ moves bucoally by excentric growth indicated by resorption at inner surface of.’ the buccal alveolar plate and lack of apposition at the inner surface of the lingual plate.

Two processes are responsible for the developing teeth attaining and maintaining their position in the growing jaw, especially in relation to the alveolar ridge: the bodily movement of the teeth, and the excentric growth of the tooth germs. Bodily movement is characterized by a shift of the entire tooth germ. It is recognized by apposition of bone behind the moving tooth, and by resorption of bone in front of it. In excentric growth one part of the tooth germ remains fixed: the growth gives rise ERUPTION or ran TEETH 289

to a. shift of the center of the tooth germ. Excentric growth is characterized solely by resorption of the bone at the surface toward which the tooth germ grows.

During most of the time when the deciduous teeth develop and grow, upper and lower jaws grow in length by apposition in the midline and at their posterior ends. Accordingly, the growing germs of the deciduous teeth shift in vestibular direction; at the same time the anterior teeth move mesially, the posterior distally, into the expanding alveolar arches." These movements of the deciduous teeth are partly bodily movements, in part caused by excentric growth. The deciduous tooth germ grows in length at about the same rate as the jaws grow in height. The deciduous teeth maintain, therefore, their superficial position throughout the preeruptive phase.

The permanent teeth which have temporary predecessors undergo an intricate movement before they reach the position from which they emerge. Each permanent incisor (Fig. 228) and cuspid develops at first lingually to the deciduous tooth germ at the level of its occlusal surface.“ At the close of the preemptive phase they are found lingual to the apical region of their deciduous predecessors. The permanent bicuspids (Fig. 229) begin their development lingually to and at the level of the occlusal plane of the deciduous molars.“ Later, they are found between the divergent roots and, at the end of the preeruptive phase, below the roots of the deciduous molars (see chapter on Shedding). The changes in axial relationship, between deciduous and permanent teeth, are due to the occlusal movement of the deciduous teeth and the growth of the jaw in height. The germs of the bicuspids move by their buccally directed excentric growth into the interradicular space of the deciduous molars.

The second phase of tooth movement, the prefunctional phase of erup-. pmucflom tion, begins with the formation of the root (page 42) and is completed! P1350 01 when the teeth reach the occlusal plane. In the beginning of this phase nmptm the crown is covered by enamel epithelium. While the crown moves toward the surface, the connective tissue between the reduced enamel epithelium and the oral epithelium disappears, probably by the desmolytic action of the enamel epithelium. When the cusp of the crown approach the oral mucosa, the oral epithelium and reduced enamel epithelium fuse. In the center of the area of fusion the epithelium degenerates and the tip of the cusp emerges into the oral cavity. The gradual emergence of the crown is due to the occlusal movement of the tooth (active eruption), and also to the separation of the epithelium from the enamel (passive eruption).

The reduced enamel epithelium remains in organic connection with that part of the crown which has not yet emerged. (See section on Epithelial Attachment.) The growth of the root or roots of a tooth occurs by simultaneous and correlated proliferation of Hertwig’s epithelial root sheath and the connective tissue of the dental papilla. The proliferation of the 290 ORAL HISTOLOGY AND EMBRYOLOGY

epithelium takes place by mitotic division of the cells of the epithelial diaphragm. The proliferation of the connective tissue cells is concentrated in the area above the diaphragm.

During the prefunctional phase of eruption the primitive periodontal membrane, derived from the dental sac, is adapted to the relatively rapid movement of the teeth. Three layers of the periodontal membrane can be distinguished around the surface of the developing root: one, adjacent to the surface of the root (dental fibers); another attached to the

9 1110.

Fig: 228.——BuccoIingua1 sections through lower central incisors of seven consecutive stages, from newborn infant to 9 years 01.’ age.

primitive alveolus (alveolar fibers) ; and a third, the intermediate plexus (Fig. 137). The intermediate plexus’ consists mainly of precollagenous fibers, whereas the alveolar and dental fibers are mainly collagenous. The collagenous fibers can be traced into the intermediate plexus for a short distance. The intermediate plexus permits continuous rebuilding

and rearranging of the periodontal membrane during the phase of rapid eruption.“ 2° ERUPTION or THE TEETH 291

In the region of the fundus, the dental sac differentiates into two layers: one, close to the bone, consists of loose connective tissue, whereas the other, adjacent to the growing end of the tooth, consists of a network of rather thick fibers and contains a large amount of fluid in the tissue spaces between the fibers (Fig. 230). Strong strands of fibers from the

‘periodontal area at the side of the root curve as a strong ligament around the edge of the root, and then divide into a network forming spaces that are filled with fluid. This entire structure is designated as “cushioned hammock ligament.”-'1

In the prefunctional phase of eruption the alveolar ridge of the jaws grows rapidly. To emerge from the growing jaws the deciduous teeth must move more rapidly than the ridge increases in height. Growth of the root is not always suflicient to meet these requirements. A rapid formation of bone begins at the alveolar fundus Where it is laid down in trabeculae, parallel to the surface of the alveolar fundus” (Fig. 231). The number of trabeculae increases markedly during the prefunctional 292 om. HISTOLOGY AND EMBRYOLOGY

phase, and varies in difierent teeth: the smallest number of trabeculae is found at the fundus of the molars. This variance in the number of trabeculae seems to depend upon the distance which the teeth have to cover during this phase of tooth eruption.

The germs of most permanent teeth develop in a crowded position. They occupy, therefore, a position which difiers markedly from their ultimateposition after emergence. The molars are tilted; the occlusal surface of the upper molars, which develop in the maxillary tuberosity, is directed distally and downward. The occlusal surface of the lower molars, which develop in the base of the mandibular ramus, is directed mesially and upward. The long axis of the upper cuspids deviates mesially. The lower incisors are frequently rotated around their long axis. In the later stages of the prefunctional phase of eruption these teeth undergo intri

i\ en:-"' ”"“"-‘-”»'%’.f’v". ,. 1

Fig. 229.—Bucco1ingus.i sections through lower deciduous flrst molar and flrst bicuspid or eight consecutive stages, from newborn infant to 14 years.

cate movements to rectify their primary position. During these tilting and rotating movements, bone apposition takes place in those areas of the tooth crypt from which the tooth moves away, and resorption occurs in the areas toward which the tooth moves. In all other details, the his tologic changes correlated to eruption are identical in permanent and deciduous teeth.. ERUPTION or run TEETH 293

The histologic findings in erupting multirootecl teeth present a picture quite diflerent from that in single-rooted teeth. The epithelial root sheath does not form an epithelial diaphragm, a cushioned hammock ligament is absent, and the proliferating pulp protrudes beyond the root end. The bone at the crest of the interradicular septum shows all signs of rapid growth. Apposition of cementum is also evident at the bifurcation. , _

After the erupting teeth have met their antagonists their movements are 1-uncuoml not easily ascertained For a long time it was believed that functioning §h“°_°f teeth do not erupt any longer. However, clinical observations and his- mph” tologic findings show that the teeth continue to move throughout their life span. The movements are in an occlusal as well as in a mesial direction.

..,,..... .... __ _ ...

 a l V E

• ’*s..,.. /A .

3 yr. 41,5 yr. 11 yr. 14 yr.

Clinically, the continued active movement of teeth can be proved by an analysis of the so-called shortened and submerged teeth (see page 322). Histologically, the changes in the alveolar bone furnish concrete evidence for the movements of the teeth in their functional period (see page 205).

During the period of growth, the occlusal movement of the teeth is. fairly rapid. The bodies of the jaws grow in height almost exclusively at‘ the alveolar crests and the teeth have to move occlusally as fast as the 294 ORAL HISTOLOGY AND EMBRYOLOGY

- - Prollferzttlon zone of pulp

‘ §~-,-— -—-—————» Epithelial ' _-V ' diaphragm

4 m4 —-»— V — Cushioned . hammock ligament

Fig. 230.—Cushioned hammock ligament Root end or an erupting 10WeI' cuspid. Proliferation zone of the pulp above the epithelial diaphI'a€m- Note the numerous tissue spaces in the ligament. (slcher-.3‘)

I Deciduous tooth Bone Q ' ’ trabeculae ,- —.’ u at fundus ,‘ -‘ .3 Enamel Permanent tooth

trabeculae at tundus

F13-. 231.—-Erupting upper deciduous cuspicl (A) and lower permanent cuspid (B), Note formation of numerous parallel bone trebeculae at alveolar fundus. Formation of bone trabeculae at the alveolar crest of deciduous cuspids (A) is 9. sign or rapid growth or the maxilla in height. (Kronteldfi) Bundle bone at fundus

me5ia-l- ; ‘.5 ‘ Bundle bone on alveolar ‘ ‘f distal wall .3 "I. , alveolar r;_'.,:l - i wall ’ 7“ Alveolar ! ; septum First bzcuspid. 2" ’ _, _ Second bicuspm"

-2‘

~. M «  ‘ \

L . ‘E

Fig‘. 232—-—1\_£[esia._l drift and vertical eruption. Meslodistal section through upper first. and second bxcuspids. Arrow indicates direction of drifting movement. Apposition or bundle bone at the distal, resorption of bone on the meslal surfaces or the alveoli. Ap Dosition of bundle bone at the tundus and alveolar crest. (Weinma.nn.")

Periodontal membrane

. . Periodontal Apposition , o! bundle membrane bone - Resorption First __.._.. p or bone bicuspid - Second J bicuspid

Avposition of - W - '‘ bundle bone Fig. Z33.—I-Iigher magnification of crest of interdental septum between first and second upper bicuspids of Fig. 232. Arrows indicate direction of movement. Apposition or bundle bone on surface of septum facing the flrst blcuspid and at alveolar crest, resorption of bone on surface of septum facing the second bicuspid. (Wein1na.nn.") 296 ORAL HISTOLOGY AND EMBRYOLOGY

jaws grow, in order to maintain their functional position. The eruptive movement in this period is masked by the simultaneous growth of the jaws. _

The continued vertical eruption also compensates for occlusal. or mcisal attrition. Only in this way can the occlusal plane and the distance between the jaws during mastication be maintaincd—a condition which is essential for the normal function of the masticatory muscles.

Epithelial rest

Epithelial rest

Epithelial rest

Epithelial rest

Epithelial rests

Fig. 234.—-A. Bundle bone at tundus of alveolus and in wall of canal leading blood vessels and nerves to apical roramina. Epitl-ielial rests some distance from apex along blood vessels and nerves. B. High magnification of epithelial rests of A.

The mobility of the individual teeth leads to friction at the contact points and to increasing wear in these areas. Sharp contact of the teeth is maintained despite the loss of substance at the proximal surfaces only because of the continuous movement of the teeth toward the midline. This movement is termed physiologic mesial drift.

Apposition of cementum continues along the entire surface of the root, but the apposition of bone is restricted principally to the fundus, alveolar crest, and distal Wall of the socket (Fig. 233). The mesial wall of the ERUPTION or THE TEETH 297

socket shows resorption in wide areas. However, even on the mesial

surface of the alveolus, zones of reparative bone apposition can always be found.

The tissue changes in the diiferent phases of tooth movements are summarized in Table V11.

TABLE VII Trssun CHANGES DURING Tm: PHASES or Tooru MOVEMENTS

”"‘E°"-'I°N cmuens or OF EPITIIELIUM ————e———— 1>,1),M_ MOVEMENT TOOTH BONE - 0ccluso-ax- Enamel organ Eccentric Growth of jaw Dental sa, Prefihrzgrve ial; buccal growth of G tooth germ Prefunc- 0ccluso-ax- Fusion of re- Root growth Apposition Intermeditional ial; duced enamel (trabecular ate plexus; Phase _straighten- organ with _ bone) at fun- cushioned of Eruption mg oral ep1thel1- due and a.1veo- hammock tuirn; ffonnagh lar ridge ligament on o 1 elial attac ment. Hert wig ’s sheath; epithelial rests

Functional 0ccIuso-ax- Down growth Attrition. Root Apposition Functional Phase ial; mesial of epithelial resorption and (bundle bone) arrange of Eruption attachment shedding of at fundus and ment of (passive erup- deciduous alveolar ridge suspensory ' tion) teeth. Ce- and distal al- apparatus

mentum appo- veolar wall; sition of per- resorption at manent teeth mesial wall

3. MECHANISM OF ERUPTION

Many theories have been advanced on the causes of tooth eruption} The following factors have been eonsidered:"”' 1‘ growth of the root;? growth of dentin; proliferation of the dental tissues; pressure from mus-p cular action; pressure from the vascular bed in the pulp and periapieal tissue; apposition and resorption of bone.

The eruptive movements of a tooth are the effect of differential growth. # One speaks of diiferential growth if two topographically related organs, or parts of an organ, grow at different rates of speed. Changes in the spatial relations of such organs, or of the parts of an organ, are the inevitable consequence of differential growth. The ontogenesis of almost any organ and of the whole embryo proves that diiferential growth is one of the most important factors of morphogenesis. In the jaws, it is the differential growth between tooth and bone which leads to the movement of a tooth.

The most obvious eruptive “force” is generated by the longitudinal growth of the root of the tooth. However, the different movements of an erupting tooth cannot be explained by the development of its root? alone. Some teeth, even while their roots develop, travel a. distance 293 ORAL HISTOLOGY AND EMBRYOLOGY

which is longer than the fully developed root. An auxiliary factor must account for the additional distance. Most teeth move in different directions, for instance by tilting, rotating, drifting; the growth of the root can only account for the axial or vertical movement. The “force” that can explain the variety of eruptive movements is generated by the growth of bone tissue in the neighborhood of the tooth germ.

1 It is also a fact that the teeth move extensively after their roots have

been fully formed. The continued growth of the cementum covering

}the root and of the surrounding bone causes the movements of the tooth 3' in this period.

Before the development of the root starts, the outer and inner enamel epithelium continue from the region of the future cemento-enamel junction as a double epithelial layer, the epithelial diaphragm, which is bent into the plane of the dental cervix. It forms a definite boundary between the coronal pulp of the tooth germ and the underlying connective tissue which intervenes between tooth germ and bony wall of the crypt. Thus,

’ growth and development of the root is possible only under active proliferation of the pulpal tissue.

The importance of this single fact for the eruption of the tooth can best be realized by comparing our knowledge of root development with the long disproved, old concept of the function of Her-twig’s epithelial root sheath. It was thought that this double layer of epithelium g_rew into the underlying mesenchyme, punching out, as it were, part of this tissue, isolating it and transforming it into pulpal tissue. If this were true, the growth of the pulp would be by incorporation of new tissue

and therefore passive rather than active. The presence of the epithelial ‘

diaphragm makes an inward growth of the epithelial sheath impossible and the pulp is “forced” to grow by multiplication of its cells and new formation of intercellular substance ;, in other words, the pulp enlarges by active growth, which creates the tissue pressure which can be seen '- as the primary “force” of eruption. 1 The pressure generated by the increase in volume of the pulp in the restricted space of the dental crypt would act against the bone in the _bottom of the crypt and cause resorption of this bone and could not cause an eruptive movement of the tooth germ if there were no auxiliary structure. The auxiliary structure, which protects the bone at the bot'; tom of the crypt from pressure, prevents resorption of the bone, and causes the tooth to grow or move away from the bottom of the crypt, is the “hammock ligament.” If, by the proliferation of the growing pulp, tissue pressure increases, this ligament is tensed, the pressure is transmitted as traction to the bone to which the ligament is anchored, and no pressure is directed against the bone at the bottom of the crypt. Thus, the hammock ligament is the fixed base or plane from which the tooth erupts because elongation of the tooth can only result in growth toward the surface of the jaws. ERUPTION or THE TEETH 299

It has been mentioned before that the growth of the root alone cannot move a crown as far as is necessary to reach the occlusal plane. Some teeth, for instance the cuspids, develop far from the surface of the jaws. While all the teeth are erupting, the jaws continue to grow at their alveolar borders. The vertical erupting movement of these teeth is aided by growth of bone at the bottom of the crypt, lifting the growing tooth

with the hammock ligament toward the surface. The formation of bone 3

at the bottom of the crypt occurs in diiferent teeth at a different rate of speed. Where the production of new bone is slow, new layers of bone are laid down upon the old bone and a more or less compact bone results. Where growth of bone is rapid, spongy bone is formed in the shape of a, framework of trabeculae. These trabeculae develop by the growth of small projections of bone from the old surface, which then, at a given distance, seem to mushroom and to form new trabeculae parallel to the

old surface (Fig. 231). In this way, tier after tier of bone tissue develops in the deep part of the socket.

The increased tissue pressure which is inevitably linked with the proliferation of bone in the crypt would tend to compress the hammock ligament, thereby destroying the fixed base which is essential for the normal eruption of a tooth; finally, the bone would encroach upon tooth andj pulp, bringing the eruption to a standstill. These consequences are prevented by a peculiar structural differentiation of the hammock ligament. Teleologically speaking, the hammock ligament is rendered incompressible by the accumulation of a fluid or a semifluid substance between the fibers and thus transformed into the “cushioned hammock ligament.” The fluid is distributed throughout the ligament in small round drop- , lets. The presence of fluid in confined spaces is, of course, the cause of the incompressibility of this ligament. The incompressibility is relative but gives entirely sufficient protection if one considers the low intensity of the pressure forces generated during tooth eruption. That this pressure normally never reaches any higher intensity is explained by the simple fact that reactive tissue changes immediately follow the increase of tissue pressure and relieve it. '

While the hammock ligament and tooth are lifted toward the surface, the anchoring fibers of the hammock ligament have to be continually reconstructed. In other words, the hammock ligament has to shift its anchoring plane toward the surface of the jaws. Details of the mechanism of this shift are, as yet, not known.

Enlargement of the root does not cease when the root is fully formed. By continuous apposition of cementum, the root grows slightly in its transverse diameters and more rapidly in length. Cementum apposition is not only increased in the apical area of roots but the bifurcation of two or three-rooted teeth is also a site of fairly intensive cementum apposition. It is also well known that there is continuous apposition of bone at the fundus of the socket and at the crests of the alveolar process. 300 omu. HISTOLOGY AND EMBRYOLOGY

The bone apposition at the fundus and at the free border of the alveolar process is very rapid in youth, slows down in the thirties, but normally never ceases. Apposition at the alveolar crest, however, is found only ‘when the tissues are entirely normal. The frequency of inflammatory changes at the gingivodental junction accounts for the fact that this site of bone growth has been overlooked for a long time. There is also constant apposition of bone on the distal wall of each socket while the mesial wall shows resorption of the bone alternating with reparative apposition.

Though the correlation of bone changes and movement of the teeth is self-evident, the question still must be raised whether the bone changes are primary and thus the cause of the movement of the teeth, or not. The impossibility of finding any internal or external “forces” which would account for the continuous vertical eruption and mesial drift is an indication that the apposition of bone in the functional period plays the same role which one can ascribe to it in the preeruptive and prefunctional eruptive movements.

The apposition of bone can lead to a movement of a tooth only if the root surface is protected against resorption. This protection is actually given by the surface layers of uncalcified cementum, the cementoid tissue, which regularly covers the surface of the cementum. The resistance of cementoid tissues to resorption has been demonstrated repeatedly.

The mechanism of tooth movement in the functional period can therefore be described in the following way: The entire surface of the root is protected against resorption by the growth pattern of the cementum which shows continuous, though not even, apposition throughout the life of the tooth. If apposition of bone occurs at the bottom of the crypt, the" slight increase of tissue pressure can lead to a movement of the tooth in occlusal direction only. This is because a relief of the pressure is not possible by resorption of the root. For the normal occlusal movement of a tooth in the functional period, the normal general growth of the cementum and the patterned growth of the bone are of equal importance. It is necessary to point out that only simultaneous growth of the opposing surfaces of cementum and bone can lead to a movement of a

itooth. It is therefore clear that the apposition of cementum at the apex - can compensate only in part for the loss of tooth substance at the occlusal surface, that is, for the shortening of the tooth by attrition. A con sequence of this behavior is the fact that the teeth do shorten during the functional period.

In the life of every tooth there comes a time in which the “forces” of eruption change abruptly. It is, of course, the time when the pulp is fully grown and the root is fully formed. From now on, it is the differential growth of bone and cementum, and not that of pulp and bone, which causes the continued vertical movement of the tooth. The eruptive mechanism of multirooted teeth differs in that the shift from one to the ERUPTION or arm: mam 301

other mechanism of eruption occurs much earlier, namely, as soon as the bifurcation is fully formed, though the roots are still growing.

The mesial drift is caused, in principle, by similar changes of bone and tooth which seem to be an adaptive, genetically determined process. However, this movement is greatly complicated by the fact that extensive bone resorption at the mesial alveolar walls has to open the space into

which the teeth move, while the vertical movement is not opposed by bone.

Apposition of bone on the distal surface of the socket leads to an increase of the interalveolar pressure. This can be relieved only by resorption of bone at the mesial wall of the socket since the growing surface of the bone and the entire surface of the root are protected by their own growth, that is, by the presence of a thin layer of uncalcified ground substance on their surface.

With both vertical and mesial movement of the functioning teeth, a continual rearrangement of the principal fibers of the periodontal membrane has to be postulated. Details of this process, however, are al most entirely unknown. The changes which prevent a destruction of the ligamentous anchorage of the tooth on its mesial surface during the con tinuous mesial drift are explained by the peculiar reaction of bone to. pressure (or during modeling resorption) which could be called “thel law of excessive resorption.” Resorption of bone under pressure is, as '~ a rule, more extensive than necessary to relieve the pressure. The sur-' face layers of a bone are structurally adapted to the functional needs of _

the particular area. If they are destroyed during resorption, the newly exposed surface lacks this adaptation. Therefore, the resorption con tinues until room is provided for a reconstruction of a functionally ,

adequate new surface. This is the reason that, under normal circumstances, resorption is almost never a continuous process but instead occurs in waves, periods of resorption alternating with periods of reparative or reconstructive apposition.

This sequence of events can also be observed during the mesial drift of a tooth. Some principal fibers lose their attachment during the period of bone resorption and are then reattached, or replaced by new fibers, which are anchored in the bone apposed during the period of repair. Furthermore, it can be observed that bone resorption does not occur at the same time on the entire extent of the mesial alveolar surface. Instead, at a given moment, areas of resorption alternate with areas of reparative apposition. It seems that the tooth moves mesially in a complicated manner. Thus, resorption occurs only in restricted areas in one period and reconstruction occurs in the same area, while the tooth, minutely tilting or rotating, causes resorption in another area. Only this can account for the fact that the functional integrity of the tooth is maintained in spite of its continued movements. 302 ORAL HISTOLOGY AND EMBRYOLOGY

4. CLINICAL CONSIDERATIONS

The eruption of teeth is a part of general development and growth, and therefore the progress of tooth eruption may serve as an indicator of the physical condition of a growing individual. The time of emergence of a tooth is readily observed by clinical examination. Considerable work has been done in compiling data regarding this particular stage of eruption. Table VIII illustrates that the time of emergence of all teeth varies widely.” 5' 13 Only those cases which are not within the range of variation may be considered abnormal. Retarded eruption is by far more frequent than accelerated eruption and may have a local or systemic etiology.

Local causes, such as premature loss of deciduous teeth and closure of the space by a shift of the neighboring teeth, may retard the eruption of some permanent teeth. Severe acute trauma may result in an arrest of active tooth eruption during the functional phase if the periodontal mem - brane of the tooth has been injured. Resorption of the root may ensue

in which event deposition of bone in the spaces opened by resorption may lead to an ankylosis by fusion of alveolar bone and root.‘‘» 29 The movement of such a tooth is then arrested whfle the other teeth continue to erupt. If this disturbance takes place in the permanent dentition, a so-called “shortened” tooth results. An ankylosed deciduous tooth may, eventually, be covered by the rapidly growing alveolar bone. Such teeth

are called submerged teeth (see chapter on Shedding).

If the eruption of the entire deciduous or permanent dentition is delayed, hereditary or systemic factors may be responsible. Among the systemic causes are: disturbances of the endocrine system and nutritional deficiencies. Hypothyroidism is of the former, and vitamin D deficiency of the latter group. The eifects of hypothyroidism and vitamin D deficiency on tooth eruption can be explained by a retardation of the growth of teeth and bone. Delayed eruption of the teeth usually accompanies cleidocranial dysostosis, a hereditary disease aifecting membrane bones.

The movements of the teeth, during eruption, are intricate and are accomplished by minute coordination of growth of tooth, growth of the alveolar bone, and growth of the jaws. Any break in this correlation may affect the direction of the movements; this, in turn, may lead to an impaction or embedding of a tooth. At the time the third molars develop, the jaw has not reached its full length. Normally, the oeclusal surface of a third lower molar turns anteriorly and upward. It is frequently prevented from straightening out because of a lack of correlation between growth in length of the lower jaw and tooth development. In such cases, the eruption of the lower third molar is arrested because its crown comes in contact with the roots of the second molar. If, at this time, the roots of the third molar are not as yet fully developed, they will grow into the bone and may become deformed. Cuspids, sometimes found in an oblique or horizontal position,

due to crowding of the teeth, may also fail to correct this malposition and remain embedded. TABLE VIII

Cnnoxonoov or THE HUMAN’ Dr.N'rI'rIoN Logan and Kronfeld (slightly modified by McCall and Schour)

FORM.A'.l‘rON ENAMEL MATRIX AMOUNT OF ENAMEL ENAMEL EMER/GENOE ROOT

TOOTH AND DEN,-MN MATRIX FORMED COMPLETED INTO ORAL COMPLETED

BEGINS AT BIRTH CAVITY

Central incisor 4 mo. in utero Five-sixths 1'} m0- 7% 1110- 1} )7!‘ Lateral incisor 4} mo. in utero Two-thirds 21} mo. 9 mo. 2 yr.

Maxillary Cuspid 5 mo. in utero One-third 9 mo. 18 mo. 31 yr.

First molar 5 mo. in utero Cusps united 6 mo. 14 mo. 2} yr.

Deciduous Second molar 6 mo. in utero Cusp tips still isolated 11 mo. 24 mo. 3 yr.

5931310“ Central incisor 4} mo. in utero Three-flftlis 2-} mo. 6 mo. 1'} yr. Lateral incisor 4} mo. in utero Three-fifths 3 ma. 7 mo. 1-} yr.

Mandibular Ouspid 5 mo. in utero One-third 9 mo. 16 mo. 3% yr.

First molar 5 mo. in utero Cnsps united 5-} mo. 12 mo. 2} yr.

Second molar 6 mo. in utero Cusp tips still isolated 10 mo. 20 mo. 3 yr.

7- 8 yr. 10 yr. 8- 9 yr. 11 yr. 11-12 yr. 13-15 yr. 10-11 yr. 12-13 yr. 10-12 yr. 12-14 yr. 6- 7 yr. 9-10 yr. 512-13 yr. 14-16 yr. 17-21 yr. 18-25 yr. 6- 7 yr. 9 yr. 7- 8 yr. 10 yr. 9-10 yr. 12-14 yr. 10-12 yr. 12-13 yr. 11-12 yr. 13-14 yr. 6- 7 yr. 9-10 yr. 11-13 yr. 14-15 yr. 17-21 yr. 18-25 yr.

Central incisor 3 - 4 mo _-_..___.._-_..___.. Lateral incisor 10 -12 mo. .___-___.._..__-..Cuspid 4 - 5 mo. ________ __---___ First bicuspid 1§- 15 yr. ______________ __ Second bicuspid 2 - 2% yr. ______________ __ xFirst molar At birth Sometimes a. trace Second molar 24- 3 yr. _--_--.._..__.._-..Permanent Third molar 7 - 9 yr. ___-- ____ -__..__

dentition Central incisor 3 - 4 mo. _______ _______-_ Lateral incisor 3 - 4 mo. ........... ---- Cuspid 4 - 5 mo. ...... ..--..----....

. First bicus id 15- 2 . .----_-_----.._.. M‘“‘d‘b“1‘“' Second bicgspid 21- 2; $1. __--______-_____

First molar At birth Sometimes a trace

Second molar 21- 3 yr. _________ ..----_..

Third molar 8 -10 yr. .......... --_--- 1

ilk‘:-Isl

Maxillary

hhhmiii _;_.

Iii.

1.! .

sis‘. sis: 1.2

>a§=>:>a?a>~.>.

-oLoL~u=r.~=ooo<o inn-n.~<oL~:.~ono:o '7‘ _..".'7‘ «swan:-seer:-‘cl vcwsucn.-::ocxn.~:u

ERUPTION on THE TEETH 303 304 ORAL HISTOLOGY AND EMBRYOLOGY

Resorptlon ** —

Repaired resorption

Enamel -'— Resorption ‘ 4" .

Alveolar bone

Alveolar bone

Periodontal membrane

B. . D. Fig. 235.—-Root resorption on distal surface or second lower molar caused by pressure or erupting third molar. and repair.

4. Relation of germ or third molar to second molar at the beginning of pretunctional phase of eruption. Note oblique position of the crown ot third molar.

B. Area. of contact between tooth erm oi third molar and root of second molar in high magnification Resorption rea into dentin.

0. Relation or lower second and third molars when third molar has a.tta.ined its up~ right position.

D. High magnification of alveolar crest. Resorption on distal root surface is partly repaired by apposition or cementum. (Orba.n.1') ERUPTION or THE TEETH 305

Erupting teeth may cause resorption on the roots of neighboring teeth.“ This has been observed very frequently on the lower second molars, due to the oblique position of the erupting third molar (Fig. 235). This tooth turns its occlusal surface mesially and upward, and attains its upright

position only in the last stages of eruption. Therefore, its crown comes into closest relation to the distal surface of the distal root of the second

molar, and exerts pressure leading to resorption of cementum and dentin to a varying depth; it can be so extensive that the pulp may be exposed. When the pressure is relieved during the normal movement of the wisdom

tooth, repair by apposition of cementum follows. Such resorption was observed in about two-thirds of investigated jaws. A horizontal position

of the lower third molar might later lead to impaction. In such cases the destruction on the root of the second molar may be severe.

Impacted or embedded upper third molars may cause similar resorption of the root of the second molar. Embedded upper cuspids may exert pressure upon the root of the lateral incisor. During the time of eruption of teeth, the reduced or united enamel epithelium may undergo changes which result in cyst formation. Such a cyst forms around the crown of the developing tooth and is known as a dentigerous cyst. Those which arise late may cause a noticeable swelling on the surface and are

sometimes known as eruptive cysts, although they are simply forms of dentigerous cysts.

References

1. Brash, J. 0.: The Growth of the Alveolar Bone and Its Relation to the Movements of the Teeth, Including Eruption, Int. J. Orthodont., Oral Surg. & Badiogr. 14: 196, 283, 393, 487, 1928.

2. Brauer, J. C., and Bahador, M. A.: Variations in Calcification and Eruption of the Deciduous and Permanent Teeth, J. A. D. A. 29: 1373, 1942.

3. Brodie, A. G.: Present Status of Our Knowledge Concerning Movement of the Tooth Germ Through the Jaw, J. A. D. A. 24: 1830, 1934.

4. Brodie, A. G.: The Growth of Alveolar Bone and the Eruption of the Teeth, Oral. Surg., Oral Med., Oral Path. 1: 342, 1948.

5. Cattell, P.: The Eruption and Growth of the Permanent Teeth, J. Dent. Research 8: 279, 1928.

6. Gottlieb, B.: Scheinbare Verkiirzun eines oberen Schneidezahnes (So-called Shortening of an Upper Lateral cisor), Ztschr. f. StomatoL 22: 501, 1924.

7. Gottlieb, B., Orban, B., and Diamond, M.: Biology and Pathology of the Tooth and Its Supporting Mechanism, New York, 1938, The Macmillan Co.

8. Gross, H.: Histologische Untersuchungen iiber das Wachstum der Kieferknochen beim Menschen (Histologic Investigations of the Growth of the Human Jaw Bone), Deutsche Zahnh. 89: 1934.

9. Herzberg, F., and Schour, I.: Effects of the Removal of Pulp and 1Iertwig’s Sheath on the Eruption of Incisors in the Albino Rat, J. Dent. Research 20: 264 1941.

10. Hoflman’, M. M.: Experimental Alterations in the Rate of Eruption of the Rat Incisor; Master’s Thesis, University Illinois Graduate School, 1939.

11. Hoffman, M. M., and Schour, I.: Quantitative Studies in the Development of the Rat Molar, II. Alveolar Bone, Cementum and Eruption (From Birth to 500 Days), Am. J. Orthodont. & Oral Surg. 26: 856, 1940.

12. Kronfeld, B.: The Resorption of the Roots of Deciduous Teeth, Dental Cosmos 74: 103. 1932.

13. Logan, W. H. G., and Kronfeld, B.: Development of the Human Jaws and Surrounding Structures From Birth to the Age of Fifteen Years, J. A. D. A. 20: 379,1933.

14. Logan, W. H. G.: A Histologic Study of the Anatomic Structures Forming the Oral Cavity, J. A. D. A. 22: 3, 1935. 306

15. 16. 17. 18. 19.

.a.a.

23. 24.

25. 26.

27. 28. 29.

ORAL HISTOLOGY AND EMBRYOLOGY

Massler, M., and Schour, I.: Studies in Tooth Development: Theories of Eruption, Am. J. Orthodont. 8: Oral Surg. 27: 552, 1941.

Orban, B.: Growth and Movement of the Tooth Germs and Teeth, J. A. D. A. 15: 1004, 1928.

Orban, B.: Resorption of Roots Due to Pressure From Erupting and Impacted Teeth, Arch. Clin. Path. 4: 187, 1940.

Orban, B.: Epithelial Rests in the Teeth and Their Supporting Structures, Proc.

Am. A. Dent. Schools, 1928, p. 121.

Reichborn-Kjennerud: Ueber die Mechanik des Durchbruches der bleibenden Ziihne beim Menschen (Mechanism of the Eruption of the Permanent Teeth in Man), Berlin, 1934, Hermann Meusser.

Sicher, IL: Tooth Eruption: The Axial Movement of Continuously Growing Teeth, J. Dent. Research 21: 201, 1942.

Sicher, B.: Tooth Eruption: The Axial Movement of Teeth With Limited Growth, J. Dent. Research 21: 395, 1942.

Sicher, B.: Oral Anatomy, St. Louis, 1949, The G. V. Mosby Co.

Sicher, H., and Weinmann, J. P.: Bone Growth and Physiologic Tooth Movement, Am. J. Orthodont. & Oral Surg. 30: 109, 1944.

Stein, G., and Weinmann, J. P.: Die physiologische Wanderung der Ziihne Physiologic Drift of the Teeth), Ztschr. f. Stomatol. 23: 733, 1925.

Wassermann, F.: Personal communication.

Weinmann, J. P.: Das Knochenbild bei Stiirungen der physiologischen Wanderung der Zahne (The Bone Picture in Cases of Disturbances of the Physiologic Movement of Teeth), Ztschr. f. Stomatol. 24: 397, 1926.

Weinmann, J. P.: Bone Changes Related to Eruption of the Teeth, Angle Orthodontist 11: 83, 1941.

Weinmann, J. P., and Sicher, H.: Bur 46: 3, 1946.

Willman, W.: An Apparent Shortening of an Upper Incisor, J. A. D. A. 17: 444, 1930.

(The

Correlation of Active and Passive Eruption, CHAPTER XII

SHEDDING OF THE DECIDUOUS TEETH

1. IN TBODUCTION AND DEFINITION 2. PROCESS OI‘ SHZEDDING 3. CLINICAL CONSIDERATIONS

a. Remnants of Deciduous Teeth b. Retained Deciduous Teeth c. Submerged Deciduous Teeth

1. INTRODUCTION AND DEFINITION

Human teeth develop in two generations known as the deciduous and permanent dentitions. The deciduous teeth are adapted in their number, size and pattern to the small jaw of the early years of life. The size of their roots, and therefore the strength of the suspensory ligament (periodontal membrane), are in accordance with the developmental stage of the masticatory muscles. They are replaced by the permanent teeth which are larger, more numerous, and possess a stronger suspensory liga— ment. The physiologic elimination of deciduous teeth, prior to thereplacement by their permanent successors, is called shedding.

2. PROCESS OF SHEDDING

The elimination of deciduous teeth is the result of the progressive resorption of their roots by osteoclasts. In this process both cementum and dentin are attacked (Fig. 236). The osteoclasts differentiate from the cells of the loose connective tissue in response to the pressure exerted by the growing and erupting permanent tooth germ. The pressure is directed against the bone separating the alveolus of the deciduous tooth from the crypt of its permanent successor and, later, against the root surface of the deciduous tooth itself (Fig. 237). Because of the position of the permanent tooth germ the resorption of the deciduous roots of the incisors and cuspids starts at the lingual surface in the apical third (Fig. 238). The movement of the permanent germ, at this time, proceeds in occlusal and vestibular directiori.) In later stages, the germ of the permanent tooth is frequently found directly apical to the deciduous tooth (Fig. 236, A). In such cases the resorption of the deciduous root proceeds in transverse planes, thus causing the permanent tooth to erupt later in the exact position of the deciduous. However, the movement in vestibular direction is frequently not complete when the crown of the permanent tooth

breaks through the gingiva. In such cases, the permanent tooth appears lingual to its deciduous predecessor (Fig. 238). In the first described

First draft submitted by Myron S. Aisenberg. 307 308 ORAL HISTOLOGY AND Emntwonoav

R°s°rpfl°n area " Resorptlon ot

_ root

.T* ‘’_T" Resorptlon or

Permanent cuspid ‘ ' b°“°

1*’.

‘ cementum

I '~ A _....s ..

“°‘°’P“°'* 'S (°3t°°°13-533) ' W .. Periodontal Jr “ membrane ' —--——,—- Resorptlon of bone

B. F . 236.—Resox-ption of root of deciduous cus id during eruption of permanent successor. Kronteld!) A. General view. B. Linguafreaorption area in higher magnification. sauonme or DECIDUOUS TEETH 309

Deciduous incisor

deciduous tooth and successor

Enamel of permanent incisor

Dentin

Fig‘. 23'I.~—.A thin lamclla of bone separates permanent tooth germ from its predecessor. 310 ORAL EISTOLOGY AND EMBRYOLOGY

r ._ _ ,,_ W , _ /._—...~_..,

Deciduous incisor -—'—-~ I

Enamel of Der-mar

Root resorption .nent incisor

Dentin

..r'

Fig. 23S.—Resorption of root of deciduous incisor due to pressure of erupting successor. SHEDDING on THE DECIDUOUS TEETH 311

alternative the deciduous tooth is lost before the permanent tooth erupts, whereas in the latter the permanent tooth may erupt while the Qleciduous tooth is still in its place.

In most cases, resorption of the roots of the deciduous molars begins on the surfaces of the roots next to the interradicular septum. This is due to the fact that the germs of the bicuspids are frequently found between the roots of the deciduous molars (Fig. 239). In such cases, extensive resorption of the roots can be observed long before actual shedding. However, during the continued active eruption the deciduous teeth

_ . . --w.....gs—.

I

deciduous :3 molar .

’ ., 4,!’ ‘X ~-_; g ' 1'.‘ V ' ‘J \ .;'~. ' ' 3‘-:, ' " - - . _ _ ,, \'_‘ , ‘wt . ”

• 4’

. R8S01‘Dl-303 ;_->':.i"'* '

.,_,__‘L.g-'3 Repaired resorp
  

°"' r°°t . ‘ tion of dentin Penngrlient ,,. .. (X) too germ

Fig. 239.——Germ or lower flrst bicuspid between the roots of lower flrst deciduous molar. Repaired resorption on the roots of the deciduous tooth (see Fig. 241).

move away from the growing permanent tooth germs which, for the most part, soon come to lie apical to the deciduous molars (Fig. 240). This change in position allows the growing bicuspid adequate space for its development. The areas of early resorption on the deciduous molar are then repaired by the apposition of new cementum and the alveolar bone regenerates’ (Fig. 241). In later stages, however, the erupting bicuspids again overtake the deciduous molars and, in most cases, their roots become entirely resorbed (Fig. 242). The resorption may even proceed far 312 ORAL msronomz AND EMBRYOLOGY

up into the coronal dentin; occasionally, greater or less areas of the enamel may be destroyed. The bicuspids appear with the tips of their crowns in the place of the deciduous teeth.

The osteoclastic resorption which is initiated by the pressure of the permanent tooth is the primary reason for the elimination of a deciduous tooth. Two auxiliary factors have to be taken into consideration. These are, first, the weakening of the supporting tissues of the deciduous tooth, due to resorption of wide areas of its roots; and continued active and passive eruption which seems to be accelerated during the period of

—— Second

deciduous ‘ molar

‘ Traumatic changes In periodontal membrane

,' (x)

"1

. ‘V Second

‘ bicuspld

germ

-'4 ' ' I . \ 1’ -. ,,_; -,-1. ~ , ,/ , 3» r K I / - 5”: ‘ / ' " w‘.‘.. .‘ . A‘ ’ f/ «r ; V: - ‘ .‘—.

\ / ,

r p ‘A ‘Ti 2", X1! ti _

6

“"‘

Fig. 240.—Germs or bicuspids below roots of deciduous molars. Traumatic changes in the periodontal membrane or the deciduous teeth. Z. See Fig. 243.

shedding. The epithelial attachment of the deciduous tooth grows down along the cementum at this time, thus causing the clinical crown of the tooth to be enlarged and the clinical root to which the suspensory fibers are anchored, to be shortened. Second, the masticatory forces increase during this period, due to the growth of the masticatory muscles, and combine with the root resorption and eruption to initiate a vicious circle resulting in rapid loosening of the deciduous tooth. The masticatory stresses act as traumatic forces upon the tooth at this stage!’ 7: ¥° Due to the loss of large parts of the suspensory apparatus the masticatory forces SHEDDING OF THE DEGIDUOUS TEETH

tooth

Repaired

dentin

Loose connec- ‘ ' ‘ five tissue surrounding permanent germ

313

cementum of deciduous

resorption

Resorption of

Fig. 241.——High magniflcaton of a. repaired resorption; from area. I of Fig. 239; new

bone formed during rest period. 314 out. HISTOLOGY AND EMBRYOLOGY

4.. \

Deciduous molar

Contact between deciduous and permanent

V f t°°th lmiaaiglliesxpgjd

4 _ , _ §—— New formation Bone resorption - . ‘ »» ' of bone

_Fig'..242.—_—Eoots of deciduous molar completely resorbed. Dentin of deciduous tooth iii contact with enamel of the bicuspid. Resorption of bone on one side. new formation

of bone on the opposite side or the bicuspid due to transmitted excentric pressure to the bicuspid. (Grimmer!) SHEDDING on THE nncmvous TEETH 315

may be transmitted to the alveolar bone not as tension but as pressure. This leads to compression and injury of the periodontal membrane with subsequent bleeding, thrombosis and necrosis (Fig. 243). These changes are most frequently found in the bifurcation and interradicular surfaces of deciduous molars. Resorption of bone and tooth substance, therefore, occurs most rapidly in such areas, thus relieving pressure. Repair of

resorbed areas may be excessive and may even lead to ankylosis between bone and tooth (Fig. 24-1).

Deciduous tooth

Necrotlc tissue remnants

—.g .- Traumatic destruc‘ tion of perio_ ; dental membrane Alveolar bone " ——-—

~ '3 - Repaired ' re resorption

Necrotic tissue remnants

51?’

Fig. 243.—Tx-aumatic changes of periodontal tissues. High magnification from area. X in Fig. 240.

The process of shedding is not necessarily continuous. Periods of great resorptive activity alternate with periods of relative rest.’ During the rest periods resorption not only ceases but repair may actually occur by apposition of cementum or bone upon the resorbed surface of cementum or dentin. Even repair of resorbed alveolar bone may take place 316 mun ms-ronoenz AND EMBRYOLOGY

Deciduous molar v \

Reaorption of bone in area. of L. ankylosis

Permanent tooth . _. ‘ p.‘ ,r -

Resorptionr: l _ . «T

a.

_L .\ 7:

L43.

i<'s.«.a..'f..-4'1;

Fig. 244.—Ankylosl.s ot deciduous tooth as a. sequence of trauma. 4. General view.

B. High magnification of area. X in A.

{ Resorption of cementum

' Ankylosis SHEDDING or THE DECIDUOUS TEETH 317

durillg rest periods (Fig. 241). The phases of rest and repair are, probably, lengthened by relief of pressure upon the deciduous tooth by its own eruptive movement. r

The pulp of the deciduous teeth plays a passive role during shedding. Even in late stages the ocelusal parts of the pulp may appear almost normal, with functioning odontoblasts (Fig. 245). However, since the cellular elements of the pulp are identical with those of loose connective tissue, resorption of the dentin may occur at the pulpal surface by the

‘W - -— Odontoblasts

Pu1p¢V—’—j——

Dentin

Fig. 245.—High magnification 01' the pulp of resorbed deciduous molar of Fig. 242. Pulp of normal structure with odontoblasts.

differentiation of osteoclasts from the cells of the pulp. The persistence of the pulpal tissue, and its organ.ic connection with the underlying connective tissue, explain the fact that deciduous teeth show, to the last, a fairly strong attachment even after total loss of their root (Fig. 242). In such cases, shedding may be unduly retarded and the erupting permanent tooth may actually come into contact with the deciduous tooth. The masticatory forces are then transmitted to the permanent tooth” before its suspensory ligament is fully differentiated, and traumatic injuries in the periodontal membrane of the permanent tooth may develop (Fig. 242). Remnants of Deciduous Teeth

Deciduous Retained Teeth

318 om. 1-nsvronocr AND EMBRYOLOGY

3. CLINICAL CONSIDERATIONS

Parts of the roots of deciduous teeth which are not in the path of erupting permanent teeth may escape resorption. Such remnants of roots, consisting of dentin and cementum, may remain in the jaw for a considerable time.‘’'‘’ In most cases, such remnants are found along the bicuspids, especially in the region of the lower second bicuspids (Fig. 246). This can be explained by the fact that the roots of the lower second deciduous molar are strongly curved or divergent. The mesiodistal diameter of the second bicuspid is much smaller than the greatest distance between the roots of the deciduous molar. Root remnants may later be found deep in the jaw bone, completely surrounded by, and ankylosed to, the bone (Fig. 247). Frequently, they become encased in heavy layers of cellular cementum. In cases where the remnants are close to the surface of the jaw (Fig. 248) they may, ultimately, become exfoliated. Progressive resorption of the root remnants and replacement by bone may cause the disappearance of these remnants. Cysts occasionally develop around the retained roots of deciduous teeth. They appear between the roots of the permanent teeth.

Root remnant of - - ,, .— — -.---.— declduous , ~ —. Root remnant of

tooth “ deciduous tooth

Fig. 246.—Remna.nts of roots of deciduous molar embedded in the interdentai septa. (Roentgenogram courtesy G. M. Fitzgerald, University of California.)

Deciduous teeth may be retained for a long time if the corresponding permanent tooth is congenitally missing.‘ This is most frequently observed in the region of the upper lateral incisor (Fig. 249, A), less frequently in that of the second bicuspid, especially the lower (Fig. 249, B), and rarely in the central lower incisor region (Fig. 2-19, 0). Also, if a permanent tooth is embedded, its deciduous predecessor may be retained (Fig. 249, D). This type of retained deciduous tooth is found mostly in

the upper cuspid region as an accompaniment of the impaction of the permanent cuspid. SHEDDING or THE zorzcmuous TEETH 319

First bicuspid second bicuapld

Remnant of deciduous root

' - Ankylosls

Fig. 247.———Remna.nt of deciduous tooth embedded in, and ankylosed to, the bone. ( Schoenbauez-.5 ) 320 mun HISTOLOGY AND EMBRYOLOGY

Interdentul papilla

31¢‘-“PW Blcusvld

-~——-V7 A Remnant of deciduous tooth

Fig. 248.—-Remnant of deciduous tooth at alveolar crest. SHEDDING or THE nncmuous TEETH 321

The fate of retained deciduous teeth varies. In some cases they persist for many years in good functional condition (Fig. 249, A); more often, however, resorption of the roots and continued active and passive eruption cause their loosening and final loss (Fig. 249, B). The loss of retained deciduous teeth has been explained by the assumption that such teeth may undergo regressive changes in their pulp, dentin, cementum, and periodontal membrane, thus losing their regenerative faculties which are necessary to compensate for the continued injuries during function? It is, however, more probable that such teeth, because of their smaller size, are not adapted to the strength of the masticatory forces in adult life. The roots are narrow and short, thus rendering the area available for attachment of principal fibers relatively inadequate. Their loss is then due to traumatism.

Fig. 249.—Roentgenogra.ms of retained deciduous teeth. A. Upper lateral permanent incisor missing’. deflduous tooth retained (age 55) B. Lower second bicuspid missing, deciduous molar retained: r00tS D8-N’-1y !‘eS°1'be5~ (Courtesy M. K. Hine, University of Indiana.)

0'. Lower central permanent incisors missing. deciduous teeth retained.

D. Upper permanent cuspid embedded; deciduous cuspid retained. (Courtesy Rowe Smith, Texarkana.)

If the permanent lateral incisor is missing, the -deciduous tooth is.in many cases resorbed under the pressure of the erupting permanent cuspid. This resorption may be simultaneous with that of the deciduous cuspid Submerged Deciduous Teeth

322 oasr. HISTOLOGY AND EMBRYOLOGY

(Fig. 250). Sometimes, the permanent cuspid causes resorption of the deciduous lateral incisor only, and erupts in its place. In such cases, the deciduous cuspid may be retained distally to the permanent cuspid.

Traumatic lesions, on the other hand, may lead to ankylosis of a deciduous tooth, rather than its loss. The active eruption of an ankylosed tooth ceases and, therefore, the tooth appears shortened later on (Fig.

Fig. 250.—Upper permanent lateral incisor missing. Deciduous lateral _incisor and deciduous cuspid are resorbed due to pressure of erupting permanent cuspid.

A. At the age of 11. B. At the age of 13.

,.‘

Fig. 251.—Submerging lower deciduous second molar. Second bicuspid missing.

(Courtesy M. K. Hine, University of Indiana.)

251), due to continued eruption of its neighbors and the relative height of their alveolar processes. The “shortening” of such a tooth may even lead to its eventual overgrowth by the alveolar bone and the tooth may become submerged in the alveolar bone.‘ The roots and crowns of such teeth show extensive resorption and apposition of bone in the tortuous cavities.

SHEDDING on THE DEGIDUOUS TEETH 323

Submerged deciduous teeth prevent the eruption of their per manent successors, or force them from their position. Submerged deciduout teeth should, therefore, be removed as soon as possible.

1.

9°

10.

.“.°’.°‘!“S'°.“"

References

Aisenberg, M. 8.: Studies of Retained Deciduous Teeth, Am. J. Orthodont. 85

Oral Stu‘ . 27: 179, 1941.

Grimmer, E. .: Trauma in an Erupting Premolar, J. Dent. Research 18: 267, 1939.

Kotanyi, E.: Histologische Befunde an Milchzahnreste (Histologic Findings on Deciduous Tooth Remnants), Ztschr. f. Stomatol. 23: 516, 1925.

Kronfeld, R.: The Resorption of the Roots of Deciduous Teeth, Dental Cosmos 74: 103 1932.

Kronfeld, R.: and Weinmann, J’. P.: Traumatic Changes in the Periodontal Tissues of Deciduous Teeth, J. Dent. Research 19: 441, 1940.

Noyes, F. B.: Snbmerging Deciduous Molars, Angle Orthodontist 2: 77, 1932.

Oppenheim, A.: Histologische Befunde beim Zahnwechsel (Histo1ogic Findings in the Shedding of Teeth), Ztschr. f. Stomatol. 20: 543, 1922.

Schoenbauer, F.: Kniichern eingeheilte Milchzahnreste bei iilteren Individuen (Ankylosed Deciduous Teeth Remnants in Adults), Ztschr. f. Stomatol. 29:

892 1931. Stafne, 0.: Possible Role of Retained Deciduous Roots in the Etiology of

Cysts of the Jew, J. A. D. A. 24: 1489, 1937. Weinmann, J. P., and Kronfeld, R.: Traumatic Injuries in the Jaws of Infants, J. Dent. Research 19: 357, 1940. CHAPTER XIII TEMPOROMANDIBULAR JOINT

1. AN ATOMIC REMARKS

2. HISTOLOGY

a.. Bony Structures

b. Articular Pibrocartilage c. Articular Disc

d. A1-ticular Capsule

3. CLINICAL CONSIDERATIONS

1. AN ATOMIC REMARKS

The mandibular articulation (temporomandibular joint) is a diarthrosis between mandibular fossa and articular tubercle of the temporal bone, and capitulum (head, condyle) of the mandible. A fibrous plate, the articular disc, intervenes between the articulating bones.

The articulating surface of the temporal bone is concave in its posterior, convex in its anterior part. The 91131 concavity, articular fossa, extends from the squamotympanic and petrotympanic fissure in the back to the con vex articular tubercle in front. Th latter is strongly convex in a sagittal and slightly concave in a frontal plane. The convexity varies considerably, the radius ranging from 5 to 15 mm. The long axes of fossa and tubercle are directed medially and slightly posteriorly. The articular surface of the mandibular head is, approximately, part of a cylinder the axis of which is placed in the same direction as that of the articular surfaces on the temporal bone. The articulating parts of the temporomandibular joint are covered by a fibrous or fibrocartilaginous tissue and not by hyaline cartilage, as in most other articulations of the human body. The

hyaline cartilage in the mandibular condyle which is present during its growth period does not reach the surface.

The articular disc is an oval fibrous plate which is united around its margin with the articular capsule (Fig. 252). It separates the articular space into two compartments: a lower, between condyle and disc, and an upper, between disc and temporal bone. The disc appears biconcave in sagittal section. Its central part is thin, in rare cases perforated; the anterior and especially the posterior borders are thickened (Fig. 253). Fibers of the external pterygoid muscle are attached to its anterior border. The disc serves to adapt the bony surfaces to each other, especially in a forward position of the mandible when the convex condyle approaches the

aonvex articular tubercle. The disc is, at the same time, the movable socket for the mandibular head.

First draft subxpitted by Donald A; Kerr. 324 TEMPOROMANDIBULAR JOINT 325

The articular capsule consists of an outer fibrous sac which is loose. It IS strengthened on its lateral side by the temporomandibular ligament.‘

The inner synovial membrane is divided like the articular space. The superior part reaches from the margin of the articular surfaces on the tem poral bone to the disc; the inferior extends from the disc to the neck of the mandible.

2. HISTOLOGY

The condyle of the mandible is composed of typical cancellous bone Bony covered by a thin layer of compact bone (Fig. 253). The trabeculae are smmm

grouped in such a way that they radiate from the neck of the condyle and

Ma.ndibula.r ..

V‘

rossa. =. _ Articular tubercle

Mandibular head

Fig. 252.—Sagitta1 section through the temporomandibular joint. (Courtesy W. Bauer,‘ St. Louis University School oi‘. Dentistry.)

Fig. 253.—Sagitta1 section through the temporomandibular joint of a 28-year-old man. (Courtesy S. W. Chase. Western Reserve University.) 326 ORAL HISTOLOGY AND EMBRYOLOGY

reach the cortex at right angles, thus giving maximal strength to the condylar bone While still maintaining a light construction. In young

individuals the trabeculae are thin and may contain islands of hyaline cartilage near the surface (Fig. 254, A). In older individuals these car

- 3- Fibrous . covering

. - .. Cartilage V; , -I islands

. A! .-.1:-::. '

1 -§'Fibrous ‘ " covering

Fig. 254.—-Sections through the mandibular head. A. Newborn infant. R. Young adult.

tilaginous islands are resorbed and replaced by bone (Fig. 254, B). The marrow spaces are large at first, but decrease in size with progressing age by a marked thickening of the trabeculae. The marrow in the condyle TEMPOROMANDIBULAR JOINT 327

is of the myeloid or cellular type; in older individuals it is sometimes replaced by fatty marrow.

In young individuals the bone of the condyle is capped by a layer of hyaline cartilage which develops as a secondary growth center in three-month-old embryos. It is interposed between the fibrocartilage and the bone. It may still be present in the jaw of a person in his twenties (Fig. 254). The cartilage grows interstitially and by apposition from the deepest layer of the covering fibrous tissue; at the same time it is, gradually, replaced by bone on its inner surface.

. Ii-,,.’

, i . <: k'V.‘»} ' I,‘ I‘ .

Fig. 255.—Higher magnification of part of the mandibular condyle of Fig. 253.

The bone of the mandibular fossa varies considerably from that of the articular tubercle (Fig. 253). In the fossa it consists of a thin compact layer; the articular tubercle is composed of spongy bone covered with a thin layer of compact bone. In rare cases islands of hyaline cartilage are found in the articular tubercle.

The condyle as well as the articular fossa and tubercle are covered by a rather thick layer of fibrous tissue containing a. variable number of cartilage cells. The fibrous or fibrocartilaginous covering of the mandibular condyle is of fairly even thickness (Fig. 255). Its superficial layers consist of a network of strong collagenous fibers. Cartilage cells or chondrocytes may be present and have a tendency to increase in number with age. They can be recognized by their thin capsule which stains heavily with basic dyes. The deepest layer of the fibrocartilage is rich in

Bone

Articular Fibro cartilage Arflcularbisc

ORAL HISTOLOGY AND EMBRYOLOG3.

chondroid cells as long as hyaline cartilage is present in the condyle; it contains only a few thin collagenous fibers. In this zone the appositional growth of the hyaline cartilage of the condyle takes place.

The fibrous layer covering the articulating surface of the temporal bone (Fig, 256) is thin in the articular fossa and thickens rapidly on the posterior slope of the articular tubercle (Fig. 253). In this region the fibrous tissue shows a definite arrangement in two layers, with a small transitional zone between them; the two layers are characterized by the different course of the constituent fibrous bundles. In the inner zone the fibers are at right angles to the bony surface; in the outer zone they run parallel to that surface. As in the fibrous covering of the mandibular condyle, a variable amount of chondrocytes is also found in the tissue on the temporal surface. In adults the deepest layer shows a thin zone of

calcification.

Bone

Calcification

\ p " ~ - ' zone

v -- --s Inner fibrous layer

-— --——a Outer fibrous layer

Fig. 256.—Higher magnification of articular tubercle of Fig. 253

There is no continuous cellular lining on the free surface of the fibrocartilage. Only isolated fibroblasts are situated on the surface itself; they are, generally, characterized by the formation of long flat cytoplasmic processes.

In young individuals the articular disc is composed of dense fibrous tissue which resembles a ligament because the fibers are straight and

tightly packed (Fig. 257). Elastic fibers are found throughout the disc, but only in relatively small numbers. The fibroblasts in the disc are TEMPOROMANDIBULAR JOINT 329

elongated and send flat cytoplasmic wing-like processes into the interstices between the adjacent bundles. The mandibular disc does not show the usual fibrocartilaginous character of other interarticular discs. This

may be regarded as a functional adaptation to the high mobility and plasticity of this disc.

Articular tubercle

Superior articular space

__ Articular disc

--- Inferior articular space

- -—= Mandibular head

43

Fig. 257.—-Higher magnification of articular disc of Fig. 253.

With advancing age some of the fibroblasts develop into chondroid cells Which, later, may become real chondrocytes. Even small islands of hyaline cartilage may be found in the discs of older persons. Chondroid cells, true cartilage cells and hyaline ground substance develop in situ by difierentiation of the fibroblasts. In the disc as well as in the fibrous tissue covering the articular surfaces, this cellular change seems to be dependent upon mechanical influences. The presence of chondrocytes increases the resistance and resilience of the fibrous tissue. Articulal: capsule

330 ormr. HISTOLOGY AND EMBRYOLOGY

As in all other joints, the articular capsule consists of an outer fibrous layer which is strengthened on the lateral surface to form the temporamandibular ligament. The other parts of the fibrous capsule are thin and loose. The inner or synovial layer is a thin layer of connective tissue.

'It contains numerous blood vessels which form a capillary network close «to its inner surface. In many places larger and smaller folds or finger like processes, synovial folds and villi protrude into the articular cavity (Fig. 258). The former concept of a continuous cellular covering of the free synovial surface has been abandoned. Only a few fibroblasts of the synovial membrane reach the surface and, with some histiocyte and lymphatic‘ wandering cells, form an incomplete lining of the synovial membrane.

I ‘ T synovial villl

Fifi 258.—Villi on the synovial capsule of ternporomandibular joint.

A small amount of viscous fluid, synovial fluid, is found in the articular spaces. It is a lubricant and also a nutrient to the avascular coverings of the bones and to the disc. Its origin is not clearly established. It is possibly in part derived from the liquefied detritus of the most superficial elements of the articulating surfaces. It is not clear whether it is a product of filtration from the blood vessels or a secretion of the cells of the synovial membrane; possibly it is both. TEMPOROMANDJBULAR JOINT ' 331

3. CLINICAL CONSIDERATIONS

The thinness of the bone in the articular fossa is responsible for fractures if the mandibular head is driven into the fossa by a heavy blow. In such cases injuries of the dura mater and the brain have been reported.

The finer structure of the bone and its fibrocartilaginous covering depends upon mechanical influences. A change in force or direction of stress, occurring especially after loss of posterior teeth, will cause structural changes. These are brought about by resorption and apposition of bone, and by degeneration and reorganization of fibers in the covering of the articulating surfaces and in the disc.“

There is considerable literature on the disturbances after loss of teeth

or tooth substance due to changes in the mandibular articulation.“ The clinical symptoms are said to be: impaired hearing, tinnitus (ear buzzing), pain localized to the temporomandibular joint or irradiating into the region of ear or tongue. Many explanations have been advanced for

these variable symptoms: pressure on the external auditory meatus exerted by the mandibular condyle which is driven deeply into the articular fossa; compression of the auriculotemporal nerve; compression of the chorda tympani; compression of the auditory tube; impaired function of the tensor palati muscle. Anatomical findings do not substantiate any one of these explanations. Probably, all the diverse symptoms are but consequences of a traumatic arthritis in the mandibular joint.“ 2 It is caused by an increase and a change in direction of the forces of the masticatory muscles upon the structures of the joint.

References

1. Bauer, W.: Anatomische und mikroskopische Untersuchungen iiber das Kiefergelenk Anatomical and Microscopic Investigations on the Temporo-Mandibular oint), Ztschr. f. Stomatol. 80: 1136, 1932.

2. Bauer, W. H.: Osteo-Arthritis Deformans of the Temporo-Mandibular Joint, Am. J. Path. 17: 129, 1941.

3. Baecker, B.: Zur Histologie des Kiefergelenkmeniskus deg Menschen und der

Siiu er (Histology of the Temporo-Mandibular Disc in Man and Mammals), Zts . f. mikr.-anat. For-sch. 26: 223, 1931.

Breitner, 0.: Bone Changes Resulting From Experimental Orthodontic Treatment, Am. J. Orthodont. 26: 521 1940.

Cabrini, R., ‘and Erausquin, La. Articulacion Temporomaxilar de la Rata (Temporo-Mandibular Joint of the Rat), Rev. Odont. de Buenos Aires, 1941.

Cowdry, E. V.: Special Cytology, ed. 2, New York, 1932, Paul B. Hoeber, Inc., pp. 981-989, 1055-1075.

Hammer, J. Aug.: Ueber den feineren Bau der Gelenke (The Microscopic Architecture of the Joints), Arch. f. mikr. Anat. 43: 266, 1894.

Marquart, W.: Zur Histologie der Synovialmembran (Histology of the Synovial Membrane), Ztschr. f. Zellforsch. u. mikr. Anat. 12: 34, 1931.

Peterson, H.: Die Organe des Skeletsystems (Organs of the Skeletal System), Moel1endorf’s Handb. d. mikr. Anat. d. Menschen. Book 2, Part 2, Berlin, 1930, Julius Springer.

10. Schaefler, J. P.: Morris’ Human Anatomy, ed. 10, Philadelphia, 1942, The

Blakiston Co.

11. Schafler, J.: Ueber den feineren Bau und die Entwicklung dos Knorpelgewebes und iiber verwandte Formen der Stiitzsubstanz (On the Microscopic Structure and Development of Cartilage and Related Forms of Supporting Tissue), Ztschr. f. wissensch. Zoo]. 80: 155, 1905.

S°9°.“‘.°’S"'." 332 omu. HISTOLOGY AND EMBRYOLOGY

12. Schaffet, J.: Die Stiitzgewebe (Supporting Tissues), Moe11endorf’s Handb. f. mikr. Anat. d. Menschen, Book 2, Part 2, Berlin, 1930, Julius Springer.

13. Shapiro, H. IL, and Ti-uex, R. 0.: The Temporo-Mandibular Joint and the Auditory Function, J. A. D. A. 30: 1147 1943.

14. Sicher, Harry: Temporomandibufar Articulation in Mandibular Overclosure, J. A. D. A. 36: 131, 1948.

15. Sicher, Harry: Some Aspects of the Anatomy and Pathology of the Temporamandibular Articulation, New York State D. J. 14: 451, 1948.

16. Steinhardt Gr.: Die Beanspruchun der Gelenkfliichen bei versehiedenen Bissarten ( vestigations on the tresses in the Mandibular Articulation and Their Structural Consequences), Deutsche Zahnh. in Vortr. 91: 1, 1934. CHAPTER XIV THE MAXILLARY SINUS

IN'1'RODUC'.|'.'ION DEVELOPMENT

ANATOMIG REMARKS FUNCTION

HISTOLOG-Y

CLINICAL CONSIDERATIONS

9‘S"'."9°!°'."

1. INTRODUCTION

The relation of the maxillary sinus to the dentition was first recognized by Nathaniel Highmore. In his Work Carports Humawi Disquisitio Anatomicafi (1651) he described the adult state of the cavity in detail, and pointed out that his attention had been called to it because a patient had an abscess there which was drained by the extraction of a cuspid tooth. This proved to be one of those misleading first observations, since it is now known that the cuspid‘ root seldom is related to this space in such a way that its simple extraction would drain it. However, the erroneous idea still persists that this relationship is generally true. The molar roots most often, and the bicuspid roots less frequently, are the dental structures which lie closest to the sinus (Fig. 259). Individual variations are great and can be determined only by careful interpretation of good roentgenographs.’

2. DEVELOPMENT

The maxillary sinus begins its development in about the third monthof fetal life. It arises by a lateral evagination of the mucous membrane of the middle nasal meatus, forming a slitlike space. In the newborn its measurements are about 8 x 4 x 6 mm. (Fig. 260); thereafter, it gradually expands by pneumatization of the body of the maxilla. The sinus is well developed when the second dentition has erupted, but it may continue to expand, probably throughout life.5

3. ANATOMIG REMARKS

The maxillary sinus, or antrum of Highmore, is situated in the body of the maxilla. It is pyramidal in shape; the base of the pyramid is formed by the lateral wall of the nasal cavity; the apex extends into the zygomatic process; the anterior wall corresponds to the facial surface of the maxilla, and the roof to its orbital surface. The posterior wall is formed by the infratemporal surface of the maxilla; the floor, usually, reaches into the alveolar process (Fig. 261).

First draft submitted by Paul C. Kitchin in collaboration with L. F. Edwards. Department of Anatomy, Ohio State University.

333 334 ORAL msronoev AND nmsnvonocv

There is a considerable variation in size, shape and position of the maxillary sinus, not only in different individuals, but also on the two sides of the same individual. Its average capacity in the adult is about one-half of one fluid ounce (14.75 c.c.) with average dimensions as follows: anteroposteriorly, 3.4 cm.; transversely, 2.3 cm.; and vertically, 3.35 cm. The maxillary sinus communicates with a recess of the middle meatus of the nasal cavity (semilunar hiatus) by means of an aperture, the ostium maxillare, which is located high on its nasal or medial wall and is, therefore, unfavorably situated for drainage (Fig. 261). An accessory ostium may occur which is, usually, lower and thus more advantageously placed for drainage than is the normal ostium.

Bony floor of sinus

Buccal « alveolar plate

.2 , :3

Fig. 259.—Bucco1ingua1 ection throu h n t b‘ ‘d. ' ; fzéom the sinusg by is thiirgpgfatenbisliione. The apex ls iepamted

Variations in the size of the maxillary sinus are explained on the basis of the degree or extent of pneumatization of the body of the maxilla (ho11owing—out by an air-filled pouch of the nasal cavity). In genera], the greater the pneumatization the thinner the walls of the sinus will be, since pneumatization occurs at the expense of bone. During THE MAXILLARY sums 335

enlargement of the sinus various recesses or accessory fossae may form. Thus, subcompartments or recesses may be present in the palatine, zygomatic, frontal and alveolar processes. The floor of the sinus may extend downward not only between adjacent teeth but also between the roots of individual teeth so that their apices cause elevations in the floor and appear to protrude into the sinus. The type and number of teeth whose

,1. : ,,,

.7!

Nasal septum

Maxillary sinus

"y Inferior nasal concha.

Fig. 260.—Fronta1 sections through the head. A. Newborn infant

B. Nine-month-old child.

Compare the size of maxillary sinus.

apices indent the floor of the space depend upon the degree and shape ofpneumatization. In the majority of cases the roots are covered by a. thin layer of bone (Fig. 259). In some instances, they are covered only by the mucous membrane which lines the cavity and by the periodontal membrane of the root of the tooth. The floor of the sinus may be on the 336 omu. HISTOLOGY AND EMBRYOLOGY

Ethmoidal cell ‘

Aperture of ,- .lnus

1

Maxillary sinus - —-—‘

Nasal septum

Inferior nasal concha

Maxtllary sinus

~ 3'. ‘;bhéiF'w.;\?L( $-or‘ '

Fig. 261.—Rela.tion or the maxillary sinus and its opening into the nasal cavity. A. Frontal section showing marked asymmetry between right and left sinus. B. Relation of sinus to root apicea. rm: MAXILLARY sINUs 337

same level with that of the nasal cavity, or higher or lower than that. In some cases the sinus may be incompletely divided by osseous and membranous ridges, commonly known as septa.

Unilateral supplemental maxillary sinuses have been observed.‘ They occur posteriorly to the sinus proper and are, from the standpoint of origin, overdeveloped posterior ethmoid cells. Clinically, they must be considered as maxillary sinus.

4. FUNCTION

In the past, various functions have been ascribed to the maxillary sinus and the other accessory nasal sinuses. It has been claimed by some, for instance, that they aid in warming and moistening inhaled air, thus acting as air-conditioning chambers. Others believe that the sinus plays an important role in vocalization. However, the most probable explanation of the development of all nasal sinuses is that bone which has lost its mechanical function is resorbed. An example is the marrow cavity in long bones where fatty tissue develops in the place of the disappearing bone. The disappearance of useless bony substance in the neighborhood of the air-filled nasal cavity leads to development of air-filled pouches which grow into the bone and occupy the place of bony tissue which is no longer needed to withstand mechanical stresses. The supporting function of bone is maintained but with a minimum of material. This is in accord with principles of economy which exist in the animal body.

5. HISTOLOG-Y

The maxillary sinus is lined by a mucosa covered with an epithelium typical of the respiratory passages. It is thinner and more delicate than that of the nasal cavity.

The lamina propria of the mucosa is fused to the periosteum of the underlying bone and consists of loose bundles of collagenous fibers with very few elastic fibers; it is only moderately vascular (Fig. 262, A). Glands of the mucous and serous type are confined largely to that part of the tunica propria which is located around the opening, or openings, into the nasal cavity.

The epithelium is pseudostratified ciliated columnar, rich in goblet cells (Fig. 262, B). The nuclei of the individual columnar cells are‘located at different distances from a delicate basement membrane. Actually, each columnar cell rests upon the basement membrane, but not all the cells reach the surface. The goblet cells secrete mucus which moistens the surface of the sinus mucosa. The cilia beat in such a way as to move any surface material toward the opening communicating with the nasal cavity, and hence act to clear the sinus cavity of inhaled substances, and

mucus. 6. GLINIGAI. CONSIDERATIONS

Pulpal infection in teeth whose root apices are in close approximation to the floor of the sinus are dangerous because it can be a cause of sinus Maxillary sinus Epithelium

- —"- ‘ “ ‘ - Mucous membrane

‘T’ --- “F” and perlosteum

Incomplete bony floor of sinus

_ _ ,_,......\‘. 7»;-w

Fig. 262.——Mucous membrane and epithelium of maxillary sinus.

A. Apical region of :1 second bicuspid. The lining oi.’ the sinus is continuous with the periapicsl tissue through openings in the bony floor of the sinus.

B. High magnification of the epithelium of maxillary sinus. (Courtesy W. 11. Bauer.‘ St. Louis University School of Dentistry.)

.- - -j-—-A .g.g3;‘.I“&' ‘S

-2‘Q

es.

F'iE- 263.—Roentgenogrs.m or upper jaw. Maxillary sinus extends toward alveolar crest after loss of flrst molar. Tl-IE MAXILLARY SINUS 339

infection.‘= 3 Thus, the prevention of the dental type of sinusitis is possible by prevention or elimination of pulpal infection. Any root canal operation in maxillary bicuspid or molar areas should be carried out with particular care, in order to prevent infection of the sinus.

The dentist should always keep in mind that disease of the maxillary sinus may produce referred dental pain. The superior alveolar nerves run in narrow canals in the thin wall of the sinus and, frequently, these canals are partly open toward the sinus. When this happens the nerves which supply the teeth are in contact with the lining of the sinus where they may become involved in an inflammation affecting the mucosa. In such cases, the pain resembles pulpal pain but involves a group of teeth or even all the teeth in one maxilla. If apices of some roots are in contact with the lining of the sinus the affected teeth may show symptoms of periodontitis during sinus infection. In cases where there is doubt whether the teeth or sinus are the cause of pain, the patient should be referred to a rhinologist before an extraction is performed.

In the course of an extraction a root may be forced into the sinus. If it cannot be easily removed through the socket the patient should be informed of the circumstances and be referred to a rhinologist. Even if it is possible for the dentist to remove the root of the tooth, subsequent treatment by the sinus specialist is advisable. Any invasion of the field of sinus surgery by the dentist operating through the alveolar wall should be discouraged by both dental and medical professions.

After loss of a single maxillary molar or, more rarely, bicuspid, the bony scar is, sometimes, hollowed out by the sinus (Fig. 263). The risk of opening the sinus during extraction of a tooth adjacent to such an extension has to be recognized. If a single molar remains in the maxilla for a long time after loss of the neighboring teeth, downward extensions,‘ of the maxillary sinus may occur mesially and distally to this tooth. If [ greater force is applied in extracting such a tooth, tooth and socket are removed together rather than extracting the tooth from its socket. To minimize the necessary force the crown should be removed, the roots separated and extracted singly. The expansion of the maxillary sinus (and other sinuses) in old individuals should not be considered a process of growth. It is rather the consequence of progressive disuse atrophy of the bones, especially after loss of teeth, or of senile osteoporosis. The senile expansion of sinuses strengthens the belief that they develop as fill-ins in bones whose core is under reduced mechanical stress.

References

1. Bauer. W. ‘EL: Maxillary Sinusitis of Dental Origin, Am. J. Orthodont. & Oral Surg.

29: 133, 1943. _ 2. Ennis, L. M., and Batson, 0.: Variations of the Maxillary Sinus as Seen in the

Roentgenogram, J. A. D. A. 23: 201, 1936. 3. Hofer, 0.: Dental Diseases and Their Relation to Maxillary Antrum, J. Dent.

Research 17: 321, 1938 (Abstract). 340 omu. HISTOLOGY AND EMBRYOLOGY

4. MacMilla.n, H. W.: The Relationship of the Teeth to the Maxillary Sinus; Anatomic Factors glnderlying the Diagnosis and Surgery of This Region, J‘. A. D. A. 14.: 1635, 19 7.

5. Schaefier, J. I’.: The Sinus Maxillaris and Its Relations in the Embryo, Child and Adult Man, Am. J. Anat. 10: 313, 1910.

6. Schaefler, J. P.: The Nose, Paranasal Sinuses, Nasolacrymal Passageways and Olfactory Organ in Man, Philadelphia, 1920, P. B1a.kiston’s Son & Co.

7. Sedwick, H. .1'.: Form, Size and Position of the Maxillary Sinus at Various Ages Studied by Means of Roentgenograms of the Skull, Am. J. Roentgenol. 32: 154, 1934.

8. Zuckerhandl, E.: N ormale und pathologische Anatomie der N asenhiihle und ihrer pneumatischen Anhiinge (Anatomy of the Nasal Cavity), Leipzig, 1893. CHAPTER XV TECHNICAL REMARKS

1. INTRODUCTION

2. PREPARATION OF EISTOLOGIC SPI:GIM:E:N S

a. Dissection

b. Fixation

c. Decalciflcation

d. Embedding

e. Sectioning

f. staining g. Altmann-Gersh Technique

3. PREPARATION OI‘ G-ROUND SECTIONS 4. PREPARATION OI‘ ORGANIC STRUCTURES IN THE ENAMEL 5. PEOTOMICROGRAPHY

1. INTRODUCTION

This chapter is intended to give the student a general idea of the preparation of microscopic slides, rather than to cover fully the subject of microscopic technique. For detailed information specialized textbooks should be consulted." 11’ 12' 1’ The various processes to which a tissue is subjected from the time it is taken from the body until it is ready to be examined under the microscope, are termed microtechnique. Its object is to prepare the specimen for examination of its microscopic structure.

2. PREPARATION OF I-IISTOLOGIC SPECIMENS

Dissection is the first step in the preparation of a specimen; the material may be secured by a biopsy (excision during life) or at an autopsy (postmortem examination). Pieces of tissue are cut as small as possible to insure satisfactory fixation and impregnation. A very sharp knife should be used to prevent tissue structures from being distorted and squeezed.

Immediately after the specimen is removed and the surface washed free of blood, it is placed in fixing solution. The object of fixing is to preserve the tissue elements in the same condition in which they are at the moment the reagent acts upon them, and harden or so affect them that they will not be altered by the processes of dehydration, embedding, staining, clearing and mounting. The amount of the fixing solution should be at least 20 times the volume of the tissue. The fixing tissue coagulates the protein content of the cells, thus preventing decomposition.

First draft submitted by Joan Launspach, research technician or the Foundation for Dental Research, Chicago College of Dental Surgery.

341

Dissection

Fixation Lciflcation

342 ORAL msronocr AND EMBRYOLOGY

There are several fixing agents in general use, the most common of which are formalin, formalin-alcohol, Zenker-formol solution, and Bouin’s fluid. A good and rapidly penetrating fixative for small specimens is Zenker-formol solution, a mixture of 9 parts of potassium bichromate and bichloride of mercury with 1 part of neutral formalin. Formalin (5 to 10 per cent) is used for large pieces of tissue, e.g., jaws. It does not deteriorate and it penetrates very rapidly. Formalin-alcohol fixes and dehydrates simultaneously, and is used mostly for surgical specimens. Bouin’s fluid is a solution of picric acid and formalin, and is especially applicable in studying cell outlines, but is rather slow to penetrate.

The length of time necessary for a fixing agent to act upon a tissue varies according to the size of the specimen and penetrating power of the fixative. Generally, it should be just long enough for the agent to saturate the piece thoroughly without allowing it to become brittle. Small pieces of tissue, e.g., gingiva, are left in Zenker-formol solution only 4 to 8 hours, while larger pieces such as jaws may be left in formalin for days. In order to obtain good fixation of pulp in an intact tooth, the surface of enamel and dentin is ground away to a thin layer of dentin around the pulp. This process not only insures rapid and thorough penetration of the fixing agent but also reduces the time of decalcification and permits a thorough impregnation with cellodin. When fixing biopsy specimens, the solution should be at approximately body temperature.

After the specimens are thoroughly fixed, they are washed in running water for twenty-four to forty-eight hours to remove all acids and reagents. Occasionally, however, special treatment is required to remove the precipitates caused by certain agents. Example: specimens fixed in Zenker-formol solution are treated with Lugol’s (iodine) solution and sodium thiosulfate, and specimens fixed in formalin are placed in a mixture of potassium hydroxide before staining. However, there is no need of this if neutral formol is used.

Animal tissues may be classified as hard and soft, or calcified and noncalcified. The dental histologist is particularly interested in the hard tissues, namely, the enamel, dentin, cementum and bone. These are impregnated with a variable quantity of calcium salts and cannot be seetioned on the microtome unless decalcified.

Decalcification of a tissue is the removal of its mineral content by an acid such as nitric, hydrochloric, trichloracetic, formic, or sulfosalycilic acid. The length of time a specimen remains in the decalcifying agent is influenced by the choice and concentration of the acid, and the size of the specimen; however, the shorter the time the better is the staining. A 5 per cent solution of nitric acid seems to be most satisfactory and is, therefore, widely used. It acts quickly without causing swelling of the tissue or any other undue changes in its elements; it does not interfere with the staining process to any marked degree.

While tissues are being decalcified they should be suspended in a large quantity of the fluid in order that the salts dissolved may sink to the TECHNICAL REMARKS 343

bottom of the jar. Occasional stirring or gentle agitation of the specimen and heating of the acid may hasten the process of decalcification, but great care should be taken not to injure the tissues.

To ascertain whether the inorganic salts have been completely removed, the specimen can be pierced with a sharp needle or pin: when no gritty substance is detected, the decalcification is sufficient. Roentgenographic check-up can also be employed. After decalcification a tooth should be as pliable as a piece of cartilage. The enamel disappears almost entirely owing to its low percentage of organic matter. The decalcifying agent may also be tested for calcium; the acid is changed periodically until the test is negative.

Following decalcification the specimen is washed thoroughly in running water for at least 24 hours. From this point it is treated as a soft tissue and is ready for the embedding process. It is possible, however, to embed hard tissues first and decalcify them later: the specimen is run through the solutions in routine fashion and, after it is blocked, the excess celloidin is cut away and the tissue is suspended in acid until decalcified. This takes much longer than the usual procedure and the results are often uncertain.

In order that a tissue may be sectioned on the microtome it has to have a certain rigidity to offer sufficient resistance to the cutting edge of the knife. This may be accomplished by freezing the tissue or, as is more commonly done, by using an embedding medium which fills the interstices of the tissue. The freezing technique is employed where immediate investigation of the specimen is required, as in the course of a surgical operation. Some substances (fat, lipoids, etc.) are dissolved during embedding: tests for such substances can be made only in frozen sections.

Embedding is a much more lengthy process but results are more satisfactory. Before the specimen is embedded, i.e, impregnated with a suitable substance such as paraffin or celloidin, the water has to be removed from the tissues. Paraffin embedding is more rapid and is used for small pieces, usually soft tissue, as decalcified pieces become brittle during the heating which is necessary in using this method. Celloidin embedding takes longer but causes less shrinkage. This technique is more commonly used in dental histology when large blocks of decalcified material have to be sectioned.

Dehydration is accomplished by placing the specimens in ascending alcohols (50, 70, 95, 100 per cent) for approximately one day each; the length of time depends on the size and permeability of the specimen. Two consecutive changes of absolute alcohol are used. As, however, paraifin or celloidin is not soluble in alcohol it has to be replaced by a fluid which is a solvent for the embedding medium.

When paraffin is selected as the embedding medium, the absolute alcohol is replaced by xylol or oil of cedarwood. The specimens are placed in the solvent 12 to 24 hours, and are then placed in liquid parafiin in the

Embedding Sectioning

344 ORAL HISTOLOGY AND EMBRYOLOGY

incubator (56 C.) for several hours. Finally the specimen is placed in a form filled with molten parafiin and quickly cooled. It is then ready to be sectioned.

If celloidin, a solution of nitrocellulose in absolute alcohol and ether, is selected as the embedding medium, a mixture of equal parts of ether and alcohol is used as a solvent in which the tissue remains for 12 hours. It is then carried through a thin (6 per cent) and medium (121/; per cent) into thick (25 per cent) solution of celloidin. The length of time which is necessary for each of the solutions to penetrate the specimen depends upon size and permeability of the tissue. Soft tissue is well infiltrated with celloidin after three weeks while decalcified specimens require at least six weeks; to insure thorough impregnation, it is wise to leave teeth longer in the lower concentration of celloidin and a somewhat shorter time in the stronger concentration. When it is necessary to “rush” a specimen the tissue in thin celloidin may be placed in a 50° C. oven in a tightly stoppered container; the embedding period is thus shortened to two or three days. This method causes considerable shrinkage. Small pieces of tissue may be placed directly on a fiber block and left to harden in a desiccator filled with chloroform vapor. Large pieces of tissue, e.g., jaws, are placed in an evaporating dish filled with celloidin which is allowed to harden down slowly. When the celloidin has reached the desired degree of hardness, blocks are cut out and, after being softened in thin celloidin a few minutes, are placed on fiber blocks,

allowed to air dry, and then placed in 70 per cent alcohol for storage or sectioning.

Tissues are sectioned by means of a microtome, ‘a machine equipped with a knife. There are three different types of microtomes: the freezing, rotary, and sliding, the use of which depends on the kind of tissue and embedding medium used. Each is a heavy specially designed machine precisely constructed, capable of slicing prepared tissues into exceedingly thin sections. The knife is wedge-shaped and made of heavy steel to aflord the greatest possible rigidity; it must have a very keen edge as the slightest nick would tear a section. Sharpening a microtome knife is one of the most important as well as the most difficult tasks of a technician. Larger nicks are removed on a coarsely grained stone, and a fine edge is achieved by grinding the knife on a fine hone. The final cutting edge is obtained by stropping on a finishing leather microtome strop. A much more rapid and just as satisfactory a method that has recently been developed is the use of a grinding machine, consisting of an ebony wheel mounted on a rotary motor. A strop, dusted with abrasive powder, is used to put the finishing edge on the knife. The possibility of making good sections depends upon the type of tissue, its preparation, and the condition of the knife. Sections of 5 to 15 microns (174000 millimeter equals 1 micron) are considered thin. TECHNICAL REMARKS 345

The importance of the freezing technique in preparing surgical specimens has been mentioned. It is well known that, by exposing tissues to an extreme degree of cold, they become hard and can be easily sectioned with the freezing microtome. The cold is generated by means of carbon dioxide which is sprayed onto the stage holding the specimen: rapid evaporation produces the required temperature.

The rotary microtome is used only for sectioning paraffin blocks; the knife is immovably fixed at a right angle to the block which is carried past the sharp edge of the knife by turning a wheel. With this machine it is possible to out long ribbons of serial sections. The ribbons are placed in lukewarm water where the wrinkles are removed as the paraffin becomes soft. The desired sections are then floated onto slides smeared with egg albumen and placed in a 37° C. oven for a few minutes. Before staining, the paraffin is dissolved in xylol. the slides rinsed in absolute alcohol, the sections are carried through descending concentrations of alcohols into distilled water; then they can be stained by water-soluble dyes.

A celloidin block is sectioned by a different method. For this purpose the sliding microtome, a heavy sledgetype instrument, is used. The longitudinal angle of the knife is adjusted to each specimen so that the entire cutting edge is used in sectioning. The angle of the cutting edge of the knife should be changed according to the hardness and density of the material. To obtain the most satisfactory results the knife should be in an almost horizontal position for large decalcified pieces, at an acute angle for soft tissue. During sectioning both specimen and knife are continually moistened with 70 per cent alcohol; the sections are placed in distilled water before staining. The celloidin is usually not removed from the section as the stain penetrates the tissues in spite of this embedding medium. However, it has to be removed from the section in the case of specific stains, i.e., Mallory, azure-eosin, etc. For this procedure the section is mounted on a slide smeared with egg albumen and is flooded with oil of cloves to dissolve the celloidin; the slide is rinsed in 95 per cent alcohol and placed in 70 per cent until ready for staining.“ When serial sections are desired, sections are mounted on glass slides which are then blotted and flooded with a very thin solution of collodion. After a coating is formed, the slides are marked with a diamond pencil or India ink, and stored in 70 per cent alcohol until ready for staining.“

Some special staining methods can be applied only to sections of undecalcified teeth and bone. To obtain such sections mature enamel has to be removed from the teeth. The tissue impregnated With celloidin is placed in a shallow dish and covered with celloidin. The solution is allowed to evaporate slowly until the celloidin is very hard (two to four weeks) . A very hard knife should be used which has been sharpened and stropped ; when checked under the microscope it has deep and even teeth and should be clamped in the microtome at a 13° angle. Staining

Altmann-Gersh Technique

346 orm. ursronoev AND nmasvonoer

Dyes used to stain specimens for microscopic examination may be classified as basic or acid, according to their affinity for different cellular elements. Basic dyes, sometimes called nuclear dyes, primarily stain nuclear chromatin, basic substance of cartilage and mucus; the more commonly used are hematoxylin, methylene blue, safranin, and carmin. Acid dyes color the cytoplasm of the cell, uncalcified bone and dentin matrix, some connective tissue fibers; eosin and phloxin are representative of this group. By using combinations of the two groups, due to their different affinities, a marked difierentiation of the cellular elements of the specimen is possible.

Sections may be stained on the slide or floating in dishes; in the latter case better differentiation is afiorded. Although the steps of the various staining methods differ considerably, they may be arranged in the following order: staining, differentiating, decolorizing, dehydrating, clearing and mounting.

Hematoxylin and eosin is one of the most commonly used combinations of stains because it is the simplest to handle. For the differentiation of more specialized tissues the following are recommended: Mallory stain,“ or Heidenhain’s Azan“ (modification of Mallory’s stain) for connective tissue; the latter is more brilliant and has greater capacity for differentiation; Silver Impregnation (modification of Foot’s stain by Gomori) for connective tissue fibers and nerve elements ;’ Van Gieson’s stain, a counterstain to hematoxylin, for differentiation of white connective tissue," and Weigert’s stain for elastic tissue.“

After sections of tissues have been stained and differentiated, they are dehydrated and then passed through a medium that will mix with the dehydrating fluid as well as the reagent in which the sections are to be mounted. These intermediary fluids are called clearing agents because they have a high refractive index, thus rendering the sections more or less transparent.

For celloidin sections a variety of clearing agents is used: terpineol (Lilacine), carbol-xylol, oil of cloves, oil of cedar wood, oil of origanum and beechwood creosote; for paraffin sections usually only two are used: xylol or toluol.

After clearing, the sections have to be placed in some medium which will preserve the stain and prevent the tissue from drying. Such solutions are termed mounting agents: among the most common are Gum damar, Canada balsam, and clarite. Loose celloidin sections are floated onto the slide and straightened out with the aid of a fine camel’s hair brush; they are carefully blotted and covered with a drop of mounting medium and a coverslip. Weights are placed on the coverslips to prevent the formation of air bubbles. When dry, they are carefully cleaned with xylol and labeled with India ink.

The Altmann-Gersh freezing and drying technique for special microchemical studies should also be mentioned. The tissues are frozen inTECHNICAL REMARKS 347

stantaneously when placed in a tube of isopentane in a Liquidair container and are dehydrated under vacuum while still frozen, thus avoiding a redistribution of minerals. Fixation, alcohol dehydration, and clearing are omitted as the dehydrated tissue can be immediately infiltrated with paraffin and sectioned according to the usual methods. This technique has proved valuable in the preparation of tissues for micro-incineration, and for special micro-chemical reactions.

Many submicroscopic structures may be seen with the electron microscope, not visible in sections prepared in the routine manner.

3. PREPARATION OF GROUND SECTIONS

Ground sections are prepared by using abrasive stones upon a tooth or bone until the tissue is reduced to translucent thinness. It is the principal method of examining the enamel which has so little organic material that it disappears almost entirely when the teeth are decalcified by ordinary methods. Therefore, this technique should complement the decalcification method. i

To prepare a ground section of a tooth it is first ground down on one side on a carborundum stone which rotates at high speed on a laboratory lathe. It is important that the tooth be kept wet constantly with cold water to lessen the heat produced by friction and to prevent the section from drying. If it is allowed to dry its organic constituents will shrink and present a picture untrue to the conditions during life. The tissue is likewise more apt to crack and break up during preparation if it becomes dry. When the desired level is reached and the ground surface is perfectly plane, this surface is polished on wet ground glass and, finally, on an Arkansas stone. The other side of the specimen is then ground down until the section is sufficiently translucent. This second side is also polished in the above described manner, to remove the gross scratches produced by the carborundum stone. The finished ground sections should have an average thickness of 25 to 50 microns and, if desired, may be

stained before they are dehydrated, cleared and mounted.”

For surface staining of ground sections the surface is well polished and the section is covered with a 0.25 per cent H01 to decalcify it slightly; then it is stained lightly with hematoxylin.“ By this method only the surface of the ground section is stained and the stained layer can be viewed with high power lenses as it is only a few microns in thickness. This method, however, causes slight decalcification of the enamel making a marked differentiation of rods from sheaths and cementing substance,

3. condition not representative of normal enamel. Enamel that has been

partially decalcified by caries, or a poorly formed enamel has this appearance.

If it is necessary to investigate an undecalcified tooth with the surrounding soft tissue, ground sections can be made by using the petrification method. The specimen is embedded in Kollolith-chloroform solution 348 omu. HISTOLOGY AND EMBRYOLOGY

or in Canada balsam”, 15 where it is left until it is sufficiently hard before it is ground down to a desired thickness. Thin “serial” ground sections of teeth and jaws may be cut in one operation by infiltrating the specimen with a plastic material and using a cutting device made up of steel wheels set at various distances."

4. PREPARATION OF ORGANIC STRUCTURES IN THE ENAMEL

The routine decalcification of whole teeth in an aqueous solution of acid usually destroys the enamel completely. At most, merely shreds of the organic structures remain near the cervical areas in a tooth of a young person.

The organic structures may be demonstrated by C. F. Bodecker’s celloidin decalcifying method.‘ When dentin is included in the specimen sections are rarely satisfactory because this tissue becomes very brittle as a result of the many media through which it passes. It is necessary only for study of the organic structures in the enamel under high magnification. In general, this method is erratic and a high percentage of failures must be expected.

The Cape-Kitchin modification‘ 5 of Bodecker’s method is quite simple and gives satisfactory results if the structures of the matrix are not magnified more than about 500 diameters.

Frisbie, Nuckolls, and Saunders’ have recently developed a technique for the successful recovery of the enamel matrix. The fresh specimen is immediately fixed in neutral formalin for a long period of time (six months) ; most of the dentin is then removed with a dental bur and the tooth is placed in the fixative again for a shorter period of time, depending on the penetrability of the specimen. The completely fixed enamel is decalcified by placing the specimen on a gauze stretched over a platinum wire frame, and immersing it in a 5 per cent solution of nitric acid in 80 per cent alcohol for 24 to 48 hours. Dehydration is begun with 70 per cent alcohol without preliminary washing. The specimen is infiltrated with celloidin at 56 C. for two weeks and then allowed to harden down slowly at room temperature until the block is very hard. Sectioning is done with a sliding microtome at 3 to 4 microns.

An aqueous decalcification of enamel under a cover-glass is the simplest but the least satisfactory method for its study. It is sufficient to show enamel lamellae, cuticle, tufts, and can be used to demonstrate gross differences in quantity of organic structures of enamel in recently erupted teeth and in teeth of old persons. However, the disadvantages are that only low magnifications up to 100 diameters are possible and that the specimens are not durable.

Another method of differentiating the organic from the inorganic content of the enamel is by incineration. It has been shown that the heating of sections of human adult enamel up to 800° 0. causes a destruction of the organic content but leaves enamel rods intact. TECHNICAL REMARKS 349

5. PHOTOMICROGRAPHY

Photomicrographs are photographs of small microscopic objects, made with the aid of a microscope. Most of the illustrations in this book are such pictures. Transmitted light is the most commonly used method of illumination as it permits the sharpest differentiation of details and the highest magnification of tissue structures in stained decalcified sections.

Refiected light is used in oral histology in photographs of ground sections of enamel and dentin. These sections should be ground perfectly smooth. There is no need for extreme thinness because the specimen is viewed only from the surface from which the light is reflected.

Polarized light also is useful in the study of the dental tissues. It vibrates in a single known plane and requires special equipment and technique. By this means it is possible to determine details of the submicroscopic structure of tissues, due to the differences in optical properties of various elements. Polarized light is particularly useful in the study of calcified tissues, but is not confined to these, because fibrous and keratinized structures also yield information when studied by this method.

Grenz rays are a form of exceedingly soft roentgen rays. When ground sections of teeth are photographed in this way, slight variation in calcification may be defined thus rendering this method useful in the study of calcified structures." 13

A method has recently been developed by Gurney and Rapp” for studying the fine structural details of tooth surface by adapting the Fax Film technique used for study of metallographic surfaces. Micro-impressions are made of the specimen, using a plastic film which may then be mounted on a glass slide for a permanent preparation. Scott and Wyckoff“ obtained similar results by shadowing collodion replicas with vaporized metal in a high vacuum, a more complicated method. The eifect of chemical agents on tooth structure and the changes in tooth surfaces (caries) may be observed using these methods. When examined under the electron microscope, many submicroscopic structures are visible.

Ultraviolet light technique‘ and fluorescence light microscopy, likewise, have been applied in special studies of dental tissues, but have not yet attained wide use.

References

1. Applebaum, E.. Hollander, F., and Bodecker. C. F.: Normal and Pathological Variations in Calcification of Teeth as Shown by the Use of Soft X-rays, Dental Cosmos 75: 1097, 1933. _

Bensley, R. R., and Bensley, S. 8.: Handbook of Histological and Cytological Technique, Chicago, University of Chicago Press. _ _

Bodecker, C. F.: Cape-Kitchin Modification of Celloidin Deoalcifymg Method for Dental Enamel, J. Dent. Research 16: 143, 1937. _ _ _ '

Bodecker, C. F.: Enamel of Teeth Decalcifled by Celloidin Decalcifying Method and Examined by Ultra Violet Light, Dental Review 20: 317, 1906.

Cape, A. T., and Kitchjn, P. 0.: Histologic Phenomenon of Tooth Tissues Observed Under Polarized Light, With a Note on Roentgen Ray Spectra of Enamel and Dentin, J. A. D. A. 17: 193, 1930.

S"l“9°.l‘-" 350 ORAL HISTOLOGY AND EMBRYOLOGY

6. Cowdry, E. V.: Microscopic Technique in Biology and Medicine, Baltimore, 1943, Williams & Wilkins Co.

7. Frisbie, H. E., Nuckolls, J., and Saunders, J. B. de G. M.: Distribution of Organic Matrix of Enamel in Human Teeth and Its Relation to Histopathology of Caries, J. Am. Coll. Dent. 11: 243, 1944.

8. Gurney, B. R, and Rapp, G. W.: Technic for Observing Minute Changes on Tooth Surfaces, J. Dent. Research 25: 367, 1946.

9. Guyer, M. F.: Animal Micrology, Chicago, 1943, University of Chicago Press.

10. Hotchkiss, R. D.: Microchernical Reaction Resulting in Staining of Polysaccharide Structures in Fixed Tissue Preparation, Arch. Biochem. 16: 131, 1948.

11. Loosli, C. G.: Outline of Histological Methods, Chicago, University of Chicago Press.

12. Mallory, F. B.: Pathological Technique, Philadelphia, 1938, W. B. Saunders Co.

13. McClung, C. Microscopic Technique, New York, 1937, Paul B. I-Ioeber, Inc., pp. 353-401.

14. McLean, F. 0., and Bloom, W.: Calcification and Ossification. Calcification in Normal Growing Bone, Anat. Rec. 78: 133, 1940.

15. Meyer, W.: Die Anfertigung histologicher Schlifie (Preparation of Histologic Ground Sections), Vrtljschr. f. Zahnheilk. 41: 111, 1925.

16. Scott, D. B., and Wyckofi, R. W. G.: Shadowed Replicas of Tooth Surfaces, Pub. Health Rep. 61: 697, 1946.

17. Sognaecs, R. F.: Preparation of Thin Serial Ground Sections of Whole Teeth and Jaws and Other Highly Calcified and Brittle Structures, Anat. Rec. 99: 133, 1947.

17a. Sognnaes, R. F.: The Organic Elements of the Enamel. I, II, III, IV, J. Dent. Research 27: 609, 1948; 28: 549, and 558, 1949; 29: 260, 1950.

18. Willman, M.: Technique for Preparation of Histological Sections Through Teeth and Jaws for Teaching and Research 16: 183, 1937.

19. Wolf, J.: Plastische Histologie der Zahngewebe (Plastic Histology of Dental Tissues), Deutsche Zahn-, Mund- und Kieferheilkunde 7: 265, 1940.

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Cite this page: Hill, M.A. (2024, May 2) Embryology Book - Oral Histology and Embryology (1944) 5. Retrieved from https://embryology.med.unsw.edu.au/embryology/index.php/Book_-_Oral_Histology_and_Embryology_(1944)_5

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