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

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Chapter XI - Eruption Of The Teeth

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 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

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.

Cite this page: Hill, M.A. (2024, May 2) Embryology Book - Oral Histology and Embryology (1944) 11. Retrieved from https://embryology.med.unsw.edu.au/embryology/index.php/Book_-_Oral_Histology_and_Embryology_(1944)_11

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