Book - Oral Histology and Embryology (1944) 9

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

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Chapter IX - The Oral Mucous Membrane

1. General Characteristics

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

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

The mucous membrane is attached to the underlying structures by a layer of connective tissue, the submucosa, which varies in character in different areas. The oral mucous membrane is composed of two layers; the surface epithelium and the lamina propria (Fig. 164). A basement membrane separates the lamina propria from the stratified squamous epithelium. The epithelium consists of several layers of cells which flatten out as they approach the surface. All these cells are connected with each ‘other by intercellular bridges. The innermost is the basal layer, consisting of cuboid cells which effect the attachment of the epithelium to the basement membrane of the connective tissue by numerous short basal processes that fit into grooves of the lamina propria. The more superficial cells form the so-called “prickle-cell” layer which consists of several layers of polyhedral cells. The term is derived from the fact

First dratt submitted by Balint Orban and Harry slcher.

Fig. 164. Diagrammatic drawing of oral mucous membrane (epithelium and lamina propria. and submucosa).

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

The cells of the prickle-cell layer flatten and pass into first the granular layer and then the keratinous layer as they move toward the surface. The cells of the granular layer contain fine kerato-hyalin granules which are basophil and stain blue in hematoxylin-eosin preparation. The nuclei of the flattened cells are pyknotic. The keratinous layer is characterized by its acidophil nature; here the nuclei have mostly disappeared. The structure of the granular and keratinous layers varies in the diiferent regions of the oral cavity. A stratum lucidum, such as is seen in regions of the skin where hornification is abundant, is, as a rule, missing in the oral mucosa.

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

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

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

• The use of the terms vestibular instead of labial and buccal, and oral instead of lingual or palatal, is suggested.

2. Transition Between Skin and Mucous Membrane

The transitional zone between the skin covering the outer surface of the lip and the true mucous membrane lining the inner surface, is the red area or Vermilion border of the lip. It is present in man only (Fig. 165). The skin of the lip is covered by a hornified epithelium of moderate thickness; the papillae of the connective tissue are few and short. Many sebaceous glands are‘ found in connection with the hairs; sweat glands occur between them. The epithelium is typically stratified and squamous with a rather thick hornified layer. The transitional region is characterized by numerous densely arranged long papillae of the lamina propria, reaching deep into the epithelium and carrying large capillary loops close to the surface. Eleidin in the epithelialcells renders them translucent. Thus, blood is visible through the thin parts of the transparent epithelium covering the papillae; hence the red color of the lips. Because this transitional zone contains only occasional single sebaceous glands, it is particularly subject to drying if not moistened by the tongue.

Fig. 165.—Section through lip.

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

3. Subdivisions of the Oral Mugosa

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

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

A. Masticatory Mucosa

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

In contrast to this, the covering of the hard palate has, with the exception of narrow areas, a distinct submucous layer. It is absent only in the peripheral zone where the tissue is identical with the gingiva, and in a narrow zone along the midline, starting in front with the palatine or incisal papilla and continuing as the palatine raphe over the entire length of the hard palate. In spite of the presence of a well-defined submucous layer in the wide lateral fields of the hard palate between palatine raphe and palatine gingiva, the mucous membrane is immovably attached to the periosteum of maxillary and palatine bones. This attachment is accomplished by dense bands and trabeculae of fibrous connective tissue Which join the lamina propria of the mucous membrane to the periosteum. The submucous space is thus subdivided into irregular intercommunicating compartments of various sizes. These are filled with adipose tissue in the anterior part and with glands in the posterior part of the hard palate. The presence of fat or glands in the submucous layer acts as a hydraulic cushion comparable to that which We find in the subcutaneous tissue of the palm of the hand and the sole of the foot.

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

A. GINGIVA

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

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

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

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

B. No hornmcation.

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

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

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

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

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

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

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

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

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

Fig. 168C.—Macropha.ges in the normal gingiva.._ Rio I-Iortega. stain. ()(1000.) (Courtesy Esther Carames de Aprile, Buenos Aires.)

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

The lamina propria of the gingiva consists of dense connective tissue Which is not highly vascular. Macrophages are present in the normal ging-iva (Fig. 168, C). These cells play an important function in the defense mechanism of the body. The papillae are characteristically long, slender, and numerous. The presence of these high papillae permits the sharp demarcation of the gingiva and alveolar mucosa in which the papillae are quite low (Fig. 169). The tissue of the lamina propria contains only few elastic fibers which are, for the most part, confined to the walls of the blood vessels. The gingival fibers of the Pariodontal membrane enter into the lamina propria, attaching the gingiva firmly to the teeth (see chapter on Periodontal Membrane). The gingiva is also immovably and firmly attached to the periosteum of the alveolar bone; here, a very dense connective tissue, consisting of coarse collagenous bundles (Fig. 170, A) extends from the lamina propria to the bone. In contrast, the submucosa underlying the alveolar mucous membrane is loosely textured (Fig. 170, B). The fiber bundles of the lamina propria are here thin and regularly interwoven. The alveolar mucosa and the submucosa contain numerous elastic fibers which are thin in the lamina propria and thick in the submucosa.

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

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

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

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

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

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

gingiva. Silver impregnation after Bielschowsky-Gros. (Courtesy F. W. Gaitns and J. A.itchiaon.

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

‘First draft of this section submitted by Bemliard Gottlieb.

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

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

Erupted enamel Glngival sulcus Free gingiva

Oral epithelium

Epithelial attachment

Enamel

Cemento-enamel junction

Dentin

Pulp

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

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

A. B. 0.

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

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

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

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

229 $5

230 omu. HISTOLOGY AND EMBRYOLOGY

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

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

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

The epithelium which forms the attachment is stratified squamous epithelium. As a rule, the junction between epithelial attachment an_d connective tissue is smooth. It may be considered as a sign of irritation if the epithelial attachment sends fingerlike projections, epithelial pegs, into the conective tissue. The cells within the epithelial attachment are elongated, and are arranged more or less parallel to the surface of the tooth (Fig. 179). There is a distinct pattern in the direction of these flattened cells which may be the result of functional influences upon the attachment.“ The cells at the surface of the epithelial attachment are firmly fastened to the tooth and must follow all its movements. The basal layer of the epithelial attachment, on the other hand, is anchored to the surrounding connective tissue and must follow all the movements to which the gingival margin is subjected. The cells within the epithelial attachment are exposed to these different stresses. The

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

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

may also occur during life.“ shift of Epithelial Attachment

First Stage

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

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

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

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

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

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

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

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

The downgrowth of the epithelial attachment along the cementum is impossible as long as the gingival and transseptal fibers are still intact. It is not yet understood whether the degeneration of the fibers is primary or secondary to the proliferation of the epithelium.“ Recent findings indicate that destruction of the fibers is secondary, the proliferating epithelial cells actively dissolving the principal fibers byenzymc action (desmolysis). A primary destruction of the principal fibers had been explained by the action of bacterial toxins from the gingival sulcus. The second stage of passive tooth eruption may persist to the age of forty or

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

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

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

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

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

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

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

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

'The width of the epithelial attachment varies from 0.25 to 6 mm.

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

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

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

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

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A. B. C.

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

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

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

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

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

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

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

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

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

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

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

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

Epithelial attachment

Epithelial

'3. attachment

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

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

4: ‘L fnaettnzfliafiaf a‘l€.?;‘l,‘;.§e.§iP($m‘;%‘:.Ef€.Ea?;:’éi“ji..f‘cu‘:‘n ,‘t°*‘€§3,d:£k§‘:z‘;,;Lb:‘:§g:; the tooth only to a certain depth; from there on it tears instead of separating from the tooth.” The firmness of the attachment may be further shown by studying ground sections prepared by a. special method of investing soft and hard tissues (Fig. 189). In such specimens the enamel. is not lost as in decalcified sections, and the relations between epithelium and enamel are undisturbed. Another confirmation of the organic connection between tooth surface and epithelium is the fact that, omar. after extraction of teeth, epithelium is often found adherent to the extracted tooth,’ The firm connection between epithelium and enamel is a primary 11111011, the enamel being a cuticular product of the ameloblasts.

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

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

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

alkalies and may act as a protective layer on the tooth surface. Even yet its method of formation is not quite clear: some investigators claim‘ that it develops by transformation of the cells which are adjacent to the tooth surface in a manner similar to normal hornification. Others contend that this cuticle is a secretory product of the epithelial cells.“ The secondary cuticle is not limited to the surface of the enamel, as is the primary cuticle, but follows the epithelial attachment when it shifts along the cementum; hence it is designated by the term cuticula. dentis The Gtngival suleus (dental cuticle) (Fig. 190). The formation of the dental cuticle by the epithelial attachment is believed to be a reaction of the epithelium to its contact with a hard structure. It is further assumed that formation of the cuticle is the first phase of a process which, ultimately, leads to separation of the epithelium from the tooth. However, some investigators claim that this cuticle is a pathologic structure, induced by inflammation of the gingiva."

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

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

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

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

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

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

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

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

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

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

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

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

C. Hard Palate

The mucous membrane of the hard palate is tightly fixed to the underlying periosteum and, therefore, immovable. Its color is pink, like that of the gingiva. The epithelium is uniform in character throughout the hard palate, with a rather thick hornified layer and numerous long pegs. The lamina propria, a layer of dense connective tissue, is thicker in the anterior than in the posterior parts of the palate. Various regions in the hard palate differ because of the varying structure of the submucous layer. The following zones can be distinguished (Fig. 193): (1) the gingival region, adjacent to the teeth; (2) the palatine raphe, also known as the median area, extending from the incisive (palatine) papilla posteriorly; (3) the anterolateral area, or fatty zone between raphe and.

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

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

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

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

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

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

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

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

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

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

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

B. Lining Mucosa

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

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

A. Lip AND CHEEK

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

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

Fig. 198.—Sa.gitta.l section through palagne pai1l>lll.la and anterior palatine canal.

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

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

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

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

B. VESTIBULAR FORNIX AND ALVEOLAR MUCOSA

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

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

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

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

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

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

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

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

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

D. SOFT PALATE

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

Fig. 202.—Mucous membrane from oral surface of soft palate.

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

G. Specialized Mucosa or Dorsal Lingual Mucosa

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

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

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

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

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

cecum which is a .remnant of the thyroglossal duct (see chapter on Development of the Face). Posterior to the vallate papillae, the surface of

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

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

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

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

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

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

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

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

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

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

Stratified squamous epithelium Taste pore Taste cells Supporting cells

Fig. 207..Taste buds from the slope of a. vallate papilla. (From .1’. Schafter.)

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

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

4. Clinical Considerations

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

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

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

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

‘The term gingival pocket designates the pathologic condition of the gingival sulcus.

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

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

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

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

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

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

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

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

References

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20. Pendleton, E. 0., and Glupker, 11.: Research on the Reaction of Tissues Supporting Full Dentures, J. A. D. A. 222 76,

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

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

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

24. Wassermann, F.: Personal communication.

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

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

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

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Cite this page: Hill, M.A. (2024, May 19) Embryology Book - Oral Histology and Embryology (1944) 9. Retrieved from https://embryology.med.unsw.edu.au/embryology/index.php/Book_-_Oral_Histology_and_Embryology_(1944)_9

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