Oral Mucosa Handout PDF

Oral Biology Department Al-Alamein International University Faculty of Dentistry Oral Mucosa Oral biology department Prof Dr. Azza Koura 1  Contents : Functions of the oral mucosa Development of th...

Oral Biology Department Al-Alamein International University Faculty of Dentistry Oral Mucosa Oral biology department Prof Dr. Azza Koura 1  Contents : Functions of the oral mucosa Development of the oral mucosa (Tissue components) Histological structure of the oral mucosa Keratinized oral epithelium. Para keratinized oral epithelium. Non-keratinized oral epithelium Non-keratinocytes in oral epithelium The junction of epithelium and lamina propria (Basement membrane) Classification of the oral mucosa a. Masticatory mucosa (keratinized mucosa) b. Lining mucosa (non-keratinized mucosa) c. Specialized mucosa Mucocutaneous junction (Vermilion border of the lip) Age changes of the oral mucosa 2 Oral mucosa: or oral mucous membrane is the moist lining of the oral cavity. Functions of the oral mucosa: 1- Protection The oral mucosa protects the deeper tissues from mechanical forces resulting from mastication and from abrasive nature of foodstuffs. Furthermore, the oral surface epithelium acts as a major barrier against the oral microorganism that would cause infection if they gain access to the deeper tissue. 2- Sensation In the mouth there are receptors that respond to temperature, touch, pain and taste. Certain receptors in the oral mucosa respond to feel thirst. 3- Secretion The major secretion associated with the oral mucosa is saliva which, is produced by the salivary glands to maintain the moist surface of the mucosa and to assist in mastication, swallowing of food and speech. In some animals (such as dogs), the oral mucosa plays a role in the regulation of body temperature. Development of the oral mucosa (Tissue components): - Composed of two layers that are completely different in character: 1. The surface or oral epithelium derived from ectoderm composed of stratified squamous epithelium. 2. The lamina propria derived from ectomesenchymal cells, a connective tissue supporting layer attached either directly to the underlying structures or through a Submucous layer. 3 These two layers are firmly cemented together by the Basement membrane. The interface between epithelium and connective tissue is usually irregular. The interface: there are upward projections from the connective tissue into the epithelium called the connective papillae, interdigitate with epithelial ridges or epithelial cones called pegs. (This arrangement makes a larger surface area that provides better attachment and distribute the forces of mastication over a wide area. The junction also insures better nutrient to the epithelium.) Functions of basement membrane: 1. It anchors epithelium to connective tissue. 2. It acts as a mechanical barrier against malignant cells to invade the Connective tissue. 3. It accelerates differentiation of endothelial cells (angiogenesis). By electron microscope it is composed of Basal lamina which made up of: a. Lamina lucida (clear zone) just below the epithelial cells. b.Lamina densa (dark zone) adjacent to the connective tissue. 4 1- The surface or oral epithelium 5  - It is a stratified squamous epithelium composed of cells called Keratinocytes (keratin producing cells). - Between these cells is a small number of different cells known as Nonkeratinocytes. The oral epithelium may be: - 1. Keratinized oral epithelium 2. Parakeratinized oral epithelium 3. Non-keratinized oral epithelium 1-Keratinized oral epithelium This type is found in areas of the oral mucosa directly subjected to the mechanical forces of mastication (Masticatory mucosa). Example: gingiva and hard palate. It is inflexible, tough, and resistant to abrasion, this results from the formation of a surface layer of keratin. Arranged in four layers named according to the morphology of the cells inside it to : 6  a. Basal layer (stratum basale) b. Spinous layer (stratum spinosum) c. Granular layer (stratum granulosum) d. Keratinous or cornified layer (stratum cornium) Note: the basal layer contains the proliferation compartment and the remaining layers contain the differentiation or maturation compartment. a. Basal layer (stratum basale) It consists of a single layer of cuboidal or low columnar cells adjacent to the basement membrane. The basal cells of the surface epithelium show many mitotic activity. The basal cells are of two types: serrated cells and stem cells which produce new cells by mitotic division and one of the daughter cells migrates to the surface to replace the desquamated one (cells renewal). b. Spinous or prickle cell layer (stratum spinosum) It consists of several rows of polyhedral cells with short cytoplasmic processes. The cytoplasmic processes are attached to each other through a mechanical adhesions called Desmosomes. They are larger than the basal cells. The basal cells and the spinous cells constitute more than half the thickness of the epithelium. The cells of the spinous layer have wide intercellular spaces and are joined together by Intercellular bridges giving the cells a spiny or prickly appearance. c- Granular layer (stratum granulosum) It consists of 3-5 rows with a larger flattened or diamond shaped cells. 7  The nuclei show signs of degeneration in the form of Karyolysis and Pyknosis. The cytoplasm loses a large number of organelles and becomes heavily packed with keratin filaments. The cells contain a large number of small granules called Keratohyaline Granules (KHG) which are basophilic (stain blue with hematoxylin). - It is thought that keratohyaline granules produce the keratin matrix (Filaggrin). d- Keratinous or cornified layer (stratum cornium) It consists of wide flat cells termed squamous with no nuclei or other cell organelles. It stains bright pink with eosin. Provides mechanical and chemical protective outer layer. The pattern of keratinization of these cells is called orthokeratinization. 2. Parakeratinized oral epithelium □ ▪ Parakeratinized epithelium is most common in the gingival mucosa. ▪ The nuclei appear pyknotic (shrunken) in the cells of the keratinous layer. ▪ The granular layer shows fewer keratohyaline granules. ▪ It is a normal event in oral tissue and does not imply disease. 3. Non-keratinized oral epithelium 8  ▪ The lining mucosa of the oral cavity is usually non-keratinized. ▪ They are found in the lips, cheeks, alveolar mucosa, soft palate, under surface of the tongue and floor of the mouth. ▪ It consists of four layers: basal, prickle, intermediate and superficial. 1- Basal cell layer - The cells are morphologically and functionally similar to those in the keratinized epithelium (low columnar or cuboidal in shape and undergoing mitosis). 2- Prickle cell layer - The cells are also morphologically and functionally similar to those in the keratinized epithelium, but they are larger with smaller intercellular spaces and fewer cytoplasmic processes (prickles) and so, they have no prickly appearance. 3- Intermediate cell layer - There are no sudden changes in the appearance of the cells above the prickle cell layer. So, the intermediate and superficial cells look like the prickle cells. 9  4- Superficial cell layer - The cells look like the previous cell layer but they become larger And flatten in appearance. - They retain their plump nuclei. 2-The Lamina Propria - It is the connective tissue supporting the oral epithelium. - It is divided into two layers: the superficial papillary layer and reticular layer. a. Papillary layer - It is a superficial zone of loose connective tissue that shows a papillary projections (C.T papillae), the length of the papillae varies according to the type of epithelium. - It has thin collagen fibers which are loosely arranged with many capillary loops in between. b. Reticular layer - It is a deeper zone of denser connective tissue found between papillary layer and the submucosa. - It has thick collagen fibers which are arranged in bundles and run parallel to the surface epithelium to prevent mucosal deformation. 10 Contents of the lamina propria: - -Ground substance, fibers, cells, nerves, blood and lymphatic vessels. Ground substance: ▪ It is highly hydrated ground substance composed of proteoglycans and glycoproteins Fibers: ▪ Consists mainly of two types: collagen and elastic. ▪ Reticulin and oxytalan fibers are also present. Cells: ▪ Synthetic cells: Fibroblasts secreting fibers and fat cells which synthesis and storage of fat. ▪ Defensive cells: Lymphocytes, plasma cells, macrophages and mast cells. ▪ Undifferentiated mesenchymal cells. Blood vessels: ▪ It is very rich and derived from the arteries in the submucosa or, in the deep part lamina propria, when a there is no submucosa. ▪ These vessels give smaller branches in the reticular layer. ▪ Form a capillary plexus network in the papillary layer. ▪ This plexus network, form a capillary loops close to the basal layer of the epithelium. Nerves: ▪ The nerve fibers are myelinated as they enter the submucosa. ▪ They branch in the reticular layer. ▪ They lose their myelin sheath in the papillary layer and re-branch forming a 11  fine subepithelial plexus. - The nerves end in one of three ways (types of sensory receptors): 1- Free nerve endings (pain). 2- Merkel discs may be act as a pressure receptor adjacent to Merkel’s cells. 4. In a form of encapsulated ends to form Meissner’s corpuscles or coiled terminals to form Krause’s (touch) corpuscles, encapsulated to form Ruffini’s corpuscles (temperature). - All these fibers transmit the sense of localization and pain. ▪ The sensory nerves are more developed in the anterior part of the oral cavity. ▪ Special sensation for taste in the oral cavity. ▪ In association with the numerous sensory nerves, some autonomic, chiefly sympathetic fibers, supply both the smooth muscles of the blood vessels, and minor salivary glands Submucosa ▪ When the submucosa is present, it 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 on the character of the submucosa. ▪ In some areas of the mouth the submucosa is absent. e.g. (gingiva & 12  median raphe), where the mucosa is attached directly to the periosteum of the bone and called a mucoperiosteum. ▪ It is inelastic attachment. ▪ Glands, blood vessels, nerves, and also adipose tissue are present in this layer. Ultrastructure of epithelial cells ❖ Keratinocyte It is the name often given to an epithelial cell because of its content of tonofilaments (keratin filaments). Two important features are related to the tonofilaments in the epithelial cells (keratinocytes): - As keratinocytes of the basal layer undergo maturation the tonofilaments increase 1- In number & 2- In density Tonofilaments of the basal cells are fewer & finer than that of superficial cells. The tonofilaments numbers in the keratinized epithelium are more than that of nonkeratinized epithelium. The density of tonofilaments in the keratinized epithelium is more than that of the nonkeratinized epithelium. ❖ Cell Junctions Since the epithelium is arranged with minimum intercellular cementing 13  substance, So, cell junctions are found to cement the cells together. Desmosome it is the most common cell junctions in the epithelium. (desmo= bond, some= body). 1-Desmosomes It is a cell junction seen by E.M. It is in a form of oval or circular area between two adjacent cell membranes (Trilaminar membranes). There is extracellular condensation at the area of junction between the cell membrane. Another intracellular cytoplasmic condensation is formed inside each cell called attachment plaques to which the tonofilaments are looped and returned back to the interior. The name of transmembrane adhesion proteins is Cadherin. 14  2-Hemidesmosome It is half a desmosome and is a type of junction that join the epithelium and another tissue like the connective tissue or tooth structures. It is found in the epithelial basal layer & located in the cell membrane adjacent to the basement membrane. It is composed of a single trilaminar cell membrane with one intracellular attachment plaque into which tonofilaments are anchored the extracellular condensation on the basement membrane. The name of transmembrane adhesion proteins is Integrins. Physiologic Importance -The desmosomes, hemidesmosomes, and tonofilaments together represent a mechanical linkage that distributes localized forces applied to the surface epithelium over a wide area. 15  Beside desmosomes other less common cell junctions are present, such as: Tight junction: It is characterized by close approximation of the adjacent trilaminar cell membranes. Gap junction: in which the opposing unite membranes are separated by an intercellular structure contain a gap of about 2nm. Such junctions may allow electrical or chemical communication between the cells. - Cell junctions: All the cells are attached to each other by desmosomes and the basal cells are attached to the basal lamina by hemidesmosomes. ❖ Non-keratinocytes They show no tendency to keratinize. They form about 10% of the epithelial cells. They are present at various levels in the oral epithelium. They different in appearance from other epithelial cells in having a clear halo around their nuclei, such cells have been termed Clear cells. Most of them have many processes so, they have been termed Dendritic cells. They are present as scattered cells and not in sheets. They are: - a. Pigment cells (melanocytes) 16  b. Langerhans’ cells c. Merkel cells d. Defensive cells (inflammatory cells) a. Pigment cells (melanocytes) They are melanin - producing cells located in the basal layer of the gingival epithelium. These cells are derived from the neural crest ectoderm and enter the epithelium at about 11th week I.U.L. Histologically: clear cells. Histochemically: They can be demonstrated by either silver impregnation or DOPA reaction. Ultra-structurally: They lack desmosomes and tonofilaments, and they elaborate melanin pigment in the form melanosomes, which when grouped together form melanin granules. The number of melanocytes is the same in black and white individuals, the degree of pigmentation is determined by the activity of the melanocytes to produce melanin or by the maturation of premelanosomes into melanosomes. Melanin pigment is most common in the labial gingiva and buccal mucosa. The melanocytes are active in synthesizing melanosomes and transferring them through their dendritic processes into the surrounding epithelial 17  cells, which are called melanophores (cells that stores melanin but do not produce it). Other cells containing melanin may be seen in the connective tissue, these cells are macrophages containing melanin and are called melanophages. b. Langerhans’ cells They appear above the basal layer of the oral epithelium at the same time, or just before, the melanocytes. These cells are derived from the bone marrow. Histologically: clear cells. Histochemically: They can be demonstrated histologically by gold chloride, (By ATPase) or by specific immunohisto-chemical reactions that stain cell surface antigens. Ultra-structurally: They lack desmosomes and tonofilaments. The Langerhans cells characterized by the presence of a small rod or racquet-shaped granule, sometimes called the Birbeck granules, Langerhans’ granules or rods. Functions: they have an immunologic function, by which recognizing antigenic material that enters the epithelium from the external environment, split it and presenting it to “helper” T lymphocytes. 18  c. Merkel cells They may arise from the epithelial cells. They are located between the basal cells. They have no dendritic processes. Ultra-structurally: They contain sparse tonofilaments, occasional desmosomes, and they are usually close to an intraepithelial nerve fiber. Synaptic junctions are found between them and the nerve fibers. And so, they function as sensory receptor cells for touch or pressure stimuli. d. Defensive cells (inflammatory cells) These cells are transient. They found at various levels of the epithelium. The cells most frequently seen are the lymphocytes, but polymorphonuclear leukocytes and mast cells are occasionally seen. Lymphocytes are often associated with Langerhans’ cells. 19  Classification of the oral mucosa ✓ It is divided according to function into three main types: 1. Masticatory mucosa (keratinized mucosa) 2. Lining mucosa (non-keratinized mucosa) 3. Specialized mucosa 1. Masticatory mucosa (keratinized mucosa) ▪ Is keratinized as it is subjected to the forces of mastication and pressure. ▪ They are: a) Gingiva and b) Mucosa covering the hard palate. a) Gingiva - The gingiva is not only part of the oral mucosa but it is considered part of the marginal periodontium. The gingiva is a pink strip of oral mucosa surrounding the cervical area of the teeth and is attached to them and to the coronal part of the alveolar bone. It is pale pink in color and it is separated from the alveolar mucosa by a scalloped line called the mucogingival junction which is also called the healthy line, which is seen facially and lingually on the lower jaw, It is absent on the palatal gingiva. Microscopic Appearance of the Gingiva: the gingiva as a part of the oral epithelium it is composed of surface epithelium and lamina propria without submucosa attached it to the underlaying structure (mucoperiosteum). 20  Macroscopically appearance of the gingiva:- Morphologically the gingiva can be divided into: A. The free or marginal gingiva B. The a]ached gingiva C. The interdental papillae A. The free or marginal gingiva - It surrounds the cervical region of the teeth; it is relatively mobile and is separated from the tooth by a fine space called the gingival sulcus. - Formed of: 1- Outer or oral part (oral gingival epithelium) Extended from the gingival margin till the gingival crest reflected to form 2. Inner or dental part (oral sulcular epithelium) Extended from the gingival crest till the attachment epithelium lining the sulcus. 21 - The dental surface lined by the gingival sulcus: - - Gingival sulcus is a shallow space between the tooth and the gingiva, it extends from the gingival crest into the junctional epithelium. - Its average depth is 1.8 mm. The free gingival groove - Runs parallel to the gingival margin at a distance of 0.5 to 2 mm labially and lingually. - It demarcates the free from the attached gingiva. - The free gingival groove is formed in 50% of cases and not always visible macroscopically. Histological structure of the free gingiva 1. Oral surface - The surface epithelium is composed of stratified squamous epithelium. - It may be keratinized or parakeratinized. - The gingival groove is found at the level of, or somewhat apical to, the bottom of the gingival sulcus. It appears as a shallow V shaped 22  notch corresponding to a heavy epithelial ridge. - The interface between the oral surface epithelium and the lamina propria is in a form of long and numerous epithelial ridges or pegs and connective tissue papillae. 2. Dental surface - Surface epithelium of the dental or inner surface (the gingival sulcus) of the free gingiva, it is also called sulcular epithelium - It differs from the gingival outer or oral epithelium in that it is thinner, nonkeratinized. - Its cells are arranged parallel to the free surface. They are closely packed with minimum intercellular spaces. They contain many tonofilaments. - The interface is smooth without epithelial pegs. - The lamina propria of the free gingiva shows all elements of the connective tissue but characterized by the presence of many fibroblasts and many lymphocytes and plasma cells below the bo]om of the sulcus. - It is also the site of insertion of many gingival fibers. B. The a]ached gingiva It is firmly attached to the cervical parts of the tooth, junctional epithelium and to the alveolar bone crest by the gingival fibers. Labially, it extends from the free gingiva to the alveolar mucosa. It is separated from the free gingiva by the free gingival groove and from the alveolar mucosa by the mucogingival junction (the healthy line.) The attached gingiva appears slightly depressed between adjacent teeth forming vertical folds. These correspond to the depression on the alveolar process between eminences of the roots of adjacent teeth. In a healthy mouth, the attached gingiva shows signs of stippling (Orange- peel appearance). The stippling (orange-peel appearance) is not found in other areas of the oral mucosa. The degree of stippling varies according to age and sex. In younger female persons the connective tissue fibers are finer than that of the male. However, with increasing age, the collagen fiber’s bundles become coarser in both sexes. The width of the attached gingiva is not uniform through the oral cavity. 23  It is widest in the region of the upper anterior teeth and It is narrowest in the regions of the lower anterior teeth. There is no attached gingiva at the palatal gingiva. Histological structure of the A]ached gingiva - The surface epithelium is keratinized or parakeratinized and it is characterized by long connective tissue papillae elevating the epithelium. Between the elevations there are shallow depressions that correspond to the center of the epithelial pegs & form the stippling (orange-peel appearance). - The interface shows long epithelial pegs interdigitate with the connective tissue papillae. ❖ Fibers of the Lamina Propria (Gingival Ligaments): - The lamina propria of the attached gingiva shows all elements of the connective tissue but characterized by the presence of coarse collagen bundles (the gingival fibers or ligaments). - Mucoperiosteum: The lamina propria of the gingiva is directly attached to the periosteum of the buccal and lingual plates of the alveolar processes & to the cervical region of the tooth by the gingival fibers. - No submucosa - Importance of the gingival fibers ✓ The gingival fibers play a very important role in maintaining the integrity of the periodontium. 1. As they support the junctional epithelium. 2. Give the free and interdental papilla their rigidity. 3. Help in stabilizing the teeth in their position in the dental arch (through the trans-septal fibers). 24  ❖ The gingival fibers are arranged in the following groups 1) Dentogingival fibers: - They are the most numerous. - They extend from the cervical cementum and radiate into the lamina propria of the gingiva. 2) Dentoperiosteal fibers: - These fibers extend from the cementum and bend apically over the alveolar crest to be inserted into the buccal and lingual periosteum of the alveolar crest bone. 3) Alveologingival fibers: - These fibers arise from the alveolar crest and radiate coronally Into the lamina propria of the free gingiva. 4) Circular and semicircular fibers: - The circular fibers are a small group of fibers that circle the tooth and interlace with the other fibers. - While the semicircular fibers arise from one of the proximal cementum and encircle only the buccal and lingual half of the tooth to be inserted into the other proximal surface. 25 5) Trans-septal fibers - These fibers extend mesiodistally from the cementum of one tooth to the cementum of the adjacent one. - They are found in the lamina propria of the interdental papillae above the interdental septum. - They contact all the teeth in the arch and form a ligament between the teeth. C. The interdental gingiva - It is that part of the gingiva that fills the space between two adjacent teeth. - In cases where there is no contact area, the interdental papilla is reduced. - It is formed of the free and attached gingivae. The attached gingiva is attached to the alveolar crest of the interdental alveolar process. 26  And the free gingiva facially and orally is connected below the contact area by the interdental col. - When viewed from the lingual and facial aspects the interdental papilla forms a triangular tissue and called gingival papilla. - In three dimensional views the interdental papilla is pyramidal between the anterior teeth where as it is tent shaped in the posterior region. The central concave area of the tent is apical to the contact area and form the col. - With age, the vestibular and oral interdental edges descend and the area of the col is flattened. Histological structure of the interdental gingiva - The surface epithelium is formed from both free and attached gingiva facially is keratinized or parakeratinized. - The surface epithelium of the attached gingiva labially shows melanocytes 27  with melanin pigment specially in dark skinned races. - The col connecting the facial and lingual surfaces shows thin nonkeratinized surface epithelium. - The interface of the col surface epithelium and the lamina propria is straight without epithelial pegs. - The lamina propria shows the connective tissue elements with many inflammatory cells and gingival fibers especially the trans-septal fibers running mesiodistally. o Blood Supply of the Gingiva - The blood flow is derived from 1- arteries found deep in the lamina propria of the gingiva. - Another supply from branches of the 2- arteries of the alveolar process & 3- periodontal ligament. - Some of these arteries run parallel to the sulcular epithelium, forming a rich network just before the basement membrane. - There is a rich network of lymph vessels in the gingiva along the blood vessels leading to the submental and submandibular lymph nodes. o Nerve Supply of the gingiva The gingiva is well innervated, like any innervation of the oral mucosa. The nerves end in one of three ways, Free nerve endings (pain), Merkel discs are presumed to be a pressure receptor adjacent to Merkel’s cells. Organized in a form of encapsulated ends to form Meissner’s corpuscles or coiled terminals to form Pacinian (touch), encapsulated to form Ruffini’s or Krause’s bulbs (temperature). These fibers transmit the sense of localization and pain. Myelinated nerves in the deep lamina propria (reticular part). Unmyelinated in the superficial lamina propria (papillary part). 28  Development of the Junctional Epithelium ✓ The junctional epithelium differs from the oral epithelium as it is embryologically derived from the reduced enamel epithelium. - The ameloblasts after the complete formation of enamel, they develop Hemidesmosomes And the typical basal lamina to be attached to the enamel surface. After that they form the reduced enamel epithelium. - Between the reduced enamel epithelium and the oral epithelium is the connective tissue of the lamina propria. - Desmolytic enzymes secreted by the reduced enamel epithelium break down the connective tissue. 29 - The cells of outer layer of the reduced enamel epithelium and the basal cells of oral epithelium proliferate and fuse together to form a double epithelial layer over the crown. - Cell death in the middle of this epithelial layers to facilitate the eruption without hemorrhage. 30  - Once the tip of the cusp of the erupting tooth has emerged into the oral cavity, The oral epithelium together with the remaining reduced enamel epithelium form the primary a]achment epithelium. - The reduced enamel epithelium is incapable, to divide (highly specialized cells) so, they undergo degenerations. - At the same time the oral epithelial cells begin to migrate over the reduced enamel epithelium in an apical direction to replace it. Then 2ry epithelium a]achment is formed. - The overgrowing epithelial cells will stratify causing thickening of this area. So, the superficial cells of the reduced enamel epithelium are now away from their nutritive supply, therefore the creation of the gingival sulcus. Shif t of the Dentogingival Junction (Passive Eruption) - Once the tip emerges into the oral cavity, the oral epithelium covers almost the entire crown. - Then the tooth moves occlusally until reaches the occlusal plane, 1/3 to 1/4 of the enamel is still covered by the gingiva. - At the same time the attachment epithelium separates from the enamel surface, while the crown erupt into the oral cavity. ✓ The actual movement of the teeth towards the occlusal plane is termed active eruption. 31 ✓ The gradual exposure of the crown by the recession of the gingiva apically is termed passive eruption. - The junctional epithelium has a coronal or superficial end at the bottom of the gingival sulcus & - An apical or deep end denote the junctional termination. ❖ The crown exposure involving passive eruption and further recession has been described in four stages: First Stage (age of 20 or 30 years): Here we find coronal end of the attachment epithelium is on the enamel, while the apical end on the cemento-enamel junction. This stage persists also in the primary teeth. 32  Second Stage (25-40 years or even later): In this stage the coronal end of the attachment epithelium is still on the enamel while the apical end had shifted to the cervical part of the root cementum. Third Stage (above 40 years): In this stage the coronal end of the attachment epithelium is at the cemento-enamel junction. The apical end is on the root cementum. Fourth Stage: both coronal and apical ends are on the root. ✓ The rate of coronal exposure varies in different individuals, in different teeth of the same individual and on different surfaces of the same tooth. 33  B- Hard palate - Mucous membrane is immovable. - Pink in color. - The lamina propria is thicker anteriorly and has numerous long papillae. - Various regions can be distinguished because of varying structures of the submucous layer. These regions are: 1. Gingival region (adjacent to the teeth). 2. Palatine raphe or median area (extending from incisive papilla posteriorly). 3. Anterolateral area (fa]y zone) between the raphe and gingival. 4. Posterolateral area (glandular zone) between the raphe and gingiva. - The peripheral zones do not have a submucosa (identical with the gingiva and the palatine raphe). - The glandular layers of the hard and soft palate are continuous. - The incisive (palatine) papilla and palatine rugae are formed of dense C.T. layer with fine interwoven fibers. 2. Lining mucosa (non-keratinized mucosa) - The epithelium is thicker than that of masticatory mucosa. - The epithelium is nonkeratinized. - The surface is flexible (withstand stretching). - The interface with C.T. is smooth. - The lamina propria is thinner than in masticatory mucosa. - It contains fewer irregular collagen fibers. 34  - It contains elastic fibers (control the extensibility). - Where lining mucosa covers muscle (lip, cheeks, underside of the tongue), the mucosa is fixed to fascia by collagen and elastic fibers. - Different zones of lining mucosa vary from one another in the structure of their submucosa. BUCCAL MUCOSA It is thick (0.5mm) In many people a slight raised whitish line is found along the buccal mucosa opposite to the occlusal plane of the teeth. It is called Linea Alba (white line), it is a keratinized area in the buccal mucosa. The submucosa: It connects the lamina propria to the muscles firmly. and it contains labial or buccal glands. The horizontal middle zone on the cheek, lateral to the corner of the mouth, may contain isolated sebaceous gland (Fordyce’s spots). ✓ The alveolar mucosa and mucosa covering the floor of the mouth are loosely attached to the underlying structure by a thick submucosa. ✓ By contrast, mucosa of the underside of the tongue is bound firmly to the underlying muscle (Submucosa is thin). Loosely A]ached “Movable” mucosa 1. Alveolar mucosa: loosely attached to periosteum and it covers the apical part of the alveolar bone. Epithelium: - Stratified squamous nonkeratinized epithelium - Few or no epithelial ridges Lamina propria: - Loose connective tissue - Thin collagen and elastic fibers 35  Submucosa: - Thick elastic fibers and mixed salivary glands 2. Vestibular fornix: is where the mucosa of the lips and cheeks reflects into the mucosa covering the apical part of the alveolar bone and allows mobility of lips and cheeks - The median and lateral labial frenula are folds of the mucous membrane (Double mucosa). - has very thin epithelium and lamina propria highly vascularized. 3. Floor of the mouth: loosely attached to the underlying structures allows mobility of the tongue. - Has very thin epithelium and lamina propria highly vascularized, which is good for the absorption of the medications. Firmly A]ached “Immovable” mucosa 1. Lip & cheek mucosa - Thick nonkeratinized epithelium. - Dense connective tissue ,collagen fibers and some elastic fibers. 2. Soft palate - Has an oral surface and a nasal surface. - The nasal surface has a pseudostratified columnar ciliated epithelium. - The oral surface is thin nonkeratinized epithelium and highly vascularized C.T. 36  3. Mucosa of the Inferior surface of the tongue - Thin nonkeratinized epithelium and highly vascularized C.T. - It is firmly attached to the muscles of the tongue. 3. Specialized mucosa - Location: dorsal surface of the tongue. - Covered by masticatory mucosa (keratinized). - Containing different types of lingual papillae. - Some of these papillae bear taste buds. - The mucosa of the tongue composed of two parts; ant. 2/3 (Papillary portion) and post. 1/3 (lymphatic portion) – divided by V-shaped sulcus terminalis. Tongue Papillae 37 1. Filiform papillae; - thread shaped and are the most numerous ,found in lines parallel to sulcus terminalis. - Giving the tongue velvet appearance. - Epithelium is keratinized with tuft like hair at its apex. - Consists of a core of C.T that carries Secondary papillae. - They do not contain any taste buds. 2. Fungiform papillae ;- mushroom shaped and less numerous, especially found at the tip and lateral sides of the tongue in between filiform papillae. - Epithelium is nonkeratinized. - Lamina propria has few secondary papillae, and rich in blood vessels and nerves. - Contain a few taste buds on the top of the papillae only. 3. Circumvallate papillae :- V-shaped row along the sulcus terminalis (8-10 papillae). - Larger than other papillae. - Inverted cone in shape slightly sunk under the surface of the tongue surrounded by a trench or a deep groove into which open the ducts of serous minor salivary glands (Von Ebner’s glands), which serve to wash out the soluble elements of food that 38  stimulate the taste buds. - It is superior surface is keratinized. - Has a central primary papilla rich in blood vessels and nerves and a secondary papilla which it is surface epithelium is thin. - Numerous taste buds at the lateral surface of the papillae. - Some taste buds are seen in the walls surrounding the papilla. 4. Foliate papillae: -at postro -lateral part (4-11 papillae). - They are pronounced in rabbits and animals but rudimentary in man. - Found at birth and childhood then disappear. ❖ Taste Buds: - Small intraepithelial barrel like organs, - Present in the: - 1. Tongue (circumvallate, fungiform and foliate papillae). 2. Soft palate. 3. Epiglottis. 4. Pharynx. - Taste buds are composed of 3 types of cells: 1. (Neuroepithelial) taste cells (type I). 10-12 in number, at the center of the 39  bud, slender with dark stained nuclei, their tips form a taste pore at which microvilli extend. 2. Supporting cells (type II), found at the periphery, crescent like with large oval nuclei. 3. Basal or regenerative cells (type III). - A rich plexus of nerve is found below the taste buds. - Some fibers enter the epithelium and end in contact with the sensory cells. Taste Sensation Any substance to be tasted must become dissolved in saliva and passed to the taste pores. This affects the microvilli of the taste cells. So, a nerve impulse is set up and transmitted along the sensory nerve fibers to the brain. The basic tastes are: Sweet, Salt, Bitter& Sour. Smell is important for taste sensation. Lymphoid Tissue - Posterior to the sulcus terminalis, the tongue is studded with the lingual follicles, together these lingual follicles form the lingual tonsils. - Each of these shows one or more lymph nodule, sometimes containing a germinal center. 40  Mucocutaneous Junction (Vermilion zone of the lip) o It is the pink to reddish transitional zone between the skin covering the outer surface of the lip and the true mucous membrane lining the inner surface. o The line separating the vermilion zone from the skin of the lip is called The vermilion border. o Very thin surface epithelium o Very thin keratinized layer. o Numerous long papillae. o Many large capillary loops close to the surface. o The vermilion zone lacks salivary glands and contains a few sebaceous glands. o Intermediate zone (suckling pad): Between the vermilion border and labial mucosa is an area covered by parakeratinized oral epithelium, In infants this region is thickened adapted for the suckling function. 41  ❖ Age Changes ✓ Clinically - By age the oral mucosa acquires a smoother dryer surface. - The level of the attachment epithelium is receded and the root is exposed. ✓ Histologically 1. The surface epithelium appears thinner. 2. Langerhans’ cells become fewer. 3. A flattening of the surface ridges and surface cells cause the oral mucosa to appear smoother. 4. Cellular activity decreases and fibrosis increase. 5. The vascularity decreased and a common feature is the presence of a varicose veins on the undersurface of the tongue. 6. Gradual atrophy of minor salivary glands. 7. Increase the (Fordyce’s spots). 8. The ability to repair is reduced and the healing time is increased. 9. Recession of the gingiva is prominent. 10.Reduction in the number of filiform papillae. 11.Fungiform papillae become more prominent. 42  Important comparisons Basal Lamina Basement Membrane It is the junction formed through the It is the junction formed through the activity of epithelium. It is part of the activity of both epithelium and basement membrane. connective tissue. Viewed by electron Viewed by light microscope. microscope. Formed of Lamina lucida (clear zone, It stains with PAS for the about 45 nm) neutral muco-polysaccharides & Lamina densa (dark zone about 50 nm) and silver stain for the reticulin fibers Comparison between types of oral epithelium Keratinized Epithelium Nonkeratinized Epithelium The surface epithelium is usually The surface epithelium is usually thicker thin The prickle cell layer appears The prickle cell layer appears larger with smaller with wide intercellular smaller intercellular spaces and less spaces & many intercellular bridges. intercellular bridges It produces keratinous layer & It does not produce keratinous layer or granular layer. granular layer The interface showing long & The interface showing short & blunt narrow epithelial ridges epithelial ridges 43  Comparison between the two layers of lamina propria The papillary layer The reticular layer Formed of C. T. ridges which C. T. lies between the papillary layer projecting into the epithelium. and the underlying structures. Their extensions differ according to the type of epithelium. The papillary layer has collagen fibers The reticular layer has collagen fibers which are thin and loosely arranged arranged in thick bundles that tend to with many capillary loops in- lie parallel to the surface epithelium between. Comparison between the lamina propria of Keratinized Nonkeratinized Contain many Collagens which are Contain few Collagens which are ▪ Thick fibrils ▪ Thin fibrils, ▪ Tightly packed ▪ Loose ▪ Take a straight course ▪ Take a wavy course No elastic fibers Contain many elastic fibers Function of collagen: is supportive Function of elastic fibers: as they resist the heavy loads applied Restore the deformed tissue in the to the surface epithelium.) deformed lining mucosa 44