Oral Mucosa Lecture 2024 (PDF)

Oral Mucosa Karla Coburn DDS, PhD [email protected] Learning Objectives 1. Describe the general structure of the oral epithelium with its different types of cells 2. Describe the location and histological features of the different types of oral mucosae (lining, masticatory, specialized). 3....

Oral Mucosa Karla Coburn DDS, PhD [email protected] Learning Objectives 1. Describe the general structure of the oral epithelium with its different types of cells 2. Describe the location and histological features of the different types of oral mucosae (lining, masticatory, specialized). 3. Describe the histological organization of the tongue, including the different types of papillae and their function. 4. Describe the structure of the gingival tissue and its different presentations. 5. Describe the structure of the lips, cheeks and soft and hard palate. 6. Describe the different types of junctions of the oral cavity: mucocutaneous junction, mucogingival junction and dentogingival junction. Lecture Outline 1. Functions of the Oral Mucosa 2. Origin of the Oral Mucosa 3. Components of the Oral Mucosa 4. Structure of the Lamina Propria and Submucosa 5. General Structure of the Epithelium 6. Structural Variations of the oral mucosa 7. Masticatory mucosa 8. Lining Mucosa 9. Specialized Mucosa 10.Junctions in the oral mucosa Oral Mucosa: Functions Protection ✓ The oral mucosa shows a number of adaptations to withstand all the stress caused by biting, chewing and hard particles from food. ✓ Major barrier to microorganisms: first line of defense Sensation ✓ The oral mucosa receptors respond to temperature, touch, pain and taste. ✓ Reflexes such as swallowing, gagging and salivating also are initiated in the oral mucosa. Secretion ✓ Saliva, produced by the salivary glands Oral Mucosa: origin ✓ Oral mucosa consist of two separate tissue components: a covering epithelium and an underlying connective tissue (lamina propria), both derived from the 1st PA. ✓ Epithelium: ectoderm from stomodeum ✓ Lamina propria: ectomesenchyme Oral Mucosa: Components and General Organization ✓ Mucosa: (stratified squamous epithelium and lamina propria - LP).No muscularis mucosae! ✓ Submucosa: dense irregular CT, with adipose tissue or minor salivary glands. Some regions lack a submucosa, so the fibers of the LP attach directly to the periosteum underneath: mucoperiosteum (mucosa is more resistant and less flexible). Absence of smooth muscle: skeletal muscle General GI mucosa Typical oral mucosa - Soft and pliable Mucoperiosteum - Firm, immobile (Lining mucosa) (Masticatory mucosa) Smooth muscle Skeletal muscle  Lamina Propria ✓ Papillary Layer: scarce loose connective tissue immediately underneath the epithelium: more cellular, fine collagen fibers, many blood capillaries ✓ Reticular Layer: dense irregular connective tissue underneath papillary PL layer: bundles of type I collagen Cells RL ✓ Fibroblasts ✓ Mast cells ✓ Macrophages ✓ Plasma cells ✓ Neutrophils, lymphocytes Interface between Epithelium and Lamina Propria ✓ This junction is a wavy interface at which papillae of the connective tissue interlock with the epithelial ridges (or rete pegs). Areas subjected to more stress have the greatest number of papillae per unit area of mucosa Connective tissue Purpose: papillae ✓ Increases the surface area Epithelium between the tissues, providing better attachment. ✓ Facilitates the metabolic exchange between the Epithelial Lamina propria avascular epithelium and the ridges connective tissue Submucosa ✓ Deeper to the lamina propria, is composed of a dense irregular connective tissue, that may contain minor salivary glands or fat tissue ✓ Absent in some regions, such as attached gingiva and most of the hard palate ✓ Helps to attach the lamina propria to underlying tissues (muscle or bone) Submucosa Oral Epithelium Lamina propria Submucosa Lecture Outline 1. Functions of the Oral Mucosa 2. Origin of the Oral Mucosa 3. Components of the Oral Mucosa 4. Structure of the Lamina Propria and Submucosa 5. General Structure of the Epithelium 6. Structural Variations of the oral mucosa 7. Masticatory mucosa 8. Lining Mucosa 9. Specialized Mucosa 10.Junctions in the oral mucosa Oral Epithelium ✓ Stratified squamous epithelium, keratinized or not. ✓ Constantly renewed (6-20 days) ✓ Cells: 1) Keratinocytes 2) Melanocytes: produce melanin 3) Langerhans cells: antigen presenting cells 4) Merkel Cells: mechanoreceptors Keratinocytes Lipid-rich layer around the cells ✓ Most numerous cells, form a stratified Exocytosis of lamellar squamous epithelium. granules ✓ Undergo a differentiation process, in Keratohyaline granules (filaggrin) which they progressively accumulate keratins and move upward. Lamellar ✓ In keratinized epithelia, the most granules (lipid) superficial keratinocytes eventually die, becoming packs of keratin, surrounded by a lipid layer that contributes to the Melanin formation of a barrier against water loss Hemidesmosome Desmosome Basal Keratin lamina General Structure of the Oral Epithelium ✓ Basal Layer (stratum basalis) ✓ Prickle Layer (stratum spinosum) ✓ Granular Layer (stratum granulosum) ✓ Keratin layer (stratum corneum) Only present in keratinized epithelium Basal Layer (Stratum basale) ✓ One layer of cells, mostly keratinocytes, but also contains melanocytes and Merkel cells. ✓ Cells attached to each other by spot desmosomes and to the basal lamina by hemidesmosomes. ✓ Function: Keratinocyte germinative layer and provides attachment to the underlying lamina Basal layer propria Melanocyte Basal layer Basal layer: Melanocytes ✓ Melanocytes derive from the neural crest cells. ✓ They synthesize melanin pigment in melanosomes and “donate” it to adjacent epithelial cells via their cytoplasmic extensions. Gingiva showing melanin pigmentation Prickle Cell Layer (Stratum spinosum) ✓ Above basal layer, it is the thickest layer ✓ Many spot desmosomes connecting cells: mechanical resistance ✓ Upper cells start to produce lamellar granules (lipid coating that acts as a cement to prevent penetration of water and other materials). ✓ Mostly keratinocytes, few Langerhans’s cells Prickle cell layer Desmosomes Basal layer Pemphigus Vulgaris ✓ Autoimmune disease in which autoantibodies attack cadherins on desmosome structure, causing epithelial cells to separate from each other. Granular layer (Stratum granulosum) Keratin layer ✓Just above the prickle cell layer ✓Cells contain two types of granules: Lamellar granules: lipid content that once released, coats the cells, acting as a cement to prevent Granular layer penetration of water and other materials Keratin Granular layer Keratohyaline granules: large, basophilic; contain filaggrin, which helps to organize and compact keratin molecules Keratin layer (Stratum corneum) Keratin layer ✓Most superficial layer in keratinized epithelium ✓Consists of flat, dead cells – basically keratin scales associated with filaggrin. Granular layer Keratin Main types of maturation in oral epithelium Orthokeratinization ✓ Nuclei are lost in the keratinized surface layer. ✓ Keratohyalin granules are visible in the granular layer. Parakeratinization ✓ The keratin squames retain their pyknotic nuclei. ✓ Granular layer often not visible ✓ Normal on oral mucosa Nonkeratinization ✓ Most common presentation within the oral mucosa ✓ No clear division of strata exists ✓ Granular layer often not visible and nuclei are apparent in the surface layer. Main types of maturation in oral epithelium Parakeratinized layer Superficial cell layer Orthokeratinized layer (cells retain nuclei) Intermediate cell layer GL GL Prickle Prickle cell cell layer Prickle layer cell layer Basal Basal cell layer layer Gingiva, Hard palate, orthokeratinized Basal layer Gingiva, parakeratinized parakeratinized Buccal mucosa, non keratinized Lecture Outline 1. Functions of the Oral Mucosa 2. Origin of the Oral Mucosa 3. Components of the Oral Mucosa 4. Structure of the Lamina Propria and Submucosa 5. General Structure of the Epithelium 6. Structural Variations of the oral mucosa 7. Masticatory mucosa 8. Lining Mucosa 9. Specialized Mucosa 10.Junctions in the oral mucosa  Structural Variations of the Oral Mucosa ✓ Throughout the oral cavity, structural variations can be observed in the: Type of surface epithelium Composition of the lamina propria Form of the interface between epithelium and connective tissue How the mucosa is attached to underlying structures Nature of the submucosa (if present or not, if holds glands or fat) Structural Variations of the Oral Mucosa ✓ The oral mucosa can be divided into three main types: Lining mucosa (60%): alveolar mucosa, floor of mouth, buccal and labial mucosa, soft palate and ventral surface of tongue Masticatory mucosa (25%): hard palate and gingiva Specialized mucosa (15%): Dorsal surface of the tongue Structural Variations of the Oral Mucosa Lining mucosa: stratified squamous non- Masticatory mucosa: stratified squamous Specialized mucosa: dorsal keratinized epithelium lines the alveolar keratinized epithelium, found on hard palate surface and postero-lateral mucosa, labial and buccal mucosa, floor of and gingiva borders of the tongue (mucous mouth, ventral surface of the tongue and membrane with taste buds) soft palate. Lecture Outline 1. Functions of the Oral Mucosa 2. Origin of the Oral Mucosa 3. Components of the Oral Mucosa 4. Structure of the Lamina Propria and Submucosa 5. General Structure of the Epithelium 6. Structural Variations of the oral mucosa 7. Masticatory mucosa 8. Lining Mucosa 9. Specialized Mucosa 10.Junctions in the oral mucosa Gingiva ✓ Stratified squamous epithelium, para or orthokeratinized. ✓ Dense lamina propria, firmly attached to the 2 periosteum (mucoperiosteum). Wavy interface epithelium-CT 3 1. Free gingival margin (marginal gingiva) which defines the gingival sulcus. 1 2. Attached gingiva: firmly attached to the tooth and bone 3. Interdental papilla: area between two adjacent teeth beneath their contact point. Gingiva ✓Free Gingival Groove: sets the superficial boundary between free and attached gingiva. ✓ Attached gingiva: continuous with alveolar mucosa Attached gingiva (Stippled) Free gingiva Gingiva ✓ The surface of the attached gingiva and interdental papilla commonly has a texture that is referred to as being stippled or resembling that of an orange peel. ✓ Stippling occurs because of the rete pegs. ✓ It is consistent with health, but not required for health. Gingival Stippling Stippled Not stippled Interdental Papilla and Col ✓Interdental papilla: gingiva located between the teeth and extending below the contact. It fills the interproximal space between the teeth. ✓Col: concave zone of gingiva between the lingual and vestibular papilla: thin non keratinized epithelium (not masticatory mucosa!).  Hard Palate ✓ Stratified squamous epithelium, para or orthokeratinized. ✓ Dense lamina propria, firmly attached to the periosteum: mucoperiosteum – no submucosa: firm and immobile). ✓ Submucosa is found mostly on the latero-posterior regions and may contain adipose tissue or minor salivary glands. Hard Palate Submucosa with salivary glands Mucoperiosteum Lecture Outline 1. Functions of the Oral Mucosa 2. Origin of the Oral Mucosa 3. Components of the Oral Mucosa 4. Structure of the Lamina Propria and Submucosa 5. General Structure of the Epithelium 6. Structural Variations of the oral mucosa 7. Masticatory mucosa 8. Lining Mucosa 9. Specialized Mucosa 10.Junctions in the oral mucosa  Lining mucosa ✓ Composed of stratified squamous nonkeratinized epithelium (SSNK), supported by a lamina propria and submucosa. ✓ Soft and pliable ✓ Lack of keratinization allows visualization of blood vessels in the lamina propria Soft Palate ✓ SSNK epithelium ✓ Lamina propria and submucosa (with minor salivary glands/fat tissue) ✓ Deep to the submucosa: muscles of the soft palate. Highly vascularized (compared to hard palate).  Ventral Surface of the Tongue ✓ SSNK epithelium ✓ Lamina propria: elastic fibers; extensive vascular supply: drug delivery ✓ Submucosa of the tongue: dense irregular connective tissue, continuous with connective tissue surrounding skeletal muscle  Floor of the Mouth ✓ Thin SSNK epithelium ✓ Lamina propria: short papillae; some elastic fibers; extensive vascular supply: drug delivery ✓ Submucosa: loose connective tissue containing fat, minor salivary glands and the two major sublingual glands Mucocutaneous Junction ✓ Interface between the skin and the oral mucosa. ✓ Skin: stratified squamous keratinized epithelium, contains skin appendages (pilosebaceous apparatus, sweat glands) ✓ Vermillion zone: thin stratified squamous keratinized epithelium. Many capillaries underneath, no appendages (but occasional ectopic sebaceous glands). ✓ Labial mucosa: thick stratified squamous nonkeratinized epithelium. Contains minor salivary glands (labial glands) Lip - Skin Lips Vermillion zone Skin Vermillion zone, 10x Labial mucosa Labial mucosa, 10x Buccal Mucosa ✓ SSNK epithelium, flat interface with lamina propria ✓ Salivary glands in the submucosa. ✓ Ectopic sebaceous glands can be occasionally found in the buccal and labial mucosa, (and even on the vermillion zone),called Fordyce's granules. Fordyce’s granules ✓ Clinically appear as clusters of yellowish spots Buccal mucosa, nonkeratinized epithelium. Fordyce granules: Ectopic sebaceous glands in the lamina propria Buccal Mucosa: Linea alba ✓ Epithelial hyperkerathosis: bilateral white lines on the occlusal plane (linea alba) Lecture Outline 1. Functions of the Oral Mucosa 2. Origin of the Oral Mucosa 3. Components of the Oral Mucosa 4. Structure of the Lamina Propria and Submucosa 5. General Structure of the Epithelium 6. Structural Variations of the oral mucosa 7. Masticatory mucosa 8. Lining Mucosa 9. Specialized Mucosa 10.Junctions in the oral mucosa Tongue Tongue: interlacing bundles of skeletal muscle that allow change shape/position Functions: Speech, Mastication, Deglutition, Taste perception Netter Dorsal Surface of the Tongue: Specialized mucosa ✓ The dorsal surface of the tongue is covered by lingual papillae, which may have a sensory function (taste perception) and or mechanical function. Fungiform papillae Vallate papillae Filiform papillae Foliate Papillae ✓Located on lateral aspects of posterior tongue ✓Numerous taste buds Foliate papillae Vallate Papillae ✓ Vallate (circumvallate) papillae: 8–12, form V-shaped row in back of tongue. ✓ Serous minor salivary glands (Von Ebner glands) have their ducts opening within the sulcus surrounding the vallate papillae. Fungiform Papillae ✓Mushroom shaped, scattered widely over tongue; look reddish (thin stratified non keratinized epithelium with a rich vascular core. Fungiform papillae Filiform Papillae ✓ Filiform papillae: conic shape, gives tongue roughness to provide friction; highly keratinized and does not contain taste buds. Functionally acts as a masticatory mucosa, possessing a mechanical function. Filiform papillae Fungiform papillae Lecture Outline 1. Functions of the Oral Mucosa 2. Origin of the Oral Mucosa 3. Components of the Oral Mucosa 4. Structure of the Lamina Propria and Submucosa 5. General Structure of the Epithelium 6. Structural Variations of the oral mucosa 7. Masticatory mucosa 8. Lining Mucosa 9. Specialized Mucosa 10.Junctions in the oral mucosa Junctions in the Oral Mucosa Within the oral mucosa are four important junctions: ✓ Mucocutaneous (interface between the skin and labial mucosa) ✓ Mucogingival (interface between the gingiva and alveolar mucosa) ✓ Soft-Hard Palate junction (interface between the hard and soft palate) ✓ Dentogingival (interface between the gingiva and the tooth). Mucocutaneous Junction ✓ Interface between the skin and the oral mucosa. The skin, which contains hair follicles, sebaceous and sweat glands, is continuous with the oral mucosa at the lips. Minor salivary glands  Mucogingival junction ✓ Interface between the attached gingiva (keratinized) and the alveolar mucosa (SSNK) ✓ Clinically visualized by a slight indentation called the mucogingival groove and by the change from the bright red of the alveolar mucosa to the paler pink of the gingiva Section through the mucogingival junction (orange dashed line). The differences in thickness, ridge pattern, and keratinization between epithelium of the gingiva and alveolar mucosa are seen. Soft Palate-Hard Palate Junction Photomicrograph of the junction (dashed line) between mucosa covering the hard and the soft palate. Note the difference in thickness and the ridge pattern between keratinized epithelium of the hard palate and nonkeratinized epithelium of the soft palate is apparent.  Dentogingival junction ✓ Interface between the gingiva and the enamel of the tooth. This is the principal seal between the oral cavity and the periodontal tissues. Sulcular epithelium: ✓SSNK epithelium, with no rete pegs ✓Not attached to the surface of the tooth. Junctional epithelium SSNK epithelium No rete pegs High rate of turnover Dual basal lamina Junctional Epithelium ✓ Primary component of the Free Gingival dentogingival junction, this is the Enamel sulcus gingiva first line of innate host defense in the periodontal region, hindering bacterial advancement into periodontal tissues. Sulcular epithelium ✓ Disturbance of this attachment Attached by infection food or gingiva debris results in deepening of the gingival sulcus (pocket). Junctional epithelium ✓Formed during eruption, when oral epithelium fuses with reduced enamel epithelium Junctional Epithelium ✓Dual basal lamina (BL): Internal BL: attaches epithelium to enamel via hemidesmosomes External BL: attaches epithelium to underlying connective tissue via hemidesmosomes Rei Sekiguchi, Kenneth M. Yamada, 2018 - Chapter Four - Basement Membranes in Development and Disease. https://doi.org/10.1016/bs.ctdb.2018.02.005 Sulcular Epithelium ✓Lines the gingival sulcus, Gingival Free therefore is not attached to Enamel sulcus gingiva the surface of the tooth. ✓Coronal to the junctional epithelium Sulcular ✓Stratified squamous non- epithelium keratinized epithelium, with Attached no rete pegs gingiva Junctional epithelium