oral mucosa

• The intestinal tract (through oral cavity and anus), nasal passage and other body cavities communicate with the exterior environment. All these are lined by a moist lining, which is called as "mucous membrane"
• Locations of mucous membranes

  • Oral cavity
  • Nasal cavity & sinuses
  • Trachea
  • Stomach & intestines
  • Urinary bladder
  • Uterus
• Oral mucosa or oral mucous membrane


  The moist lining of the oral cavity that is in continuation with the exterior surface of skin on one hand & esophagus on the other end
• Oral mucous membrane

  • Consists of 2 layers: Oral Epithelium and Connective Tissue
• Oral Epithelium


  The epithelium that forms the surface of oral mucosa, forms primary barrier between oral environment & deeper tissues, ectodermal in origin (except the tongue, which is endodermal)
• Maintenance of structural integrity of oral epithelium

  Continuous cell renewal, cells produced by mitotic division in the deepest layers migrate to the surface to replace those cells that are shed
• Cells of the oral epithelium

  • Progenitor cells
  • Maturing cells or keratinocytes
• Progenitor cells


  Divide & produce new cells
• Maturing cells or keratinocytes


  Undergo a process of continuous maturation or differentiation & form a protective surface layer
• Regions of the oral cavity with keratinizing epithelium

  • Gingiva
  • Hard palate
  • Alveolar mucosa
• Regions of the oral cavity with non-keratinizing epithelium

  • Lips
  • Cheeks
  • Floor of mouth
  • Soft palate
  • Underside of the tongue

  
• Layers of keratinizing epithelium

  • Stratum basale (basal layer)
  • Stratum spinosum (Prickle layer)
  • Stratum granulosum
  • Stratum corneum
• Layers of non-keratinizing epithelium

  • Stratum basale
  • Stratum spinosum (Prickle layer)
  • Stratum intermediate
  • Stratum superficiale
• Keratinization


  A process by which epithelial cells exposed to the external environment lose their moisture & are replaced by horny tissue containing keratin, a fibrous protein that is insoluble in most solvents
• Keratinized epithelium


  • More resistant to infections & irritation than nonkeratinized epithelium
• Stratum Basale or Basal Layer


  Also called the proliferative or germinative layer, cells are capable of division, synthesize DNA & undergo mitosis, providing new cells
• Stratum Spinosum


  Also called the prickle cell layer, cells are irregularly polyhedral & larger than basal cells, joined by intercellular bridges, contain tonofibrils that run next to the attachment plaque
• Stratum Granulosum


  Contains flatter & wider cells with larger size than spinous cells, contains keratohyalin granules that stain intensely with basic dyes, cells show signs of degeneration & pyknosis
• Stratum Corneum


  Keratinized layer, cells are larger & flatter than granular cells and are eosinophilic in nature, all nuclei & other organelles disappear
• Types of keratinization

  • Orthokeratinization or True keratinization
  • Parakeratinization
• Linea alba


  A non-keratinized area in the cheek opposite the occlusal plane that gets keratinized due to continuous stress of friction
• Palate of smokers


  Becomes hyperkeratotic due to irritation produced by tobacco smoke
• Mild inflammation


  Increases keratinization but severe inflammation reduces the degree of keratinization
• Lamina Propria or Corium


  The connective tissue layer supporting the oral epithelium, interface with epithelium is irregular with connective tissue papillae interdigitating with epithelial ridges or pegs
• Parts of the lamina propria

  • Papillary portion
  • Reticular portion
• Papillary portion


  Associated with epithelial ridges, consists of finger-like projections of connective tissue that interlock with similar epithelium projections
• Reticular portion


  Named because of the reticular fibers
• Submucosa


  Connective tissue layer that attaches the lamina propria of the oral mucosa to the underlying bone or muscle, contains glands, blood vessels, nerves & adipose tissue
• Nerve supply to the oral mucosa is sensory
• Masticatory mucosa


  Covers the gingiva, hard palate & alveolar ridges, bears chewing forces, does not stretch & is attached to bone, epithelium is thicker and generally orthokeratinized or parakeratinized
• Zones of the gingiva

  • Free or Marginal zone
  • Attached gingiva
  • Interdental zone (groove)
• Free gingival groove


  Indistinct groove on the surface of the epithelium separating the free & attached gingivae
• Interdental papilla


  Gingiva located between the teeth & extending high on the interproximal area of the crowns on the labial & lingual surfaces

  
• Col


  Concave zone of the gingiva that follows the contour of each crown, characterized by thin, nonkeratinized epithelium
• Hard palate


  Epithelium is thick orthokeratinized, stratified squamous epithelium
• Rugae


  Located at each side of the median raphe, supported by dense lamina propria
• Epithelial pearls


  Circular or concentrically arranged, keratinized epithelial cells, remnants of epithelium formed in the line of fusion of palatine processes, found mostly in the region of incisive papilla
• Both the hard & soft palates have mucous glands
• Lining or reflecting mucosa


  Does not function in mastication, adapts itself to the movements of cheeks, lips, & tongue & of the mandible, lines most of the surfaces of the oral cavity except the areas of masticatory mucosa & dorsum of the tongue, composed of a thin layer of junction between the oral mucosa & the epithelium & an underlying lamina propria, epithelium is composed of a basal layer of cuboidal cells, termed the stratum basale
• Keratinized epithelial cells


  Remnants of epithelium formed in the line of fusion of palatine processes