Oral Mucosa

Oral Mucosa

Definition

  • Mucous Membrane: Moist lining of the intestinal tract, nasal passages, and other body cavities communicating with the exterior.
  • Oral Mucous Membrane (Oral Mucosa): Moist lining of the oral cavity that is continuous with the skin at the lips and the lining of the intestine at the pharynx.

Main Types of Oral Mucosa

  1. Masticatory Mucosa:

    • Has keratinized epithelium due to abrasive forces (biting, grinding).
    • Includes:
      • Gingiva
      • Hard palate

  2. Lining Mucosa:

    • Acts as a protective lining in sheltered areas.
    • Includes:
      • Firmly Attached Lining Mucosa:
        • Covering of the soft palate
        • Covering of the lips
        • Covering of the cheeks
        • Covering of the inferior surface of the tongue
        • Covering of the tonsils
      • Loosely Attached Lining Mucosa:
        • Alveolar mucosa
        • Vestibular mucosa
        • Mucosa of the floor of the mouth (sublingual sulcus)

  3. Specialized Mucosa:

    • Rough and irregular due to protruding papillae.
    • Possesses taste buds.
    • Includes:
      • Dorsum of the tongue
        • Anterior 2/3 (masticatory)
        • Posterior 1/3 (lining)

Functions of the Oral Mucosa

  1. Protection:

    • Separates and protects deeper tissues and organs from the oral cavity environment.
    • Acts as a barrier against mechanical forces (biting, chewing, abrasion).

  2. Sensation:

    • Receptors respond to temperature, touch, pain, and taste.
    • Certain receptors respond to the taste of water.
    • Initiates reflexes of swallowing, gagging, retching, and salivating.

  3. Permeability & Absorption:

    • The floor of the mouth is the thinnest and most permeable region.
    • Certain drugs (e.g., nitroglycerin for angina pectoris) are absorbed sublingually.

  4. Secretion:

    • Saliva maintains a moist surface; sebaceous glands are present but insignificant.

  5. Thermal Regulation:

    • In some animals, mucosa dissipates heat through panting. In humans, it plays no role in regulating body temperature.

Histologic Characteristics of Oral Mucosa

  • Consists of two layers:

    1. Surface Epithelium:

      • Keratinized
        • Fully keratinized (orthokeratinized)
        • Parakeratotic (incomplete hornified)
      • Non-keratinized

    2. Lamina Propria:

      • Papillary layer
      • Reticular layer
Layers of Keratinized Epithelium
  • Keratinous layer or stratum corneum
  • Granular layer or stratum granulosum
  • Prickle cell layer or stratum spinosum
  • Basal cell layer or stratum basale
  • Basal lamina (basement membrane or membrana propria)
Layers of Non-Keratinized Epithelium
  • Superficial layer (stratum superficiale)
  • Intermediate layer (stratum intermedium)
  • Basal cell layer (stratum basale)
  • No stratum corneum and stratum granulosum
Lamina Propria

  • Papillary Layer:

    • Connective tissue papillae that indent the epithelium (may be short or absent in some mucosa)

  • Reticular Layer:

    • Consists of densely arranged connective tissue fibers.

Clinical Features of Oral Mucosa

  1. Color:

    • More deeply colored than skin, especially at the lips.
    • Factors affecting coloration:
      • Concentration and state of dilation of small blood vessels in the underlying connective tissue
      • Thickness of the epithelium
      • Degree of keratinization
      • Amount of melanin in the epithelium
    • Color indicates the clinical condition (e.g., inflamed tissues are red, normal tissues are pink).

  2. Surface:

    • Moist and lacks appendages (e.g. hair follicles, sweat glands).
    • Minor salivary glands are present; sebaceous glands (Fordyce's spots - pale yellow spots) may be present in the upper lip and buccal mucosa.
    • Smoother and has fewer folds or wrinkles than skin, but topographic features like lingual papillae, rugae of hard palate, and gingival stippling are apparent.

  3. Firmness and Texture:

    • Varies considerably.
    • The gingiva and hard palate are covered by a firm, immobile layer, important for local anesthesia and biopsies.

Gingiva

  • Part of the firm oral masticatory mucosa.
  • Surrounds the necks of the teeth.
  • Covers the alveolar processes of the jaws.
  • Color: normally pink or coral pink, sometimes with grayish tinge. It May be pigmented brown or black.
Clinical Parts of the Gingiva

  • Free Gingiva:

    • Freely movable, not attached to underlying structures.
    • Marginal gingiva tapers to a knife-like edge, extending along the cervical level of the tooth.

  • Attached Gingiva:

    • Attached to the teeth and bone.
    • Possesses stippling (tiny pinpoint depressions).

  • Interdental Papilla:

    • Fills the space between the teeth.
    • Pyramidal or triangular shape in the anteriors, tent-shaped in the posteriors (with a valley called the col).
Free Gingival Groove
  • Slight indentation separating the free gingiva from the attached gingiva.
Gingival Sulcus
  • Gingival crevice
  • A shallow groove between the free gingiva and the tooth extending around the circumference of the teeth.
  • Depth varies from 0−60-6 mm; average depth is 1.81.8 mm.
Mucogingival Junction
  • Separates the attached gingiva from the alveolar mucosa.
Alveolar Mucosa
  • Present only in the vestibular region.
  • Extends from the mucogingival junction to the vestibular fornix.
  • Movable and deep red in color with a smooth surface.

Dentogingival Junction

  • The interface between the gingiva and the tooth surface. Characterized by 2 attachment mechanisms:

    1. Epithelial Attachment:

      • Attached Epithelial Cuff: Part of the gingival epithelium attached to the surface of the tooth.
      • Consisting of 3−43-4 layers of cells initially then Increases to 10−2010-20 rows of cells with age.

    2. Connective Tissue Attachment:

      • The fibers bundles of the gingival connective tissue that insert into the supraalveolar cementum.
      • Occurs between the crest of the alveolar bone or interdental bony septum and cementoenamel junction
Fundamental Compartments of the Dentinogingival Junction

  1. Junctional Epithelium:

    • Epithelial part of the free gingiva (not visible from outside).
    • Forms a collar around the neck of the tooth on the cervical enamel.
    • Forms and supports the epithelial attachment and is continuous with the oral sulcular epithelium.

  2. Oral Sulcular Epithelium:

    • Lines the lateral wall of the gingival sulcus.
    • Continuous with the occlusal end of the junctional epithelium and oral gingival epithelium.

  3. Oral Gingival Epithelium:

    • Part of the epithelial lining of the entire oral cavity.
    • Covers the vestibular and lingual/palatal surfaces of the marginal and alveolar gingiva and the interdental gingival papillae.

Histology of Gingiva

  • Epithelium:

    • Stratified squamous type, smooth in free gingiva, stippled in attached gingiva.
    • Types of gingival epithelium:
      • Fully keratinized (15%)
      • Parakeratinized (75%)
      • Non-keratinized (10%)

  • Lamina Propria:

    • Consists of dense connective tissue, not highly vascular.
    • Fibroblasts are abundant, macrophages, plasma cells, and lymphocytes are present.

  • Blood & Nerve Supply:

    • Blood supply of the gingiva is derived from periosteal vessels in the periosteum of the alveolar process and intraalveolar arteries.
    • Innervated by terminal branches of periodontal nerve fibers and by the alveolar branches of the infraorbital and palatine or lingual, mental & buccal nerves

Gingival Ligament / Supra-Alveolar Fiber Apparatus

  1. Dentogingival Fibers:

    • Most numerous.
    • Radiate from the supra-alveolar cementum into the free and attached gingiva.
    • Groups:
      • Extend from cementum to the connective tissue papilla between the oral sulcular epithelium & oral gingival epithelium.
      • Stream horizontally from cementum to free gingival margin.
      • Run from the cementum to the attached gingiva covering the alveolar process.

  2. Dentoperiosteal Fibers:

    • Inserts from the supra-alveolar cementum to the periosteum of the outer and inner cortical plates of the alveolar process.

  3. Alveologingival Fibers:

    • Inserts into the crest of the alveolar bone to the free and attached sections of the marginal and interdental gingiva.

  4. Circular & Semi-circular Fibers:

    • Circular fibers form a band around the neck of the tooth to bind the free gingiva to the tooth.
    • Semi-circular fibers inserts in the interdental cementum and encircle only the vestibular or oral half of the root

  5. Transseptal Fibers:

    • Binds the supra-alveolar cementum of one tooth to that of the adjacent tooth (interdental ligament).

  6. Transgingival & Intergingival Fibers:

    • Transgingival fibers inserts interdentally into supra-alveolar cementum, pass obliquely to the interdental tissue and stream to the free gingiva of the adjacent tooth, where they unite with the circular fibers
    • Intergingival fibers forms a continuous series of fibers running under the epithelium along both the vestibular & oral aspect of the dental arch, converging distal to the last molars

  7. Interpapillary Fibers:

    • Cross through the free portion of interdental gingival tissue in an orovestibular direction to tie the oral and vestibular gingival papillae together

  8. Periosteogingival Fibers:

    • Inserts into the periosteum of the outer and inner cortical plates of the alveolar process and pass facially and orally into the section of all attached gingiva lying over it

  9. Intercircular Fibers:

    • Located on the vestibular and oral sides of the interdental gingiva, they connect the circular fiber bundles of neighboring teeth and form part of the intergingival fiber bundles.
Functions of the Supra-Alveolar Fiber Apparatus
  • Supports the junctional epithelium.
  • Gives the free segments of the marginal and interdental gingiva their characteristic turgor, resistance to tearing, and their flat shape.
  • Secures against shearing forces.
  • Attaches the gingival tissue to the supra-alveolar cementum and to the crest of the alveolar bone stabilizing the position of the teeth and unite the teeth of one jaw into a continuous dental arch.

Passive Eruption

  • The gradual exposure of the crown by the separation of the epithelial attachment from the tooth surface and by the recession of the gingiva.
Stages of Passive Eruption

  1. 1st Stage:

    • Bottom of gingival sulcus is on enamel region & end of epithelial attachment is at CEJ.

  2. 2nd Stage:

    • Bottom of gingival sulcus still in enamel region, end of epithelial attachment is at cervical part of the root.

  3. 3rd Stage:

    • Bottom of the gingival sulcus is at CEJ, entire epithelial attachment is on cementum surface.

  4. 4th Stage:

    • Bottom of sulcus and epithelial attachment are on the cementum surface.

Clinical Considerations

  • Loose connective tissue submucosa leads to swelling and rapid spread of infection.
  • Denture attachment should be on firm oral mucosa.
  • Local anesthesia should be made into loose connective tissue such as the vestibular fornix and areas between the marginal and hard palate
  • In young individuals, clinical crown are smaller than the anatomical crown
  • If artificial crowns have been constructed, they need replacement when the gingiva has receeded
  • In young persons, extra care must be taken during cavity preparation not to injure the gingiva to avoid premature recession
  • When the root has been exposed by recession, preparation of gingival floor need not extend to the gingiva
  • Keratinization can be induced by mechanical stimulation and serves as a natural protection.

Systemic Diseases Manifested in Oral Mucosa

  • Measles: Small red spots with bluish center in the mucous membrane of the cheeks (Koplik's spots).
  • Scarlet fever: Strawberry tongue.
  • Stomatitis: Inflammation of Oral Mucosa
  • Gingivitis: Inflammation of gingiva
  • Glossitis: Inflammation of tongue