Anatomy of the Submucosa Layer

The Submucosa Layer

• Divided into irregular compartments by dense bands of fibrous tissue, perpendicular to the underlying bone.
• Compartments filled with adipose tissue in the anterior lateral zone and with palatine salivary gland in posterior lateral zone.
• Acts as a cushion due to the presence of fat.
• Thicker in the posterior than in the anterior.

The Gingival Zone and the Palatine Raphe

• Do not have a submucosa.
• The lamina propria is attached to the periosteum (mucoperiosteum).

Incisive Papilla

• Formed by dense connective tissue.
• Contains the oral parts of vestigial nasopalatine ducts (Jacobson's organ).

Palatine Rgae

• Ridges of mucous membrane extending laterally from the incisive papilla.
• Core made up of dense connective tissue.

Anterolateral and Posterolateral Regions

• Have a prominent submucosa.
• Submucosa filled with adipose tissue in the anterior lateral zone and with palatine salivary gland in posterior lateral zone.

Histological Structure of the Antero-lateral and Postero-lateral Zones

• Based on function: Masticatory mucosa, lining mucosa, and specialized mucosa.

Gingiva

• Part of the oral mucous membrane that covers the alveolar process and surrounds the teeth like a collar.
• Extends from the dentogingival junction to the alveolar mucosa.
• Normally pale pink in color and firm in consistency.
• Surface appears stippled.
• Divided into free gingiva, attached gingiva, and interdental papilla.

Functions of the Oral Mucosa

• Sensation: temperature, touch, pain, taste buds, and reflexes like swallowing, gagging, and salivating.
• Lubrication: salivary secretion.
• Protection: protects the deeper tissues.
• Thermal regulation: important in dogs, not in humans.

Structure of the Oral Mucosa

• Consists of three main parts: epithelium, lamina propria, and submucosa.
• Epithelium is of stratified squamous variety, which may be keratinized or non-keratinized.
• Cells of the epithelium are of two types: progenitor cells and maturing cells.

Epithelium

• All oral mucosa epithelium is stratified squamous type.
• May be keratinized or non-keratinized.
• Keratinized mucosa is seen on the hard palate and gingiva.
• In keratinizing oral epithelium, the cells are arranged in four layers: basal cell layer, prickled cell layer, granular cell layer, and cornified cell layer.

Keratinized Epithelium

• Stratum basale: a single layer of cuboidal cells capable of undergoing mitosis.
• Stratum spinosum: polyhedral cells with prominent intercellular bridges (desmosomes).
• Stratum granulosum: a layer of cells with prominent granules.
• Stratum corneum: a layer of dead cells.

Submucosa

• Consists of connective tissue of varying thickness and density.
• Glands, blood vessels, nerves, and adipose tissue are present in this layer.
• Attaches the epithelium to the underlying structures, whether this attachment is loose or firm depends on the character of the submucosa.
• Larger arteries divide into smaller branches, which then enter into the lamina propria.

Classification of Oral Mucosa

• Based on function: Masticatory mucosa, lining mucosa, and specialized mucosa.
• Masticatory mucosa: Gingiva and Hard Palate.
• Lining mucosa: Cheek mucosa, inner side of the lip, alveolar mucosa, oral vestibule, inferior surface of the tongue, and soft palate.
• Specialized mucosa: Dorsal surface of the tongue.

Hard Palate

• Lined by keratinized stratified squamous epithelium.
• Divided into various zones based on the structure of the sub mucous layer.
• Zones: Palatine gingiva, Medial Palatine raphe, Palatine rugae, Anterolateral (fatty) zone, Posterolateral (glandular) zone, and Incisive papilla.

Microscopical Structure of Hard Palate

• Epithelium: The oral side of the hard palate is covered by ortho keratinized epithelium, while the nasal side is lined by pseudostratified columnar epithelium with Goblet cells.
• Lamina propria: Consists of dense connective tissue that is thicker in the anterior than in the posterior parts of the palate and has numerous long papillae.