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Oral Cavity and Salivary Glands — Seminar Notes

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1. ORAL CAVITY — Overview

Boundaries

Two Compartments

1. Oral Vestibule — horseshoe-shaped space between dental arches and cheeks/lips
2. Oral Cavity Proper — inner space enclosed by the dental arches

Seven Anatomic Subsites (clinically important)

1. Lips
2. Oral tongue (anterior 2/3)
3. Floor of mouth
4. Buccal mucosa
5. Gingiva / alveolar ridges (upper and lower)
6. Retromolar trigone (RMT)
7. Hard palate

Functions

• Digestion: mastication + initial chemical breakdown (salivary amylase)
• Speech: modulates sounds from the larynx; palate, tongue, teeth act as articulators
• Breathing: alternate airway when nasal passages are obstructed
• Dental access: rubber dams prevent debris passage into airway

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2. WALLS AND SKELETAL FRAMEWORK

Bones Contributing to the Oral Cavity

• Maxillae — form anterior 2/3 of the hard palate (via palatine processes)
• Palatine bones — form posterior 1/3 of hard palate (horizontal plates); contain the greater palatine foramen (transmits greater palatine nerve + vessels) and lesser palatine foramen (transmits lesser palatine nerve → soft palate)
• Mandible — movable lower jaw; establishes separation between dental arches
• Sphenoid, temporal, hyoid — associated muscular attachments

Incisive Canal

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3. TONGUE

Surface Features

Innervation

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4. PALATE

Hard Palate

• Formed by palatine processes of maxillae (anterior 2/3) and horizontal plates of palatine bones (posterior 1/3)
• Sensory: maxillary nerve (V2) via greater/lesser palatine nerves and nasopalatine nerve

Soft Palate

• Posterior muscular extension; can be raised to close off nasopharynx (during swallowing/speech)
• All muscles innervated by vagus nerve (X) via pharyngeal plexus — except tensor veli palatini (innervated by V3)

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5. INNERVATION OF THE ORAL CAVITY

• Upper cavity (palate, upper teeth): maxillary nerve (V2)
• Lower cavity (lower teeth, anterior tongue): mandibular nerve (V3)

• Anterior 2/3 of tongue → facial nerve (VII)
• Posterior 1/3 → glossopharyngeal nerve (IX)

• Parasympathetic (secretomotor): carried by CN VII branches → submandibular & sublingual glands; and CN IX → parotid gland
• Sympathetic: from T1 → superior cervical ganglion → travel with trigeminal branches

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6. SALIVARY GLANDS

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6A. MAJOR SALIVARY GLANDS

1. Parotid Gland

• Largest of the three major glands
• Located in a shallow triangular space bounded by:
  • Posteriorly: sternocleidomastoid muscle
  • Anteriorly: ramus of mandible
  • Superiorly: external acoustic meatus + posterior zygomatic arch
• Extends over the masseter muscle anteriorly and posterobelly of digastric inferiorly
• Stensen's duct (parotid duct): passes anteriorly across the masseter → turns medially → penetrates the buccinator → opens at the parotid papilla opposite the crown of the 2nd upper molar
• Encloses: external carotid artery, retromandibular vein, facial nerve (VII) (extracranial portion)
• Secretion: purely serous (watery, high enzyme content)
• Produces ~2/3 of mouth's saliva when stimulated

2. Submandibular Gland

• Hook-shaped gland; smaller than parotid, larger than sublingual
• Superficial (larger) part: lies in submandibular fossa (below mylohyoid line, outside oral cavity proper), against medial surface of mandible
• Deep part: loops around posterior margin of mylohyoid → enters floor of oral cavity; lies lateral to root of tongue on hyoglossus
• Wharton's duct: emerges from deep part → passes forward → opens at sublingual caruncle (papilla) beside the base of the frenulum of the tongue
• The lingual nerve loops under Wharton's duct — crosses first lateral then medial as it descends
• Secretion: mixed (serous + mucous) — thicker saliva; produces 2/3 of mouth's saliva when unstimulated

3. Sublingual Gland

• Smallest of the three major glands
• Almond-shaped; immediately lateral to Wharton's duct and lingual nerve in floor of oral cavity
• Rivinus ducts (multiple): drain directly into floor of mouth or join the submandibular duct
• Secretion: mainly mucous

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Summary Table — Major Salivary Glands

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6B. MINOR SALIVARY GLANDS

• 600–1000 small glands embedded in the mucosa and submucosa of lips, cheeks, tongue, palate, and floor of mouth
• Secrete mainly mucous; primarily lubricate the oral mucosa
• 5% of salivary gland tumors arise here, but ~80% of these are malignant — clinically important!

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7. HISTOLOGY OF SALIVARY GLANDS

Ductal Architecture

• Acini: secretory end-pieces; surrounded by myoepithelial cells (contract to expel saliva)
  • Serous acini (parotid): produce watery, protein-rich secretion
  • Mucous acini (sublingual, minor glands): produce viscid, mucin-rich secretion
  • Mixed acini (submandibular): both types, often with serous demilunes capping mucous acini
• Intercalated ducts: small caliber; lined by low cuboidal cells
• Striated ducts: lined by columnar cells with basal striations (abundant mitochondria) — responsible for ion modification of saliva
• Excretory ducts: larger, stratified epithelium

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8. SALIVA — Composition and Functions

Composition (Whole Saliva)

• 99.5% water; specific gravity 1.002–1.012; pH 6.2–7.4
• Produced at ~1500 mL/day

Functions of Saliva

1. Digestion: salivary amylase initiates starch hydrolysis
2. Lubrication: mucins coat food bolus, aiding swallowing
3. Dental protection: bicarbonate buffers plaque acids; calcium/phosphate promote remineralization
4. Antimicrobial: secretory IgA (sIgA), lysozyme, lactoferrin, leukotaxins, opsonins
5. Taste: dissolves food molecules, delivering them to taste receptors
6. Wound healing: growth factors (EGF) in saliva

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9. AUTONOMIC INNERVATION OF SALIVARY GLANDS

• Parasympathetic stimulation (via ACh/muscarinic M3) → increased watery saliva (IP3 → Ca²⁺ mobilization → fluid secretion)
• Sympathetic stimulation (β-adrenergic) → protein-rich secretion (cAMP → protein exocytosis)

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10. DISORDERS OF THE SALIVARY GLANDS

A. Infectious

B. Non-infectious

C. Neoplastic Disease

Key Rule: The smaller the gland, the higher the malignancy rate.

• Pleomorphic adenoma — most common salivary neoplasm overall; 85% in parotid (90% in superficial lobe tail); slow, painless, firm; mixed epithelial + myoepithelial + stromal elements; Rx: excision with cuff of normal tissue; risk of malignant transformation to carcinoma ex-pleomorphic adenoma
• Warthin tumor (papillary cystadenoma lymphomatosum) — 2nd most common parotid tumor; older white males, smokers; bilateral in 10%; Tc-99m uptake on scan; Rx: excision
• Oncocytoma — elderly; Tc-99m uptake; sheets of granular oncocytes

Poor prognostic signs: pain, CN VII involvement, fixation to adjacent structures.

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11. TEETH AND DENTAL FORMULA

• Deciduous (primary): 20 teeth
• Permanent: 32 teeth — numbered superiorly right to left (1–16), inferiorly left to right (17–32)
• Each quadrant: 2 incisors, 1 canine, 2 premolars, 3 molars

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Quick Revision Summary

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