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Anatomy of the Oral Cavity

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I. INTRODUCTION AND OVERVIEW

1. Oral vestibule - Horseshoe-shaped space between the dental arches and the inner surfaces of the cheeks and lips. The oral fissure (mouth opening) opens into it.
2. Oral cavity proper - The main space enclosed within the dental arches.

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II. BOUNDARIES

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III. ROOF OF THE ORAL CAVITY - THE PALATE

A. Hard Palate (Anterior 2/3)

• Bony framework: Palatine process of maxilla (anterior) + Horizontal plates of palatine bones (posterior)
• Covering: Stratified squamous epithelium firmly attached to underlying bone
• Foramina:
  • Incisive foramen - midline anteriorly; transmits nasopalatine nerve and branch of sphenopalatine artery
  • Greater palatine foramen - palpable 1 cm medial to 2nd molar; transmits greater palatine nerve and descending palatine vessels
  • Lesser palatine foramen - posterior to greater palatine foramen; transmits lesser palatine nerve and artery to soft palate
• Sensory innervation: Nasopalatine nerve + greater palatine nerve (both from CN V2)
• Blood supply: Maxillary artery → descending palatine artery → greater palatine artery
• Lymphatics: Upper cervical lymphatics or lateral retropharyngeal nodes

B. Soft Palate (Posterior 1/3)

• Elevation: Closes the pharyngeal isthmus, sealing nasopharynx from oropharynx (prevents food reflux into nasopharynx during swallowing)
• Depression: Closes the oropharyngeal isthmus, sealing oral cavity from oropharynx (allows simultaneous chewing and breathing)

Note: Tensor veli palatini is the only soft palate muscle NOT supplied by the vagus nerve - it is supplied by CN V3.

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IV. LATERAL WALLS - THE CHEEKS

• Each cheek consists of: skin (external) → buccinator muscle → oral mucosa (internal)
• Buccinator muscle is the key muscle of the cheeks:
  • Origin: Pterygomandibular raphe, alveolar process of maxilla and mandible
  • Insertion: Blends with orbicularis oris at the modiolus (fibromuscular nodule at the angle of the mouth)
  • Function: Holds cheeks against alveolar arches, keeps food between teeth during chewing
  • Innervation (motor): Buccal branch of facial nerve [VII]
  • Innervation (sensory): Buccal branch of mandibular nerve [V3]
• The pterygomandibular raphe connects the buccinator anteriorly to the superior pharyngeal constrictor posteriorly, providing structural continuity between the oral and pharyngeal cavities.

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V. FLOOR OF THE ORAL CAVITY

1. Mylohyoid muscle (paired) - forms a muscular diaphragm filling the U-shaped gap between the two sides of the mandibular body
   • Origin: Mylohyoid line of mandible
   • Insertion: Body of hyoid bone and a median raphe
   • Innervation: Mylohyoid nerve (branch of inferior alveolar nerve, CN V3)
   • Function: Elevates floor of mouth and tongue during swallowing; depresses mandible
2. Geniohyoid muscles (paired, cord-like) - run above the mylohyoid, from mental spine of mandible to hyoid bone
   • Innervation: C1 fibers traveling with hypoglossal nerve
3. Tongue - overlies the geniohyoid muscles; the largest structure in the oral cavity

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VI. THE TONGUE

A. Division

• Anterior 2/3 (oral tongue) - lies within the oral cavity proper
• Posterior 1/3 (tongue base/pharyngeal surface) - lies in the oropharynx

B. Surface Features

C. Muscles of the Tongue

Key Rule: All tongue muscles are supplied by CN XII (hypoglossal), EXCEPT palatoglossus which is supplied by CN X (vagus nerve via the pharyngeal plexus).

D. Blood Supply of the Tongue

• Arterial: Lingual artery (2nd branch of external carotid artery)
• Venous: Lingual vein + vena comitans of the hypoglossal nerve (ranine vein)

E. Lymphatic Drainage of the Tongue

• Tip: Submental nodes (level I)
• Central anterior tongue: Bilateral submandibular and deep cervical nodes
• Lateral anterior tongue: Ipsilateral nodes (levels I-III), may skip to level IV
• Posterior tongue (base): Bilateral deep cervical (jugulodigastric) nodes - clinically important as carcinoma of tongue base metastasizes bilaterally

F. Nerve Supply - Sensory and Motor

• Anterior 2/3: Lingual nerve (branch of CN V3 - mandibular nerve)
• Posterior 1/3: Glossopharyngeal nerve (CN IX)

• Anterior 2/3: Chorda tympani (branch of CN VII - facial nerve), which joins the lingual nerve; fibers travel to geniculate ganglion → nucleus solitarius
• Posterior 1/3: Glossopharyngeal nerve (CN IX) → inferior petrosal ganglion → nucleus solitarius
• Epiglottic taste: Superior laryngeal nerve → Vagus (CN X) → nucleus solitarius

• All tongue muscles: Hypoglossal nerve (CN XII)
• Exception - Palatoglossus: Vagus nerve (CN X)

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VII. SALIVARY GLANDS AND DUCTS

Major Salivary Glands

• At rest: ~2/3 produced by the submandibular gland
• When stimulated: >1/2 produced by the parotid gland
• Total daily production: 1000-1500 mL/day (~1 mL/min)
• pH: slightly acidic (6-7)

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VIII. SKELETAL FRAMEWORK

• Maxillae (paired): Palatine process forms anterior 2/3 of hard palate; alveolar process carries upper teeth
• Palatine bones (paired): Horizontal plates form posterior 1/3 of hard palate
• Mandible: Bears lower teeth; body forms the lateral and anterior walls of the floor
  • Mylohyoid line on inner surface is the origin of the mylohyoid muscle
  • Mandibular foramen on medial ramus transmits inferior alveolar nerve and vessels
  • Retromolar triangle and pterygomandibular raphe attachment are located behind last molar
• Hyoid bone: U-shaped bone connecting the floor of oral cavity to the pharynx and larynx below
• Sphenoid: Contributes pterygoid hamulus (for tensor veli palatini and pterygomandibular raphe attachment)

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IX. NERVE SUPPLY SUMMARY

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X. BLOOD SUPPLY SUMMARY

• Upper oral cavity (palate, upper gingiva): Branches of maxillary artery (descending palatine, sphenopalatine)
• Lower oral cavity and tongue: Lingual artery and facial artery
• Cheeks and lips: Facial artery (superior and inferior labial branches)

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XI. LYMPHATIC DRAINAGE SUMMARY

• Upper lip and cheek: Parotid/pre-auricular and submandibular nodes
• Lower lip: Submental (midline) and submandibular (lateral) nodes
• Hard palate: Upper cervical and retropharyngeal nodes
• Tongue tip: Submental nodes
• Tongue body/base: Submandibular → deep cervical (jugulodigastric) nodes; base drains bilaterally

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XII. FUNCTIONS OF THE ORAL CAVITY

1. Digestion: Initial mechanical processing of food (mastication); initiation of enzymatic digestion by salivary amylase
2. Speech: Tongue, lips, teeth, and palate shape sounds produced by the larynx
3. Breathing: Alternative airway when nasal passage is obstructed; used clinically for endotracheal intubation
4. Swallowing: Oropharyngeal isthmus can be opened/closed by soft palate and tongue movements

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CLINICAL PEARLS (ENT Examination Context)

• Tongue deviation on protrusion: Toward the side of CN XII lesion (ipsilateral genioglossus is paralyzed; the intact contralateral side pushes tongue toward the affected side)
• Lingual thyroid / thyroglossal duct cyst: Both arise from incomplete descent of thyroid from the foramen cecum
• Ankyloglossia: Short frenulum restricting tongue movement; may affect speech and breastfeeding
• Submandibular duct stones (sialolithiasis): Wharton's duct is longer and more tortuous than other ducts; most common site for salivary calculi
• Parotid duct (Stensen's duct) pierces the buccinator opposite the upper 2nd molar - a landmark during cheek surgery
• Ludwig's angina: Rapidly spreading cellulitis of the submandibular space and floor of mouth - can elevate the tongue and cause airway compromise
• Unilateral soft palate palsy: Uvula deviates away from the lesion (intact levator pulls uvula to normal side)

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