Boundaries and Divisions of the Oral Cavity
Topographically, the oral cavity is bounded anteriorly by the lips, laterally by the cheeks, superiorly by the palate, and inferiorly by the muscular floor and the tongue. Posteriorly, this space is open and transitions into the pharynx via the isthmus of the fauces (isthmus faucium).
The jaws and their growing teeth divide the oral cavity into two functional zones:
- Oral vestibule (vestibulum oris) — the anterolateral part. This is a slit-like, horseshoe-shaped space bounded externally by the lips and cheeks, and internally by the gingivae and dental arches.
- Oral cavity proper (cavitas oris propria) — the posteromedial part, located posterior to the teeth.
Communication between the vestibule and the oral cavity proper occurs through natural gaps — the interdental spaces.
Oral Vestibule: Lips and Cheeks
The lips (labia oris) are folds consisting predominantly of skeletal muscle. They are covered by skin externally and mucosa internally. Three zones are distinguished in the structure of the lip: the cutaneous zone, the intermediate zone (where the skin lacks a stratum corneum), and the mucosal zone.
The upper lip (labium superius) is separated from the cheek by the nasolabial sulcus, and along the midline of its cutaneous surface runs the philtrum (philtrum), ending in a tubercle. The lower lip (labium inferius) is bounded inferiorly by the horizontal mentolabial sulcus. At the angles of the mouth, the lips merge to form the labial commissures (commissurae labiorum). Transitioning to the gingivae, the mucosa forms folds — the frenula of the upper and lower lips (frenulum labii superioris et inferioris). Motor innervation is provided by the facial nerve, while sensation is supplied by branches of the infraorbital and mental nerves.
The cheeks (buccae) also have cutaneous and mucosal linings. Within their thickness lies the buccinator muscle (m. buccinator), and between it and the masseter muscle is the buccal fat pad (corpus adiposum buccae). The buccal mucosa transitions gradually into the gingivae (gingivae).
Mucosa and Glands
The oral mucosa (tunica mucosa oris) forms various folds, frenula, and elevations. The submucosa of the lips is rich in small labial glands (glandulae labiales). The cheeks also contain their own glands: buccal glands (glandulae buccales), whose bodies lie between the bundles of the buccinator muscle, and molar glands (glandulae molares), located in the region of the last molar tooth.
Particular attention should be paid to the ducts of the salivary glands:
- The duct of the parotid salivary gland (ductus parotideus) pierces the cheek and opens at the level of the upper second molar.
- On the floor of the oral cavity is the sublingual caruncle (caruncula sublingualis), where the ducts of the submandibular and sublingual glands open.
- Extending from the caruncle is the sublingual fold (plica sublingualis).
Openings and Canals of Bony Structures
To supply blood and innervation to the oral cavity, a system of foramina and canals exists within the jaws and palate:
- The nasopalatine nerve (n. nasopalatinus) emerges from the nasal cavity onto the hard palate through the incisive canals/foramina (canales/foramina incisiva).
- The greater descending palatine artery and greater palatine nerve pass through the greater palatine canal (canalis palatinus major). They enter the oral cavity via the greater palatine foramen (foramen palatinum majus).
- Similarly, lesser palatine vessels and nerves emerge through the lesser palatine foramina (foramina palatina minora).
- Within the body of the mandible runs the mandibular canal (canalis mandibulae), into which the inferior alveolar vessels and nerve enter via the mandibular foramen (foramen mandibulae).
- On the facial surface of the mandible opens the mental foramen (foramen mentale), transmitting the mental artery, veins, and nerve (a., vv., n. mentales).
- On the medial surface of the mandible, the mylohyoid groove (sulcus mylohyoideus) is visible, lodging the artery and nerve branch of the same name.