Anatomy of the Mouth / Oral Cavity

Overview

• Roof - hard and soft palates
• Floor - muscular diaphragm (mylohyoid) and tongue
• Lateral walls - cheeks (buccinator muscle)
• Anterior opening - oral fissure, bordered by the lips

Two Regions

1. Oral vestibule - horseshoe-shaped space between the dental arches and the inner surfaces of the cheeks and lips.
2. Oral cavity proper - the inner space enclosed by the dental arches.

Skeletal Framework

• Paired: maxillae, palatine bones, temporal bones
• Unpaired: mandible, sphenoid, hyoid

Roof - The Palate

Hard Palate

• Bony plate covered by mucosa above (respiratory) and below (oral).
• Anterior 3/4 formed by the palatine processes of the maxillae; posterior 1/4 by the horizontal plates of the palatine bones.
• Mucosal features: transverse palatine rugae, a median palatine raphe, and anteriorly an incisive papilla overlying the incisive fossa (transmits nasopalatine nerve and greater palatine vessels).

Soft Palate

• A muscular, mobile extension of the hard palate posteriorly.
• Ends in the uvula - a small, tear-shaped muscular projection.
• Acts as a valve: depressed to close the oropharyngeal isthmus; elevated to seal off the nasopharynx from the oropharynx during swallowing.
• Formed by 5 paired muscles:

All soft palate muscles are innervated by the vagus nerve [X] via the pharyngeal plexus, except tensor veli palatini (innervated by the mandibular nerve [V3] via the nerve to medial pterygoid).

Floor of the Oral Cavity

The Tongue

Parts

• Oral (anterior 2/3) - in the oral cavity, horizontal surface bearing papillae; apex points forward behind the incisor teeth.
• Pharyngeal (posterior 1/3) - curves inferiorly into the vertical plane; covered by irregular mucosa with lingual tonsil (lymphoid nodules).
• Separated by the V-shaped terminal sulcus, at the apex of which is the foramen cecum (embryonic thyroglossal duct origin).
• The tongue is divided into left and right halves by a median fibrous septum.

Papillae (on dorsal surface of oral part)

Inferior Surface

• No papillae.
• A midline frenulum connects the tongue to the floor of the oral cavity.
• On each side of the frenulum: a lingual vein, and laterally a fimbriated (plica fimbriata) fold.

Muscles of the Tongue

Innervation of the Oral Cavity

• Maxillary nerve [V2] - upper parts: palate, upper teeth, upper gums
• Mandibular nerve [V3] - lower parts: lower teeth, anterior 2/3 of tongue (general sensation via lingual nerve)

• Anterior 2/3 of tongue - chorda tympani branch of facial nerve [VII]
• Posterior 1/3 of tongue - glossopharyngeal nerve [IX]

• Parasympathetic to glands: facial nerve [VII] (via chorda tympani to submandibular ganglion for submandibular/sublingual; via lesser petrosal to otic ganglion for parotid)
• Sympathetic from T1 via the superior cervical ganglion, travelling on blood vessels and trigeminal branches

Salivary Glands

Parotid Gland (largest)

• Located outside the oral cavity in a triangular space bounded by the sternocleidomastoid (behind), the ramus of the mandible (in front), and the external acoustic meatus/zygomatic arch (superiorly).
• Contains the external carotid artery, retromandibular vein, and the facial nerve [VII].
• Parotid (Stensen's) duct passes anteriorly over the masseter, then pierces the buccinator to open opposite the crown of the 2nd upper molar tooth.

Submandibular Gland

• Hook-shaped; the large superficial part lies below the mylohyoid in the submandibular triangle; the deep part hooks around the posterior border of mylohyoid into the floor of the oral cavity.
• Submandibular (Wharton's) duct runs forward and opens on the sublingual caruncle beside the frenulum.
• The lingual nerve loops beneath the submandibular duct (crossing lateral then medial) before entering the tongue.

Sublingual Gland (smallest)

• Located on the floor of the oral cavity beneath the tongue mucosa, resting on the mylohyoid muscle.
• Drains via multiple small ducts (ducts of Rivinus), some joining Wharton's duct, others opening directly onto the sublingual fold.

Blood Supply

• Upper oral cavity: branches of the maxillary artery (greater palatine, posterior superior alveolar, infraorbital arteries)
• Lower oral cavity and tongue: lingual artery (branch of external carotid); inferior alveolar artery (branch of maxillary)
• Venous drainage follows the arterial supply into the internal jugular vein.

Lymphatic Drainage

• Tip of tongue and lower lip → submental nodes → deep cervical nodes
• Body of tongue, floor of mouth, cheeks → submandibular nodes → deep cervical nodes
• Posterior tongue → directly to deep cervical (jugulodigastric) nodes
• Upper lip and cheek → parotid and buccal nodes → submandibular nodes

Functions of the Oral Cavity

1. Digestion - mechanical processing of food (mastication), lubrication and initial chemical digestion by saliva (amylase, lipase).
2. Deglutition - tongue shapes a bolus and propels it through the oropharyngeal isthmus.
3. Speech - the tongue, lips, teeth, and palate modify sounds produced by the larynx.
4. Breathing - the oral cavity can substitute for the nasal airway (pharynx is a shared food-air pathway).
5. Taste and sensation - taste buds on papillae and somatosensory receptors throughout the mucosa.