Oral cavity

Cavitas oris

Also known as: mouth, buccal cavity

The oral cavity is the first part of the digestive tract, running from the lips to the oropharyngeal isthmus. Food is taken in, tasted, chewed and mixed with saliva here before it is swallowed.

Overview

The dental arches divide the oral cavity into two parts. The oral vestibule is the slit between the lips and cheeks on the outside and the teeth and gums on the inside. The oral cavity proper lies inside the dental arches. Its roof is the hard and soft palate, its floor is the mylohyoid muscle (the oral diaphragm) carrying the tongue, and behind it the oropharyngeal isthmus (fauces), bounded by the palatoglossal arches, opens into the oropharynx.

The lining is a mucous membrane of stratified squamous epithelium that varies with mechanical load. Masticatory mucosa on the gingivae and hard palate is keratinised and firmly bound down. Lining mucosa on the cheeks, lips, floor of mouth and ventral tongue is non-keratinised and mobile. Specialised mucosa on the dorsum of the tongue carries papillae and taste buds. Hundreds of minor salivary glands open throughout the mucosa, and the three pairs of major salivary glands drain into the cavity through ducts.

The mouth does more than handle food. It takes part in speech, acts as a secondary airway, and starts chemical digestion with salivary α-amylase and lingual lipase. Because its floor mucosa is thin and highly vascular, drugs such as glyceryl trinitrate can be absorbed sublingually and bypass first-pass hepatic metabolism.

Location

Lower face, below the nasal cavity. It is bounded by the lips in front, the cheeks at the sides, the palate above, the mylohyoid and tongue below, and the palatoglossal arches behind.

Parts & subdivisions

Oral vestibule

Space between the lips and cheeks and the teeth and gingivae. The parotid duct opens into it at the parotid papilla, opposite the maxillary second molar.

Oral cavity proper

Space inside the dental arches, mostly filled by the tongue when the mouth is closed.

Lips (labia oris)

Musculofibrous folds containing orbicularis oris, covered by skin outside, mucosa inside, and the red vermilion zone in between. The labial frenula attach them to the gums.

Cheeks (buccae)

Formed mainly by the buccinator muscle and the buccal fat pad. They keep food between the teeth during chewing.

Palate

Roof of the mouth: a bony hard palate in front and a muscular soft palate behind.

Teeth and gingivae

Two dental arches set in the alveolar processes of the maxillae and mandible.

Oropharyngeal isthmus

Opening into the oropharynx, bounded by the soft palate, the palatoglossal arches and the dorsum of the tongue.

Anatomy

Innervation

Sensory: the maxillary nerve (V2) supplies the palate and upper teeth and gums (greater and lesser palatine, nasopalatine and superior alveolar nerves). The mandibular nerve (V3) supplies the lower teeth and gums, cheek, floor of mouth and anterior tongue (inferior alveolar, buccal and lingual nerves). Motor: facial nerve (VII) to the lips and buccinator; hypoglossal nerve (XII) to the tongue.

Arterial supply

Branches of the external carotid artery: the facial artery (labial branches), the lingual artery, and the maxillary artery (alveolar, palatine and buccal branches).

Venous drainage

Into the pterygoid venous plexus and the facial and lingual veins, then the internal jugular vein.

Lymphatic drainage

Submental nodes (central lower lip, floor of mouth, tip of tongue) and submandibular nodes (most of the rest), draining to the deep cervical nodes.

Histology

Stratified squamous epithelium on a lamina propria with no muscularis mucosae. It is keratinised in masticatory mucosa and non-keratinised in lining mucosa. Minor salivary glands are numerous in the lips, cheeks and palate.

Function

Ingestion, and mastication with the teeth, tongue and cheeks.

Bolus formation and the voluntary (oral) phase of swallowing.

Start of chemical digestion (salivary α-amylase, lingual lipase).

Taste and general oral sensation, which trigger salivary and gastric cephalic-phase reflexes.

Articulation of speech; secondary airway.

Clinical significance

Oral squamous cell carcinoma

Tobacco, alcohol and betel quid are the main risks; HPV-16 is important for oropharyngeal tumours. The lateral border of the tongue and the floor of the mouth are high-risk sites. Persistent white (leukoplakia) or red (erythroplakia) patches are potentially premalignant. Spread is to the submandibular and deep cervical nodes.

Ludwig angina

A rapidly spreading cellulitis of the submandibular and sublingual spaces, usually from an infected lower molar whose roots lie below the mylohyoid line. The floor of the mouth swells and pushes the tongue up and back, threatening the airway.