Human mouth

Mouth cavity

The mouth, consists of 2 regions, the vestibule and the oral cavity proper. The vestibule is the area between the teeth, lips and cheeks. The oral cavity is bounded at the sides and in front by the alveolar process (containing the teeth) and at the back by the isthmus of the fauces. Its roof is formed by hard palate and soft palate and the floor is formed by the mylohyoid muscles and is occupied mainly by the tongue. Mucous membrane lines the sides and under surface of the tongue to the gum lining the inner aspect of the jaw mandible. It receives the secretions from the submaxillary and sublingual salivary glands.

Orifice

While shut, the orifice of the mouth forms a line between the upper and lower lip. In facial expression, this mouth line is iconically shaped like an up-open parabola in a smile, and like a down-open parabola in a frown. A down-turned mouth means a mouth line forming a down-turned parabola, and when permanent can be normal. Also, a down-turned mouth can be part of the presentation of Prader-Willi syndrome.

Nerve supply

The teeth and the periodontium (i.e. the tissues that support the teeth) are innervated by the maxillary and mandibular divisions of the trigeminal nerve. Maxillary (upper) teeth and their associated periodontal ligament are innervated by the superior alveolar nerves, branches of the maxillary division, termed the posterior superior alveolar nerve, anterior superior alveolar nerve, and the variably present middle superior alveolar nerve. These nerves form the superior dental plexus above the maxillary teeth. The mandibular (lower) teeth and their associated periodontal ligament are innervated by the inferior alveolar nerve, a branch of the mandibular division. This nerve runs inside the mandible, within the inferior alveolar canal below the mandibular teeth, giving off branches to all the lower teeth (inferior dental plexus). The oral mucosa of the gingiva (gums) on the facial (labial) aspect of the maxillary incisors, canines and premolar teeth is innervated by the superior labial branches of the infraorbital nerve. The posterior superior alveolar nerve supplies the gingiva on the facial aspect of the maxillary molar teeth. The gingiva on the palatal aspect of the maxillary teeth is innervated by the greater palatine nerve apart from in the incisor region, where it is the nasopalatine nerve (long sphenopalatine nerve). The gingiva of the lingual aspect of the mandibular teeth is innervated by the sublingual nerve, a branch of the lingual nerve. The gingiva on the facial aspect of the mandibular incisors and canines is innervated by the mental nerve, the continuation of the inferior alveolar nerve emerging from the mental foramen. The gingiva of the buccal (cheek) aspect of the mandibular molar teeth is innervated by the buccal nerve (long buccal nerve).

Development

The philtrum is the vertical groove in the upper lip, formed where the nasomedial and maxillary processes meet during embryo development. When these processes fail to fuse fully, either a hare lip or cleft palate, (or both) can result.

The nasolabial folds are the deep creases of tissue that extend from the nose to the sides of the mouth. One of the first signs of age on the human face is the increase in prominence of the nasolabial folds.

Function

The mouth plays an important role in eating, drinking, breathing and speaking. Infants are born with a sucking reflex, by which they instinctively know to suck for nourishment using their lips and jaw. The mouth also helps in chewing and biting food.

Clinical significance

Mouth ulcers are common and can occur singly or in clusters.

Society and culture

Lips can be adorned with lipstick or lip gloss, although in most cultures, this is typically only practiced by females. Both men and women, however, apply lip balm in order to soothe chapped or dry lips.

Piercings in or around the area of the mouth have been made popular by younger generations, including those on the lip or tongue. The uvula piercing, while increasing in popularity, remains relatively rare.