Oral cavity and
sublingual fold The mouth consists of two 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 the
hard palate. The floor is formed by the
mylohyoid muscles and is occupied mainly by the anterior two-thirds of the
tongue. A
mucous membrane – the
oral mucosa, lines the sides and under surface of the tongue to the
gums, and lines the inner aspect of the jaw (
mandible). It receives secretions from the
submandibular and
sublingual salivary glands. The posterior border of the oral cavity (ie, junction between the oral cavity and the
oropharynx) includes the junction of the
hard palate and the
soft palate superiorly, the
circumvallate papillae of the
tongue inferiorly, and the
retromolar trigone.
Lips The
lips come together to close the opening of the mouth, forming 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 (the
tissues that support the teeth) are innervated by the
maxillary and
mandibular nerves – 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 depression formed between the
philtral ridges between the upper lip and the nasal septum, formed where the
nasomedial and
maxillary processes meet during
embryo development. When these processes fail to fuse fully, a
cleft lip,
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 ==