The term used to designate the side of the face, and limited in its forward extent by the naso-labial groove which runs from the side of the nose to the corner of the mouth.
The interior of the cheek is the mucous membrane of the mouth, which is confluent with the gums of upper and lower teeth and with the pharynx posteriorly. Salivary glands are in the mucosa deep to the muscular bulk of the cheek which is the buccinator (the mouth is the buccal cavity) which has a bone attachment to the maxilla and its fibres pass forward to blend with orbicularis oris the mouth’s sphincter equivalent to orbicularis oculi at the eye. Buccinator assists the tongue in moving food around inside the mouth while it is chewed between the teeth and mixed with saliva.
Superiorly the cheek is defined by the “cheek bone” in fact an arch of bone formed partly by maxilla, partly by zygoma and posteriorly by temporal bone. The temporalis muscle passes deep to the arch to insert into the coronoid process of the mandible.
Posteriorly, the well-defined masseter muscle would probably be considered the limit of the cheek area, it is in part covered by the largest of the salivary glands, the parotid gland, which extends forward into the cheek; when it is excised for cancer, it leaves an obvious difference in the symmetry of the face.
Some persons have what might be called a “chipmunk” appearance with well-defined swollen cheeks which must usually be due to an unusually thickly developed pad of fat; it is not seen in persons of lean build. In the opposite direction, the cheeks may appear sunken in those who have over-dieted or suffer from AIDS, and may appear ill-defined in those who have poorly developed zygomatic arches (cheek bones).