Masseters

Masseters are a pair of thick facial muscles that form part of the muscles of mastication. They lie in the cheek region, superficial to the pterygoid muscles, and contribute to the contour of the lower face. Each masseter originates from the zygomatic arch and has fibers that extend to the mandible, attaching mainly to the angle and lower ramus, with some fibers reaching the coronoid process. The muscle is described as having superficial and deep parts, which differ in fiber direction and insertion.

They are innervated by the masseteric nerve, a branch of the mandibular division (V3) of the trigeminal nerve. Blood supply principally comes from the masseteric artery, a branch of the maxillary artery.

Function: the primary action is elevation of the mandible, closing the jaws, enabling biting and chewing. The muscle can also contribute to protrusion of the mandible and, depending on fiber orientation, to lateral movement during mastication.

Development and anatomy: masseters develop from the first pharyngeal (mandibular) arch. They are paired symmetrical muscles with similar size in typical anatomy.

Clinical relevance: masseteric hypertrophy can occur with bruxism or heavy chewing and may alter facial contour. Injections of botulinum toxin into the masseter are used in some cases to reduce bite force or treat cosmetic prominence. Rarely, masseteric spasm or pain can occur due to overuse or injury.