Four pairs of muscles are considered the major muscles of mastication. These muscles are used for chewing and swallowing food. The masseter, the temporalis, and the medial pterygoid raise the mandible against the maxilla with considerable force. The fourth pair of muscles, the lateral pterygoids, acts to thrust the mandible forward. Acting with other muscles, it opens the mouth. a. Masseter. The masseter is one of the primary muscles that close the jaws and exerts pressure on the teeth, particularly in the molar region.
b. Temporalis. The temporalis muscle is a fan-shaped muscle that attaches along the side of the head. Like the masseter, it closes the jaws. Because of its posterior horizontal fibers, it can also pull the mandible backward.
c. Medial Pterygoid. Together with the masseter and temporalis muscles, the medial pterygoid muscle elevates the mandible against the maxilla. The combined action of the three muscles creates a very strong masticating pressure between the opposing maxillary and mandibular posterior teeth.
d. Lateral Pterygoid. The main action of the lateral pterygoid muscle is to draw the condyle and the articular disk forward while opening the mouth. This protrusive movement is accomplished when the right and left muscles act as one. Alternate contractions of the right and left muscles produce the sideward movements of the mandible used during mastication.
(1) Buccinator. The primary action of the buccinator (or cheek) muscle is to compress the cheek, thus moving food between the teeth during the chewing or grinding process.