The purpose of the examination of jaw strength is to look for evidence of dysfunction of the motor component of the trigeminal (fifth) nerve in patients who are clinically suspected of having a lesion of this nerve.

Jaw strength needs to be tested only in patients who are suspected of having trigeminal nerve dysfunction, such as patients who complain of facial numbness.

The muscles that move the jaw—the masseters and the pterygoids—are supplied by motor branches of the trigeminal (fifth) cranial nerve that originate in the pons and reach the muscles by traveling through the mandibular (V3) division of the nerve. The action of the masseter muscle on each side is to close the jaw. The action of each pterygoid muscle is to pull the jaw forward toward the center; the left pterygoid muscle, therefore, pulls the jaw to the right, and the right pterygoid muscle pulls the jaw to the left.