Anterior disc displacement in the temporomandibular joint (TMJ) most likely involves dysfunction of which muscle?

The lateral pterygoid muscle has two heads. The inferior head protracts and depresses the mandible. The superior head inserts on the articular disc and condyle of the TMJ and is active during jaw closure to stabilize the disc. Spasm or hyperactivity of the superior head of the lateral pterygoid muscle is believed to pull the disc anteriorly, contributing to anterior disc displacement (internal derangement). MRI studies have confirmed pathological signal changes in the superior head of the lateral pterygoid in patients with disc displacement. The medial pterygoid, masseter, and temporalis do not insert on the articular disc.