Clinical Presentation of Temporomandibular Disorder (TMD) Practice Test

Opening the jaw is produced by muscles that pull the mandible downward or reposition the hyoid to permit downward movement. The muscles that close the jaw—masseter, temporalis, and medial pterygoid—are not involved in this action, so they aren’t the correct choice.

The lateral pterygoid helps open the mouth by protruding the mandible and guiding the condyle and articular disc forward, which facilitates downward movement of the lower jaw. At the same time, the hyoid muscles (the suprahyoid group, including digastric, mylohyoid, and geniohyoid) pull the hyoid bone upward and forward. This action assists depression of the mandible, especially when the jaw is being opened rather than closed.

Relying on the digastric alone misses the contribution of the other hyoid muscles, and overlooks the key role of the lateral pterygoid in initiating depression. That combination—lateral pterygoid with the hyoid muscles—best explains how the mandible is depressed.