If a person has hypermobility in the TMJ, which direction will the jaw deviate upon opening?

When a person has hypermobility in the temporomandibular joint (TMJ), it typically results in an altered pattern of movement during jaw opening. Specifically, the jaw will tend to deviate toward the uninvolved side as it opens. This occurs because the hypermobile side experiences excessive movement, allowing the other side—while it still maintains normal function—to pivot and guide the motion.

The biomechanics of jaw movement involve coordinated functions of the muscles and ligaments around the TMJ. In a case of hypermobility, the affected side can displace more than it normally would, causing the jaw to drift towards the opposite side during opening. This reactive motion leads to a compensatory adaptation where the structure shifts away from the side that is overly mobile, thus creating a deviation towards the uninvolved side.

In contrast, if there was a restriction or stiffness in the joint, the deviation would tend to favor the restricted side. Hence, understanding the mechanics of TMJ and how hypermobility affects movement is crucial to grasp the underlying principles of this condition.