Loss of directional orientation control of lower jaw movements in persons with internal derangement of the temporomandibular joint.

Lateral mandibular movements were performed on command by 50 patients with TMJ disk displacement associated with severe pain. In 22 patients the displacement was reversible, and in 28 patients it was permanent. An additional 50 patients with disorders of the masticatory system other than disk displacement were examined, as well as a group of 50 subjects without any signs or symptoms involving the masticatory system. The results showed that 22 patients (4 with reversible and 18 with permanent disk displacement) failed to move the mandible without tooth contact toward a predetermined direction and, instead, moved it in the opposite direction. The persons themselves were convinced that the direction of movement was correct. If finger pressure was applied to the joint area on the affected side, 25% of the patients with loss of directional control were able to move correctly. A normalization of the directional control was attained in 20% of the cases if lateral movements were performed with light tooth contact. All the patients with disorders of the masticatory system other than anterior disk displacement demonstrated a correct lateral mandibular movement pattern. In the control group, 2% demonstrated incapability of directional control of lateral jaw movements. The results indicate that loss of directional control of the lower jaw is associated with disk displacement.