Mouth-opening Exercises Produce a Decrease in Pain Perception in Patients with Disk Displacement with Reduction

This study was intended to determine whether mouth-opening exercise reduces pain sensitivity in remote regions as well as in the trigeminal region. Seven female subjects with disk displacement with reduction were asked to perform a three-minute repetitive mouth opening and closing exercise (exercise A) and a three-minute continuous mouth opening exercise (exercise B) on two separate days. Sensory/nociceptive perception thresholds were measured at the point over the right masseter and the skin overlying the volar aspect of the right forearm immediately after exercises A and B, and were compared to data in which no exercise was performed (baseline). Significant elevation in the heat-induced pain threshold was seen as a result of both exercises in the cervical region and in the trigeminal region. Also, a significant elevation in the cold-induced pain threshold was seen after exercise B in the cervical region. Further, there was a tendency toward a higher warm sensation threshold after exercise A in the cervical region. These results indicate that mouth opening training produces non-segmental analgesic effects mediated by C fiber and Adelta fiber.