Does clenching reduce indirect head acceleration during rugby contact?

BACKGROUND Concussions are common among athletes, with the potential to cause memory-related, physical, cognitive, emotional, and behavioral damage. A concussion is an acceleration/deceleration injury resulting from direct and indirect biomechanical forces transmitted to the cerebral tissues. From a sports dentistry viewpoint, increased mastication muscle activity or clenching due to the presence of a mouthguard may enhance cervical muscle activity, thereby reducing damage following impact. This relationship has not been previously investigated in the context of rugby. The purpose of this study was to investigate the effect of voluntary clenching on indirect head acceleration during attack- and defense-related drills. MATERIALS AND METHODS A total of 12 high school rugby players participated in the study. Linear acceleration of the head was measured using an accelerometer that took measurements in three axes. Masseter and sternocleidomastoid muscle activities were measured using wireless electromyography. These data were synchronized using digital video imaging software for analysis. The study protocol was approved by the Tokyo Dental College Ethics Committee. RESULTS AND CONCLUSIONS Within the limitations of this study, the following results were obtained: the activities performed during rugby practice involved relatively small indirect head acceleration and masseter and sternocleidomastoid muscle activities. After the young male rugby players were instructed to clench their masseter muscles, a marked decrease in head acceleration was observed.