Influence of Teeth Clenching on the Bodily Equilibrium against Striking Weight Impact

Purpose: The purpose of this study was to elucidate the influence of teeth clenching on the head posture and body sway during an impact lord to the greater trochanter of the femur.Methods: The sternocleidomastoid muscle activities, head posture, and the total locus length of head movement and body sway during and in the absence of a striking weight impact under the resting position of the mandible and during 50% and 100% voluntary maximal clenching were analyzed.Results: 1) The activity of the sternocleidomastoid muscles increased with the teeth clenching force, and the increase was greater during a striking weight impact than that in the absence of a striking weight impact. 2) The decrease in the lateral bending and rotation angles of the neck observed during a striking weight impact was greater under the voluntary teeth clenching conditions as compared with that under the resting position of the mandible. 3) The total locus length of the head movement and body sway were shorter under the voluntary teeth clenching conditions as compared with that under the resting position of the mandible. 4) In contrast to the observations under the resting position of the mandible during a striking weight impact, the ratio of the total locus length of the head movement to that of the body sway under the voluntary teeth clenching during a striking weight impact decreased to the level noted under the resting position of the mandible in the absence of a striking weight impact.Conclusion: The results of this study suggest that teeth clenching stabilizes the head in cooperation with the activities of the sternocleidomastoid muscles, and prevents excessive head movement and body sway during a striking weight impact.