Influence of Teeth Clenching on Bodily Equilibrium against Striking Weight Impact

目的：本研究的目的是阐明在对股骨大转子施加冲击载荷时，咬牙对头部姿势和身体摇摆的影响。方法：采用音频反馈系统控制下颌骨静止位、25%、50%、75%和100%自主最大握紧力，分析和讨论在有和没有显著重量冲击的情况下，胸锁乳突肌活动、头部姿势、头部运动轨迹总长度和身体摆动。结果与讨论：所得结果如下。1)胸锁乳突肌活动随握力的增加而增加，且有显著重量冲击时的活动大于无显著重量冲击时的活动。2)与非咬牙组相比，咬牙组受冲击性重量冲击时颈部侧弯、旋转和前后屈角度减小。3)咬牙时头部运动轨迹和身体摆动轨迹的总长度比不咬牙时短。4)与不紧咬牙条件相反，在不紧咬牙条件下，不紧咬牙条件下，头部运动-身体摆动轨迹总长度与击打体重冲击的比值与不紧咬牙条件下相似。5)紧咬牙力与头部运动/身体摆动的关系无统计学意义。研究表明，咬牙与胸锁乳突肌协同稳定头部，防止头部运动和身体在重物冲击下的摇摆。也有人建议，自愿最大握紧力是不必要的，以防止头部运动和身体摇摆。

Objectives : The purpose of this study was to elucidate the influence of teeth clenching on head posture and body sway when making the impact load to the greater trochanter of the femur.Methods : Under the mandibular position at rest, 25%, 50%, 75% and 100% voluntary maximal clenching controlled by use of an audio feedback system, the sternocleidomastoid muscle activities, head posture, total locus length of head movement and body sway with and without the striking weight impact were analyzed and then discussed.Results and Discussion : The results obtained were as follows.1) The sternocleidomastoid muscle activities were increased with clenching force, and the activities with the striking weight impact were greater than that without the striking weight impact.2) The lateral bending, rotation and antero-postero flexion angle of the neck with the striking weight impact were decreased under the teeth clenching condition, compared to the non-clenching condition.3) The total locus length of head movement and body sway were shorter under the teeth clenching condition, compared to the non-clenching condition.4) Contrary to the non-clenching condition, under the teeth clenching condition, the ratio of the total locus length of head movement-body sway with the striking weight impact showed a similar value under the non-clenching condition without the striking weight impact5) There was no statistical significance in the relationship between clenching force and head movement / body sway.From the study, it was suggested that teeth clenching stabilized head in cooperation with the sternocleidomastoid muscle, and prevented the head movement and body sway with the striking weight impact. It was also suggested that the voluntary maximal clenching force was not necessary to prevent the head movement and body sway.