The influence of clenching on head posture and body equilibrium

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The purpose of this study was to elucidate the relationship among teeth clenching, head posture and body equilibrium.Results were as follows,In comparison to the rest mandibular position, neck was flexed anteriorly in the VMC condition. In the condition of unilateral occlusal support, neck was bent laterally to the occlusal support side. Positive correlation was found between the asymmetry index of the jaw closing muscles and the sternocleidomastoid muscle under both the eyes-closed condition (r=0.57, p<0.05) and the eyes-opened condition (r=0.78, p<0.05). Positive correlation was found between the asymmetry index of the sternocleidomastoid muscle and the angle of the lateral bending (r=0.43, p<0.05). From these results, it was suggested that there is a close relationship between occlusion and head posture.Against the impact load disturbing the body balance, cooperative movement between the head and body was observed during the dynamic event in 10%, 50%, and 100%VMC and RP. From the analysis of head movement, the maximum angle of lateral bending and rotation in RP was statistically greater than those in 10%, 50% and 100%VMC (p<0.05). From the analysis of head movement and body sway, total locus length in RP was statistically greater than those in 10%, 50% and 100%VMC (p<0.05). From the analysis of EMG activity, as the clenching force increased, the measurement of sternocleidomastoid muscle activity statistically increased (p<0.05). It is speculated from these results that the teeth clenching suppresses the head movement and body sway during the dynamic event. This speculation is supported by previous studies that activities of sternocleidomastoid muscles are synchronized to activities of jaw closing muscles during VMC.It is concluded that stomatognathic function and body equilibrium have an interdependent relationship.