In order to examine the relationship between occlusal support and head posture, the electromyographic (EMG) activities of the jaw closing muscles and the sternocleidomastoid muscle during voluntary maximal clenching (VMC) under several conditions of occlusal support in eight healthy dentates were recorded and analysed. The head posture was also recorded simultaneously by the electromagnetic, 6-degree-of-freedom tracking instrument (POLHMUS Co. 3 SPACE-WIN*). In the VMC with lateral imbalance of occlusal support, EMG activity of the jaw closing muscles and the sternocleidomastoid muscle on the occlusal support side was greater than those on the non-occlusal support side, and the neck was bent in the direction of the occlusal support side. Moreover, a positive correlation was found between the asymmetry of muscle activity (asymmetry index) of the sternocleidomastoid muscle and the angle of lateral bending of the neck. From these results, it can be said that lateral imbalance of the occlusal support could promote imbalance in sternocleidomastoid muscle activity, causing lateral bending of the neck. From this study, it is suggested that there is a close relationship between occlusal support and head posture.

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