The up-and-down head mobility during repetitive jaw open-close movement with (jaw tapping) and without tooth contact were studied in ten healthy participants. The accelerometers were attached to the forehead and the mentum, and the direction of their mobilities were observed around the onsets of jaw open-close movement. The results were as follows:
1. During the jaw tapping movement, forehead mobilities in the opposite direction to the ones of the mentum were observed in 94.0% of the strokes around the onset of jaw open movement, and in 96.5% at the beginning of jaw close movement.
2. In the jaw open-close movement without tooth contact, the incidence of the forehead and mentum mobilities opposite to each other were significantly lower than those in the jaw tapping movement, and the same-directed mobilities thereof were observed with increasing frequency (p<0.0001).
3. It was suggested that the jaw open-close movement is accompanied by the head mobility and there would be functional relations between the mobilities of the head and the mandible, but their coordination pattern depends on the type of jaw movement.
