Study on the relationship between the head movements and the body movement during rhythmical jaw movements

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The aim of this study was to evaluate the relationship between the stomatognathic function and the systemic condition from a viewpoint of body movements in the standing and seating positions. We designed and developed a new six-degree-of-freedom tracking device (TRIMET□), and used it for the three-dimensional registration of head and mandibular movements. Body movements were also measured using two motion capture devices (ProReflex), placed in the ceiling. Furthermore, we built a new system to analyze simultaneously these three kinds of data on the same time-axis. For mandibular movement, the lower incisal point was recorded on the maxilla reference frame. For head movement, the upper incisal point, the parietal point, the occtipital point, and the condylar points were recorded on the ground reference frame. Simultaneously, the motion of the sternum point was recorded and analyzed on the ground reference frame. The subjects were 6 males with normal stomatognathic functions, aged 25〜29 … More years, with a mean age of 27 years.On the seating position, the head extension was observed during mouth opening and the head flexion was observed during mouth closure. Synchronizing with these head movements, the body moved anteriorly with mouth opening and moved posteriorly with mouth closure. On the standing position, similar head movements and body motions were also observed in the same rhythm with mandibular movements.The body movement in the standing position was also synchronized with the mandibular movement, and was observed as antero-posterior drifts of small amplitude within the large amplitude of antero-posterior drifts, which seemed to be the effects of breathing. On the other hand, the effects of breathing were not observed in the seating position. The distance of antero-posterior body movements, synchronized with mandibular movement, showed a tendency to increase with the increment of range of mouth opening, both in the standing and seating positions. However, the absolute values were differed among the subjects. The average ratio of the body movements to the range of mouth opening was 2.3〜6.1% in the standing position and 2.0〜4.8% in the seating position. The ratio was increased from 0.2〜1.3% in the standing position in comparison with the seating position. Less