The effect of head posture on direction and stability of mandibular closing movement

This study investigated the effects of head posture on mandibular habitual closing movement. Ten healthy subjects were examined. Head posture was evaluated as a sagittally viewed inclination of the head, and was changed from 25 degrees forward bending up to 30 degrees backward bending in 5 degrees increments. The mandibular opening and closing movement was measured at each head posture. As the head bended forward, the closing path approached the maximum intercuspal position from the anterior region, and as the head was bent backward, the closing path approached the maximum intercuspal position from the posterior region. However, the limit of this relationship was found when the head was bent forward to some extent. There was also a correlation between the head posture and the stability of the closing movement. The forward bending of the head decreased the stability of the closing path, and conversely, the backward bending increased the stability of the closing path. It was concluded that the head posture affects the direction and stability of the mandibular closing movement. Possible underlying reasons for these findings are masticatory muscle activity and the tension and resistance of inframandibular soft tissue varying with the change of head posture.