Head, neck and trunk movements accompanying jaw tapping.

Several studies have examined the functional relationship between mandibular movement and head or body posture, but head and body motion during jaw movement have not been extensively investigated. Ten healthy participants performed repetitive jaw tapping movement. Piezoelectric accelerometers were attached on the surfaces of the participant's forehead, mentum, and over the spinous processes of the sixth cervical, twelfth thoracic and third lumbar vertebrae. The direction in which the antero-posterior acceleration signals appeared around the onsets of jaw opening and closing were observed for the period from the 6th to the 25th strokes of the jaw tapping. Around the onset of jaw opening, the forehead and the lumbar vertebra tended to move posteriorly, but the cervical and thoracic vertebrae moved anteriorly with significant frequencies. The directions of the motions of these locations reversed themselves at the beginning of jaw closing; so the motions of the forehead and the lumbar vertebra were opposed again to the ones of the cervical and thoracic vertebrae. The results suggest that the head extend-flex motion often accompanied the jaw open-close movement, and the motions of the neck and trunk existed, which would serve the purpose of promoting the mandible to move smoothly.