[Mandibular movements and the position of the head]

The aim of this study was to evaluate the relation between head position and mandibular movements. The movements of the incisal point were evaluated on a sagittal plane in a group of 4 subjects unaffected by anomalies of the masticatory system. It was observed that there was a marked increase in rotary movement along the hinge axis when the head was extended and vise versa. The author attribute this to interference between the sternocleidomastoid muscles and the mandibular corners (ISM). ISM limits rotary movement, activates mandibular translation and might be the cause of some deviations during opening, malocclusion and ATM disorders. The present study does not establish whether or not ISM plays a functional role.