Kinematics of the human mandible for different head posture

The influence of head posture on movement paths of the incisal point (IP) a nd of the mandibular condyles during free open-close movements was studied. Ten persons, without craniomandibular or cervical spine disorders, partici pated in the study. Open close mandibular movements were recorded with the head in five postures, viz., natural head posture, forward head posture, mi litary posture, and lateroflexion to the right and to the left side, using the Oral Kinesiologic Analysis System (OKAS-3D). This study showed that in a military head posture, the opening movement path of the incisal point is shifted anteriorly relative to the path in a natural head posture. in a for ward head posture, the movement path is shifted posteriorly whereas during lateroflexion, it deviates to the side the head has moved to. Moreover, the intra-articular distance in the temporomandibular joint during dosing is s maller with the head in military posture and greater in forward head postur e, as compared to the natural head posture. During lateroflexion, the intra -articular distance on the ipsilateral side is smaller. The influence of he ad posture upon the kinematics of the mandible is probably a manifestation of differences in mandibular loading in the different head postures.