A kinematic investigation of mandibular border movement by means of an electronic measuring system. Part II: A study of the Bennett movement.

Fifty adults with orthognathic maxillomandibular relationships were selected as the test group. The movement of the working condyle was examined during lateral movement of the mandible with an electronic system capable of measuring six degrees of freedom of the mandible with an accuracy of +/- 0.06 mm. The results were: Orbits of the points on the terminal hinge axis d mm from the midpoint during lateral movement of the mandible varied appreciably as the value of d changed. The orbits more affected were the working side on the horizontal and frontal planes. The point on the working side moved forward, laterally, and downward as the value of d was small; and it moved backward, laterally, and upward as the value of d increased. Depending on the value of d, orbits moved in opposite directions. As the value of d varied from small to large, the point on the working side moved only laterally along the terminal hinge axis when d was 55 mm. From this observation, the Bennett movement is explained as the lateral shift of the working condyle along the terminal hinge axis. Reports concerning the directions and mode of motion of the Bennett movement differ because of the lack of specification of location of the positions (targets) assigned for measurement.