A kinematic investigation of mandibular border movement by means of an electronic measuring system. Part III: Rotational center of lateral movement.

M any theories regarding the rotational center of the mandible have been propounded. Spee,’ Hall,’ Monson,’ Needle? and others, formulated theories based on anatomic observations. Gysi” reported a theory based on two-dimensional geometric principles, while McCollum and Stuart” developed a theory based OJ~ their experimentations. Although the rotational center concept of the mandible was discussed, the theories were not proven three dimensionally by means of modern kinematics. ‘l’arget orbits 55 mm from the midpoint of the terminal hinge axis were discussed.” It was found that the orbits shift straight laterally on the terminal hinge axis and do not show any deviation in the sagittal plane. Based on these findings, it was believed that the Bennett movement was a straight lateral shift of the working condyle along the terminal hinge axis. If a point 55 mm from the midpoint is considered the kinematic center of the lateral movement of the mandible, it may be defined as the three-dimensional rotational center of the mandible because it is situated on the terminal hinge axis, which is the rotational center of the mandible in the sagittal plane. In other words, the mandible may rotate in three-dimensional space around a specific point during lateral movement and shift in the lateral direction an amount equivalent to the Bennett movement. The purpose of this study is to explain and illustrate the rotational center of the lateral movement of the mandible by means of an electronic measuring system8 that measures 6 degrees of free movement.