Three-dimensional unilateral method for the bilateral measurement of condylar movements

Using a unilateral optoelectronic tracking system (JAWS-3D), a method was developed for the simultaneous measurement of the three-dimensional kinematics of both ipsilateral and contralateral human condyles, the latter being represented by virtual points beyond the field of vision of the camera system during the actual recording. The method leaves the subject's head unrestrained while measuring the movements of two sets of three light-emitting diodes rigidly attached to the upper and lower teeth. The Tait-Bryan angles method was employed for calculating the jaw rotations in three dimensions. Movements were referenced to both a skeletal and a dental coordinate system. The worst-case static measurement errors were 0.24 mm for a 20 mm translation and 0.71 degrees for a 35 degrees rotation. The mean dynamic measurement errors were 9.73 microns s-1 at a constant linear velocity of 200 microns s-1 and 0.73 degrees s-1 at a constant angular velocity of 149 degrees s-1. The utility of the method was demonstrated in a subject who was asked to open and close the mouth in a cyclic fashion.