3046 New criterion to verify the position of the kinematic center
M.K.A. VAN SELMS, J.J.R. HUDDLESTON SLATER, F. LOBBEZOO, and M. NAEIJE, Academic Centre for Dentistry Amsterdam, Netherlands

To describe the kinematics of the human temporomandibular joint, the kinematic center is often used. Since this center is not an anatomical point, it has the disadvantage that its position can only be calculated from the kinematic data collected during symmetrical movements. The coincidence of protrusive and opening movement traces is often used as mathematical criterion to find the kinematic center. Since a less successfully found kinematic center may give rise to equivocal findings, additional criteria should be formulated to verify the calculated position of the kinematic center. A previous study has shown that differences between opening and closing movement traces of the kinematic center are strongly reduced when a mechanical load counteracts the closing movements. Objectives: the present study tests the hypothesis that the largest reduction is found for the kinematic center traces. Methods: a six-degrees-of-freedom opto-electronic jaw movement recording system (OKAS-3D) recorded 7-12 free opening and loaded closing movements from 10 healthy participants. Off-line, the average distances between the opening and closing traces of the kinematic center and of 20 nearby points, centered around the kinematic center and located along the anterior/posterior and superior/inferior axes, were calculated. Results: the average distances showed a parabolic relationship for both axes (Rē=0.9897, P<0.0001 and Rē=0.8898, P<0.0001). The coordinates of the kinematic center coincided with the minima of the parabolas. Conclusions: the kinematic center shows the best coincidence in opening and loaded closing movement traces. This coincidence can be used as additional criterion to verify the position of the kinematic center.

Seq #275 - TMJ - Structure and Function II
3:45 PM-5:00 PM, Friday, 8 March 2002 San Diego Convention Center Exhibit Hall C

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