Differences Between Traces of Adjacent Condylar Points and Their Impact on Clinical Evaluation of Condyle Motion

Purpose: Recent research revealed that races of single posterior reference points can depend on the location of the monitored point. The aim of this study was to quantify this dependence and to point our its consequences for clinical application of condylar path registrations. Materials and Methods: In 60 asymptomatic volunteers, mandibular motion was recorded during protrusion, lateral excursion, and opening-closing of the jaw. Simultaneous trace-patterns of 10 condylar points including the hinge-axis point and the kinematic-axis point were compared with respect to length, inclination angles, coordination, and shape. Results: In protrusion, traces of the difference condylar points were equal and independent of the location of the monitored point. Bennett angles depended on the sagittal position of the reference point and varied by 0.8 degrees per 1 mm change of location. Opening-closing traces differed considerably. Their lengths varied by up to 9 mm and inclination angles varied by 40 degrees. Opening-closing patterns also shoed irregularities like those observed in temporomandibular disorders. Irregularities were minor for the hinge-axis point and least for the kinematic-axis point. Conclusion: In tooth-guided movements condyle motion is repr esented by the traces of any point near the condyle. In opening-closing, however, the trajectory of a single condylar point will not reliably represent condylar motion. For articulator adjustment, condylar angles must not be taken from opening-closing, but only from protrusion. In diagnostic applications, one has to be aware that irregular traces may not only result from dysfunction, but may as well be a result of the choice of reference point.