DIFFERENCES BETWEEN TRACES OF ADJACENT CONDYLAR POINTS AND THEIR IMPACT ON CLINICAL-EVALUATION OF CONDYLE MOTION

Purpose: Recent research revealed that traces of single posterior refe rence points can depend on the location of the monitored point. The ai m of this study was to quantify this dependence and to point out its c onsequences for clinical application of condylar path registrations. M aterials and Methods: In 60 asymptomatic volunteers, mandibular motion was recorded during protrusion, lateral excursion, and opening-closin g of the jaw. Simultaneous trace-patterns of 10 condylar points includ ing the hinge-axis point and the kinematic-axis point were compared wi th respect to length, inclination angles, coordination, and shape. Res ults: in protrusion, traces of the different condylar points were equa l and independent of the location of the monitored point. Bennett angl es depended on the sagittal position of the reference point and varied by 0.8 degrees per 1 mm change of location. Opening-closing traces di ffered considerably. Their lengths varied by up to 9 mm and inclinatio n angles varied by 40 degrees. Opening-closing patterns also showed ir regularities like those observed in temporomandibular disorders. Irreg ularities were minor for the hinge-axis point and least for the kinema tic-axis point. Conclusion: In tooth-guided movements ''condyle motion '' is represented by the traces of any point near the condyle. In open ing-closing, however, the trajectory of a single condylar point will n ot reliably represent condylar motion. For articulator adjustment, con dylar angles must not be taken from opening-closing, but only from pro trusion. In diagnostic applications, one has to be aware that irregula r traces may not only result from dysfunction, but may as well be a re sult of the choice of reference point.