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Relationship between Kinematic Center and TMJ Anatomy and Function

Clinic for Masticatory Disorders, Removable Prosthodontics and Special Care, Center for Oral Medicine, Dental and Maxillo-Facial Surgery, University of Zürich, Plattenstrasse 11, CH-8032 Zürich, Switzerland

^* corresponding author, luigi{at}zui.uzh.ch

The kinematic center (KC)—defined by coinciding jaw-opening/-closing and protrusion-retrusion trajectories—has been proposed in the literature as a reference point to represent TMJ movements. In this study, we tested whether the KC lies in a peculiar anatomical point and whether its trajectory reflects intra-articular distance. In 11 asymptomatic individuals (seven females, four males, aged 24–37 yrs), 4 openings/closings and 4 protrusions/retrusions were tracked with dynamic stereometry. In a 3D lattice (0.5 mm grid) constructed solidly around each condyle, the KC was the point with maximal cross-correlation between opening-closing and protrusion-retrusion paths. KC trajectories were more cranial on closing than on opening, consistent with intra-articular distances being smaller on closing than on opening. However, KCs were never located on condylar main axes (distance, 4.5 ± 2.9 mm), nor did they coincide with points best approximating fossa shapes (distance, 12.5 ± 6.4 mm). The kinematic center’s anatomical and functional significance therefore appears to be questionable.

KEY WORDS: biomechanics • kinematics • kinematic point • MRI • temporomandibular disorders • temporomandibular joint