OBJECTIVETo investigate the relationship between the contour of articular eminence and traces of the condylar kinematic center during jaw opening movement in healthy subjects, and compare trace characteristics of condylar kinematic center and MRI findings in TMD patients.

METHODSIn 10 healthy subjects, jaw-opening motion was recorded. The kinematic center and terminal hinge axis point of the condyle were used as trace reference points. The contour of articular eminence was examined by MRI. Seven patients with TMD signs and/or symptoms (disk displacement) were selected for this study. The condylar trace was recorded during jaw protrusion and opening-closing. The internal derangement in temporomandibular joints was detected by MRI and defined as: (1). normal disk position, (2). disk displacement with reduction, (3). disk displacement without reduction.

RESULTSIn healthy subjects, most of the opening traces of the kinematic center coincided with the contour of articular eminence (8/10 joints in left, 9/10 joints in right). For terminal hinge axis point, no trace coincided with the contour of articular eminence (0/20 joints in left and right). In TMD patients, according to MRI findings, the condylar traces of kinematic center in 3 normal disk position joints showed normal shape. However, in 6 disk displacements with reduction joints and 5 disk displacement without reduction joints, the condylar traces of kinematic center showed irregular patterns except 1 disk displacement with reduction joint.

CONCLUSIONSIn comparison with the terminal hinge axis point, the opening traces of the kinematic center can be interpreted as the translatory movement of the condyle/disc along the articular eminence. The study suggests the use of kinematic center in condylar movement studies.