Measurement of condylar motion: a plea for the use of the condylar kinematic centre.

In this study, a plea is given for the use of the kinematic centre in studies of the kinematics of the human temporomandibular condyle. The concept of the kinematic centre is based upon the assumption that the movements of the condyle-disc complex within the temporomandibular joint can reasonably well be described by those of a ball-shaped condyle-disc complex. The kinematic centre is then the centre of the sphere. Its movement traces have the advantage that they are smooth and have a good reproducibility between consecutive movements. Moreover, the open and close traces are just a few tenths of a millimetre apart and show no crossings. This makes the kinematic centre a suitable choice in order to avoid false-positive diagnoses in the study of internal derangements by means of condylar movement recordings. However, the kinematic centre has the disadvantage that the mandibular movements have to be recorded by rather complicated six degrees of freedom recording equipment and that the exploration algorithm for its location may sometimes have difficulties in finding the right location.