Location of the hinge axis and the kinematic centre in asymptomatic and eliciting temporomandibular joints

The study aimed to compare the locations of the hinge axis and the kinemati c centre in both clicking and non-clicking TMJs. The six degrees of freedom optoelectronic jaw movement recording system OKAS-3D was used to record op en/close movements in 10 asymptomatic subjects and 30 subjects with a click ing joint. Movement paths of the hinge axis and the kinematic axis were cal culated. A t-test was used in the analysis of the locations of the two cond ylar movement reference points. Variances between the values of the hinge a nd the kinematic axes were compared with the F-test. Locations of the hinge arris and the kinematic centre on the average did not differ significantly for the asymptomatic subjects at the group level (P > 0.05), while individ ually the locations differed 4.96 mm on the average. The difference between the hinge axis and the kinematic axis was significant for the group of sub jects with clicking joints (P < 0.01), with the average individual level di fference of 9 mm. Variances differed significantly between the coordinates of the hinge and the kinematic axes between the two groups of subjects (P < 0.01). The study shows the importance of the choice of a condylar movement reference point for the study of condylar movements and suggests the use o f the kinematic centre in such studies.