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

The study aimed to compare the locations of the hinge axis and the kinematic centre in both clicking and non-clicking TMJs. The six degrees of freedom optoelectronic jaw movement recording system OKAS-3D was used to record open/close movements in 10 asymptomatic subjects and 30 subjects with a clicking joint. Movement paths of the hinge axis and the kinematic axis were calculated. A t-test was used in the analysis of the locations of the two condylar movement reference points. Variances between the values of the hinge and the kinematic axes were compared with the F-test. Locations of the hinge axis and the kinematic centre on the average did not differ significantly for the asymptomatic subjects at the group level (P>0. 05), while individually 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 subjects with clicking joints (P<0.01), with the average individual level difference 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 of the kinematic centre in such studies.