Determination of the kinematic axis point of the temporomandibular joint regardless of cyclic mandibular movement data.

The term 'kinematic axis' refers to a theoretical intercondylar axis of the mandible, any point on it nearly reciprocating on a single surface during all sagittal movements. Thus the axis can simplify kinematic features of the temporomandibular joint. In order to locate the axis point on a desired sagittal plane kinematically, a cyclic mandibular movement along the sagittal border has been employed, due primarily to its locational efficiency. For purposes of extracting entire features of condylar movements, however, not only the border movement, but as many other types of movements as possible should be employed. Location methodology applicable to such a wide variety of movement data has yet to be established. To surmount this restriction, this paper presents a technique applicable to any sagittal movement data. The axis point can be obtained as a condylar point, the motion range of which is the narrowest. This range has been provided as the region surrounded by a closed trajectory, whereas it is here defined by the region lying between the superior and inferior trajectories, thereby achieving a discarding of kinetic cyclicity. A condylar point minimizing the area of this region was verified to be a valid estimate of the kinematic axis point, through experiments employing actual mandibular movement data.