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An analysis of controlled mandibular movement.

Kinematographic traces enable an assessment of jaw movements in the sagittal and coronal planes and the relationship of centric relation to centric occlusion can be determined. Centric relation in this context does not necessarily imply the ligamentous position but rather to an actively obtained physiological border position possibly corresponding to the retruded direct contact position. This position in normal subjects is either postero-inferior to or coincident with centric occlusion. Normal subjects were able to make lateral movements of the jaws to and from centric occlusion on either side and certain subjects were able to describe a plateau in or about the horizontal position of centric occlusion. Rhythmic traces showed that opening and closing movements of the jaws could be made in about 550 msec and reflex jaw opening was usually elicited after centric occlusion had been achieved. The significant correlation coefficients found by measuring the angles of opening, terminal opening and closing indicated that jaw movement was integrated. The TMJ series differed from the normal series in nearly all phases of jaw movement recorded. Centric relation was found to be lateral and antero-inferior to centric occlusion. On the side of the first interceptive tooth contact the patient was not able to return the jaws to centric occlusion. Intermittent traces indicated that there was no significant correlation between the angles of opening, terminal opening and closing suggesting that jaw movement were incoordinated. This was reflected in rhythmic traces which were considerably longer than those of the normal series. This increase in duration was found to be due partially to centric slides and partially to asynergistic movements of the mandible. The jaw-opening reflex was not usually elicitable. It is considered that in the TMJ series centric occlusion is a strained position and is usually lateral to and postero-superior to centric relation. This relationship of centric occlusion to centric relation is the reverse of normal relations and indicates that the mandible is displaced in centric occlusion. In general, patients with the TMJ syndrome have a postero-lateral displacement of the mandible.