Methods: EMG activity of the masseter (MS) and lateral pterygoid (LP) muscles was simultaneously recorded along with movement of the condyle and the disk during fictive mastication. Movement of the condyle and the disk in the sagittal plane was directly video-recorded at a time resolution of 8 ms with a high speed CCD camera. For the direct video imaging of the disk, a lateral one thirds of articular eminence of the temporal bone which makes upper and lateral roof of the upper articular cavity of the TMJ was partly removed and lateral portion of the disk was exposed.
Results: The bite-raising splint on the working side induced an unusual movement of the working-side condyle, which was transient and consisted of postero-inferior movement appearing in the second half of the occlusal phase. The disk showed also transient deviation approximately 0.35 mm postero-inferior to the trajectory typically observed under pre bite-raising condition. The unusual movement of the condyle and disk was also found on the balancing side, but quite different in nature and degree from those on the working side.
Conclusion: The transient unusual postero-inferior movement of the condyle and disk in the occlusal phase should be noteworthy in terms of the TMJ disorder because of generation of wide space between the condyle and articular eminence, into which the posterior part of the disk could possibly slip off anteriorly.