Effect of limited jaw motion on ankylosis of the temporomandibular joint in sheep

The purpose of this study was to investigate the effect of limited movement of the jaw on ankylosis of the temporomandibular joint (TMJ). Eighteen adult sheep were divided into two groups. In Group 1, the temporal and condylar articular surfaces were removed together with the disc on the right. In Group 2, we did the same procedures but in addition the jaw movements were limited by a wire. One sheep was killed just after the operation, four at one month, and four at three months, in each group. The range of jaw movements preoperatively and at the time of death were recorded. The joints were examined radiologically, macroscopically, and histologically. We used a scoring system to assess the radiological changes and histological extent of ankylosis. At one month, the joint spaces were filled with fibrous tissue, but a small joint space existed in all four joints in Group 1. In Group 2, there was full ankylosis in two joints and partial ankylosis in two joints. At three months, similar ankylotic changes were seen in both groups. The histological score for ankylosis at one month showed that those in Group 2 were significantly more ankylosed than in Group 1 (P<0.01). The range of jaw movements was more limited at one month in Group 2, both vertically and to the left, and was significantly decreased in both groups (P<0.01) at three months. Limitation of jaw motion hastens the progress of TMJ ankylosis.