A sheep model for temporomandibular joint ankylosis

Purpose: The purpose of this study was to develop an animal model for tempo romandibular joint (TMJ) ankylosis. Materials and methods: Five sheep had removal of the temporal and condylar articular surface plus discectomy in the right TMJ; the left side was used as a control. One sheep was killed just after operation and four at 3 month s. The joints were examined histologically, and a scoring system was develo ped to evaluate the extent of the ankylosis. The range of jaw movement was compared between preoperatively and 3 months. Results: Two sheep lost 4% of their body weight by 3 months. The range of j aw movement, particularly to the left, decreased at 3 months (P < .001). Th e joint spaces were filled with fibrous tissue and cartilage-like tissue. D evelopment of new bone from the damaged temporal and condylar surfaces was seen, but full bony fusion did not occur. The average histologic score of a zone was 4.9 on the degree-of-ankylosis scale and 1.7 on the degree-of-cal cification scale. There were statistically significant differences between the operated and control TMJs for both changes (P < .0001). Conclusion: Fibrous ankylosis occurs rapidly after removal of the TMJ artic ular surfaces and the disc. This model can be further developed to isolate relative factors in the development of ankylosis and in evaluation of diffe rent treatment methods.