Objective To establish a stable animal model of temporomandibular joint（TMJ） synovitis. Methods Sixteen 6-week-old male SD rats were classified into four groups, control group, occlusal dimension increase group, masseter resection group, occlusal dimension increase group and masseter resection group. The rats in the occlusal dimension increase group were adhered composite resin to their maxillary molars in order to increase the occlusal vertical dimension when they were 9-week-old. The rats in the masseter resection group were cut off their bilateral masseter muscles when they were 6-week-old. In the occlusal dimension increase group and masseter resection group, rats′ bilateral masseter muscles were resected and occlusal vertical dimension was increased. All rats were sacrificed at their 10 weeks old. TMJ samples were prepared for histology to evaluate the animal model. Results The control group showed non -inflammatory changes. The occlusal dimension increase group and the masseter resection group showed vascular dilation and synovial lining proliferation, but there were no statistically significant differences between the two groups（P＞0.05）. Compared to the two disposed groups, the occlusal dimension increase group and masseter resection group showed significant inflammatory changes（P＜0.05）, including synovial lining proliferation, vascular dilation and fibrin deposit. Conclusion The animal model of TMJ synovitis created in the present investigation could simulate the real pathological features of synovitis in vivo, and this animal model showed the obvious merits of high stability and reproduction.
