Six rabbits with unilateral occlusal splints on the mandibular left molars for one month, three months or five months were examined to study the ultrastructure of the surface of the temporomandibular joint. Four rabbits were used as control. The results showed that the surface layer of the disk and articular cartilage were damaged. Severe fibrillation with sheets of fibers, collagen fibrils and collagen bundles inside fissures and craters were observed. These changes were seen in all rabbits with occlusal trauma and also in control rabbits for five months. The findings suggested that occlusal trauma could result in degenerative changes of the temporomandibular joint.