| Anterior disc displacement (ADD) is the most common type of temporomandibular disorders. Although displaced disc could cause pathological lesions to temporomandibular joint (TMJ) by persistent micro-trauma, in the meantime, the joint itself makes repair and remolding process to adapt to the new disc-condyle relationship. For human displaced disc is unavailable, it is important to establish a proper animal model of ADD for studying the histopathological changes of TMJ after ADD. Some authors have reported ADD models, but each had its lacks and shortcomings. The present study tried to make an improvement in the animal model of TMJ ADD.Ten adult healthy Japanese white rabbits were used in this study. Eight rabbits were subjected to operation. Right side of them was considered as experimental side and left side as sham-experimental side. Following general and local anesthesia, an about 2.5 to 3cm arc incision with the concave side facing upward was made from the top of zygomatic root to 1cm inferior to the lower eyelid. The inferior and posterior walls of orbit were exposed. Then a suture needle with elastic rubber band was vertically passed through the anterior part of disc from inferior to superior in the inferoanterior to the temporal root. The double strands of the elastic rubber were stretched forward from 7mm to 16mm and fixed in the hole drilled in the near superior margin of the junction ofanterior and intemediate Ird of the zygomatic arch with stainless steel wire. Then the disc was pulled anteriorly. Finally the wound was washed and closed. Two of them were killed respectively at 1 week and 2,4,6 weeks post-surgery. The other two rabbits were used as control group and sacrificed at the time before operation. When the rabbits were killed, both sides of TMJ were removed en bloc. Then the specimens were fixed, decalcified and embedded into paraffin. Finally 3-5um serial sections were cut and stained with hematoxylin & eosin.In the first three days post-operation, the lower eyelid had a slightly swelling and eversion. It returned normal at 5 days. The weight of all rabbits did not decreased significantly. The mandible deviated to the left side with inclined attribution of incisors.In normal TMJ, the anterior borders of articular eminence, mandibular condyle and the anterior margin of disc were in a vertical line. The apex of articular eminence faced to the intermediated part of disc and the posterior margin of posterior band lied in the posterior to the posterior border of articular eminence. The surfaces of the condyle, articular eminence and disc were smooth. Chondrocytes were major cells in the disc proper, but the bilaminar zone is primarily composed of fibroblasts. After operation, the disc of each rabbit was displaced forward accompanying the elongation and deformation of disc. The degree of ADD between rabbits was similar. Anterior band displaced in front of the anterior border of condyle and articular eminence. Intermediated band were in a line with the anterior border of condyle and articular eminence. The posterior margin of the posterior band of disc moved into the inferior to the posterior border of articular eminence.At the early stage following ADD, most of the articular cartilages of the condyle and articular eminence losted and the experimental TMJ appeared characteristic of osteoarthritis. But at 4 and 8 weeks post-surgery, articular cartilage of condyle and articular eminence regained. Fragment or perforation was not found in the surface of disc in each rabbit. Chondrocyte-like cells appeared in the anterior part of the lower part of bilaminar zone which looked like disc proper. An area of chondroid metaplasia was present in the junction of posterior band of disc and bilaminar zone in one animal at 2-6-weeks post-surgery. So the bilaminar zone made an adaptive change following ADD and could exert the function of the disc proper.On the basis of successful improvement in the animal model of TMJADD, we established another 16 rabbit ADD models. Each 4 of them were sacrific...
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