OBJECTIVETo investigate whether the gradually induced disordered occlusion can induce degenerative changes in rabbit TMJ.

METHODS27 male New Zealand Rabbits, age of 5 months were divided equally and randomly into three groups: Group A: One premolar in upper dentition at one side and another premolar in lower dentition at the other side were pulled to move medially to the anterior intrinsic space by an orthodontic string to cause the corresponding premolars not to occlude with the opposites coincidently. Group B: the sham-operating controls, all animals were treated similar to those in Group A but without pulling. At the age of 6, 7 and 8 months, three rabbits of each group were killed by deeply anaesthetizing and bilateral condyles of TMJs were excised, sectioned and stained with HE.

RESULTSThere was no significant histological difference in condylar cartilage between Group B and C. The cartilage of TMJs condyle in Group A was found with significant degenerative changes that increased with age. The thickness of cartilage of anterior and intermediate part of condyles decreased, the disturbance of continuation of hypertrophic layer appeared and part of hypertrophic layer was locally replaced by fibrous tissue. While the thickness of cartilage of posterior part of condyle increased obviously with a significant increase of the proportion of immature chondrocytes.

CONCLUSIONThe gradually induced disorder occlusion may lead to degenerative changes in rabbit condyle.