Objective To investigate the effect of gradually induced disordered occlusion（GIDO） on the expression of tumor necrosis factor- α（TNF- α）in condylar cartilage in rat. Methods Fourty- eight SD rats, aged 8 weeks, were included, and were divided into experimental and control groups randomly, with the same gender distribution. By inserting elastic rubber band the first mandibular lower and maxillary upper molar was moved medially. Four weeks later the third mandibular lower and maxillary upper molars were moved distally with the same method. In this way the GIDO was established in rats. The rats were sacrificed at the end of 2nd, 4th, 6th, 8th week respectively after the application of the GIDO and the temporomandibular joints were stained with HE. The cartilage thickness was measured. The expression of TNF- α in condylar cartilage was examined by immunohistochemistry and calculated by the percentage of positive cells areas. Results The cartilage thickness increased in 4th, 6th, 8th week subgroups of experimental group（P0.05）. Conclusion The present results suggest that TNF- α take part in the procedure of the abnormal remodeling activities of condylar cartilage in GIDO rat model. The catabolism in condylar cartilage in GIDO rats was even obvious when the experimental period was longer with more serious GIDO.
