Abstract： Objective To establish the condylar neck osteotomy or fracture rat model,and to determine the effects of stress changes on the growth and development of mandible.Methods Seventy-two SD rats of 4 weeks age were randomly assigned to unilateral condylar process osteotomy group (n=24),fracture group (n=24) and Sham operation group (n=24).Following construction of the models of unilateral condylar process osteotomy,the imaging characteristics,histological and anatomical changes were recorded at 1,3,5 and 9 weeks.Expressions of development-associated connective tissue growth factor (CTGF) and type X collagen (Col X) were assayed by immunohistochemical staining.Results The condyle on the operated side was enlarged and the neck separated on imaging at weeks 1 and 3 in unilateral condylar process osteotomy group.However,in fracture group,the condyle appeared to be cylindrical,which demonstrated the fracture line at week 1.Unilateral condylar process osteotomy was associated with retarded growth and development of mandible in the operated side at weeks 1,3,5 and 9.The thickness of condylar cartilage enlarged compensatorily to (1468.28±53.73) μtm at week 1 compared with that in fracture group (P＜0.05).This was followed by a gradual decline in the thickness at weeks 3 and 5 that was not statistically different from that in fracture group at week 9 (P＞0.05).Both groups yielded a reduced level of thickness compared with Sham operation group (all P＜0.05).The CTGF expression at the operated side in unilateral condylar process osteotomy group was 60.18±1.23,72.43±2.82 and 86.00±2.90 at weeks 1,3 and 5,respectively,which were higher compared with those in fracture group and Sham operation group (all P＜0.05).At week 1,Col X expression (64.46±3.76) was significantly augmented compared with that in fracture group and Sham operation group (both P＜0.05).Conclusion Unilateral condylar process osteotomy may result in asymmetry of the mandible at operated and non-operated side as well as altered expression of CTGF and Col X in the condyle chondria,which arises from significantly altered stress and retarded development of the mandible and condyle.