Effect of asymmetric force on the condylar cartilage, subchondral bone and collagens in the temporomandibular joints.

This study aimed to define the effects of asymmetric force on rat temporomandibular joints (TMJs). A total of 232 10-week-old rats were used in the experiment. Their left TMJs were kept forward and upward with 40g or 120g. The histological and osteogenic changes, as well as the expression of type I, II and III collagens were observed. Our results showed that the curve of the cartilage thickness changes in the anterior part of the treated side in the heavy force group (HS) decreased first and increased later during the strength and the recovery periods, while the reverse changes were shown in the middle and posterior parts. The cartilage thickness change on the other side in the heavy force group (HO) was the opposite. Additionally, the cartilage thickness change on the treated side and the other side of the light force group (LS and LO) were similar to but not as significantly changed as HS and HO. There were significant differences among the experimental groups. The subchondral bone trabecula also decreased after the pressure loading and removing, then recovered, without significant differences among these groups. Furthermore, more pathological changes such as fractures, bone cysts, the degradation of type II collagen and the increased expression of type III collagen were observed on the treated sides following the application of heavy force. In contrast, more osteogenesis and more active changes were found in the light force group. In conclusion, our study demonstrated that asymmetric force exerted different effects on the cartilage, subchondral bone and collagens of TMJs. Greater changes occurred in the heavy force group, and light force provided more benefits for TMJs remodelling.