Role of articular disc in cartilaginous growth of the mandible in rats

Displacement of the temporomandibular joint (TMJ) disc causes a lateral shift of the mandible and less-developed and/or distally located mandible unilaterally and bilaterally, respectively, if occurred in growing individuals. The purpose of this study was to evaluate mandibular condylar growth in growing rats after TMJ discectomy and to explore a certain significant role of articular disc in the TMJ in mandibular or cartilaginous growth. Eighteen 4-week-old Wistar strain male rats were divided into two groups with nine in each group, i.e., rats with TMJ discectomy (discectomy group) and only sham operation (control group). Four weeks after initiating the experiment, morphometric analyses of the mandible were performed using a rat and mouse cephalometer and micro-computed tomography. Then, the mandibular condyles were subjected to histomorphometric analyses. Condylar and mandibular growth was reduced significantly in the discectomy group than in the control group. In the discectomy group, the condyle also became flatter and smaller. In addition, the 4-layer structure of condylar cartilage was unclear with thicker fibrous and thinner lower hypertrophic layers in the discectomy group when compared to the controls. It is shown that resection of the articular disc substantially affects condylar and mandibular growth in terms of the cartilaginous growth, suggesting that TMJ disc is indispensable for maintaining normal growth of the condyle and mandible, leading to optimal development of the TMJ and the entire mandible