In the initial phase of dental occlusion, there was predominant loss of subchondral bone in the TMJ condyles.16 Cartilage degeneration in TMJ-OA is often accompanied by a high OARSI score and abnormally enhanced Col X and matrix metalloproteinase 13 expression.14,33,34,40 In our study, Safranin O and HE staining revealed increased thickness of the calcified cartilage layer and cartilage matrix degeneration in the TMD models. This evidence concerns the gene MMP13 and temporomandibular joint disorder.