Histological Changes in the Temporomandibular Joint of Rats with Mandibular Condyle Deformity Induced by Articular Disc Displacement

Abstract

Temporomandibular joint osteoarthritis (TMJ-OA) is a widespread joint pathology and has a heightened risk of occurring in patients with anterior disc displacement (ADD), suggesting a potential link between disc displacement and TMJ-OA. However, how ADD causes condylar cartilage deformity without excessive loading on the condyle remains unclear. Therefore, in this study, we aimed to investigate the effects of ADD on temporomandibular joint (TMJ) in rats. Twelve-week-old male Wistar rats were randomly assigned to three groups: ADD, sham surgery, and control. A 4-0 silk thread was used to ligate the anterior part of the articular capsule to the posterior part of the zygomatic arch, securing the articular disc 3 mm forward. The ADD and sham groups were sacrificed 4, 6, and 8 weeks after surgery to perform radiological analysis on the TMJ using micro-computed tomography (micro-CT) and histological analyses. CT images of both coronal and sagittal sections revealed bone deformities in the condyles of the ADD group. The obtained images closely resembled the damaged surface of condyles observed in a clinical case of TMJ-OA. Histologically, anterior disc displacement was observed in the ADD group, along with an increase in thickness of the cartilage layer and a reduction in the cartilage matrix within the hypertrophic layer. The expressions of matrix metalloproteinase-13 and alkaline phosphatase were significantly upregulated in the hypertrophic layer and subchondral bone beneath the cartilage layer, indicating that ADD activated cartilage and bone remodeling. This study reported morphological changes of mandibular condyle and histological changes throughout the TMJ and showed that ADD without excessive loading could cause TMJ-OA