Muscle-bone relationship in temporomandibular joint disorders after partial discectomy.

Objectives: Temporomandibular joint osteoarthritis (TMJ-OA) causes degenerative changes in TMJ tissues. The inter-tissue crosstalk that exacerbates illness and organic changes in bone secondary to TMJ-OA potentially affects the muscles; therefore, patients with a muscular disease might also suffer from bone disease. However, knowledge gaps exist concerning muscle pathology at the onset of TMJ-OA. In this study, we documented the pathogeneses of the bone and muscle at the onset of TMJ-OA using a mouse model.

Methods: We performed a partial resection of the TMJ disk to establish a mouse model of TMJ-OA. After the onset of TMJ-OA, we performed various measurements at 8, 12, and 16 weeks post-surgery in the defined groups.

Results: The volume of the mandibular head in the TMJ-OA group was significantly greater than that in the control group. The temporal muscles in the TMJ-OA group were significantly deformed compared with those in the control group; however, between-group comparisons did not reveal significant differences in the mandibular head or temporal muscles after surgery. Therefore, we hypothesized that the degree of mandibular head hypertrophy would alter the temporal muscles. A subsequent analysis of the correlation between the bone and muscle confirmed that the deformity of the temporal muscle increased with increasing hypertrophy of the mandibular head. Temporal and masseter muscle contact was observed in 25% of surgical groups.

Conclusions: This study demonstrates that TMJ-OA progressed when organic changes occurred in bones and muscles, supporting the symbiotic relationship between bones and muscles.