Structural Changes in the Temporomandibular Joint After Botulinum Toxin Injection Into the Masseter Muscle in Experimentally Induced Osteoarthritis in Rats.

[BACKGROUND] Botulinum neurotoxin (BoNT) injections into the masticatory muscles have been used as a treatment to improve symptoms related to temporomandibular joint (TMJ) disorders. However, its safety and long-term effects on TMJ structures remain inconclusive and are still under discussion.

[OBJECTIVE] The purpose of this study is to evaluate whether the effects of BoNT injection into the masseter affect the mandibular condyle in a rat model of TMJ osteoarthritis (TMJ-OA).

[METHODS] Sixteen male Wistar albino rats were used. The 32 TMJ joints were divided into four groups: (1) TMJ-OA with BoNT (OA + BTX), (2) TMJ-OA without BoNT (OA), (3) BoNT without TMJ-OA (BTX) and (4) control. TMJ-OA was induced by CFA injections. One week later, BoNT was administered to the masseter in the OA + BTX and BTX groups. Micro-CT imaging was performed 8 weeks later to assess the TMJ condyle.

[RESULTS] The analysis revealed significant differences in bone mineral density and microarchitectural changes between the BTX/control and the OA/OA-BTX groups, except for trabecular separation (p < 0.05). The OA and OA + BTX groups exhibited lower bone volume fraction and bone mineral density compared to the BTX and control groups. No significant differences were observed between the BTX and the groups without BoNT, suggesting that BoNT did not result in bone loss in healthy TMJs or in TMJ-OA cases.

[CONCLUSIONS] BoNT does not have a significant effect on healthy or existing degenerative conditions in the TMJ. Long-term experimental studies and clinical trials are needed to validate the safety of BoNT in managing TMJ-OA.