Evaluating The Effect of Botulinum Neurotoxin on the Improvement of Parafunctional and Dysfunctional Symptoms of the Temporomandibular Joint: A Pilot Study

Background: Temporomandibular disorders (TMD) are a wide range of clinical abnormalities affecting the masticatory muscles, the temporomandibular joint (TMJ), the surrounding bony structures, the soft tissues. Botulinum Neurotoxin Type A (BoNT-A) is one of the newest ways to slow or stop muscle activity. So this study aimed to evaluate the efficacy of BoNT-A injections in reducing symptoms of TMD. Materials and Methods: This pilot experimental study was conducted in the oral and maxillofacial surgery department of Isfahan University of Medical Sciences in 2022. Fifty patients with TMD were recruited. Participants received BoNT-A injections as the intervention. Outcomes measured included mouth opening, bite force, and joint pain/discomfort, assessed before and 4, 8, and 12 weeks after injection. Statistical analysis was performed using SPSS software. Results: Chewing force significantly decreased four weeks after the injection compared to the baseline. From the fourth to the eighth week, the chewing force continued to decrease, but this was not statistically significant (P=0.820). Finally, chewing force gradually and significantly increased by the twelfth-week post-injection (P<0.001), although it did not return to the pre-injection level. After the injection, pain-free mouth opening began to increase, which was not significant during the first four weeks (P=0.711) but became significantly greater in the eighth and twelfth weeks post-injection (P<0.001In addition, compared to before the injection, pain and discomfort were significantly reduced four weeks later, according to the VAS test results. Furthermore, pain significantly decreased from week four to week eight (P<0.001), and discomfort decreased steadily from week eight to week twelve. Nevertheless, the statistical significance of this decline was not established (P=0.132). Conclusion: Based on the results, BoNT-A injections reduce chewing force, alleviate pain and discomfort, and increase pain-free mouth opening. Therefore, BoNT-A has beneficial therapeutic effects on relieving symptoms of parafunction and dysfunction in the temporomandibular joint.