BoNT Injection into Temporomandibular Joint Alleviates TMJ Pain in Forced Mouth Opening Mouse Model

Temporomandibular disorder (TMD) significantly impairs the quality of life of patients due to chronic pain and limited jaw function. Many treatment options have been used such as pharmacologic management, physical therapy, oral appliance therapy, and surgery. However, effective treatment options remain limited. In this study, we investigated the potential of botulinum toxin (BoNT) as a therapeutic approach for TMD using a forced mouth opening-induced TMD male mouse model. BoNT injection significantly alleviated mechanical hypersensitivity in the temporomandibular region over a 2 week period as demonstrated by von Frey behavioral tests. Additionally, the mouse grimace test confirmed that BoNT alleviated pain in mice. The open field test and pasta gnawing test showed that BoNT injection effectively alleviated mouth motor and food intake problems and did not cause impairments in general behavior. Moreover, direct observation of neural activity via in vivo Pirt-GCaMP3 calcium imaging of intact trigeminal ganglia (TG) revealed that BoNT suppressed both stimulus-evoked and spontaneous activity in TG neurons. Mechanistically, BoNT downregulated the expression of pain-promoting proteins (TRPV1, TRPA1, and TRPC1) and glutamate transporting protein (VGLUT2), thereby suppressing peripheral neural activity in the TG. In summary, our study identified a novel mechanism by which BoNT alleviates TMD pain. These new findings not only expand our understanding of the effects of BoNT on pain but also provide a new therapeutic approach to TMJ pain management.