Effect of multiple injections of botulinum toxin into painful masticatory muscles on bone density in the temporomandibular complex

Background Adverse effects of masticatory muscle injections of Botulinum Toxin (Btx) have been noted in animal and, less dramatically, human studies. Objective Among women treated in multiple community-based private practices, to compare TMJ bone density and mandibular condylar volume between patients with myofascial TMJD receiving multiple masticatory muscle Btx treatments and similarly diagnosed women not receiving such treatment. Methods Cohorts consisted of women whose treatment charts indicated a diagnosis of myofascial TMJD: 35 received at least 2 Btx treatment cycles; 44 received none. Bone density at pre-specified regions of interest (ROI) was defined by grey scale values from Cone Beam CT, adjusting for a fixed density phantom included in each scan. Mean bone density and mandibular condyle volume were compared between groups. Dose-response effects were tested within the Btx-exposed group. Results The mean density of primary and secondary ROIs was similar between exposure groups, as was condylar volume. Among Btx-exposed women, increasing dose of Btx to the temporalis muscle was inversely proportional to the density of the trabecular area of the mandible body. Many Btx-exposed women received smaller doses of Btx to the masseter muscles than in most TMJD Btx clinical trials. Conclusion Masticatory muscle injections of Btx failed to produce clinically significant TMJ bone-related changes. Should Btx receive regulatory approval for treatment of myofascial TMJD, a phase IV study is recommended to evaluate potential adverse effects of Btx on bone and muscle when administered at higher doses and/or for more treatment cycles.