Longitudinal Computed Tomography Indicates No Negative Impact of OnabotulinumtoxinA on Mandibular Bone Density in a 12-Month, Double-Blind, Randomized, Repeat Treatment, Placebo-Controlled Study in Healthy Adults With Masseter Muscle Prominence

Background Botulinum neurotoxins are used to treat masseter muscle prominence (MMP), benign bilateral masseter muscle enlargement which can be aesthetically undesirable. Limited data report botulinum neurotoxin injections in the muscles of mastication, with subsequent reduction in biomechanical loading, may impact mandibular bone density. Objectives This study evaluates whether changes in mandibular bone density occur after bilateral masseter treatment with a botulinum neurotoxin, onabotulinumtoxinA, in individuals with MMP. Methods Analyses were performed on a prespecified subpopulation (n=123) from a 12-month, double-blind, placebo-controlled, dose-escalation, Phase 2 study (N=187). Participants received 1 or 2 bilateral masseter treatments of onabotulinumtoxinA (48, 72, or 96 U) or placebo and had multi-detector computed tomography (MDCT) scans at baseline and Days 90 and 360 post-treatment. Cortical and trabecular bone densities, estimated in Hounsfield units, were calculated for the bilateral condyle, premolar dentoalveolus, and ramus. Results No clinically significant changes in mandibular bone density were observed in condyle, premolar area, or ramus of onabotulinumtoxinA-treated participants, as compared to placebo or baseline, after 1 or 2 treatments. Conclusions In healthy adults with MMP, 1 or 2 bilateral masseter treatments with onabotulinumtoxinA at doses of 48, 72, or 96 U over 1 year did not negatively impact mandibular bone density.