BACKGROUND:Masseter muscle prominence (MMP) may be aesthetically bothersome to some individuals, leading them to seek treatment for a slimmer lower face. OBJECTIVES:The aim of this study was to evaluate the safety and efficacy of onabotulinumtoxinA for the treatment of MMP, including patient-reported outcomes (PROs). METHODS:This was a prospective, multicenter trial including a randomized, double-blind, placebo-controlled period (Days 1-180) in which adults rated Grade 4 or 5 (marked/very marked) on the investigator-assessed MMP Scale (MMPS) were randomized to onabotulinumtoxinA 72 U or placebo. Efficacy endpoints were assessed at Day 90. The primary endpoint was ≥2-grade improvement from baseline on the investigator-assessed MMPS. Secondary endpoints included achieving Grade ≤3 on the MMPS and participant-assessed MMPS-Participant (MMPS-P), ≥2-grade improvement on the participant-assessed MMPS-P, and change from baseline in lower-facial width. Outcomes were assessed using validated measures. Adverse events (AEs) were monitored. RESULTS:Of 376 enrolled participants (onabotulinumtoxinA, n = 283; placebo, n = 93), 310 (82.4%) completed the study. At Day 90, a greater proportion of onabotulinumtoxinA-treated participants vs placebo achieved MMPS ≥2-grade improvement (51.2% vs 2.2%, P < .0001), and more onabotulinumtoxinA-treated participants vs placebo achieved the secondary endpoints (all P < .0001), with a mean lower-facial width reduction of -5.24 mm for onabotulinumtoxinA vs -0.04 mm for placebo (P < .0001). Participants reported benefits for onabotulinumtoxinA vs placebo in self-perceived change in MMP, treatment satisfaction, and psychosocial impact. Improvements were sustained through Day 180. Most AEs were mild, nonserious, and resolved. CONCLUSIONS:OnabotulinumtoxinA effectively reduced the appearance of MMP and improved PROs, with effects lasting up to 6 months and a favorable safety profile. LEVEL OF EVIDENCE: 1 (THERAPEUTIC):

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 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, when compared with 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. LEVEL OF EVIDENCE: 1 (THERAPEUTIC):

BACKGROUND:Masseter muscle prominence (MMP) is a benign condition characterized by a wide, square, or trapezoidal lower facial shape, which may be considered undesirable. OBJECTIVES:To evaluate onabotulinumtoxinA (onabotA) efficacy and safety for MMP treatment. METHODS:In a Phase 2b study, adults with investigator- and participant-assessed bilateral Grade 4/5 MMP on the 5-grade MMP Scale (MMPS) and MMPS-Participant, respectively, were randomized 1:1:1 to receive a single intramuscular injection of onabotA 48 U, 72 U, or placebo in the masseter muscles. The primary endpoint was the proportion of patients achieving investigator-assessed MMPS Grade ≤3 at Day 90. Adverse events were monitored throughout. RESULTS:Patients received onabotA 48 U (n = 53), 72 U (n = 46), or placebo (n = 46). Significantly greater proportions achieved MMPS Grade ≤3 with onabotA vs placebo (90.6%, 91.3%, and 21.7% for onabotA 48 U, 72 U, and placebo, respectively, at Day 90; P < .0001). Improvements in lower facial volume, width, and angle were significantly greater for onabotA vs placebo at all time points. At Day 90, the proportion of patients perceiving improvements was significantly greater with onabotA treatment vs placebo. Significantly more patients were "satisfied/very satisfied" with onabotA vs placebo through Day 180. Treatment was well tolerated; both onabotA groups had a similar incidence of treatment-emergent adverse events (TEAEs). Nasopharyngitis (onabotA, 3.9% vs placebo, 0%) and upper respiratory infection (2.9% vs 0%, respectively) were the most common TEAEs. CONCLUSIONS:One injection of onabotA 48 or 72 U was well tolerated and effective in reducing MMP severity as assessed by investigators and patients. LEVEL OF EVIDENCE: 1 (THERAPEUTIC):

BACKGROUND:OnabotA is used to treat masseter muscle prominence (MMP). OBJECTIVE:To assess the safety and efficacy of OnabotA for MMP in a randomized study. METHODS:This 12-month, multicenter, double-blind, placebo-controlled, phase 2 study randomized adults (18-50 years of age) with marked/very marked bilateral MMP (≥4 on the Masseter Muscle Prominence Scale [MMPS]) to OnabotA (24, 48, 72, or 96 U) or placebo; retreatment occurred at day 180 if MMPS ≥4. Lower facial volume at day 90 was measured using Vectra 3-dimensional photography. Safety assessments included computed tomography and dental exams. Evaluations occurred monthly through day 360. RESULTS:Among 187 randomized subjects, significant lower facial volume reductions and percentage of responders (MMPS grade ≤3) were greater with OnabotA versus placebo at day 90 (P < .001 and ≤.008, respectively). Similar efficacy was observed with retreatment. No dose-related safety trends or clinically relevant changes in the mandible or teeth occurred. Localized impact on smile was reported with 96 U OnabotA (n = 4). LIMITATIONS:Limited sample size per individual treatment group. CONCLUSION:OnabotA administered in 1 or 2 treatments over 1 year was associated with significant reductions in masseter muscle volume and MMP severity, with an acceptable safety profile.