INTRODUCTION: Botulinum neurotoxin A (BoNT-A) is a minimally invasive and technically straightforward treatment of masseter muscle (MM) volume reduction and facial contouring, but the literature on its long-term effect on MM volume remains unclear. OBJECTIVE: This study aimed to assess quantitatively for progressive volume changes of lower facial contour after 3 BoNT-A injections in patients with bilateral MM hypertrophy causing square facial morphology using 3-dimensional computed tomographic scans. MATERIALS AND METHODS: Ten female patients with square facial morphology due to bilateral MM hypertrophy were recruited to, and 6 completed, this clinical study. Each received 24 U of BoNT-A into the inferior portion of each MM on both sides, repeated 6 monthly to complete 3 treatments. Masseter muscle volume changes were assessed using 3-dimensional computed tomography at pretreatment (before injections) and posttreatment (1 year after the third injection). RESULTS: Mean MM volume significantly reduced from 26.39 ± 4.18 cm before treatment to 23.26 ± 4.31 cm 1 year after treatment (P = 0.002). CONCLUSION: Three consecutive 6-monthly BoNT-A injections into the MMs reduced their volume by 12% when assessed 1 year after completion of treatment.
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