Background: A prominent mandibular angle is a common reason for aesthetic treatment among Asian women. Such women usually present with hypertrophic masseteric muscles, and one treatment for this uses botulinum toxin A (BoNTA). Detailed effectiveness and physiologic influences of this therapy are still under investigation. Methods: The authors report a prospective study of 10 female volunteers with hypertrophic masseteric muscles who received a single treatment comprising intramuscular injection of BoNTA. The facial change and the discomfort of the injection were self-rated using a visual analog scale, and the patients were regularly inspected up to 1 year. Bite forces also were measured for chronological documentation. Volume changes of masticating muscles were evaluated by three-dimensional computed tomography (CT) scans before and 3 months after injection of BoNTA. Results: The serial photographs and patient subjective evaluation showed an obvious facial change 3 to 6 months after injection. Bite forces decreased from the first day after injection, but started to recover during week 3 and were normal 3 months after injection. Three-dimensional CT evaluation showed a statistically significant mean masseter reduction of about 30%, but no change in the volume of other masticating muscles. There were no serious complications during this study. Conclusions: Injection of BoNTA is an effective alternative for contouring of the lower facial profile by reducing the bulkiness of masseteric muscles. Its effectiveness was noticed as early as 2 weeks after injection and reached a peak effect in month 3. The facial contour gradually returned 6 months after injection. The reduction in bite force was temporary and caused no daily life interference.
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