Mandible changes evaluated by computed tomography following Botulinum toxin a injections in square-faced patients

Background: A facial contour that is oval is more pleasing in Asian women. Patients with a square face often seek facial contouring procedures to improve their appearance. Treatment often involves various combinations of Botulinum NeuroToxin A (BoNTA) injections into the masseters and/or mandibular angle resection. Many physicians claim that muscle paralysis with injections alone will decrease pulling on the underlying bone and also treat underlying bony flaring when present. Muscular changes after BoNTA injections have been well documented. However, the effect of BoNTA injections on the underlying mandibular bone morphology has not been studied to the best of the authors' knowledge. The goal of this study was to determine whether there are mandibular changes after masseter injection with botulinum toxin. Methods: In this retrospective study of ten female patients seeking treatment for a square face, three-dimensional CT scans were taken before and 3 months after standardized BoNTA injections in bilateral masseters. Mandibular cortex thickness, mandibular bone thickness, and mandibular volume were measured. Results: Soft-tissue changes were observed but no bony changes were observed 3 months after injections. Conclusions: In this study of adult patients, there were no statistically significant mandibular changes 3 months after BoNTA injection. The current theory of mandibular flaring resolution after partial muscle paralysis is not supported by our findings. Therefore, a patient presenting both masseteric hypertrophy and bony flaring will most likely require a combined muscular and bony procedure.