Effect of unilateral injection of botulinum toxin on lower facial asymmetry as evaluated using three-dimensional laser scanning

Background Many patients with a hypertrophic masseter muscle desire its reduction to decrease the prominent mandibular angle. Surgical reduction has been widely used to this end, but bilateral injection of botulinum toxin into the masseter muscle is a less-invasive alternative to surgical reduction that has recently become the focus of public interest. The aim of this study was to measure changes in volume and thickness unilaterally in hypertrophic masseter muscles after unilateral botulinum toxin type A (BoNT-A) injection using three-dimensional (3D) laser scanning as a method of evaluation. Methods and Materials The volume and thickness of the lower facial contour of 10 patients with unilateral hypertrophic masseter muscle were measured using 3D laser scanning before and 4, 8, and 12 weeks after a unilateral injection of 25 U of BoNT-A. The 3D scans were superimposed to determine postinjection changes in volume and thickness. Results Although there was little change in the noninjected side over the experimental period, the mean volume and thickness of the injected side at each time point clearly and statistically significantly decreased between preinjection and 4, 8, and 12 weeks postinjection. Conclusion Unilateral BoNT-A injection appears to be an effective esthetic treatment for patients with muscle-induced facial asymmetry.