Effect of a second injection of botulinum toxin on lower facial contouring, as evaluated using three-dimensional laser scanning

Abstract

Botulinum toxin type A (BoNT-A) injection therapy—which is less invasive and safer than surgical treatment—has been widely used to treat masseteric hypertrophy to improve the lower facial contour. There have been many studies on BoNT-A therapy, but in most cases only a single BoNT-A injection was administered and the effects of that injection on the volume and thickness of the masseter muscle and the duration of those effects were evaluated using ultrasonography and computed tomography. Few studies have compared changes in the facial contour resulting from single and double BoNT-A injections using three-dimensional (3D) laser scanning. This imaging method is a useful and accurate method of assessing changes in the external lower facial contourThe aim of this study was to characterize differences in the changes in the lower facial contour achieved with a single injection of BoNT-A and with two injections, using 3D laser scanning, with the aim of establishing the effect of a second injection.In this study, twenty volunteers were randomly divided into two groups. The group I (n=10) received a single BoNT-A injection, while the group II (n=10) received two BoNT-A injections, the second being administered 4 months after the first. Each injection comprised 25 U of BoNT-A, and was administered to the masseter muscle, bilaterally. Evaluation of the effect of BoNT-A injection was performed using 3D laser scan images obtained before the injection and 6 months thereafter in the group I, and before the first injection and 6 months thereafter in the group II (i.e., 2 months after the second injection). The volume and thickness of the most prominent area of the lower face were measured bilaterally.1. There were significant changes in the volume and thickness of the most prominent area of the lower face in the group I. The volume and thickness reduced by 1186 mm3 (P<0.05) and 1.52 mm (P<0.001), respectively.2. There were significant changes in the volume and thickness of the most prominent area of the lower face in the group II. The volume and thickness reduced by 4072 mm3 (P<0.001) and 3.84 mm (P<0.001), respectively.3. The reductions in volume and thickness were significantly greater in the group II than in the group I. (P<0.001).The volume and thickness of the lower facial contour decreased significantly at 6 months after BoNT-A injection in groups I and II. However, the second injection administered 4 months after the first in the group II further reduced the volume and thickness compared to the group I. These findings demonstrate that the administration of a second BoNT-A injection is appropriate and effective for maximum esthetic results for the lower facial contour.