"Optimizing Injection Sites of Botulinum Toxin Type A for Improving Oral Commissure Position: A Two-Stage, Prospective, Double-Blind, Randomized Trial".

Abstract

Drooping oral commissures can impart a displeased appearance, negatively affecting psychosocial interactions and well-being. Botulinum toxin type A (BTX-A) is an efficacious treatment for mouth corner lift. However, the optimal injection strategy is controversial. Therefore, this study aims to compare the efficacy and safety of BTX-A injection at different sites of depressor anguli oris (DAO) muscle and to assess the added benefit of BTX-A injection into the platysma (PLT). This two-stage, single-center prospective study included a randomized, double-blind randomized trial (stage 1) and a non-randomized prospective study (stage 2). Primary outcomes were oral commissure position (OCDA, OCLA) and lip asymmetry (DSL) using three-dimensional photogrammetry. Secondary outcomes included patient satisfaction, pain, and side effects. Both methods improved OCDA and OCLA across all time points, with lower DAO injection showing greater effects than the upper site. DAO+PLT further improved OCLA at 1 month and OCDA at 6 months. Satisfaction was higher with DAO+PLT (P < 0.05). DSL differences were <1 mm. No severe adverse events occurred. Lower DAO injection is more effective in inhibiting DAO movement. DAO+PLT yields superior commissure lifting with minimal side effects.