The Comparison of Long-term Effect of Botox(R) Injection on Lower Face Contouring after Single Injection and Long-term Repeated Injections by Standardized Photograph Analysis

PURPOSE: A botulinum toxin type A(BoNT-A) injection has been used as a noninvasive management for lower face contouring since 2000. The aim of this study is to compare reduction rate of lower face width for a longtime according to repeated Botox(R) injections on masseter muscles for lower face contouring procedure. METHODS: Forty-five patients were analyzed for single session of Botox(R) injection and 13 patients were evaluated for repeated Botox(R) injections for over two years. Single injection group was tracked regular intervals at 1, 3, 6, 10, 12 months after the injection, and repeated injection group was measured at every injection time. Twenty-five to thirty units of Botox(R) was injected into each masseteric muscle at five to six points at the prominent portions of the mandibular angle. Standardized frontal view of digital photographs were analyzed by Adobe Photoshop(R)(version CS3) to measure an reduction rate of lower face's width. RESULTS: Reduction rate was 3.7%, 6.9%, 6.2%, 4%, 4% at 1, 3, 6, 10, 12 months post injection each other in single injection group. However, more than 8% reduction rate was found in repeated injection group persistently for more than two years. CONCLUSION: This study shows that effective duration of Botox(R) injection for lower face contouring is expected to continue over one year clinically. Moreover, repeated injections maintained lower reduction rate consistently for a long time. Therefore, repeated injections on masseter muscles at regular intervals is the most effective procedure for lower face contouring.

The Change of the Maximal Bite-force after Botulinum Toxin A Injection for Lower Face Contouring

The temporary effects of muscle atrophy, followed by chemodenervation due to acetylcholine blockade at the neuromuscular junction by botulinum toxin type A(BTX-A) were mainly used for the treatment of hypertrophied muscle. In the treatment of masseter hypertrophy or cosmetic contouring of the lower face with injection of botulinum toxin type A, these muscle atrophy causes the change of the bite-force inevitably. Although several reports about the histological change of muscle, ultrasound and computerized tomography measurement studies of the change of muscle thickness in the treatment of masseter hypertrophy with injection of BTX-A have become available recently, it is necessary to study further the change of the bite-force and the relationship between the bite-force and clinical effects after the botulinum toxin A injection. The aim of this study was to evaluate the change of maximal bite-forces after botulinum toxin type A injections for treating the contouring of the lower face. Botulinum toxin type A(BTXA(R), Lanzhou, China) of 25U per side was carried out in 7 subjects. The change of maximal bite-forces was evaluated at pre-injection and 2 week, 4 week, 8 week, 12 week post-injections using bite- force measuring machine(MPM-3000, Japan). There were statistically significant differences between pre-injection and 2 week, 4 week, 8 week post-injections(p<0.05). However, there was no significant difference between pre-injection and 12 week post-injection. In conclusion, the change of maximal bite-forces after BTX-A injections according to the period was similar to the histological change of the muscle. The clinical effects last more longer than maximal bite force. Therefore, it is necessary to evaluate further these difference with more larger samples and the relationship between the change of maximal bite force and clinical effects.