Background: Since type A botulinum toxin was first reported for the treatment of masseter muscle hypertrophy in 1994, there have been few reports about cosmetic indications for contouring procedures of the lower face with injection of botulinum toxin type A, and this procedure remains unpredictable.
Objectives: This study attempted a quantitative prospective analysis of reduction of masseter muscle hypertrophy after Botox injection, using ultrasound and computerized tomography (CT) scans to analyze the possible use of botulinum toxin type A as a contouring procedure for the lower face.
Methods: Forty-five patients consented to the study and received a contouring procedure of the lower face from November 2001 to April 2002. Twenty five to 30 U of Botox per side was injected at five to six points into the prominent portions of the mandibular angle. Serial measurements were made of the thickness of the masseter muscle by ultrasound and CT before the injections and at 1 and 3 months thereafter. A quantitative analysis for the masseter thickness changes was performed on just one patient who underwent all ultrasound and CT scans. Statistical analysis of the masseter thickness change was by two-way and multiple comparison analysis. To evaluate clinical long-term effects, the patient's satisfaction with the procedure and any side effects after injections were monitored during 4 to 10 months of follow-up.
Results: Among the total of 45 patients, 15 underwent the three ultrasound measurements, and 14 had the three CT measurements. With regard to quantitative analysis of the thickness change to the masseter on both sides of the face according to time points, this was gradually reduced by both the ultrasound and CT measurements during the first 3 months. By ultrasound, the maximum reduction in masseter thickness was seen 1 month after the injections, with a slight increase being observed at 3 months after injection. A continued reduction of masseteric muscle thickness was seen on the CT up to 3 months after injection. In terms of patient satisfaction for up to 10 months of follow-up, the results were as follows: very satisfied, 1; satisfied, 36; slight improvement, 3; no change or dissatisfied, 5. Main local side effects included masticatory difficulties, muscle aching at injection sites, and speech disturbance. However, these side effects were transitory, usually lasting from 1 to 4 weeks after the injections.
Conclusions: Preliminary results from this study suggest that an injection of Botox resulted in relatively satisfactory clinical effects, although there was only a short-term follow-up. It is suggested that the use of botulinum toxin type A for contouring of the lower face can be established as a simple, predictable, alternative facial contouring procedure without a prolonged recovery time.