Background: Botulinum toxin type A has been increasingly used to improve the lower face contour in masseter hypertrophy. Different dosages and injection techniques are suggested in the literature, but the ideal approach remains unclear. This study aimed to establish an objective masseter classification method for a personalized botulinum toxin type A injection protocol.
Methods: A combination of clinical palpation, B-mode ultrasound examination, and anatomical dissection studies was applied to classify the masseter regarding bulging type on clenching and muscle thickness in a normal population and in patients desiring reduction of masseter hypertrophy. Based on these findings, a tailored botulinum toxin type A injection protocol was set up and evaluated in a prospective clinical study regarding masseter thickness, facial measurements, patient satisfaction, and complications.
Results: A total of 504 masseters were classified into five bulging types (minimal, mono, double, triple, and excessive) and three degrees of thickness (<10 mm, 10 to 14 mm, and >14 mm). Two hundred twenty cases were treated using individualized botulinum toxin type A injection dosages (20 to 40 units) and sites (one to three per muscle); the treatment was applied in 220 cases, according to the respective classification. Masseter thickness decreased significantly, from 12.9 ± 2.9 mm to 8.7 ± 1.7 mm, 3 months after injection (p < 0.01). The initial ratio of the widest width of the lower face to the intercanthal distance (3.3 ± 0.18) was also significantly reduced (3.0 ± 0.2; p < 0.01). The overall patient satisfaction rate was 95.9 percent. No serious complications occurred..
Conclusions: The present study provides the scientific basis for individualized botulinum toxin type A injection for masseter hypertrophy. This protocol allowed for reduction of injection dosage and complication rates, and showed beneficial clinical effects in terms of significantly reduced masseter volume and improved lower face contour.
CLINICAL QUESTION/LEVEL OF EVIDENCE: Therapeutic, IV.
Shanghai, People’s Republic of China; and Munich, Germany
From the Department of Plastic and Reconstructive Surgery, Shanghai Ninth People’s Hospital Affiliated to Shanghai Jiao Tong University School of Medicine; and Hand, Plastic, and Aesthetic Surgery, Department of General, Trauma, Hand, and Plastic Surgery, University of Munich.
Received for publication October 7, 2013; accepted December 30, 2013.
The first two authors contributed equally to this work as first authors.
Disclosure: None of the authors has any commercial associations or financial interest in any of the drugs, products, or instruments used in this study. All of the authors conform to the Declaration of Helsinki.
Qingfeng Li, M.D., Ph.D., Department of Plastic and Reconstructive Surgery, Shanghai Ninth People’s Hospital Affiliated to Shanghai Jiao Tong University School of Medicine, 639 Zhizhaoju Road, Shanghai 200011, People’s Republic of China, firstname.lastname@example.org