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Masseter Muscle Volume Changes Evaluated by 3-Dimensional Computed Tomography After Repeated Botulinum Toxin A Injections in Patients With Square Facial Morphology

Chang, Chun-Shin, MD, MS*†; Lin, Susie, DDS, MD; Wallace, Christopher Glenn, MD, MS, FRCS(Plast)†§; Hsiao, Yen-Chang, MD; Lin, Che-Min, DDS, MS†∥; Kang, Gavin Chun-Wui, MD, MEng; Chen, Zung-Chung, MD; Chen, Philip Kuo-Ting, MD; Lo, Lun-Jou, MD; Chen, Yu-Ray, MD; Chen, Jyh-Ping, PhD*

doi: 10.1097/SAP.0000000000001705
Aesthetic Surgery

Introduction Botulinum neurotoxin A (BoNT-A) is a minimally invasive and technically straightforward treatment of masseter muscle (MM) volume reduction and facial contouring, but the literature on its long-term effect on MM volume remains unclear.

Objective This study aimed to assess quantitatively for progressive volume changes of lower facial contour after 3 BoNT-A injections in patients with bilateral MM hypertrophy causing square facial morphology using 3-dimensional computed tomographic scans.

Materials and Methods Ten female patients with square facial morphology due to bilateral MM hypertrophy were recruited to, and 6 completed, this clinical study. Each received 24 U of BoNT-A into the inferior portion of each MM on both sides, repeated 6 monthly to complete 3 treatments. Masseter muscle volume changes were assessed using 3-dimensional computed tomography at pretreatment (before injections) and posttreatment (1 year after the third injection).

Results Mean MM volume significantly reduced from 26.39 ± 4.18 cm3 before treatment to 23.26 ± 4.31 cm3 1 year after treatment (P = 0.002).

Conclusion Three consecutive 6-monthly BoNT-A injections into the MMs reduced their volume by 12% when assessed 1 year after completion of treatment.

From the *Graduate Institute of Chemical and Materials Engineering, College of Engineering, Chang Gung University, Taoyuan, Taiwan, and

Craniofacial Research Center, Departments of Medical Research, Plastic Surgery, and Craniofacial Orthodontics, Chang Gung Memorial Hospital, Taoyuan, Taiwan;

Department of Oral and Maxillofacial Surgery, Vanderbilt University Medical Center, Nashville, TN;

§Department of Plastic Surgery, Royal Devon and Exeter Hospital, Exeter, UK;

Graduate Institute of Dental and Craniofacial Science, College of Medicine, Chang Gung University, Taoyuan, Taiwan; and

Department of Plastic, Reconstructive, and Aesthetic Surgery, KK Women's and Children's Hospital, Singapore.

Received September 19, 2018, and accepted for publication, after revision September 21, 2018.

Conflicts of interest and sources of funding: none declared.

Reprints: Jyh-Ping Chen, PhD, Department of Chemical and Materials Engineering, College of Engineering, Chang Gung University, Taoyuan, Taiwan. E-mail:

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