Jung-Hee Bae1, Da-Yae Choi, Jae-Gi Lee, Kyle K Seo, Tanvaa Tansatit, Hee-Jin Kim. 1. *Division in Anatomy and Developmental Biology, Department of Oral Biology, Human Identification Research Center, BK21 PLUS Project, Yonsei University College of Dentistry, Seoul, South Korea; †Department of Dentistry, College of Medicine, Inha Research Institute of Medical Science, Incheon, South Korea; ‡Department of Dental Hygiene, School of Health and Medicine, Namseoul University, Cheonan, South Korea; §Department of Dermatology, Modelo Clinic, Seoul National University College of Medicine, Seoul, South Korea; ‖Department of Anatomy, Chula Soft Cadaver Surgical Training Center, Faculty of Medicine, Chulalongkorn University, Bangkok, Thailand.
Abstract
BACKGROUND: The botulinum neurotoxin Type A (BTX) injection into the masseter muscle often causes a change in the facial expression. There is as yet no precise anatomic evidence to support this etiologic factor of constrained facial expressions. OBJECTIVE: The aim of this study was to clarify the location and boundaries of the risorius muscle and its topographical relationship with the surrounding structures. MATERIALS AND METHODS: This study involved the dissection of 48 hemifaces. The locations of origin and insertion points of the risorius muscle were measured, and the masseter muscle was divided into 6 equally sized rectangular areas. RESULTS: Cases where the masseter muscle was covered by the risorius muscle were classified into the following 4 types: in Type A, Area III was partially covered by the risorius (17.8%); in Type B, Area VI was partially covered (20.0%); in Type C, Areas III and VI were partially covered (53.3%); and in Type D, Areas II, III, and VI were covered (6.7%). CONCLUSION: These findings suggest that the medial part of the masseter muscle represents a hazard zone into which the injection of BTX may affect the risorius muscle, potentially resulting in iatrogenic unnatural facial expressions.
BACKGROUND: The botulinum neurotoxin Type A (BTX) injection into the masseter muscle often causes a change in the facial expression. There is as yet no precise anatomic evidence to support this etiologic factor of constrained facial expressions. OBJECTIVE: The aim of this study was to clarify the location and boundaries of the risorius muscle and its topographical relationship with the surrounding structures. MATERIALS AND METHODS: This study involved the dissection of 48 hemifaces. The locations of origin and insertion points of the risorius muscle were measured, and the masseter muscle was divided into 6 equally sized rectangular areas. RESULTS: Cases where the masseter muscle was covered by the risorius muscle were classified into the following 4 types: in Type A, Area III was partially covered by the risorius (17.8%); in Type B, Area VI was partially covered (20.0%); in Type C, Areas III and VI were partially covered (53.3%); and in Type D, Areas II, III, and VI were covered (6.7%). CONCLUSION: These findings suggest that the medial part of the masseter muscle represents a hazard zone into which the injection of BTX may affect the risorius muscle, potentially resulting in iatrogenic unnatural facial expressions.
Authors: Kyu-Lim Lee; Hyun Jin Cho; Hyungkyu Bae; Hyun Jin Park; Min Sun Park; Hee-Jin Kim Journal: Toxins (Basel) Date: 2020-03-22 Impact factor: 4.546