The Anatomical Basis of Paradoxical Masseteric Bulging after Botulinum Neurotoxin Type A Injection

Hyung-Jin Lee,Hee-Jin Kim,Seong-Taek Kim,Kyung-Seok Hu,In-Won Kang,Kyle Seo,You-Jin Choi

doi:10.3390/toxins9010014

Abstract

The aim of this study was to determine the detailed anatomical structures of the superficial part of the masseter and to elucidate the boundaries and locations of the deep tendon structure within the superficial part of the masseter. Forty-four hemifaces from Korean and Thai embalmed cadavers were used in this study. The deep tendon structure was located deep in the lower third of the superficial part of the masseter. It was observed in all specimens and was designated as a deep inferior tendon (DIT). The relationship between the masseter and DIT could be classified into three types according to the coverage pattern: Type A, in which areas IV and V were covered by the DIT (27%, 12/44); Type B, in which areas V and VI were covered by the DIT (23%, 10/44); and Type C, in which areas IV, V, and VI were covered by the DIT (50%, 22/44). The superficial part of the masseter consists of not only the muscle belly but also the deep tendon structure. Based on the results obtained in this morphological study, we recommend performing layer-by-layer retrograde injections into the superficial and deep muscle bellies of the masseter.

Highlights

The masseter is the most powerful jaw-closing muscle of the masticatory muscle group and is more developed in Asians than in Caucasians
Themuscle musclefibers fibersoriginated originated the superficial from the superficial aponeurosis of the masseter muscle, descended, and changed the from the superficial aponeurosis of the masseter muscle, descended, and changed into theinto tendon structure attaching to the inferior mandibular border
The relationship between the masseter and deep inferior tendon (DIT) could be classified into three types according to the coverage pattern: Type A, in which areas IV and V were covered by the DIT (27%, 12/44); Type B, the coverage pattern: Type A, in which areas IV and V were covered by the DIT (27%, 12/44); Type B, in which areas V and VI were covered by the DIT (23%, 10/44); and Type C, in which areas IV, V, and in which areas V and VI were covered by the DIT (23%, 10/44); and Type C, in which areas IV, V, VI were covered by the DIT (50%, 22/44) (Figure 3)

Summary

Introduction

Various anatomical studies have attempted to determine the most effective BoNT-A injection investigated the intramuscular nerve distribution, motor nerve entry point of the masseteric points and obtain optimal results while minimizingthe complications. Several of these studies have nerve into the masseter, and the relationship between the parotid gland and the marginal investigated intramuscular nerve distribution, the motor nerve entry point of the masseteric nerve mandibular branch facial nerve [11,12,13,14]

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Conclusion