New Insights into the Three-Dimensional Anatomy of the Facial Mimetic Muscles Related to the Nasolabial Fold: An Iodine Staining Technique Based on Nano-computed Tomography.

Abstract

This study aimed to introduce a novel approach to study the facial mimetic muscles (FMMs) in relation to the nasolabial fold (NLF) and realize the visualization of complex three-dimensional (3D) structures and spatial relationships of the FMMs. Nano-computed tomography (nano-CT) and iodine staining techniques were used to obtain the two-dimensional (2D) radiographs of the FMMs. Materialise Mimics software was then used to reconstruct the 3D model of the FMMs. The zygomaticus major muscle (ZMM) was divided into trunk fibers and branch fibers. The trunk fibers of the ZMM were subdivided into branch fibers layer-by-layer. Adipose tissue in the cheek was not a mass of unorganized fat. It was separated and fixed by branch fibers. Moreover, the trunk fibers of the ZMM were directly connected to the levator anguli oris (LAO), not the skin. On the contrary, the ZMM was connected to the skin by its subdivided branch fibers indirectly. The muscle fibers in the modiolus were organized, rather than disorganized. In other words, the terminal of the trunk fibers of the ZMM was located in the LAO. Moreover, the terminal of the trunk fibers of the LAO was located at the terminal of the trunk fibers of the musculus depressor anguli oris at the corner of the mouth. Furthermore, the levator labii superioris alaeque nasi was not directly connected to the orbicularis oris muscle. It was connected to the combination of the LLS and the rhinaeus. Although nano-CT has many disadvantages, it enabled the 3D anatomical study of the FMMs in relation to the NLF when combined with iodine staining. We imported the 2D images obtained by nano-CT scanning into the Mimics software, successfully reconstructed the FMMs, and finally obtained images of complex 3D structures of the FMMs. The shapes, positions, and 3D spatial relationships of the FMMs were clearly visualized. The novel insights into the 3D anatomy of the FMMs may help understand the formation of the NLF. Finally, the results of this study may help improve the rejuvenation surgery of the NLF soon. This journal requires that authors assign a level of evidence to each article. For a full description of these Evidence-Based Medicine ratings, please refer to the Table of Contents or the online Instructions to Authors www.springer.com/00266.