Anatomical Characterization and Three-Dimensional Modeling of the Muscles at the Corner of the Mouth: An Iodine Staining Technique Based on Micro–Computed Tomography

These comments refer to an article published recently in the Journal, “Anatomical Characterization and Three-Dimensional Modeling of the Muscles at the Corner of the Mouth: An Iodine Staining Technique Based on Micro–Computed Tomography.”1 Sun et al. obtained three-dimensional images from two aborted fetuses using iodine staining and micro–computed tomography. The authors observed that only the transverse fibers of the buccinator muscle were visible in the modiolus region in the deep buccal layer. Based on this finding, they concluded that the pars peripheralis of the orbicularis oris muscle is mainly responsible for the sphincter function and carries the traction of the surrounding facial expressive muscles, whereas the pars marginalis is dragged inward by the buccinator muscles.1 I agree that iodine staining and micro–computed tomography can be good tools for visualizing certain areas of the musculature. However, several questions remain regarding the Results and Discussion of this article. According to Lightoller’s article, which Sun et al. did not cite, the modiolus is the area of insertion of all the muscles entering it except the orbicularis oris, for which it forms an area of origin. Because the buccinator is a direct anatomical antimere of the orbicularis oris, it probably helps to control the modiolus, but only to a minor extent. For the most part, the buccinator, like the orbicularis oris, is free to perform its own functions between its lateral and median fixed points; namely, the lateral origin from bone and raphe and the medial modiolar insertion.2 In my previous research, the pars marginalis had more slow fibers (30 percent) than the pars peripheralis (22 percent). Fast fibers react quickly, but have low endurance. Slow fibers respond slowly, but have high endurance. This means that the pars marginalis has a slower reaction, but great endurance, and it mostly takes part in closing the mouth and whistling. The fiber reaction of the pars peripheralis is faster than that of the pars marginalis. This quick-reacting pars peripheralis is important in speaking.3 The reason for this discrepancy between Sun and previous authors is likely that Sun took specimens from only two fetuses, with unknown abortion dates, and the musculature of the fetus is different from that of newborns and adults. ACKNOWLEDGMENT This study was supported by a grant from National Research Foundation of Korea (NRF-2019001834). DISCLOSURE The author has no conflict of interest to declare.