Three-dimensional Construction Of The Muscles At The Corner Of The Mouth

[Research background] The muscle arrangement at the corner of the mouth is complicated, different anatomical structures closely associated with different facial expressions and facial morphology. At present, the main research methods are gross anatomy and histological observation. Few researchers have studied the three-dimensional relationship between the muscles at the corner of the mouth. For plastic surgeons, to be familiar with the structure of the modiolus and the muscles at the corner of the mouth have significance for an understanding of the injection therapy, facial soft tissue repair and rejuvenation[Objective] Using iodine staining and Micro-CT scanning to obtain tomographic images, import them to Mimics for three-dimensional reconstruction and establish a three-dimensional visualization model to fully understand the structures of the modiolus and the muscles at the corner of the mouth.[Materials and methods] Lip-cheek tissues were cut from aborted fetuses without facial deformity, the tissues were fixed in formaldehyde solution for 24hours, then one specimen was put into the iodine vapor for 2 days another was soaked into the Lugol’s solution for 7days. Finally, the two specimens were studied through Micro-CT scanning and clear images were acquired. Save the images as Dicom format and import into Mimics for editing. A three-dimensional structure model of the modiolus and the muscles at the corner of the mouth was established.[Results]1.The specimen soaked in Lugol’s solution shows clear images of muscle fibers, we can find the modiolus was composed of different muscle fibers such as:orbicularis oris, depressor anguli oris, risorius, zygomaticus major muscles and buccinators. The order of the appearance of the muscles from the skin to oral mucosa at the corner of the mouth are:the pars marginals of orbicularis oris muscles, the pars peripheralis of orbicularis oris muscles, depressor anguli oris and depressor labii inferioris, the zygomaticus major muscles around the modiolus and levator labii superioris, risorius, the main body of zygomaticus major muscles, buccinators. The orbicularis oris muscles appeare in all layers of muscles, and after depressor anguli oris appeared, the muscle fibers are continued until the risorius show up. While the levator anguli oris muscles are not obvious in the specimen. Besides, some muscle fibers form pars marginals of orbicularis oris muscles in upper lip and lower lip are connected in the corner of the mouth, these fibers are not originate from the modiolus.2. From the images, we can see the modiolus contain a lot of muscle fibers. After being soaked in Lugol’s solution, muscles stained more than collagen, permitting their distinction in images. In the upper layer, the modiolus presents as homogeneous low density shadow. In the deeper layer, the muscle fibers show up as white, cord-like structures from different directions converge at the central of the modiolus. Deep in the buccinator, the modiolus is almost composed of muscle fibers.3. The contrast between the two staining methods:In the procession of iodine vapor staining, the specimen is easy to get dehydrated and shrinked and the iodine vapor may cause irritation to respiratory and digestive tracts, while 3.75% Lugol’s solution is relatively safe, easy-to-handle and if the soaking time was extended for a few days, the specimen will not change too much. After Micro-CT scanning, we find the images which are obtained from the soaked specimen are clearer than the images obtained from the specimen that put into the iodine vapor.[Conclusions] A new method (iodine staining and Micro-CT scanning) which was used to build a three-dimensional model of the modiolus and the muscles at the corner of the mouth can clearly reflect the spatial structures of them, and the results make us have a better understanding of the structures of the modiolus and the muscles at the corner of the mouth too.