Three Dimensional Anatomical Study And Biomechanical Simulation Of Nasolabial Fold

Objective:One of our goals is to explore the relationship between the shape of the nasolabial fold and the facial expression muscles.Moreover,this study attempts to use advanced imaging techniques,combined with appropriate computer 3D software,to understand the shape of the facial expression muscles in the nasolabial fold region in a lossless manner,their walking and the three-dimensional spatial relationship between them,to visualize the three-dimensional structure of the complex muscles in the nasolabial fold region.Methods:Based on the existing general anatomical data,the three-dimensional structural skin-muscle-maxillofacial bone model of the nasolabial fold was established by using the engineering design module of the Catia software.After establishing the solid model of the nasolabial fold with the Catia software,the model was then imported into the Hypermesh software.The unit type was set up,the grid division was performed and the material properties were then assigned.Finally,the three-dimensional finite element model of the skin-muscle-maxillofacial bone structure in nasolabial fold region was generated,and then introduced into the Abaqus software with HM format for mechanical loading and biomechanical analysis.In order to further understand the three-dimensional anatomical characteristics of the nasolabial fold,Micro-CT and Nano-CT scans were then performed on the isolated specimens of the nasolabial fold from the cadaveric heads in this study.The 3D reconstructive models of two CT scanning data obtained from the nasolabial fold were carried out with Mimics software.And the similarities and differences between the two scanning methods were compared to visualize the three-dimensional structure of the complex muscles in the nasolabial fold region.Results:In this study,the finite element analysis method was applied to the adjustment of the nasolabial fold muscle system.The connection direction of each group of muscle fibers in the nasolabial fold region was simulated by computer,and the relationship between the shape of nasolabial fold and the facial mimetic muscles was clarified by force loading.The levator labii superioris alaeque nasi,levator labii superioris,zygomaticus minor muscle and zygomaticus major muscle play an important role in the formation of the concave nasolabial fold.And the zygomaticus minor muscle is more important in the formation of the concave nasolabial fold.For the formation of the short linear nasolabial fold,the contraction of the levator labii superioris alaeque nasi,levator labii superioris and zygomaticus minor muscle plays a major role.And their strength balance plays an equal role.For the formation of the midline nasolabial fold,the contraction of the levator labii superioris alaeque nasi,levator labii superioris,zygomaticus minor muscle,zygomaticus major muscle,musculus risorius and musculus depressor anguli oris plays a major role.Their strength is balanced,and plays the same role.For the formation of the long linear nasolabial fold,the contraction of the levator labii super:ioris alaeque nasi,levator labii superioris,zygomaticus minor muscle,zygomaticus major muscle,musculus risorius and musculus depressor anguli oris all plays an important role.But the e:ffect of the musculus risorius is even greater.The contraction of the levator labii superioris alaeque nasi and zygomaticus major muscle plays an important role in the formation of the protuberant nasolabial fold.And the zygomatic major muscle plays a more important role in the formation of the protuberant nasolabial fold.In Micro-CT images,we found that the insertion point of the zygomaticus major muscle was located at the middle and lateral muscle fiber of the levator anguli oris,but not on the orbicularis oris muscle.Similarly,the insertion point of the levator anguli oris was located at the stop fiber of the musculus depressor anguli oris,but not on the orbicularis oris muscle.In Nano-CT images,we also found that the insertion point of the zygomaticus major muscle was located at the middle and lateral muscle fiber of the levator anguli oris,but not on the orbicularis oris muscle.Similarly,the insertion point of the levator anguli oris was located at the stop fiber of the musculus depressor anguli oris,but not on the orbicularis oris muscle.This two findings mentioned above are consistent with that of the Micro-CT scans.In Nano-CT images of the same specimen,we found that the orbicularis oculi muscle beneath the palpebral fissure consists of two parts:upper and lower.And there is a clear boundary between two of them.The upper orbicularis oculi muscle is closer to the skin,while the lower orbicularis oculi muscle is located in the deep subcutaneous layer.And the lower orbicularis oculi muscle is connected with the zygomaticus minor muscle and the levator lip muscle.Furthermore,we found that in Nano-CT images,the relationship between muscle fibers and skin can be clearly observed.After the muscle fibers are issued from its main fiber,the muscle fibers are subdivided layer by layer,and the dermis of each region is controlled by the branches of each muscle fiber to realize the connection between the muscle fibers and the skin.The above findings of Nano-CT make up for the deficiency of previous gross anatomy and Micro-CT scan results,and fill the gaps in this field.Conclusions:Based on the existing anatomical data,a skin-muscle-maxillofacial bone finite element model of the nasolabial fold was established successfully,combined with the Mimics,Geomagic Studio,Catia,Hypermesh and Abaqus software together.This model has good geometric similarity and good biomechanical properties,which provides an ideal biomechanical model for the deformation and biomechanical study of soft tissue such as nasolabial fold.In this study,the relationship between the shape of the nasolabial fold and the facial expression muscles was analyzed by the finite element method.And this advanced biomechanical simulation method was used to explore the clinical rejuvenation surgery of the nasolabial fold,which is very advanced and innovative.Finally,the relationship between the shape of the nasolabial fold and the facial expression muscles was roughly defined.In addition,in this study,the three-dimensional anatomical structure of the nasolabial fold was studied by Micro-CT and Nano-CT scanning,combined with iodine staining technology.And the morphology of each group of muscle fibers in the nasolabial fold region was successfully elucidated in a non-destructive manner.The 3D structure of the complex muscles in nasolabial fold region was visualized by walking and spatial relationship between them.