| The human cranial temporomandibular joint is more vulnerable to be damaged.Especially in the modern society,although there are fewer and fewer threats from war in peaceful times,due to the continuous progress of society,we humans are inevitably exposed to some unavoidable disasters in daily life.Among them,for example,a fall or an impact will cause great damage to the temporomandibular joint.Therefore,in human life,when a human is exposed to a disaster such as an explosion or a traffic accident,the temporomandibular joint is more likely to be impacted and the location It is easy to cause joint damage to other parts.Therefore,in the field of clinical surgery research,how to fully understand the damage mechanism of the temporomandibular joint when subjected to external force,as well as the damage and cushioning effect of the musculoskeletal system of the jaw joint has become very important.The Finite Element Method(FEM)has shown its increasingly important position in the field of biomechanics nowadays.The FEM is based on a computer system and uses numerical calculations to analyze some engineering mechanics problems.In the field of biomechanics,its main advantage is that it can accurately simulate the complex parts of the human body through detailed refinement of the research object step by step.Therefore,this method can simplify each part of the human body into a limited number of geometric units with simple shapes.In this way,the study of the complex structure of the human body can be simplified into the study of each simplified unit.In the past few decades,the finite element method has been rapidly developed in the fields of stomatology,orthopedics,rehabilitation,and other fields.Especially as computer technology becomes more mature,the development and optimization of various finite element analysis software have allowed simulation results Getting closer to reality.Our research group has accumulated a lot of practical experience in the use of finite element simulation to study biomechanics,especially various types of maxillofacial injuries.We have also verified the simulation results using animal experiments and other methods,and have received positive feedback.The finite element method has the advantages of maneuverability and reproducibility when studying the problems caused by external force impact on the temporomandibular joint.In addition,the simulation experiment obtains the damage mechanism by simulating different impact conditions,which can ensure the safety of the experiment.Therefore,based on the previous work of our team,this work intends to establish a three-dimensional finite element model of the human craniofacial face and simulate the impact of the chin impact,mandibular body impact,and mandibular angle impact.We analyze force distribution of key parts such as mandible,condyle,articular disc and massetermuscle to understand its damage mechanism.The findings of this work provide a theoretical basis for surgeons to understand the possible damage to the musculoskeletal system of the mandibular joint when subjected to different impacts.Methods:1.First,a representative adult male of Chinese Han nationality was contacted as a volunteer,and CT and MRI images of the volunteers’ heads were obtained by computerized scanning(CT)and Magnetic Resonance Imaging(MRI).Then the bone tissue pixels belonging to the mandible were separated by the MIMICS software,and a three-dimensional STL geometric model of the mandible was finished.Further,NURBS surface fitting was performed by Geomagic Studio software,and finally the three-dimensional geometric entity of the TMJ system was harvested.Finally,the TMJ system was meshed using Hypermesh software to complete the construction of the 3D model.2.Finite element post-processing was performed by LS-Pre Post to obtain the Von Mises stress cloud map and mandible fracture dynamic map of mandible,joint disc,mandibular fossa,masseter muscle and other tissues.Results:1.Using the collected human maxillofacial CT and MRI data,we complete the 3d digital image reconstruction of each TMJ structure and the facial mesh model processing.2.The three-dimensional finite element model of human mandible impact injury was successfully established,which include parameter settings such as material parameters,interaction between various structures of TMJ system,boundary conditions and so on.3.In this research model,after being impacted in the middle of the mandible,the first fracture site was the right condylar neck,and then the left condylar neck and the impact point were successively fractured;after the mandible was impacted,the first fracture site was the contralateral condyle The neck,followed by the impact of the condylar neck and the impact point were successively fractured;after the impact of the mandibular angle,the first fracture site was the impacted condylar neck,and then the contralateral condylar neck and the impact point were fractured.The fracture sites of mandibular impingement are mainly the bilateral condylar neck and the impingement sites,but when there are multiple mandibular fractures,the fracture sites caused by different impingement sites have different order of occurrence.4.The impact energy of the mandible is different,and the fracture conditions are different.When hitting the midpoint of the mandible,the critical velocity of one or three fractures is between 2.78 ～ 8.33m/s.When impacting the mandible or mandibular angle,the critical velocity of one fracture is between 2.78 ～ 8.33m/s;the critical velocity of two or three fractures is between 8.33 ～ 9.72m/s.5.The stress nephogram of mandibular shows that despite the high stress area is easier to appear in the condylar neck,due to the existence of the special structure of articular disc and articular capsule,the outer surface of the condylar on both sides is in a low stress level.It acts as a good buffer against the high stress from the condyle neck.It shows a stepped decline in the stress distribution on the bone tissues on both sides of the articular disc,and the stress transferred to the articular socket and the skull base is significantly lower than the stress in the mandibular condyle neck,thus avoiding the injury to the brain.When the stress intensity exceeds the maximum deformation performance of the articular disc,the cushioning effect of the articular disc will be weakened and the stress level of the articular fossa will be higher.At this time,the possibility of contusion of the articular disc,perforation of the articular disc and skull base injury will be increased.6.The masseter muscle is deformed by force and the load is transferred to the mandible.Under relatively low speed impact,there was no tearing in each group in this experiment,but there was a large deformation,and the damage was mainly contusion.Conclusions:1.The TMJ system impact injury biomechanical finite element model was successfully established,and the mechanical response analysis of the mandible under different speed and impact at different locations was completed.The fracture laws of the mandible were basically in line with clinical phenomena.2.In the process of transmitting stress from the condyles to the mandibular fossa,a "stepped" decline occurred,which has a certain protective effect on the skull and brain.The joint disc plays a good buffer role in the TMJ system when the mandible is impacted.The diagnosis and treatment should pay attention to the examination of contusion of articular disc perforation and skull base injury.3.In this study,while simulating the biomechanical response of TMJ and bone tissue,the mechanical response of muscle tissue was also preliminarily explored,which can be used for more detailed and more accurate prediction of injuryand can guide clinical protection.When the mandibular angle is impacted,the masseter muscle can play a good role of buffer and reduce the stress on the bone tissue,so as to slow down the degree of injury to a certain extent.In a certain range of impact velocity,the damage degree of masseter muscle and other soft tissue was positively correlated with impact velocity. |
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