Development Of Finite Element Models, Simulations And Preliminary Biomechanical Analyses For Blast Injuries To The Mandible

The maxillofacial region is often damaged by explosives as an exposed part of thebody sustained in wartime and peacentime. At a time when explosive weapons areincreasingly used and terrorist activities are on the rise, blast injuries to the maxillofacialarea, especially the mandible, are increasing. Hence, researches for mandibular blastinjuries have become an important subject in the researches of maxillofacial and evenfull-body trauma. Currently, researches on mandibular blast injuries are focused on traumatreatment and reconstruction; however, the basic science that includes the creation of a blastinjury model and subsequent biomechanical analyses have been overlooked. The traditionalmodels of blast injury can reliably mimic the damage to the human body from an explosion;however, scientific, technological and social developments are making this approachobsolete, especially because it increasingly faces challenges associated with medical ethics.The finite element method (FEM) is a mature computer simulation methods of60-yearhistory in the engineering and mechanical fields and has became the most widely usedmethod of computer simulation technology now. FEM has been applied to the medical fieldfor fifty years, in the past fifty years, the FEM has been widely used in the in medicineparticular in oral medicine and has become one of the conventional methods ofbiomechanical analysis. Because the FEM can compensate for the deficiencies of thetraditional experimental studies of blast injury mechanisms, so it can be used inmaxillofacial blast injury and contribute to the in-depth study of maxillofacial blast injurymechanisms and can provide new ideas and methods of fast injury judgment, rapidtreatment, wartime protection, assessment of wounding effect of maxillofacial blast injury.In this study,3D FE models of the pig mandible were developed to simulate blastinjuries and experimental studies were carried out to validate the FE model and simulatedmethod. Then,3D FE models of mandible of Chinese Visible Human (CVH) for blast injuries were developed and dynamical simulations were carried out by using these models.Based on the simulation results of FEM, the biomechanical mechanism of blast injuries ofthe human mandible were investigated and discussed. The main methods and conclusionswere as follows:Methods and Results:1. Based on the improved animal model of blast injuries of the pig mandible, anexperimental study was carried out to measure impact load parameters from the pigmandibles that were damaged at the mandibular angle by standard600mg RDX paperelectric detonators at5cm and15cm distances. The experimental results showed that thedata were reliable and representative. The improved animal model of blast injuries of thepig mandible was reasonable and repeatable. The results of the experimental study can beused to validate the FE model and simulated results.2. Computed tomography (CT) data of the pig mandible was imported into MIMICSsoftware. A three-dimension computer-aided design (CAD) model of the pig mandible wasreconstructed by using certain functions of MIMICS. Then, the original triangular surfacemesh model of the pig mandible was generated by the “remesh” module of MIMICS. Basedon the surface model of the pig mandible, a combined hexahedral-tetrahedral FE model ofthe pig mandible was developed by ANSA software. The results showed that the number ofthe elements and node were36254and38875respectively, and all the elements were solidelements. The FE model of the pig mandible was similar to its anatomical structure. Withlower cost of modeling, the combined hexahedral-tetrahedral FE model of the pig mandiblecan meet the demand of biomechanical research of blast injury of the pig mandible.3. By choosing appropriate constitutive model, biomechanical parameters and contactalgorithm for the FE models of the pig mandible, finite element analysis (FEA) wasperformed through the LS-DYNA code under impact loads similar to those obtained fromthe experimental study. The FEM of simulation of blast injuries of the pig mandible wasvalidated based on the results of comparison between the results of FE simulation andexperimental study. The results showed that the constitutive models, algorithm and theparameters, which were chosen for the FE model of blast injuries to pig mandible in ourstudy, were reasonable and reliable. The FEM utilized in our study had a fairly capability ofpredicting on blast injuries of the pig mandible. 4. Firstly, the head and facial CT image of Visible Chinese Human were imported intosoftware MIMICS to reconstituted3D computer-aided designing surface mesh models.Then, the model was imported to the finite element pre-processing software ANSA toreconstituted combined hexahedral-tetrahedral FE model of the pig mandible for blastinjuries. The number of the elements and node were26644and27522. The results showedthat the model had good quality and good similarity and met the requires of next stepsimulation absolutely.5. Based on the previous FE simulation of blast injuries to the pig mandible,compatible material model, internal parameters, boundary condition and algorithm ofcontact in LS-DYNA software were selected. After computation of simulation, the dynamicdamage process, stresses and strains distributions in its various regions under differentinjury conditions(two injured parts,three explosions equivalents,three injured distance)were simulated by using3D FE model of blast injuries of the human mandible. The resultsshowed that the FE model and methods could dynamically simulate dynamic damageprocess of blast injuries to the human mandible, and could dynamically simulate the processof the spreading and the stress distribution patterns of stresses and strains in each region ofthe mandible affected by blast.Conclusions:1. The3D FE model of blast injuries of pig mandible were successfullyestablished.The animal experiment results demonstrate the rationality and reliability of theFE model and simulated results.When concerned with the investigation of biomechanicalmechanism of blast injuries, FEM can make up for the insufficiency of traditionalexperimental models.2. The3D FE model of blast injuries of human mandible were established and thedamage process of the mandible in different injury conditions were simulated successfully.The simulation results show the feasibility and reliability of the applications of FE methodin maxillofacial blast injuries and can provide a reference for maxillofacial blast injurymechanism.3. The biomechanical analyses of the human mandible blast injuries were carried outsuccessfully, Von Mises stress and effective strain could be used as criteria of judgment andevaluation of bone damage severity and could be used as indicators of finite element simulation predicted of bone damage.4. In the injury process of blast, the regions of condyle and simoid notch presentedhigh stress and high strain, and produced fracture easily.5. The3D finite element models and simulation results of our experiments had somedeficiencies and needed to be refined and improved continually.