| As an exposed part of human body, the maxillofacial region is more susceptible to kinds of firearm-related injuries. The firearm-related injuries of the maxillofacial region have a much higher ratio than the other parts of human body, either in war or peace time. So, it is important to find out the biomechanical mechanism and basic principles of wound ballistics of the maxillofacial region, for clinical, forensic and military purposes. However, due to the difficulty of reproducing the complex anatomical structures of the maxillofacial region by using animal or synthetic material models, the dynamic interactions between projectiles and facial tissues have not been extensively researched.Being an effective mathematical method for solving complex mechanical problems with complicated geometries, the finite element method (FEM) is widely used in study of biomechanical mechanisms. FEM can provide an"insight view"of the interaction processes and clarify transient dynamic mechanisms between the projectile and tissues. It may offer the possibility to precisely measure the amount of energy or force delivered to the tissues, which may correlate with the degree or patterns of biological tissue injury. Moreover, FEM has the advantages of good repeatability, low cost and manageable load conditions, which makes up for the insufficiency of human cadavers, animal and synthetic material models.In this study, a finite element (FE) model of the pig mandible was developed to simulate ballistic impact, and experimental studies were carried out to validate the FE model. Based on the simulation results of FEM, the biomechanical mechanism of wound ballistics of the mandible was investigated and discussed. The main methods and conclusions were as follows:Methods and Results:â… Computed tomography (CT) data of the pig mandible was imported into MIMICS software. A three-dimension computer-aided design (CAD) model of the pig mandible was reconstructed by using certain functions of MIMICS. Then, the original triangular surface mesh model of the pig mandible was generated by the"remesh"module of MIMICS. Based on the surface model of the pig mandible, a combined hexahedral-tetrahedral FE model of the pig mandible was developed by ANSA software. The results showed that the number of the elements and node were 674863 and 261997 respectively, and all the elements were solid elements. The FE model of the pig mandible was similar to its anatomical structure. With lower cost of modeling, the combined hexahedral-tetrahedral FE model of the pig mandible can meet the demand of biomechanical research of wound ballistics of the pig mandible.â…¡Based on the improved animal model of wound ballistics of the pig mandible, an experimental study was carried out to measure impact load parameters from the pig mandibles that were shot at the mandibular angle by a standard 7.62 mm M43 bullet or 6.3 mm steel ball. The experimental results showed that the data were reliable and representative. The improved animal model of wound ballistics of the pig mandible was reasonable and repeatable. The results of the experimental study can be used to validate the FE model.â…¢By chosing appropriate constitutive model, biomechanical parameters and contact algorithm for the FE model of the pig mandible, finite element analysis (FEA) was performed through the LS-DYNA code under impact loads similar to those obtained from the experimental study. The FEM of simulation of wound ballistics of the pig mandible was validated based on the results of comparison between the results of FEA and experimental study. The results showed that the constitutive model, contact algorithm and the parameters, which were chosen for the FE model of pig mandible in our study, were reasonable and reliable. The FEM utilized in our study had a fairly capability of predicting on wound ballistics of the pig mandible.â…£By using the validated FEM utilized in our study, FEA was made under different loads and boundary conditions, including different velocities and shape of projectiles. Based on the results of comparison of the output data of FEA among different velocities and shape of projectiles, the biomechanical mechanism of wound ballistics of the mandible was investigated and certain conclusion was drawn.â…¤By using the element free Galerkin (EFG) method, the process of muscle tissue penetrated by a 7.62mm bullet was simulated. The results showed that the EFG method can meet the need of simulation of penetrating wound of muscle tissue.Conclusions:â… When concerned with the investigation of biomechanical mechanism of wound ballistics, FEM can make up for the insufficiency of human cadavers, animal and synthetic material models.â…¡During the process of penetration, besides the physical characteristics of projectiles, the biomechanical mechanism between the projectiles and bone tissue and the interactive force among bone tissue can play an important role in the difference between the surface area of entrance and exit.â…¢During the process of penetration, strain rate of bone tissue can be used to predict and evaluate the severity of damage of bone tissue, both in terms of FEA and experimental study.â…£When the mandible was penetrated by projectiles at mandibular angle, besides the damage of penetrated region, there was little possibility for associated fracture to other regions of mandible.â…¤Bony stress conducted from the mandible was not the main factor of the brain injury associated with the penetrating injuriy of mandibular angle.â…¥The EFG method can meet the need of simulation of penetrating wound of muscle tissue. |
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