The Simulation Using Three Dimension Finite Element Method On Mandible Gunshot Wound Of Pigs

Whether peacetime or wartime,the maxillofacial firearm wound is the important issue of maxillofacial trauma research. It's always difficult to analyze the dynamic injury procedure of gunshot wound and the biomechanical changes of injury tissues. Because the previous studies on gunshot wound is mostly based on cadaver, animal or artificial materials model, it was difficult to make an accurate analysis of dynamic injury process and relevant biomechanical changes.FEM (Finite Element Method) is the numerical methods most widely used today in engineering analysis. Because of its versatility and effectiveness, along with the rapid development of computer science and technology, it has become an important part of computer-aided design (CAD) and computer-aided manufacture (CAM).A three-dimensional (3D) mandibular finite element model was set up , its geometric shape was highly similar to the pig's mandible. The VPG,LS-DYNA,PREPOST softwares were used to make a simulation on the injury process of pig mandibular gunshot wound. Some simulation data were compared to that of animal experiments. The possibility of using finite element method to imitate the injury process of maxillofacial gunshot wound had been discussed.Method:Computer simulation: MIMICS software was used to make a 3D reconstructive model of pig's mandible from DICOM data of CT Scan. The 3D model was used to built a FE(Finite Element) model of pig's mandible with ANSA software. The parameters and boundary conditions of FE model were defined with VGP software. The penetrating procedure of mandibular injury by 7.62mm bullet was simulated with LS-DYNA software. The simulative result was analyzed with LS-PREPOST software.Animal experiments: 10 fresh pig's heads (5.7-6.2Kg) were fixed on the injury stand. The injury point was the mid-point of masseter which was overlap on the mandible angle bone surface. The mandibles were wounded by 7.62mm bullets. A copper target and a 6-channel transient velocimeter were used to record the impact velocities (V₁) and ejected velocities (V2) of bullets and the impact energy (E₁=V₁²m/2) and transferred energy (E₂ = (V₁²-V₂²) m/2) were calculated. The strain values, strain curves and wound tracts were displayed and recorded simultaneously. The recorded data were collected to compare with the FE analyzing results.Results:1.A 3D finite element model representing the geometric shape of gunshot wound to a pig's mandible was set up. The mandible model has 628465 tetrahedrons, 2604 pentagons, 50833 hexagons and 322670 nodes. The bullet model has 7053 tetrahedrons and 3512 nodes. The grid quality of the 3D finite element model is better than previous mandible finite element models ever reported by scientific documents.2.The injury procedure of the pig's mandible by a 7.62mm bullet gunshot was simulated successfully, The splash of the broken bone bits and the fracture line was also simulated with bone defect being 1.07cm and 2.73cm in diameter at the entrance and exit of the bullet respectively.3.Through the introduction and adjustment of material properties, boundary conditions and loads, the finite element analysis (FEA) was conducted. The stress and strain nephograms, stress-time curves and strain-time curves as well as data of stresses and strains at different positions when a 7.62mm bullet penetrated the mandible were obtained.4.Datum from experiment of real pig mandible wounded by gunshot were recorded such as the impact speeds, ejecting speeds, impact energies, entrance and exit of wound tract in diameter, strain curves and wound conditions.5.Comparison of data from the 3D FE model and those from animal experiment at laboratory shows that there is no statistical difference between the two (P>0.05). The simulative wound tract and dynamic damage process were highly similar to the actual injury results.Conclusions:1.A 3D FE model of pig mandible gunshot wound was built up with MIMICS and ANSA software. The 3D FE modeling method has improved greatly from the past modeling approach, and the 3D FE model's mechanic and geometric simulative accuracy has been significantly improved. The 3D FEM would have great application potential and developmental prospects.2.The dynamic injury procedure of pig's mandible wounded by gunshot can be vividly simulated using the VGP, ANSA and LS-DYNA software. The simulative injury results were similar to the actual experiment results.3.The 3D FEM can be a good tool for the research of gunshot wound biomechanics. Through generation of grid, introduction and adjustment of material properties, boundary conditions and load, the stress and strain distributions of pig mandible gunshot wound has been precisely simulated. The data from simulation were similar to those from actual animal experiment and other related documents. The result proves that the modeling and simulation method is feasible and effective.