Finite Element Analysis Of 3D Printing Customized Titanium Plates For The Reconstruction Of Mandible Segmental Defects

Baclgrounds and Objectives:The reconstruction of segmental defect of mandible has always been a challenge in oral and maxillofacial surgery.At present,autologous bone grafts are recognized as the gold standard for repairing bone defects.In some cases,such as the malignancy having a high probability of recurrence,patients cannot obtaining sufficient autologous bone due to age and other factors,and cases with this procedure being rejected,reconstruction plate only is also considered as a feasibly transitional mean of rehabilitation and reconstruction.However,a large number of clinical cases have been reported that commercial reconstruction plate has a high incidence of postoperati-ve complications including exposure and fracture of the titanium plate,and screw being loose.The reasons for postoperative complications of commercial reconstruction plates are various and complicated,and the morphological structure of reconstruction plate is an important factor,including the profile,thickness,height and length of the reconstruction plate,and the selection of screws.The influence of different structural optimization schemes were studied,which would provide certain data support for the standardized design of customized reconstruction plates and theoretical basis for the application of the 3D printed customized reconstruction plates in the reconstruction of mandibular defects.Materials and Methods:The customized reconstruction plates were designed by computer software including Mimics Medical 21.0,Geomagic Design,and NX 12.0,basing on computed tomography image data,which were divided into nine experimental groups with different height of 12mm,16mm and 20mm,and different thickness of 2.0mm,2.4mm and 2.8mm.The design of commercial reconstruction plate was simplified according to the parameters of reconstruction plate commonly used in clinical.Then the biomechanical and mechanical properties of the reconstruction plates and bone tissue were simulated by the three-dimensional finite element analysis software,Workbench 14.5,under normal physiological condition including incisal clenching and left molar clenching.Results:1.In this experiment,the volume and mass of the customized reconstruction plates are 1.42-2.44 times that of the commercial reconstruction plate,the bone-plate contact surface area is 1.74-2.16 times of that of the commercial.Under the condition of incisal clenching,the maximum relative stress on the 12mm-2.4mm customized reconstruction plate is maximum,which is 1358.3MPa.The maximum relative stress on the 20mm-2.0mm customized reconstruction plate is the minimum,which is 442.54MPa.Under the condition of left molar clenching,the maximum relative stress on the 12mm-2.4mm customized reconstruction plate is maximum,which is 1193.1 MPa.The maximu,m relative stress on the 20mm-2.0mm customized reconstruction plate is the minimum,which is 410.91 MPa.And the maximum relative stress on the commercial reconstruction plate are 907.16MPa and 1006.1 MPa,respectively,less than the customized reconstruction plate with a height of 12mm,and more than the customized reconstruction plates with a height of 16mm and 20mm.The relationship between maximum relative strain and maximu,m relative stress is consistent.In all reconstruction plates,the relative stress and strain on the reconstruction plates adjacent to the edge of the defect gap are larger than those around,and the mesial area is larger than the distal area.Moreover,the line chart of the maximum relative stress and strain of the commercial reconstruction plate is steeper than that of customized reconstruction plates.2.In this experiment,under the condition of incisal clenching,the minimum relative strain on conmmercial reconstruction plate on the bone surface in the bone-plate contact area near the gap of bone defect is 1.2655 10-5mm/mm,which is located in the stress shielding window and prone to disused bone resorption.The maximum relative strain on most reconstruction plates is greater than 5-10-3mm/mm,which is located in the pathological overload window and prone to bone resorption injury.Under the condition of left molar clenching,the results are similar to those of the anterior teeth incisal clenching.According to the strain distribution cloud diagram of bone tissues in the cancellous bone-screw,cortical bone-screw and bone-plate contact area,most bone tissues are in the mechanical environment of bone remodeling and balance,and there is only an obvious area of excessive stress around the screws far away from the defect area and near the lower margin of the mandible.3.There are significant differences in the force of screws between commercialreconstruction plate and customized reconstruction plate including the distribution of stress and the location of the maximum relative stress of all the screws.In the commercial reconstruction plate,the screw on the mesial titanium plate near the defect receive more pulling force than the distal titanium plate,and the screw farthest from the defect in the mesial titanium plate receive the maximum pulling force.In the customized reconstruction plates,and both distal screws receive propulsion force,and the screw which is furthest from the defect area and near the lower margin of the mandible is always received the most force.Conclusions:In this experiment,in the internal fixation systems of reconstruction of mandible with titanium reconstruction plates,the stress shielding effect is not obvious,and postoperative complications may mainly come from the excessive local stress.The customized reconstruction plates indeed have better biomechanical and mechanical properties than the commercial reconstruction plate.For example,the stress dlstrnbutxon on the customized reconstruction plates is more uniform and the maximum stress is less,than the commercial reconstruction plate,and the retention screws on the customized reconstruction plates are more stable.