| Objective:To carry out bio-mechanical analysis by establishing three-dimensional finite element models of implant-supported fixed partial denture in three kinds of arch form;To provide more bio-mechanical methods for the continuous loss of the lower anterior teeth.Methods:1.Experimental equipmentThis experiment used a cone-beam CBCT scanner(Philips Company Netherlands).The computer's operating system was Asus Windows7,the processor was Intel(R)CPU b820@1.70 ghz,8G memory,1TB hard disk.Software used: Mimics(Materialise Software Company,Belgium);Geomagic Studio(3D System Company,USA);Solid Works(Dassault Company,France);Ansys Workbench19.0(Swanson Analysis Company,USA).2.Creation of finite element modelsUsing cone beam CT(cone beam computed tomography,CBCT)scan for mandibular DICOM line data,import the initial data of the teeth and jaws into Mimics software.Reconstruct the 3d modules of 33 to 43 consecutive missing mandible pieces,implants,abutments and crowns through the Geomagic and Solidworks software.Through combination and assembly,the following three kinds of implant-supported fixed bridge models were obtained: Finite element model 1,2 implants were implanted at the sites of the bilateral cusp(33 and 43).Finite element model 2,two implants were implanted at the sites of the bilateral cusp(33 and 43),and one implant was implanted at incisor area(41).In finite element model 3,2 implants were implanted at the sites of the bilateral cusp(33and 43)and 2 implants were implanted at the sites of bilateral central incisors(31,41).3.The finite element model was fitted with three dental arch shapes.Import 3 type of dental arch of MBTTMsystem(3M company)into computer,three models were combined with the cuspate,ovoid and square arch respectively to obtain 9 sets of models.Import the 9 groups of models into the Workbench for grid generation.4.Test the loading stressFinite element software Ansys Workbench19.0(Swanson Analysis Company USA)was used to load and analyze the model forces.In order to simulate the stress form of mandibular teeth in general chewing motion,two loading methods were used to load the finite element model,and static analysis was used to apply force to the model and to apply full constraints on the top surface.Results:1.The finite element models of implant supported fixed bridge in mandibular anterior area of continuous missing tooth was established;2.The maximum stress around the implant appeared in the cervical cortical bone layer;The bone stress around the implant was closely related to the loading mode.In the same arch shape of the same model,the maximum stress of the bone cortex around the implant under oblique loading was always greater than that of under the loading mode of the parallel tooth length axis.In model 1,the maximum stress of the bone cortex in the oblique loading of the square,ovoid and cuspid shaped dental arch was 1.26,1.80 and 1.65 times of that respectively under the vertical loading.In model 2,under the oblique loading,the maximum stress of the bone cortex in the cervical region of the implant in the square,ovoid and cuspid-shaped dental arch was 1.10,1.43 and 1.65 times that of the vertical loading respectively 1.56,1.55 and 1.65 times in model 3.3.When vertical loading,in the square dental arch,the maximum stress around the implant showed a decreasing trend in model 1,model 2 and model 3(87.13 MPa >67.49 MPa > 39.57MPa).In the ovoid dental arch,there was a decreasing trend in model 1,model 2 and model 3(91.98MPa>37.02MPa> 28.62MPa).In the cuspid dental arch,there was a decreasing trend(112.02MPa> 40.69MPa> 22.93MPa)in model 1,model 2 and model 3.In the square dental arch,the absolute value difference between model 1 and Model 2,model 2 and Model 3 are 19.64 and 27.92 respectively.In ovoid dental arch,the absolute difference between Model 1 and Model 2,model 2 and Model 3 is 54.96 and 8.4.In the cuspid dental arch,the absolute difference between model 1 and Model 2,model 2and Model 3 is 71.33 and 17.76.By comparing the above differences,it can be found that the influence of the implant number on the stress is significantly different among the three dental arch shapes:In ovoid and cuspid dental arch,the stress of three implants was significantly reduced compared with that of two implants(54.96?71.33),and the difference was significantly smaller than that of the other two arch shapes(19.64).In the oval and cuspate dental arch,there was little change in stress when 4 and 3 implants were selected(8.4,17.76).Under oblique loading,the same law was observed in the same arch shape.4.Stress distribution around the implant in model 1In model 1,when vertical and oblique loading were applied,the stress around the implant increased in the radius,ovoid and cuspid-circular arch.The stress in the square arch is the least.Meanwhile,in the stress distribution map,the red and yellow range of bone around the cuspid-circular arch implant was larger and the stress distribution was uneven.According to the experimental data,it can also be observed that in all combination of three types of dental arch shapes and three types of implant fixed bridges,the stress value around the implant of model 1 was the largest.5.Stress distribution around the implant in model 3In model 3,the stress around the implant decreased significantly compared with that in model 1,and the stress around the implant decreased in the square,oval,and tapered dental arch(39.57Mpa>28.621Mpa>22.933Mpa).In the stress distribution map around the implant,the three dental arch shapes were mainly green and blue,indicating that the stress distribution was relatively uniform and the stress concentration area was less.In model 3,compared with the square and square arch with more straight and concentrated abutments,the curvature of the sharp and round arch was better than the other two arch shapes through the implant under the same loading mode.Conclusion:1.The stress distribution around the implant is significantly different in the shapes of the square,ovoid and pointed dental arch.2.Three-dimensional finite element analysis is an effective method to simulate the stress distribution of different implant-supported fixed bridges in different arch shapes.3.The stress distribution of implant-supported fixed bridge bone is closely related to the loading method.When the load is the same,the stress around the implant is greater than that under vertical loading under oblique loading.4.When mandibular 33-43 was continuously missing,the safety of increased with the increase of the number of implants,regardless of the shape of the dental arch.5.In condition of mandibular 33-43 missing continuously,when two implants were implanted in bilateral cuspid sites only,the safety of the implantation of square arch was higher than that of oval or sharp arch.6.When the mandibular 33-43 was continuously missing,3 or 4 implants were selected compared with 2 implants for oval and cusp arch shape,which could significantly increased the implant safety;however,compared with 3 implants,4 implants had little significance in increasing implant safety.7.This experiment provides reference for clinical optimization of various dental arch shapes,and the specific selection should be combined with clinical practice. |
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