Influence Of Four Methods To The Stress Distribution Over Loading Of Mandibular First Permanent Molar With Different Degree Of Defect

ObjectiveFour methods were designed to repair a varity forms of defect of mandibular first permanent molar. The objective of this study was to investigate the stress distribution over loading of the molar studied by using three-dimensional finite element analysis(FEA), which would furth provide a theory basis to guide the selection of different prosthesis in clinical situation. Methods1. A standard mandibular first permanent molar was selected according to the data reported by previous resercher. Micro CT scaning vertically to the tooth long axil of the molar was done to collect data for computer model building. Slice thickness of the scanning was 0.02 mm, and totally 1024 images was obtained.2. The images above obtained were input into 3D modeling softwares Mimics, Geomagic, CATIA et al. After a great trail of operations, model A of the sound mandibular first permanent molar differentiating enamel, dentin, pulp, together with periodontal ligament and alveolar bone surrounding it was built. Based on model A,model B, C and D were generated. Model B was model A with a occlusal cavity, model C was model A with a distal-occlusal(DO) cavity,and model D was model A with a mesial-occlusal-distal(MOD) cavity. Sub-types of model B, C and D were built by mimic restoration of them respectively by using four methods(1-direct filling with resin, 2-ceremic inlay, 3-ceremic onlay, 4-ceremic crown) and a total of thirteen models(A, B1-4, C1-4, D1-4) were obtained in this study.3. Models were input into Ansys workbench and mesh were generated to them. Then, loading was added at two directions(parallel to the long axis or 45 degree to the long axis lingually) respectively and the corresponding stress distributions of the molar were analyzed. Results1. 3D FEA models of mandibular first molar with a varity forms of defect repaired respectively by four possible methods were established by computer software using Micro CT.2. When loading vertically the models restored by ceramic inlays show the lowest maximum principal stress values,and Von-mises stress mainly distributed in the floor of pulp chamber. When loading laterally, models repaired by ceramic onlays and ceremic crown show lower maximum principal stress values than those of the other two prosthodontic methods, and Von-mises stress mainly distributed in the enamel and dentin.3. The Von-mises stress distributes homogeneously on the models restored by onlays when loaded laterally, but concentrated on the remainding enamel on the models restored by crowns.4. Stress concentration areas were appeared on the models which were filled directly by compound resin. Conclusions1. The maximum principal stress of the models restored by inlays were less than those obtained form models restored by the other methods when loaded vertically, while its maximum principal stress were focus on the lining resin. The Maximum principal stress of the models restored by onlays and crowns were higher when loaded vertically, while their maximum principal stress was focused on enamel and dentin.2. The maximum principal stress of the models restored by onlays and crowns were less than those of models which were restored by the other two methods when loaded vertically. But the Von-mises stress distributes homogeneously on the models restored by onlays while concentrated on the remainding enamel on the models restored by crowns. Onlay was the method more reasonable than crown.3. Stress concentration areas were appeared on the models which were filled directly by compound resin. Filling directly by compound resin may not be a healthy long lasting method to repaire the defect of mandibular first molar.