| Objective: The objective of the study was to reveal the pressure-bearing properties of the whole molar in vitro by biomechanical research technique, which was adjoined experimental stress analysis and numerical stress analysis. By designed the different load devices to simulate the different stress condition when we took soft, middle and hard foods, the study revealed the stress distribution laws of the molar in vitro in differ load working conditions as well as the compression resistance of the molar in static state pressure affection. The pressure-bearing properties could be used to direct the clinical restoration design of the teeth defect.Methods:The first part, electrical resistance strain gauge experiment The dissertation select the third molar as test sample, which was in good condition in visual inspection and was extracted in policlinic. The study designed and manufactured three kinds of load devices to left the molar in vitro in three kinds of representative load supporting working conditions, which were flexibility pressurizing load, aluminum slab load, and rigidity unbalance load. The study stuck 90?strain rosettes in the middle part ofcervical 1 / 3 of buccal surface of molar in vitro. The circuit was jointed, which was referred to half bridge circuit diagram. By electrical resistance strain gauge experimental study we obtained the load and axial strain value. Then the axial strain value was reduced to axial stress value, which was referred to Hooker's law formulae (O*=EEX).Secondly Part the molar in Vitro compression Assay: The molar was put at WDS100 universal testing machine to proceed compression Assay. By compute signal acquisition and record system, the study recorded the trial curve and fracture ultimate load.Thirdly Part, three-dimensional finite-element method analyses the stress Field under compression of the molar in Vitro: The study Select two patients who had good dissection formation of first molar or third molar, and then the two patients were screened by helices CT. We obtain the digitized information of solid model from helices CT. Then we proceed three-dimensional entity reestablish according the digitized information and protracted three kinds of load devices in AutoCAD soft ware, which were same as the load devices in experimental stress analysis. In ABAQUS finite element soft ware, we put up mechanical model of finite element computation according to these three-dimensional entities. In the mechanical model, we defined molar for succession, homogeneity, isotropic linear-elastic material; defined dentinal elasticity modulus for 2.5*1010Pa, Poisson ratio for 0.30; enamel elasticity modulus for 4.5*1010Pa, Poisson ratio for 0.30. We defined the side-side interaction between the occlusal surface of molar and the load device, and to realize three kinds of representative load working conditions according to experimental stress analysis. We fixed the root in boundary condition, hi finite element computation, we defined the displacement of the load devices for following Z directional displacement, size for 0.03mm,output variable for displacement counterforce and Stress. Compare the load - Stress curve of electrical resistance strain gauge experimental study and finite element-5-study to reveal the pressure-bearing property laws of whole molar in three kinds of representative load working conditions.Results:The first part By electrical resistance strain gauge experimental study, the study obtained load-axial stress curve line of molar in vitro in representative press working condition. From curve line, we found: 1, Load and axial stress submit linear relationship in definite loading range. These declared that dental material was in elastic range within test specification of the experimental study, so the strain could be reduced to stress value referred to Hooker's law formulae. 2, under same pressure, identical region of identical teeth generated different stress field in three kinds of load working conditions. The study thought that the differ property...
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