| Because the porcelain fused to metal crown(PFM) has many advantages such as aesthetic perception , high strength , excellent seal and excellent biocompatability, it is widely used for teeth restorations on clinical application now. Because PFM crown is made by the method of sintered with metal and porcelain and it is integrated with teeth by the cement, the stress distribution of PFM crown under the force is related with the property and thickness of its components.The three dimensional finite element analysis is a method using computer to solve mechanical question about continuous medium. This method is widely used in medical field. In this paper, the PFM crown of the first molar of mandibular was built by the method of three dimensional finite element analysis and it having different rate of the thickness of metal base and porcelain different material and thickness of metal base , different thickness of porcelain, different material and thickness of cement were analyzed. The results are as following:1. While the overall occlusal thickness of 2.0mm was maintained and the thickness of cement is 0.1mm, the rate of the thickness of metal base and porcelain is 0.2:17, 0.4:1.5, 0.6:1.3, 0.8:1.1 respectively, the peak compress stress and the peak Mises stress are increased and the peak tensile stress isreduced as the thickness of metal base is increased from 0.2mm to 0.8mm. But the peak tensile stress is larger than that of the thickness 0.4mm , 0.6mm, 0.8mm of metal base as the thickness of metal base is 0.2mm and there are no obvious difference on the peak tensile stress between these crown with 0.4mm, 0.6mm, 0.8mm thickness of metal base . Then concerning with the trend of the changing stress and the magnitude of stress, the rate 0.4:1.5 of the thickness of metal base and porcelain is reasonable.2. While the thickness of porcelain and is 1.1mm and the thickness of cement is 0.1 mm, the thickness of metal base is 0.2mm , 0.4mm , 0.6mm, 0.8mm respectively, as the thickness of metal base is increased from 0.2mm to 0.8mm, the peak compress stress and the peak Mises stress on the metal base and the porcelain are increased and the peak tensile stress is reduced. But as the thickness of metal base is 0.2mm, the peak tensile stress are larger than that of the metal base and the porcelain with the thickness 0.4mm, 0.6mm, 0.8mm and there are no obvious difference on the peak tensile stress between these metal base s and the porcelains with the thickness of 0.4mm, 0.6mm, 0.8mm. Then it is concluded that the thickness of 0.4mm of metal base is reasonable.3. While the thickness of metal base is 0.4mm and the thickness of cement is 0.1mm, the thickness of porcelain is 0.3mm, 0.6mm, 0.9mm 1.2mm, 1.5mm respectively, as the thickness of porcelain is increased from 0.3mm to 0.6mm and 0.6mm to 0.9mm, the peak tensile stress is reduced obviously and the peak compress stress is increased indistinctively and as the thickness of porcelain is increased from 0.9mm to 1.2mm and 1.2mm to 1.5mm, the peak tensile stress is reduced indistinctively and the peak compress stress is increased indistinctively. It show that the change of the thickness of porcelain has obvious effect on the peak tensile stress and indistinctive effect on the peak compress stress. Then it is concluded that the thickness of porcelain is not less than 0.9mm.4. While the thickness of metal base is 0.4mm and the material of cement is zinc polycarboxylate, the material of metal base is Au-Pd alloy , Ni-Cr alloy ,In-ceram alumina porcelain respectively, as the Yang's modulus of the metal base is increased, the peak tensile stress is reduced slightly and the peak compress stress and the peak Mises stress are increased obviously, it show that the change of the Yang's modulus has obvious effect on the stress of crown. Then it is concluded that the magnitude of stress on Au-Pd alloy of metal base is reasonable.5. While the material of cement is zinc phosphate - composite resin- glass ionomer- zinc polycarboxylate respectively, a...
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