Evaluation of Fracture Toughness and Residual Stress in Dental Porcelain by Indentation-microfracture Method

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  • 微小圧子圧入破壊法による焼付用陶材の残留応力, 破壊力学特性の評価

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The indentation microfracture(IM)method was applied to estimate the fracture toughness and residual stress in the surface of dental porcelains which were slowly cooled and tempered by two different treatments.The shape parameter, m, in Weibull plots of the Kc`s which were measured by IM method, was calculated to be 7.7 to 9.1 for the slow cooled specimen.Tempering had no significant effect on Weibull parameter.Factor of safety for the porcelain used for prosthesis was estimated to be 3.4 to 4.9 for the failure probability of 10-5.Surface residual stress was estimated to be 26-28 and 64-88MPa(in compression)for the porcelain tempered in ambient air and forced air, respectively, from the median crack size after indentation.Estimated residual stress was in good agreement with the results of computer simulation by Asaoka et al.However, the residual stress could not be calculated for the porcelain with crystallization in its glass transition range during cooling because the reference sample was difficult to prepare.In concludsion, the fracture toughness and residual stress in micro-area(100〜400μm)of the dental baked-on porcelain prosthesis can be measured by the IM method.

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