金属焼付ポーセレン冠の破折に関する実験的研究

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Ceramo-metal restorations have been extensively used because of their superior strength, esthetics and stability. However, fractures are sometimes encountered in ceramo-metal crowns. This study was designed, therefore, to evaluate the fracture strength of ceramo-metal crowns in relation to the material and design of metal coping, and mode of loading by means of fracture test and two-dimensional finite element analysis. A gold alloy and a nickel-chromium alloy were employed as the coping material. The designs of the crown were type A with the metal frame being bare by cervical one third ; type B with the metal frame being bare by cervical two thirds ; and type C with the metal frame being almost all bare in the lingual surface. The results were summarised as follows : 1. When the compressive load was applied to the incisal edge along the tooth axis, type C showed the lowest fracture strength and no significant difference was found between type A and B. The gold alloy coping offered higher strength than the nickel-chromium alloy coping. 2. When the load was applied in 45° to the tooth axis, there were no significant differences among the coping designs and materials. 3. In the finite element analysis, the estimated peak and distribution of the maximum principal tensile stress were in good agreement in their tendencies with the results of the fracture tests. 4. Further stress analysis with the finite element method showed that the potentiality of fracture in the porcelain increased as the loading point was shifted from incisal edge to cervical side. Such a tendency was especially marked in type C. 5. In considering the normal occlusion, however, very low level of tensile stress was introduced in type C because the load was to be directed to the metal coping. 6. The estimated residual stress in the porcelain caused by the thermal stress during cooling process was higher in the nickel-chromium alloy coping and type C, which may promote the fracture of the ceramo-metal crown. 7. From the foregoing findings, it is recommended to minimize the fracture that the metal backing should not be too large when the occlusal force is applied to the porcelain itself.
1991-02-25

金属焼付ポーセレン冠の破折に関する実験的研究

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