Studies on the Mechanical Properties of a Metal-Ceramic Restoration : (Part 2) Residual Stress and Deformation during Cooling Down

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  • ASAOKA Kenzo
    Department of Dental Engineering, School of Dentistry, Tokushima University
  • KUWAYAMA Norihiko
    Department of Dental Engineering, School of Dentistry, Tokushima University

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  • 金属焼付陶材の機械的性質に関する検討 : 第2報 焼成後の残留応力と変形について

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Residual stress and deformation of the porcelain fused to metal restoration were calculated by the theory of statically indeterminate beam and the finite element method. Physical and mechanical properties of the materials were supposed not to change from the softening temperature of ceramic to the room temperature. The effect of the thermal expansion coefficient, the elastic modulus of metal, the softening temperature of ceramic, and the thickness ratio of metal to ceramic were calculated.<br>　The following results were obtained.<br>(1) Theory of statically indeterminate beam was good agreement with the finite element analysis.<br>(2) From the calculation on the effect of the thermal expansion coefficient, the residual stress and the deformation were directly in proportion to the difference in thermal expansion coefficients of metal and ceramic.<br>(3) If the metal had low elastic modulus, so the residual stress in ceramic was low, and the deformation of the sintered porcelain veneer was small. But the elastic modulus had smaller effect on the internal stress and the deformation than the thermal expansion coefficient.<br>(4) If the softening temperature of ceramic dropped, so internal stress decreased.But the softening temperature had only smaller effect.<br>(5) If the thickness of the metal took under 20% of the sintered porcelain veneer, residual stress in ceramic was low. But over 80%, the stress rapidly increased. If the metal thickness took from 20% to 80% the stress at the interface had nearly constant value. So, the change of metal thickness for this range is not effective for the arrest of the interface fracture.

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