1989 Fiscal Year Final Research Report Summary
Residual Stress in Porcelain-fused-to-Metal Restorations as Affected by Cooling Rate.
| Project/Area Number |
62570878
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| Research Category |
Grant-in-Aid for General Scientific Research (C)
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| Allocation Type | Single-year Grants |
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| Research Field |
補綴理工系歯学
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| Research Institution | The University of Tokushima |
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Principal Investigator |
ASAOKA Kenzo Tokushima University School of Dentistry Associate Professor, 歯学部, 助教授 (50014189)
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| Project Period (FY) |
1987 – 1989
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| Keywords | Porcelain-fused-to-Metal / Residual stress / Compatibility / Thermal expansion / Glass transition / Transformation / Palladium alloy / Cooling rate |
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| Research Abstract |
Residual stress in Poreelain-fused-to-metal (PFM) restorations was studied by computer simulation of the firins process using measured data. Thermo-mechanical properties of alloys for ceramics and dental porcelains were measured as follows. Temperature dependences of thermal expansion coefficients for the alloys of Pd-Ag, Pd-Cu and Pd-Co binary systems were measured. The coefficient of thermal expansion of the alloy with no transformation was well approximated by linear equation of temperature. The constants in the equation were shown as a function of the added element. Dimensional changes at order-disorder transformation in Pd-Cu alloys and at magnetic transformation in Pd-Co alloys were measured.
Relationships between residual stress in porcelain and in PFM restorations and cooling conditions were simulated. The temperature dependence of elastic moduli, thermal expansion coefficients, and shear viscosity and cooling rate dependence of glass transition temperature were considered in this calculation. A method for strengthening of porcelain was revealed. Calculated results of cooling process of the PFM strip display stress profiles which agree well with reported measured profiles in quenched PFM. Simulated results sustest that PFN restorations with an alloy of high thermal expansion coefficient require rapid cooling; on the contrary, PFN restorations with the alloy of lower coefficients require slow cooling.
The simulated results of heating process of porcelain and cooling process of PFN strips, suggest that the temperature where the incompatibility stress develops in the PFN strips during cooling can be estimated closely from the deformation point of the heating curve of the porcelain with an applied stress of about 1.2 - 3.3 MPa. A method for measuring temperature dependence of viscosity is proposed.
Thermal shock test was employed to estimate residual stress in porcelains and in PFM strips.
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