Thermal shear stresses that arise from a mismatch of expansion coefficients (Δα) between porcelain and gold alloy can exceed the 13,000 psi shear resistance of the bond. Therefore, calculations of the Aa tolerance were made. A Aa of 0.125 X 10-6 inch/inch/degrees F is safe.
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References
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Shell, J.S., and Nielsen, J.P.: Study of Bond Strength of Dental Porcelain Fired to Metal, J Dent Res45:32-36, 1966.
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Leone, E.F., and Fairhurst, C.W.: Bond Strength and Mechanical Properties of Dental Porcelain Enamels , J Prosthet Dent18:155-159, 1967.
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Anthony, D.H. ; Burnett, A.P.; Smith , D.L.; Brooks, M.S.: Shear Test for Measuring Bonding in Cast Gold Alloy-Porcelain Composites, J Dent Res49:27-33, 1970.
