Porcelain adherence vs force to failure for palladium–gallium alloys: a critique of metal–ceramic bond testing

Objectives: The purpose of this study was to characterize the metal–ceramic bond of four commercial Pd–Ga alloys by two separate tests: porcelain adherence and bond failure force. A Pd–Ag alloy was the control. A secondary goal was to investigate a possible correlation between the percent porcelain retained and bond failure forces. Methods: For adherence testing, five cast plates of each alloy were air abraded and oxidized. The porcelain was applied on a circular area in the center of each plate and fractured using constant-strain flexure. The area fraction of adherent porcelain (%) was calculated via a standardized spectrometric technique. Bond failure forces were measured in three-point bending using bar specimens. The modulus of elasticity of the five alloys was also measured. No attempt was made to calculate bond strength since the residual thermal stresses at the interfacial region were unknown. Data were compared via ANOVA and the Tukey multiple range test (p<0.05). Results: All failures occurred at the porcelain termination sites with no tensile fracture of the porcelain. Two Pd–Ga alloys exhibited porcelain adherence comparable with previously studied Pd–Cu–Ga alloys. There was no correlation between the porcelain adherence and the force to failure (r2=0.0159). Additionally, no statistically significant differences were found among the moduli of elasticity of the five alloys. Significance: The new Pd–Ga alloys have been commercially introduced with little information on the quality of the bond with porcelain. The use of two different means for assessing the metal–ceramic bond provides information on the relationship of data using different experimental techniques.