Porcelain adherence vs force to failure for palladium–gallium alloys: A critique of metal–ceramic bond testing Efstratios Papazoglou, William A. Brantley Section of Restorative Dentistry, Prosthodontics and Endodontics, College of Dentistry, The Ohio State University, Columbus, Ohio, USA ABSTRACT 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. Therewas no correlation between the porcelain adherence and the force to failure (r 2 = 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.  1998 Academy of Dental Materials. Published by Elsevier Science Ltd. INTRODUCTION In the early 1980s new alloys, containing even greater percentages of palladium than the earlier palladium– silver alloys, were developed for metal–ceramic re- storations. The main reason for the great interest in these new alloys, which were named high-palladium casting alloys and contained greater than approxi- mately 75% Pd, was economic (Carr and Brantley, 1991). The alloy CM Metal (78% Pd, 9% In, 7.6% Sn, 5% Co, 0.2% Si), patented by Boyajian (1981), was the precursor of this group of alloys. Although CM Metal never became commercially successful, this alloy served to catalyse research for the development of other high- palladium alloys (Vrijhoef and Greener, 1988). Later Schaffer (1983) patented the alloy Option (79% Pd, 10% Cu, 9% Ga, 2% Au) for the J.M. Ney Company (Bloomfield, CT, USA). This alloy became commercially successful and stimulated development efforts by other manufacturers (Vrijhoef and Greener, 1988) for a series of alloys with Option-like compositions. However, these Pd–Cu–Ga alloys presented high levels of hardness and yield strength which might cause problems during finishing and polishing of cast restorations for dental laboratories and clinicians (Carr and Brantley, 1991). Additionally, their marginal creep was questioned, since it was shown that Pd–Cu–Ga alloys have relatively poor creep resistance at high stress levels and temper- atures close to the glass transition temperature of porcelain (Anusavice et al., 1985). Moreover, it has been shown that some Pd–Cu–Ga alloys are difficult to mask for metal–ceramic restorations, and that sometimes a thicker opaque porcelain layer is required to avoid excessive darkness, i.e. low value, with certain porcelain Dent Mater 14:112–119, March, 1998 112 Papazoglou & Brantley/Porcelain adherence and force to failure for Pd–Ga alloys PII: S0109-5641(98)00017-7