COMPARISON OF THE METAL-TO-CERAMIC BOND STRENGTHS OF FOUR NOBLE ALLOYS WITH PRESS-ON-METAL AND CONVENTIONAL PORCELAIN LAYERING TECHNIQUES

Statement of problem. New noble alloys for metal ceramic restorations introduced by manufacturers are generally lower-cost alternatives to traditional higher-gold alloys. Information about the metal-to-ceramic bond strength for these alloys, which is needed for rational clinical selection, is often lacking. Purpose. The purpose of this study was to evaluate the bond strength of 4 recently introduced noble alloys by using 2 techniques for porcelain application. Material and methods. Aquarius Hard (high-gold: 86.1 gold, 8.5 platinum, 2.6 palladium, 1.4 indium; values in wt. %), Evolution Lite (reduced-gold: 40.3 gold, 39.3 palladium, 9.3 indium, 9.2 silver, 1.8 gallium), Callisto 75 Pd (palladium-silver containing gold: 75.2 palladium, 7.1 silver, 2.5 gold, 9.3 tin, 1.0 indium), and Aries, (conventional palladium-silver: 63.7 palladium, 26.0 silver, 7.0 tin, 1.8 gallium, 1.5 indium) were selected for bonding to leucite-containing veneering porcelains. Ten metal ceramic specimens that met dimensional requirements for International Organization for Standardization (ISO) Standard 9693 were prepared for each alloy by using conventional porcelain layering and press-on-metal methods. The 3-point bending test in ISO Standard 9693 was used to determine bond strength. Values were compared with 2-way ANOVA (maximum likelihood analysis, SAS Mixed Procedure) and the Tukey test (alpha=.05). Results. Means (standard deviations) for bond strength with conventional porcelain layering were as follows: Aquarius Hard (50.7 +/- 5.5 MPa), Evolution Lite (40.2 +/- 3.3 MPa), Callisto 75 Pd (37.2 +/- 3.9 MPa), and Aries (34.0 +/- 4.9 MPa). For the press-on-metal technique, bond strength results were as follows: Aquarius Hard (33.7 +/- 11.5 MPa), Evolution Lite (34.9 +/- 4.5 MPa), Callisto 75 Pd (37.2 +/- 11.9 MPa), and Aries (30.7 +/- 10.8 MPa). From statistical analyses, the following 3 significant differences were found for metal-to-ceramic bond strength: the bond strength for Aquarius Hard was significantly higher for conventional porcelain layers compared with the press-on-metal technique; the bond strength for Aquarius Hard with conventional porcelain layers was significantly higher than the bond strengths for the other 3 alloys with conventional porcelain layers; and the bond strength for Aquarius Hard with conventional porcelain layers was significantly higher than the bond strength for Callisto 75 Pd with conventional porcelain layers and the other 3 alloys with the press-on-metal technique. Conclusions. For both conventional layering and press-on-metal techniques, all 4 noble alloys had a mean metal-to-ceramic bond strength that substantially exceeded the 25 MPa minimum in the ISO Standard 9693. The results for Aries support the manufacturer's recommendation not to use the press-on-metal technique for alloys that contain more than 10% silver.