Effectiveness of different adhesive primers on the bond strength between an indirect composite resin and a base metal alloy

Statement of problem There is a need for achieving reliable chemical bond strength between veneering composites resins and casting alloys through the use of simplified procedures. Purpose The purpose of this study was to examine the shear bond strength of an indirect composite resin to a Ni-Cr alloy, using 4 primers and 2 airborne-particle-abrasion procedures. Material and methods Fifty-six Ni-Cr (Heraenium NA) discs, 10 mm in diameter and 1.5 mm in height, were fabricated. Twenty-four discs were airborne-particle abraded with 50-μm Al2O3 particles, while another 24 were airborne-particle abraded with 250-μm Al2O3 particles. The following primers were applied on 6 discs of each airborne-particle-abrasion treatment group: Solidex Metal Photo Primer (MPP50, MPP250), Metal Primer II (MPII50, MPII250), SR Link (SRL50, SRL250), and Tender Bond (TB50, TB250). The Rocatec system was used on another 6 discs, airborne-particle abraded according to the manufacturer's recommendations, which served as the control group (R). Two more discs were airborne-particle abraded with 50-μm and 250-μm Al2O3 particles, respectively, to determine the Al content on their surfaces, without any bonding procedure. The indirect composite resin used was Sinfony. Specimens were thermally cycled (5°C and 55°C, 30-second dwell time, 5000 cycles) and tested in shear mode in a universal testing machine. The failure mode was determined with an optical microscope, and selected specimens were subjected to energy dispersive spectroscopy (EDS). Mean bond strength values were analyzed using 2-way ANOVA followed by Tukey's multiple comparison tests (α=.05) and compared to the control group using 1-way ANOVA followed by Tukey's multiple comparison tests (α=.05). Results The groups abraded with 50-μm particles exhibited significantly higher bond strength compared to the groups abraded with 250-μm particles. Group MPII50 exhibited the highest mean value (17.4 ±2 MPa). Groups MPP50, MPP250, and TB50, TB250 showed adhesive failures and significantly lower bond strength compared to group R. Groups MPII50, MPII250, and SRL50, SRL250 showed combination failures and no significant difference compared with group R. EDS revealed interfacial rather than adhesive failures. Conclusions Airborne-particle abrasion with 50-μm Al 2 O 3 particles may result in improved bond strength, independent of the primer used. The bond strength of Metal Primer II and SR Link specimens was comparable to that of specimens treated with Rocatec. (J Prosthet Dent 2008;99:377-387)