Bond strength and surface characterization of a Ni-Cr-Be alloy

Objectives. Since resin composite cements adhere directly to base metal surfaces, the composition and integrity of the surface oxide layer is considered critical for adequate bonding. The aims of this study were to determine the tensile bond strength, and assess predominant surface oxides and oxide layer depth on the surface of a Ni-Cr-Be alloy after subjecting the alloy to various surface treatments. Methods. Cylinders of Ni-Cr-Be (Rexillium III, Jeneric/Pentron) were cast and the following test groups were investigated: Group 0: no furnace oxidation, no air abrasion; Group 1: air fired, starting temperature 650°C, ending temperature 1000°C (1 min hold); Group 2: same firing sequence under vacuum; Group 3: same air firing sequence followed by air abrasion with 50 μm Al2O3; Group 4: vacuum fired, air abraded with 50 μm Al2O3; Group 5: air fired, air abraded with 280 μm Al2O3; Group 6: vacuum fired, air abraded with 280 μm Al2O3; Group 7: no furnace oxidation, air abraded with 50 μm Al2O3; and Group 8: no furnace oxidation, air abraded with 280 μm Al2O3. The oxide composition of three cylinders per group was analyzed with x-ray photoelectron spectroscopy (XPS) and Auger electron spectroscopy (AES). Twenty cylinders from each group were bonded together with Panavia 21 (Kuraray), stored in water for 30 d, and tensile tested. Data were analyzed using one-way ANOVA and Duncanʹs Multiple-Range test (p=0.05). Results. Furnace oxidation brough Be to the surface and increased the oxide thickness. Air abrasion removed the oxide layer and resulted in surfaces containing significant amounts of Al2O3. Bond strengths for Group 0 were significantly lower than bond strenghts for Groups 1, 3, 4, 5, 6, 8, but not significantly different from bond strengths for Groups 2 and 7 (p<0.05). Significance. Results of this study suggest differences in oxide composition and thickness due to various surface treatments. Furnace oxidation did not significantly affect bond strength and may not be required as a separate step for metal preparation if a resin adhesive is used.