Brushing-induced surface roughness of nickel-, palladium-, and gold-based dental casting alloys

Statement of problem Alloys with high nickel content have been increasingly used for dental prostheses. These alloys have excellent hardness, elastic modulus, and strength, yet have high corrosion rates when exposed to chemical or physical forces that are common intraorally. Purpose The purpose of the current study was to measure the susceptibility of several types of nickel-based alloys to brushing abrasion relative to gold- and palladium-based alloys. Material and methods Au-Pt, Au-Pd, Pd-Ag, Ni-Cr, and Ni-Cr-Be dental alloys were brushed with a toothbrush (Oral-B Soft) and toothpaste (Ultrabrite) in a linear brushing machine, then the surface roughness was measured by profilometry (Ra , Rv , Rp ). Specimens (n=4) were brushed for 48 hours in a saline solution (pH 7). The effect of brushing was determined using 2-sided t tests (α=.05), and roughness among alloys postbrushing was compared using 1-way ANOVA with Tukey post hoc analyses (α=.05). Results All polished alloy surfaces (before brushing) had roughnesses of ≤0.1 μm (Ra ). The Pd-Ag alloy was the most resistant to brushing. The Ni-Cr-Be alloy abraded the most, with a postbrushing surface roughness of >1 μm (Ra ). Ni-Cr alloys without Be had a postbrushing surface roughness of 0.25 μm (Ra ). Postbrushing roughness of all other alloys ranged from 0.1-0.25 μm (Ra ). Rv and Rp values behaved similarly to Ra values for all alloys. Conclusions Although they have many excellent mechanical properties, Ni-Cr-Be alloys may be prone to degradation from brushing. (J Prosthet Dent 2008;99:455-460)