Potentiodynamic polarization study of the in vitro corrosion behavior of 3 high-palladium alloys and a gold-palladium alloy in 5 media

Abstract

Statement of Problem. Corrosion of cast alloy restorations may lead to their failure or adversely affect their biocompatibility. Although some documentation of the corrosion behavior of the high-palladium dental alloys exists, questions remain about their corrosion resistance and mechanisms. Purpose. This study compared the in vitro corrosion characteristics of 3 high-palladium alloys and 1 gold-palladium alloy in simulated body fluid and oral environments. Material and Methods. Two Pd-Cu-Ga alloys and 1 Pd-Ga alloy were selected; an Au-Pd alloy served as the control. The corrosion behavior for the as-cast and simulated porcelain-firing (heat-treated) conditions of each alloy (N = 5) was evaluated in 0.9% NaCl, 0.09% NaCl, and Fusayama solutions. Heat-treated specimens of each alloy (N = 5) were also tested in N2-deaerated 0.09% NaCl and Fusayama solutions (pH 4). After immersion in the electrolyte for 24 hours, the open-circuit potential (OCP) was measured, and linear polarization was performed from −20 mV to +20 mV (vs. OCP) at a scanning rate of 0.125 mV/s. Cyclic polarization was performed from −300 mV to +1000 mV and back to −300 mV (vs. OCP) at a scanning rate of 1 mV/s. Data were evaluated with analysis of variance and the Ryan-Einot-Gabriel-Welsch multiple-range test (α=.05). Results. The OCP of each alloy varied with the condition (as-cast or heat-treated) and electrolyte used. Corrosion resistance was similar for the 4 alloys tested. For cyclic polarization, all alloys showed active-passive or spontaneous passive behavior in nearly all electrolytes. During some reverse scans, the 3 high-palladium alloys displayed 3 or 5 anodic peaks. No positive hysteresis was observed for any of the alloy/electrolyte combinations evaluated. Conclusion. The corrosion resistances of the 3 high-palladium alloys in simulated body fluid and oral environments were comparable to that of the gold-palladium alloy. The similar corrosion resistance for the 3 high-palladium alloys was attributed to their high noble metal content and theorized stable structure at the submicron level. Selective corrosion of different phases and elements, surface enrichment of palladium, and adsorption of species are possible corrosion mechanisms. The cyclic polarization results suggest that none of the 4 alloys would be prone to pitting or crevice corrosion under in vivo conditions, but crevice conditions should nonetheless be avoided for these alloys in the oral environment. (J Prosthet Dent 2002;87:86-93.)