Electrochemical Impedance Spectroscopy Study of Corrosion of Palladium-Silver Dental Alloys

Purpose: The purpose of this study was to evaluate the corrosion behavior of palladium-silver dental alloys in simulated body fluid and oral environments. Methods: Three representative Pd-Ag alloys [Rx 91(53.5Pd–37.5Ag–8.5Sn–In–Ru), Jeneric Pentron, Wallingford, CT; Super Star (59.8Pd–28.1Ag–6In–5Sn–Ga–Ru/Re) Heraeus Kulzer Jelenko, Armonk, NY; and W-1 (53.3Pd–37.7Ag–8.5Sn–In–Ru/Re], Ivoclar Vivadent, Amherst, NY] were selected. A well-known high-noble gold alloy [Olympia (51.5Au-38.5Pd-8.5In-1.5Ga-Ru), Heraeus Kulzer Jelenko] was used as a control. Disk-shaped specimens of 1.25 cm diameter and 0.13 cm thickness were cast and oxidized. Simulated porcelain-firing heat treatment was then performed for all four alloys. All specimens were ground and polished through 0.05 µm alumina slurries. Electrochemical impedance spectroscopy (EIS) over a frequency range of 6 to 8 decades was performed on all four alloys at open circuit potential (OCP) and elevated potentials of interest in 0.09% and 0.9% NaCl solutions and Fusayama solution. ANOVA, REGW multiple-range test and Dunnett's method were used to identify differences for a given EIS parameter between each of the alloys. Results: The corrosion resistances of the Pd-Ag alloys were equivalent to that for the Olympia alloy in these in vitro environments. The corrosion resistances of these Pd-Ag alloys at potentials relevant to the oral environment decreased no more than one order of magnitude compared with those at OCP. The three Pd-Ag alloys investigated were resistant to chloride ion corrosion, and the corrosion process for these alloys was generally controlled by charge transfer and charge accumulation process. Conclusion: The corrosion resistances of the investigated palladium-silver alloys at OCP and elevated potentials appeared satisfactory for clinical usage. Supported by NIDCR Grant DE10147.