RESEARCH AND EDUCATION Potentiodynamic polarization study of the corrosion behavior of palladium-silver dental alloys Desheng Sun, MAS, PhD, a William A. Brantley, PhD, b Gerald S. Frankel, ScD, c Reza H. Heshmati, DDS, MPH, MS, d and William M. Johnston, PhD e Because of high gold prices, palladium-silver (Pd-Ag) alloys have become popular for metal- ceramic restorations. The more expensive high-noble gold- based and gold-palladium alloys have been widely used for metal-ceramic restorations for several decades because of their excellent physical and mechanical properties, good porcelain adherence, high corrosion resistance, and su- perb biocompatibility. 1 The Pd-Ag alloys, which were introduced in the 1970s, 2 have values for elastic modulus and yield strength similar to those for the Au-Pd-Ag and Au-Pd alloys but with much lower densities. 1 The Pd-Ag alloys also have high distortion resis- tance during porcelain firing, 3 excellent metal-ceramic bond strength, 4 and satisfactory tar- nish and corrosion resistance. 5,6 Moreover, earlier concerns that Supported by National Institute of Dental and Craniofacial Research (grant DE10147). This study was based on a portion of a dissertation submitted by D.S., in partial fulfillment of the PhD degree, Graduate School of The Ohio State University. a Senior Materials and Corrosion Engineer, BP America, Naperville, Ill. b Professor, Division of Restorative Science and Prosthodontics, College of Dentistry, The Ohio State University, Columbus, Ohio. c Professor, Department of Materials Science and Engineering and Director, Fontana Corrosion Center, The Ohio State University, Columbus, Ohio. d Associate Professor, Clinical, Division of General Practice and Materials Science, College of Dentistry, The Ohio State University, Columbus, Ohio. e Professor Emeritus, Division of General Practice and Materials Science, College of Dentistry, The Ohio State University, Columbus, Ohio. ABSTRACT Statement of problem. Although palladium-silver alloys have been marketed for over 3 decades for metal-ceramic restorations, understanding of the corrosion behavior of current alloys is incomplete; this understanding is critical for evaluating biocompatibility and clinical performance. Purpose. The purpose of this in vitro study was to characterize the corrosion behavior of 3 representative Pd-Ag alloys in simulated body fluid and oral environments and to compare them with a high-noble Au-Pd alloy. The study obtained values of important electrochemical corrosion parameters, with clinical relevance, for the rational selection of casting alloys. Material and methods. The room temperature in vitro corrosion characteristics of the 3 Pd-Ag alloys and the high-noble Au-Pd alloy were evaluated in 0.9% NaCl, 0.09% NaCl, and Fusayama solutions. After simulated porcelain firing heat treatment, 5 specimens of each alloy were immersed in the electrolytes for 24 hours. For each specimen, the open-circuit potential (OCP) was first recorded, and linear polarization was then performed from e20 mV to +20 mV (versus OCP) at a rate of 0.125 mV/s. Cyclic polarization was subsequently performed on 3 specimens of each alloy from e300 mV to +1000 mV and back to e300 mV (versus OCP) at a scanning rate of 1 mV/s. The differences in OCP and corrosion resistance parameters (zero-current potential and polarization resistance) among alloys and electrolyte combinations were compared with the 2-factor ANOVA (maximum-likelihood method) with post hoc Tukey adjustments (a=.05). Results. The 24-hour OCPs and polarization resistance values of the 3 Pd-Ag alloys and the Au-Pd alloy were not significantly different (P=.233 and P=.211, respectively) for the same electrolyte, but significant differences were found for corrosion test results in different electrolytes (P<.001 and P=.032, respectively). No significant interaction was found between the factors of alloy and electrolyte (P=.249 and P=.713, respectively). The 3 Pd-Ag silver alloys appeared to be resistant to chloride ion corrosion, and passivation and de-alloying were identified for these alloys. Conclusions. The Pd-Ag alloys test results showed excellent in vitro corrosion resistance and were equivalent to those of the high-noble Au-Pd alloy in simulated body fluid and oral environments. Passivation, de-alloying, and formation of a AgCl layer were identified as possible corrosion mechanisms for Pd-Ag alloys. (J Prosthet Dent 2017;-:---) THE JOURNAL OF PROSTHETIC DENTISTRY 1