A proposal for the classification of dental alloys according to their resistance to corrosion

Objectives. The purpose of this study was to establish a method to compare and classify dental alloys in relation to their resistance to corrosion. Methods. Alloy samples and pure metal samples were prepared and tested in chemical and electrochemical corrosion according to ISO 10271. For electrochemical test, the rest potential versus time and a potentiodynamic scan were recorded. After chemical corrosion test, the ions released were analyzed by ICP (induced coupled plasma) spectroscopy. Results. High gold alloys had a similar polarization curve than gold. The same effect was observed for Pd-base alloys, their curves were similar to the one of palladium. The ions released during chemical corrosion were non-precious metallic ions. Thereby Ni-Cr alloys were found to release the most ions. Au-Pt alloys showed the highest release of ions compared with other precious alloys but low compared with Ni-Cr. Electrochemical corrosion was more aggressive than chemical corrosion and every type of elements was etched, the higher the precious metal content, the higher the resistance to corrosion of the alloy. Discussion. Using the recorded data, a classification system for electrochemical corrosion was developed and discussed to judge the results. Hereby were gold and zinc used as reference materials. The applied classification system defines five classes and it is proposed that alloys of class V are not acceptable. For chemical corrosion resistance, three classes were distinguished according to the quantity of metallic ions released and it is proposed that class III (100-1000 mu g/cm(2) week) is not acceptable. Palladium and Pd-base alloys showed a higher electrochemical and chemical corrosion resistance than gold. (C) 2007 Published by Elsevier Ltd on behalf of Academy of Dental Materials. All rights reserved.