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Influence of the pH and of the chloride concentration on the corrosion of metallic alloys for frameworks reinforcing dental prostheses. Part 1: Soldering alloys

Pascal De March, Patrice Berthod, Carine d�?�?�?�?�?�?�?�?Agostino, F�?�?�?�?�?�?�?©lix Romder

Themaking of frameworks reinforcing the ceramic part of fixed partial denture involves joining alloys of different natures. Some of the solder joints, made of post-solder alloys, can be in contact with buccal saliva and then possibly suffer corrosion. In this work electrodes were prepared from four soldering alloys classically used after ceramic deposit, and were immersed in three different simple solutions derived from an artificial saliva usually used for such tests of dentalmaterials. Their corrosion behaviourswere characterized by the measurement of the open circuit potential and their polarization resistances according to the Stern-Gearymethod for estimating their corrosion currents. The recorded open circuit potentials are high ( 100mV/NHE) or very high ( 300mV/NHE) and they generally depend both on the chemical composition of the studied soldering alloy as well as on the electrolyte (its pH: 6.6 or 7.4 and its NaCl concentration: 9 or 90g/L). The Eocp potentials logically indicate that the noblest elements are in their immunity domains while the others are in their passivation ones (criterion: 1mol/L). Polarization resistances are high (several k × cm²) or very high (almost 1 M × cm²), and they lead to low or very low corrosion currents (less than 0.1 µA/cm² in several cases).