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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 2: Parent alloys

Patrice Berthod, Pascal De March, Felix Romder, Carine Agostino

This second part of the study deals with eight parent alloys, which are considerablymore present in the frameworks reinforcing fixed partial denture, but which also are more preserved from the buccal milieu and then from possible corrosion phenomena than post-solder alloys, because covered by the ceramic part. However, to anticipate what can occur in case of emergence of parent alloyÂÂ’s extremities, the same electrochemical experiments as for the post-solder alloys in the first part were realized in the same three simple solutions (open circuit potential follow-ups, polarization resistance measurements followed by estimation of corrosion currents according to Stern-Geary.Here too the recorded open circuit potentials are high ( 100mV/ NHE) or very high ( 450mV/NHE) for the high noble alloys (but significantly lower for the Pd-based and NiCr-based alloys). Generally, the elements Cu, In, Ga, Sn, Zn, Ni, Cr, ... which are not in their immunity domain as gold, platinum or palladium, are in their passivation domain and the corrosion of the alloys containing them is limited, as proven by the high and even very high values of polarization resistance (at least several k × cm² but often of several hundreds of k × cm²). Corrosion currents are thus of only 10µA/ cm² to 10nA/cm².