N.Baltzer*, U. Renfer, J. Fischer, A.H. Geering. (Cendres & Métaux SA, Bieland Klinik für zahnärztliche Prothetik der Universität Bern)
Potentio-dynamic measurements are more and more used to classify the corrosion behaviour of dental alloys. The advantage compared to the conventional immersion test is the fast acquisition of results. The aim of this work was to evaluate the aptness of potentio-dynamic measurements with ten ceramic-fused-to-metal alloys in three different states (as cast, oxidised with the oxide layer left in place and simulation firing according to ISO 9693) as well as with the pure alloying elements.
Samples having a surface area of 1 cm² were cast with the lost wax process. A physiological salt solution was used as electrolyte. After immersion for 2 hours the potentio-dynamic scan was started at a potential minus 150 mV of the open circuit potential at a sweep rate of 2 mV/s. The reference electrode was an Ag/AgCl electrode, the working electrode a platinum electrode.
The alloys tested showed highest currents in the as cast state, followed by lesser ones in the simulation fired state. The lowest corrosion rate was obtained in the oxidised state. The breakdown potential of the alloys was found to be identical to that of the precious metal element being the main constituent of the alloy.
Because of their passivating property the corrosion behaviour of the oxide layers cannot be assessed by potentio-dynamic measurements. The breakdown potential should not be used for the assessment of the corrosion behaviour of alloys, because it only shows the behaviour of the surface cleared of non-precious elements by the corrosion.