Cobalt-Chromium Dental Alloys Enriched with Precious Metals

The objective of this study is to verify if the new generation of cobalt-chromium (Co-Cr) alloys enriched with precious metals (Au, Pt, Ru), now coming on the market are characterized by improved corrosion resistance, compared to "classic" Co-Cr alloys. The study was carried out on four different commercial Co-Cr alloys enriched with precious metals. Alloys no.1 and no.4 contain only Au (2%), no. 2 Au and Pt (4%), no.3 Pt and Ru (25%). Before electrochemical testing, the alloys were analyzed micrographically, analysis of phases by energy-dispersive X-ray spectroscopy (EDX) was carried out and hardness properties were also tested. Electrochemical measurements were conducted in artificial saliva of the Fusayama type (deaerated with nitrogen, temperature 37°C, pH=5) using the rotating electrode technique. The microstructures of alloys no.1 and no.4 exhibited round "inclusions" with a diameter up to 0.1 mm. The chemical analysis of these zones showed of In (42-51%), Pt (arround 28%) and Au (18- 27%). The Vickers tests of such zones for no. 4 gave a mean hardness value more than twice lower (147 HV) compared to the overall hardness value of the alloy (326 HV). The potentiodynamic curves reveal important differences in the behaviour of the studied alloys as compared to the conventional Co-Cr alloy. The worst behaviour was given by the alloys containing only Au (no.1 and no.4). Alloys no.1 and no.4 showed a very complex microstructure compared to the other studied alloys. The round "inclusions" are in part non miscible phases with a very low corrosion resistance. Au is not miscible to Co and Cr. From the point of view of corrosion behaviour, the classical Co-Cr alloy is the best material followed by the alloys no.2 and no.3. The worst alloys are no.1 and no.4 (with only addition of 2% Au). Scientifically speaking Co-Cr dental alloys enriched with precious metals is a non-sense. Keywords: cobalt-chromium dental alloys, precious metals