Corrosion of CoCr and NiCr dental alloys alloyed with palladium

Abstract

Statement of problem: A new subclass of casting alloy composition involving the addition of palladium (25 wt%) to traditional base metal alloys, thereby raising their classification to that of a noble alloy, has been recently introduced. Little is known about this class of casting alloy, particularly its corrosion properties, which influence its biocompatibility and esthetics.

Purpose: The purpose of this study was to evaluate the corrosion properties of 2 new CoPdCr and one new NiPdCr alloy and compare them to traditional CoCr and NiCr alloys.

Material and methods: The casting alloys investigated were: CoPdCr-A (NobleCrown NF), CoPdCr-I (Callisto CP+), NiPdCr (Noble Crown), CoCr (Argeloy N.P. Special), and NiCr (Argeloy N.P. Star). Cylindrical (4.8-mm diameter) as-cast and oxidized specimens were assessed electrochemically in phosphate-buffered saline at 24°C (n=8 and n=6, respectively). The open circuit potential (OCP) was monitored for 20 hours, followed by linear polarization and cyclic polarization tests. A generalized linear mixed model was used to determine whether differences existed between alloys and to examine the effect of oxidation (α=.05). Representative alloy surfaces were scanned and examined with light microscopy.

Results: The palladium-containing alloys possessed a significantly greater OCP (P<.001); however, their polarization resistance was less and the corrosion current density was significantly greater (P<.05) than their traditional CoCr and NiCr alloy counterparts. Additionally, a greater incidence of pitting was observed in the palladium-containing alloys. Some differences were noted within alloys between the as-cast and oxidized conditions, but a major trend was not observed.

Conclusions: Overall, the inclusion of palladium in CoCr and NiCr alloys had deleterious effects on electrochemical corrosion properties.