Electrochemical characteristics of high-Pd alloys in relation to Pd-allergy

By Berzins, D.W.; Kawashima, I.; Graves, R. & Sarkar, N.K.
Published in Dental Materials NULL 2000

Abstract

Objective: The aim of this study was to determine whether the Pd–Cu-based dental ceramic alloys possess any electrochemical characteristics distinguishable from that of other Pd-containing alloys. Of all Pd-containing alloys, this particular alloy group has been linked to frequent incidence of allergy and hypersensitivity reactions. Electrochemical corrosion may instigate these reactions. Methods: Four groups of alloys, Pd–Cu, Pd–Ga-(with and without Ag), Pd–Ag, and Au–Pd, were evaluated by traditional corrosion measurement techniques in a phosphated buffer saline solution at 20°C. The electrochemical characteristics measured were: (1) 20 h open circuit potential (OCP); (2) 20 h corrosion rate (Icorr); and (3) anodic polarization (E–i) curves. Results: The OCP values (232±25 mV) of the Ag-free Pd–Ga and Pd–Cu-based alloys were higher than and distinctly different from that (144±52 mV) of the Ag-containing alloys. The Icorr values of different alloys, despite varied compositions, were indistinguishable from one another. The E–i curves of all alloys were essentially similar, with the Ag-containing (>5 wt%) alloys showing a subtle difference in their anodic slope within 100 mV above their corrosion potentials. Significance: The OCP values of Pd–Cu alloys and the Ag-free Pd–Ga alloy are comparable to that reported for pure Pd (239±21 mV), which indicates that during corrosion these alloys undergo dealloying and consequent Pd-enrichment on their surface. Such a condition is conducive to the release of allergenic Pd++ ions and offers a plausible explanation for the frequent incidence of hypersensitivity reactions associated with the Pd–Cu alloys. The OCP values in other alloys are attributed to dealloying followed by surface enrichment with Ag and/or Au and the possible formation of an insoluble AgCl surface film on the respective alloy surfaces. These events have the potential to suppress or prevent Pd++ ion release. Alloys showing these characteristics have seldom been linked to allergic reactions.

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