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


CONCLUSIONS
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.
Berzins
D W
DW
School of Dentistry, Louisiana State University, 1100 Florida Avenue, New Orleans, LA, USA.
Kawashima
I
I
Graves
R
R
Sarkar
N K
NK
D000485:Allergens / Q000737:chemistry*; D002021:Buffers; D003300:Copper / Q000737:chemistry; D003343:Corrosion; D003722:Dental Alloys / Q000737:chemistry*; D004553:Electric Conductivity; D004563:Electrochemistry; D005708:Gallium / Q000737:chemistry; D006046:Gold / Q000737:chemistry; D006801:Humans; D006967:Hypersensitivity / Q000209:etiology; D015994:Incidence; D008422:Materials Testing; D016876:Metal Ceramic Alloys / Q000737:chemistry; D010165:Palladium / Q000737:chemistry*; D010710:Phosphates; D012834:Silver / Q000737:chemistry; D018030:Silver Compounds / Q000737:chemistry; D012965:Sodium Chloride; D013499:Surface Properties
D000485:Allergens; D002021:Buffers; D003722:Dental Alloys; D016876:Metal Ceramic Alloys; D010710:Phosphates; D018030:Silver Compounds; D012834:Silver; D012965:Sodium Chloride; D010165:Palladium; D006046:Gold; D003300:Copper; D005708:Gallium; C037548:silver chloride