Use of x-ray photoelectron spectroscopy and cyclic polarization to evaluate the corrosion behavior of six nickel-chromium alloys before and after porcelain-fused-to-metal firing.
BACKGROUND
Nickel-chromium casting alloys rely on a surface oxide layer for corrosion resistance to the oral environment. Porcelain-fused-to-metal (PFM) firing procedures may alter the surface oxides and corrosion properties of these alloys. Changes in alloy corrosion behavior affect metal ion release and therefore local and/or systemic tissue responses.


OBJECTIVE
The aim of this study was to evaluate changes in alloy surface oxides and electrochemical corrosion properties after PFM firing.


METHODS
The electrochemical corrosion behavior of 6 commercial nickel-chromium alloys was evaluated in the as-cast/polished and PFM fired/repolished states. Surface chemistries of the alloys were analyzed by x-ray photoelectron spectroscopy.


RESULTS
Results indicated an increase in corrosion rates after PFM firing and repolishing for alloys containing 14% to 22% Cr and 9% to 17% Mo. This increase in corrosion rates was attributed to a decrease, caused by the PFM and repolishing process, in the Cr and Mo levels in the surface oxides of these alloys. The PFM firing and repolishing process did not alter the corrosion behavior of the alloys containing lower levels of Cr and Mo and/or Be additions in their bulk composition. These alloys exhibited low levels of Cr and Mo surface oxides in both test conditions. Si particles became embedded in the surfaces of the fired alloys during repolishing and may have contributed to the changes in surface oxides and the corrosion behavior of some alloys.


CONCLUSIONS
The effects of PFM firing and repolishing on Ni-Cr dental casting alloy surface oxides and corrosion properties appear to be alloy dependent.
Roach
M D
MD
Mississippi State University, Mississippi State, Jackson 39762, USA.
Wolan
J T
JT
Parsell
D E
DE
Bumgardner
J D
JD
D000704:Analysis of Variance; D002858:Chromium Alloys / Q000737:chemistry*; D003343:Corrosion; D003735:Dental Casting Technique; D003776:Dental Porcelain / Q000737:chemistry*; D004563:Electrochemistry; D012464:Saliva, Artificial; D013057:Spectrum Analysis / Q000379:methods* / Q000706:statistics & numerical data; D013499:Surface Properties
D002858:Chromium Alloys; D012464:Saliva, Artificial; D003776:Dental Porcelain