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

Statement of problem. Nickel-chromium casting alloys rely on a surface oxid e layer for corrosion resistance to the oral environment. Porcelain-fused-t o-metal (PFM) firing procedures may alter the sur face oxides and corrosion properties of these alloys. Changes in alloy corrosion behavior affect met al ion release and therefore local and/or systemic tissue responses. Purpose. The aim of this study was to evaluate changes in alloy surface oxi des and electrochemical corrosion properties after PFM firing. Material and methods. The electrochemical corrosion behavior of 6 commercia l nickel-chromium alloys was evaluated in the as-cast/polished and PFM fire d/repolished states. Surface chemistries of the alloys were analyzed by x-r ay 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 corr osion 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 embed ded in the surfaces of the fired alloys during repolishing and may have con tributed to the changes in surface oxides and the corrosion behavior of som e alloys. Conclusion. The effects of PFM firing and repolishing on Ni-Cr dental casti ng alloy surface oxides and corrosion properties appear to be alloy depende nt.