Metallurgical, surface, and corrosion analysis of Ni-Cr dental casting alloys before and after porcelain firing.
OBJECTIVE
A porcelain veneer is often fired on nickel-chromium casting alloys used in dental restorations for aesthetic purposes. The porcelain-fused-to-metal (PFM) process brings the temperature to over 950 degrees C and may change the alloy's corrosion properties. In this study, the metallurgical, surface, and corrosion properties of two Ni-Cr alloys were examined, before and after PFM firing.


METHODS
Two types of alloy were tested-a high Cr, Mo alloy without Be and a low Cr, Mo alloy with Be. Before the PFM firing, specimens from both alloys were examined for their microstructures, hardness, electrochemical corrosion properties, surface composition, and metal ion release. After the PFM firing, the same specimens were again examined for the same properties.


RESULTS
Neither of the alloys showed any differences in their electrochemical corrosion properties after the PFM firing. However, both alloys exhibited new phases in their microstructure and significant changes in hardness after firing. In addition, there was a slight increase in CrO(x) on the surface of the Be-free alloy and increased Mo-Ni was observed on the surface of both alloys via X-ray photoelectron spectroscopy (XPS) and X-ray diffraction (XRD). This might be one of the reasons why both alloys had increased Ni and Mo ion release after firing.


CONCLUSIONS
The PFM firing process changed the alloys' hardness, microstructure, and surface composition. No significant changes in the alloys' corrosion behavior were observed, however, the significant increase in metal ion release over a month may need to be further investigated for its clinical effects.
Lin
Hsin-Yi
HY
Department of Chemical Engineering and Biotechnology, National Taipei University of Technology, 1, Sec 3, Zhongxiao E Rd., Taipei 106, Taiwan. hbrunken@ntut.edu.tw
Bowers
Bonnie
B
Wolan
John T
JT
Cai
Zhuo
Z
Bumgardner
Joel D
JD
D000704:Analysis of Variance; D002858:Chromium Alloys / Q000737:chemistry; D003343:Corrosion; D003735:Dental Casting Technique; D003799:Dental Stress Analysis; D017097:Electric Impedance; D006244:Hardness; D006358:Hot Temperature; D008422:Materials Testing; D016876:Metal Ceramic Alloys / Q000737:chemistry; D009532:Nickel / Q000032:analysis; D013052:Spectrometry, X-Ray Emission; D013499:Surface Properties; D014961:X-Ray Diffraction
D002858:Chromium Alloys; D016876:Metal Ceramic Alloys; D009532:Nickel