Corrosion of nickel-based dental casting alloys.
OBJECTIVE
To study the microstructure, corrosion behaviour and cell culture response of two nickel-based dental casting alloys before and after a heat treatment to simulate porcelain firing.


METHODS
The microstructure was studied using scanning electron microscopy (SEM) and energy dispersive X-ray analysis (EDX). Corrosion behaviour was evaluated by electrochemical measurements in artificial saliva at different values of pH in the presence of a crevice. 3T3 mouse fibroblasts were exposed indirectly to alloy specimens and the number of viable cells counted after 3 and 6 days compared to a control culture.


RESULTS
Small changes in microstructure were observed after heat treatment but had a negligible effect on the corrosion properties in the conditions tested. The alloy with a lower bulk level of Cr (12.6 wt.%) showed lower corrosion resistance, indicated by an increased passive current density and this stability was greatly reduced at pH 2.5, where crevice corrosion was observed. Selective dissolution occurred at regions within the microstructure containing lower levels of Cr and Mo. Furthermore, the proliferation of 3T3 mouse fibroblasts was reduced (p<0.05) when exposed indirectly to this alloy. The alloy containing a higher level of Cr (25 wt.%) showed superior corrosion resistance, which was associated with a more uniform distribution of Cr in the alloy microstructure.


CONCLUSIONS
The presence of crevices combined with an inhomogeneous distribution of Cr in the microstructure can lead to accelerated corrosion of Ni-based alloys with lower Cr contents. This effect can be avoided by increasing the Cr content of the alloy.
Wylie
Christopher M
CM
Department of Metallurgy and Materials, University of Birmingham, Birmingham B15 2TT, UK.
Shelton
Richard M
RM
Fleming
Garry J P
GJ
Davenport
Alison J
AJ
D016475:3T3 Cells; D000704:Analysis of Variance; D000818:Animals; D049109:Cell Proliferation / Q000187:drug effects; D002858:Chromium Alloys / Q000737:chemistry* / Q000633:toxicity; D003343:Corrosion; D004563:Electrochemistry; D004577:Electron Probe Microanalysis; D005347:Fibroblasts / Q000187:drug effects; D051379:Mice; D009532:Nickel / Q000032:analysis / Q000737:chemistry* / Q000633:toxicity
D002858:Chromium Alloys; D009532:Nickel