Surface characterization of passive film and elemental release analysis of a Ni-Cr alloy during bleaching, part I: effects of different bleaching agents

The aim of this study was to evaluate the elemental release from a Ni-Cr dental casting alloy subjected to 10% hydrogen peroxide (HP) or 10% carbamide peroxide (CP) solutions and to determine the composition of surface oxide layer formed on alloy samples. Cylinder-shaped 15 specimens were cast from a Ni-Cr alloy and divided into three groups (n = 5). Samples were exposed either to phosphate-buffer solution, HP, or CP for 30 days, and total mass and individual elements (Ni, Cr, Mo) released into solutions were measured by means of atomic absorption spectrometry. Before and after elemental release measurements, a scanning electron microscope (SEM) accompanied by energy dispersive spectroscopy (EDS) (SEM/EDS) was used to analyze the surface morphology, and surface characterization of passive film formed on alloy samples was also performed by using X-ray photoelectron spectroscopy (XPS). The presence of bleaching agents induced the mass released compared to control group (4.9 mu g/cm(2)); this effect was recorded in both HP (171.2 mu g/cm(2)) and CP (59.7 mu g/cm(2)). XPS data showed that Cr and Ni levels in oxide layers formed on HP group were higher, Mo level was lower than those of CP group.