Corrosion behavior and cytocompatibility of a Co–Cr and two Ni–Cr dental alloys before and after the pretreatment with a biological saline solution
Objectives. The aim of this study was to evaluate the corrosion behavior and cytocompatibility of a Co–Cr and two Ni–Cr dental alloys before and after the pretreatment with a biological saline solution. Methods. A commercial cobalt–chromium (Co–Cr) and two nickel–chromium (Ni–Cr) dental alloys [beryllium (Be)-free and Be-containing] were selected and pretreated with a biological saline solution containing 3% bovine serum albumin (BSA) for 72 h. Before and after the pretreatment, alloy specimens were examined for surface element compositions using X-ray photoelectron spectroscopy (XPS). Corrosion behavior and metal ion release were measured by electrochemical corrosion and immersion tests in artificial saliva respectively. The released metal ions in the exposed biological saline solution were also detected after the pretreatment for 72 h. 3T3 fibroblasts were cultured and exposed to specimens. After 4 hours of incubation, cell morphology and spreading were observed under a laser scanning confocal microscope. Cell proliferations were evaluated using CCK-8 assay after culturing for 1, 3 and 6 days. Results. After the pretreatment with a biological saline solution, the corrosion potential (Ecorr) and breakdown potential (Ebr) of the three dental alloys increased significantly, which corresponded with evident decreases of Co, Ni and Be levels on the alloy surfaces measured by XPS. The corrosion current (Icorr) and the polarization resistance (Rp) of the three alloys were not significantly affected by the pretreatment, corresponding to the slight reductions of Cr, molybdenum (Mo) and oxygen (O) levels on the surfaces of alloys except the Be-containing alloy. For the three alloys, the pretreatment obviously decreased the metal ions release in artificial saliva. There were a large amount of metal ions, including Co, Ni and Be ions, released from the alloys in the exposed biological saline solution after the pretreatment for 72 h. The results of in vitro study demonstrated that the pretreatment up-regulated cell spreading and proliferation on the three metallic substrates. Conclusions. The pretreatment with a biological saline solution optimized the surface elemental compositions of a Co–Cr and two Ni–Cr dental alloys by removing more labile metal elements from the alloy surfaces in form of cations. The corrosion susceptibility and metal ion release of the three dental alloys decreased significantly after the pretreatment, which led to improvements of their cytocompatibility.