Influence of Cerium on Corrosion and Biocompatibility of Co-Cr-PFM-Alloys

Introduction: The element Cerium is supposed to stabilize the oxide layer in non-noble alloys. However, there is little knowledge about the amount necessary for dental casting techniques and its correlation in terms of corrosion and biocompatibility. Materials and Methods: Three experimental CoCr22Mo7W4SiMn alloys with Ce contents of 0, 0.2 and 0.4wt% with and without oxide layer were investigated. After casting the surfaces of the test specimens were wet- polished to #1200 SiC, ultrasonically cleaned in 70% isopropyl alcohol for 2min and then dried. Half of the samples of each alloy were heat treated at 930°C (simulated porcelain firing) for a total time of 5min (4min in vacuum and 1min in air). Ion release in 0.1 mol/L lactic acid/sodium chloride (pH 2.3, 37°C) was analyzed after 1, 4, 7, 14, 21, 28 and 35 days using ICP-OES. Cytotoxicity was determined by XTT test following incubation of L-929 fibroblast cell cultures with extracts for 24h at 37°C (ISO 10993-5). Results: The addition of 0.2wt% Ce to the CoCr alloy decreased the corrosion rate, whereas 0.4wt% Ce showed no statistically significant further effect. As an example the accumulated mean (±SD, n=3) total substance loss values in µg/cm² after 35 d immersion revealed: (1) polished surface: 3.3±0.3 (Ce=0), 3.0±0.1 (Ce=0.2wt%), 3.5±0.1 (Ce=0.4wt%); (2) polished and oxidized surface: 54.7±6.4 (Ce=0), 7.1±1.3 (Ce=0.2wt%), 6.5±0.7 (Ce=0.4wt%). The XTT test showed a good over all biocompatibility and no influence of the Ce content could be found for the polished as well as for the polished & oxidized samples. Conclusions: The addition of Ce to CoCr PFM alloys enhanced the corrosion resistance of oxidized surfaces, whereas the biocompatibility was not affected. Supported by Association of German Dental Manufacturers (FGD/VDDI e.V.), DAAD (Germany), CAPES (Brazil) and Dentaurum J. P. Winkelstroeder KG (Germany).