Evaluation of genotoxicity of recycled Ni-Cr dental casting alloys: an in vitro study.

This study was conducted to evaluate the genotoxicity of nickel-chromium (Ni-Cr) base metal alloys in their reused state at different time intervals. Two commercially available Ni-Cr alloys (Wiron 99, remanium Cse) were evaluated. Three groups of alloy specimens (disks 3 mm x 5 mm) were fabricated from each of these alloys. The first groups were made with 100% new alloy, the second groups with 50 wt% of new alloy and 50 wt% of once used alloy and the third groups with 100% once used alloy. Distilled water conditioned with the alloy specimens for four time intervals of 1, 2, 4 and 8 weeks was used for testing the genotoxicity on Chinese hamster V79-HG04 fibroblasts using the micronucleus assay. Cells were examined for the number of micronuclei in the cytoplasm. More numbers of micronuclei the more the DNA damage. Statistical analysis was carried out using one-way ANOVA to determine whether the group means differed from one another significantly. Post hoc analysis was done using Bonferroni 't' test to compare the differences in mean values between groups. The highest genotoxicity was noticed at 4 weeks. It did not alter significantly when the length of conditioning was increased to 8 weeks. The lowest genotoxicity was observed for the first groups, intermediate results for the second groups and the greatest genotoxicity for the third groups when compared to controls. There were no significant differences between Wiron 99 and remanium CSe. Considering the elevated genotoxicity of Ni-Cr alloys in their reused state, the practice of reusing the alloy just for economic reasons should be discouraged.