Cytotoxicity of dental casting alloys pretreated with biologic solutions

Statement of problem. Short-term (72-168 hours) in vitro tests are used to evaluate the cytotoxicity of dental casting alloys. The ability of these sh ort-term tests to predict long-term in vivo cytotoxicity has been questione d. A procedure to accelerate the testing of casting alloys would be useful in predicting longer-term alloy cytotoxicity. Purpose. This study hypothesized that preconditioning casting alloys by soa king in a biologic liquid would change subsequent cytotoxicity by removing some elements. Preconditioning map be I method of accelerating short-term i n vitro tests. Material and methods. Dental casting alloys were exposed to either saline, cell culture medium, or a saline/bovine serum albumin (BSA) solution for 72 hours before standard in vitro cytotoxicity testing. Six types of alloys w ere tested (n = 6): 5 Au-Ag-Cu-Pd alloys (single phase) and 1 Ag-Pd-Cu allo y (multiple phase). Teflon (Tf) samples served as a control. After precondi tioning, alloys were placed in direct contact with Balb/c fibroblasts for 7 2 hours, after which cell viability was measured by succinic dehydrogenase activity (MTT method) relative to Tf controls (100% = no toxicity). Element s released into the preconditioning solutions were measured by atomic absor ption spectroscopy. Cytotoxicities of preconditioned alloys and amounts of elemental release were compared with unconditioned alloys. Results. A preconditioning time of 72 hours was sufficient to change the cy totoxicity of the tested alloys. The alloys that were more cytotoxic initia lly became less cytotoxic after preconditioning. For all the alloys tested, except the Ag-Pd-Cu multiphase alloy, preconditioning with either the sali ne or the saline/BSA solution caused an increase in cellular activity, ther efore the preconditioned alloys were less cytotoxic. The cell culture mediu m preconditioning solution had a variable effect, causing increased or decr eased cellular activity depending on the alloy treated. Conclusion. Preconditioning of casting alloys decreased subsequent cytotoxi city. However, not all preconditioning solutions are equivalent. A precondi tioning strategy may be useful in accelerating the short-term cytotoxicity test toward a longer-term result.