Cytotoxicity of dental casting alloys pretreated with biologic solutions

Short-term (72-168 hours) in vitro tests are used to evaluate the cytotoxicity of dental casting alloys. The ability of these short-term tests to predict long-term in vivo cytotoxicity has been questioned. A procedure to accelerate the testing of casting alloys would be useful in predicting longer-term alloy cytotoxicity.

This study hypothesized that preconditioning casting alloys by soaking in a biologic liquid would change subsequent cytotoxicity by removing some elements. Preconditioning may be 1 method of accelerating short-term in vitro tests.

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 were tested (n = 6): 5 Au-Ag-Cu-Pd alloys (single phase) and 1 Ag-Pd-Cu alloy (multiple phase). Teflon (Tf) samples served as a control. After preconditioning, alloys were placed in direct contact with Balb/c fibroblasts for 72 hours, after which cell viability was measured by succinic dehydrogenase activity (MTT method) relative to Tf controls (100% = no toxicity). Elements released into the preconditioning solutions were measured by atomic absorption spectroscopy. Cytotoxicities of preconditioned alloys and amounts of elemental release were compared with unconditioned alloys.

A preconditioning time of 72 hours was sufficient to change the cytotoxicity of the tested alloys. The alloys that were more cytotoxic initially became less cytotoxic after preconditioning. For all the alloys tested, except the Ag-Pd-Cu multiphase alloy, preconditioning with either the saline or the saline/BSA solution caused an increase in cellular activity, therefore the preconditioned alloys were less cytotoxic. The cell culture medium preconditioning solution had a variable effect, causing increased or decreased cellular activity depending on the alloy treated.

Preconditioning of casting alloys decreased subsequent cytotoxicity. However, not all preconditioning solutions are equivalent. A preconditioning strategy may be useful in accelerating the short-term cytotoxicity test toward a longer-term result.