Accelerated toxicity testing of casting alloys and reduction of intraoral release of elements

Short-term (72-168 hours) in vitro testing of dental casting alloys for cytotoxicity may not reflect in vivo biocompatibility. An accelerated test for evaluation of dental casting alloy cytotoxicity could help screen newly developed alloys more rapidly and accurately.

This study evaluated a method of accelerating alloy cytotoxicity by short-term conditioning of alloys. Cytotoxicity and mass release of these conditioned alloys were compared with alloys conditioned for 10 months or unconditioned alloys. The hypothesis was that a short-term conditioning procedure could be developed that would give cytotoxicity and mass release values similar to alloys exposed to a biologic solution for 10 months.

Dental casting alloys were conditioned in either saline, cell-culture medium, or a saline/bovine serum albumin (BSA) solution for 168 hours before standard in vitro cytotoxicity testing. Eight types of casting alloys with a range of nobilities (98% to 0%) were tested (n = 6). Controls were Teflon (Tf). Conditioned alloys were placed in direct contact with Balb/c fibroblasts for 72 hours, and cell viability was measured by succinic dehydrogenase activity (MTT method) relative to Tf controls. Elements released into the conditioning solutions were measured by atomic absorption spectroscopy. The cytotoxicities of conditioned alloys and total mass released were compared with unconditioned alloys (0 month) and alloys that were exposed to cell culture medium for 10 months. ANOVA and Tukey multiple comparison intervals (alpha =. 05) were used to compare mass released and cytotoxicity.

Conditioning for 168 hours altered the cytotoxicity of the alloys. The saline/BSA conditioning solution reduced cytotoxicity of the alloys compared with unconditioned alloys, except for the Ni-Cr alloy. Other conditioning solutions were not as uniform in their effects, some increasing toxicity, others decreasing it. Overall, the saline/BSA solution was the most effective at changing alloy cytotoxicity from the unconditioned (0 month) toward the 10-month values. Mass loss during saline/BSA conditioning most closely approximated 10-month loss for most alloys.

Conditioning of casting alloys appeared to be a useful method for predicting long-term cytotoxicity with a short-term in vitro test, but all conditioning solutions were not equivalent.