Toxicity of copper-based dental alloys in cell culture

The biocompatibility of three commercial copper-based dental casting alloys--Duracast MS, Goldent, and Trindium--three experimental copper alloys, and a control gold alloy, Modulay, were investigated. Trindium, Duracast MS, experimental alloys 1 and 2 are aluminum bronzes; Goldent is a hybrid aluminum-brass alloy; and experimental alloy #3 is a high zinc brass alloy. ASTM F813-83 Standard Practice for Direct Contact Cell Culture Evaluation of Materials for Medical Devices, a 3-day direct-contact cell culture regimen and atomic absorption spectroscopy were utilized for evaluating the biocompatibility of these alloys in both Waymouth's and RPMI 1640 complete media. Cellular proliferation assays, using 3H-thymidine uptake, were also conducted in Waymouth's media. In this investigation, only the experimental alloy #3 elicited alterations in morphology and viability of the fibroblast monolayer during the ASTM and 3-day culture tests in either media. Cell cultures exposed to experimental alloy #3 experienced copper concentrations greater than 16.0 ppm in Waymouth's and 10 ppm copper in RPMI 1640 media. Differences in the size of the cytotoxic zone around experimental alloy #3 were also observed, with the larger zone occurring in Waymouth's media. In contrast to the direct cell contact studies, all alloys caused decreases in 3H-thymidine uptake in Waymouth's media at much reduced metal ion concentrations as compared to the controls. Thus, adverse changes in DNA synthesis occurred at much lower copper and zinc concentrations than changes in morphology and viability. Consequently, the assessment of biocompatibility is dependent on the parameters evaluated, and several parameters must be analyzed before a material may be considered biocompatible.