In vitro cytotoxicity of dental casting alloys over 8 months

Although in vitro cytotoxicity tests have been a valuable part of the biological testing of dental casting alloys, these tests are generally limited by their short-term nature ( < 168 h). The objective of the current study was to measure the in vitro cytotoxicity of representative types of dental casting alloys over a relatively long-term interval (months) and compare longer-term cytotoxicity with that seen initially. Polished casting alloy samples were exposed to cell-culture medium for 30-day intervals. During the last 3 days of each interval, the medium was changed to provide a 3-day extract which was then placed on fibroblast or macrophage cultures for 48 h. The mitochondrial activity of the cells was measured and compared to control cultures to assess the cytotoxic effect of the alloys. The cytotoxic effect was plotted versus time of medium exposure. The total time of exposure was 8 months. For most alloys, the mitochondrial response was constant over the 8 months, indicating that the cytotoxic effect of the alloys did not change significantly after extended exposure to the medium. A trend of improving biological response was suspect for a reduced-gold alloy, but this trend was not statistically significant. The mitochondrial activity of the macrophages was less sensitive to the alloy extracts than the activity of the fibroblasts, which was significantly suppressed for several alloy types. However, mitochondrial activity of the macrophages was significantly increased for several alloys in the early time intervals. The total noble metal content of the alloys was not necessarily predictive of the biological response. Thus, it appears that in this indirect test of in vitro cytotoxicity, the short-term cytotoxicity is predictive of the longer-term for many types of dental casting alloys.