THE EFFECT OF CELL MONOLAYER DENSITY ON THE CYTOTOXICITY OF METAL-IONS WHICH ARE RELEASED FROM DENTAL ALLOYS

The effect of cell density (number of cells per unit area of a monolay er culture) on the in vitro cytotoxicity of metal ions which are known to be released from dental materials was investigated. The effects of cell density (1) may explain previous discrepancies in in vitro tests , (2) may be important in wound healing where cell density changes ove r time, and (3) may help clarify the mechanisms of cytotoxicity of met al ions. Balb/c 3T3 fibroblasts were plated at cell densities ranging from 10,000-80,000 cells/cm2 and were exposed to 8 concentrations of 1 0 different metal ions. After 24 h, the succinic dehydrogenase activit y and DNA synthesis were measured to quantify the cytotoxic effect. Hi gher cell densities markedly reduced the sensitivity of these fibrobla sts to all metal ions except Al+3 and Zn+2, but the magnitude of the r eduction was metal dependent. In addition, the DNA synthesis was inhib ited more than the succinic dehydrogenase activity for all metal ions except Zn+2. The unique effect of cell density on each metal ion suppo rted the hypothesis that the effect was not simply caused by a dilutio n of the number of metal ions per cell. Given these results, the eff e ct of cell density should be carefully selected in in vitro cytotoxici ty tests.