Chemical-biological interactions of NaF with three different cell lines and the caries pathogen Streptococcus sobrinus.

Fluoride is used in dentistry as a prophylactic agent to reduce caries rates due to the demineralization/remineralization effect and its influence on the metabolism of cariogenic bacteria. The purpose of this study was to evaluate the cytotoxic effects of sodium fluoride (NaF) on three different cell lines and the antibacterial potency on Streptococcus sobrinus. Cell lines were treated with various concentrations of NaF ranging from 0.039 mM to 10 mM for 24 h. For microbial assays, concentrations of NaF between 0.03 mM and 10 mM were added to liquid cultures of bacteria. Our results showed that immortalized human keratinocytes (HaCaT) and human osteogenic sarcoma cells (SAOS-2) were similarly affected by concentrations up to 2.5 mM. However, cell growth of HaCaT was slightly more inhibited at 2.5 mM of NaF than SAOS-2. At concentrations between 0.62 mM and 10 mM, 3T3 mouse fibroblast cells reacted more sensitively than HaCaT and SAOS-2 to NaF. The 3T3 cells did not survive in the presence of 10 mM NaF. NaF caused no significant effect on all tested cells at concentrations of < or = 0.31 mM. NaF at 0.039 mM and 0.06 mM did not affect growth of S. sobrinus. At concentrations of 0.125 mM and 0.5 mM, growth was slightly reduced. The proliferation of S. sobrinus significantly decreased at 1 mM and 2 mM NaF. S. sobrinus survived at 4 mM, revealing a delayed log phase with a decreased proliferation. No viable S. sobrinus cells were detected at concentrations of > or = 8 mM NaF. Data analysis revealed that overall treatment effects were highly significant (P<0.05, analysis of variance, Tukey's difference test). This study indicates that cytotoxic effects due to NaF significantly vary in dependence upon the applied cell line. The toxicity of NaF approached 50% (TC50) at concentrations of 6 mM for HaCaT, 2.3 mM for 3T3 cells, and 7.5 mM for SAOS-2. Additionally, NaF revealed antimicrobial effects only at concentrations that are significantly higher than oral fluoride concentrations.