Effect of fluoride on cariogenic oral microorganisms (an in vitro study)

The effect of sodium fluoride and sodium monofluorophosphate at concentrations of 1, 5, 10, 50, 100 and 1000 mg/l in phosphate buffer (pH 6.5) as well as in UHT milk were studied on cultures and suspensions of Streptococcus mutans, Lactobacillus acidophilus and Candida albicans. Using serial tenfold dilutions up to 10(-7) of 24-48 hour cultures, a subsequent 0, 60 and 120 min incubation caused no decrease in the number of CFUs. Growth kinetic studies in the Bioscreen biophotometer (Labsystem, Finland) revealed that sodium fluoride in different concentrations (from 0.875 mg/l up to 500 mg/l) influenced the growth dynamics of S. mutans and C. albicans: the exponential phase flattened out at the highest fluoride concentrations (500 mg/l) present in the growth media. The lag phase of C. albicans became longer. The results of these experiments indicate that sodium fluoride administered at higher concentrations than the usual caries preventive dosage made the generation time of cariogenic oral bacteria and fungi longer, slowing down their multiplication.