Studies on intermittent fluoride administration.

The effects of the supplementation of equal amounts of fluoride given at different frequencies on caries inhibition and on fluoride uptake and retention by the molar surfaces were investigated in 3 rat caries tests. In the first experiment fluoride was supplemented to the drinking water, in the second it was incorporated in the cariogenic diet and in the third it was applied topically. In the first caries test fluoride was administered in the drinking water either continuously at concentrations of 20, 40 and 60 ppm F or at the double concentrations of 40, 80 and 120 ppm F every second day for 10 days prior to a cariogenic period of 21 days. At the end of the 10-day fluoride administration period the fluoride concentration in the molar surfaces (F-M) were closely correlated to the fluoride concentrations of the drinking solutions and to the intake by the animals. The molar surface disolution rates (S-M) were significantly lower in all fluoride groups than in the control groups but were not correlated to the F-M. At the end of the subsequent 21-day cariogenic period the S-M were not significantly lower in the fluoride than in the control groups. The F-M, significantly higher in the fluoride than in the control groups, were in the former groups not significantly different from each other. Irrespectively of the fluoride administration schedule, the caries incidences were equally lower in all fluoride groups than in the control groups. In the second caries test NaF and Na2PO2F were incorporated in the cariogenic diet and given to the rats at the same daily dose but at frequencies of 12, 18 and 36 times. The concentrations tested were 225, 150 and 75 ppm F. There were no significant differences between NaF and Na2PO3F in caries inhibitions, F-M and S-M. The frequency of fluoride administration had no significant effects on the parameters investigated. In the third caries test NaF and Na2PO3F were applied topically once, twice or thrice daily during a 20-day cariogenic period at concentrations of 4500, 2250 and 1500 ppm F respectively. While NaF and Na2PO3F were equally effective in inhibiting caries, NaF was more effective than Na2PO3F in enriching the F-M and in reducing S-M. Again the frequency of fluoride application had no significant effects. Because of the lack of influence of the frequency of fluoride supplementation on caries inhibition and the lack of correlation between caries reductions and F-M and S-M it was concluded from the caries tests that in the rat the interference of fluoride with the bacterial metabolism through its continous presence at the plaque-enamel interface rather than the reduction of enamel solubility and the promotion of enamel remineralization seems to be its most important cariostatic mechanism. A second series of experiments investigated the effects of the daily intragastric administration to pregnant rats of either 3.5 mg F once daily or 1...