Fluoride passes the placenta in limited amounts and may bestow caries resistance upon developing teeth. In a recent report, offspring of rats fed a diet containing sodium pentafluorostannite during gestation were found to have reduced caries incidence compared to offspring of rats fed sodium fluoride. In order to determine whether this observation was related to increased placental transfer of fluoride, pregnant rats were fed diets containing 50, 100, and 200 ppm fluoride or equivalent, from the following salts: sodium pentafluorostannite, sodium pentachlorostannite, sodium fluoride, stannous fluoride, or a mixture of sodium and stannous fluorides. On day 20 of gestation, fetuses and placentas were obtained for analyses. The average fluoride levels of the fetuses from rats fed 50, 100, and 200 ppm fluoride diets ranged from 0.6 to 0.9 ppm, 1.1 to 2.0 ppm, and 3.0 to 4.0 ppm fluoride, respectively. None of the salts appeared to have a significantly different efficiency of placental transfer of fluoride. Fetal tin values were elevated when the maternal diet contained tin salts, but without apparent relation to dietary tin level.
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Fetal fluoride and tin levels. Two-way analysis of variance of the values for animals fed salts containing fluoride indicated that the variable of test salt did not have a significant effect on fetal fluoride level (P > 0.25). However, the dietary level of fluoride had a highly significant effect (P << 0.01 ) on the fetal level of fluoride. The fetuses of rats fed the 200 ppm fluoride diets had significantly (P < 0.05) higher fluoride levels than the fetuses of rats fed diets with 0, 50, or 100 ppm fluoride. Although the fetuses of rats fed the diet containing 200 ppm fluoride as stannous fluoride had a significantly (P < 0.05) higher fluoride level than those of rats fed the same level of fluoride as sodium fluoride, significant differences between fetal fluoride levels were not observed at the two lowest levels of these two salts. The fetuses of animals fed diets containing no test salt or nonfluoride test salts all had lower fluoride levels than those of animals fed test salts containing fluoride, with the exception of the group fed sodium chloride (table 5). The values in this group were not normally distributed.
These fetal fluoride levels correspond quite closely to those found previously when rats were fed diets containing 0, 50, 100, and 200 ppm fluoride as sodium fluoride during and before gestation (13). The fetuses of females fed diets containing 200 ppm fluoride as sodium fluoride in that study were found to have fluoride levels of 3.1 and 4.0 ppm, compared to the value of 3.0 ppm in this study
… Placental levels of tin and fluoride bore little relationship to the tin and fluoride levels in the diet. Placental levels of fluoride were similar to those found by Feltman and Kosel (2) in women receiving 1 mg fluoride daily during pregnancy and in control women. The placenta contained relatively little tin whether the diet contained detectable tin or not.
The fetal fluoride level was considerably higher than the placenta fluoride level at the highest level of fluoride intake. Fluoride is deposited in the fetal skeleton (1). An approximation of the absolute efficiency of fluoride transfer to the fetus can be calculated from the fluoride accumulated by the fetuses and the total fluoride intake during gestation. The average female rat fed the diets containing 200 ppm fluoride consumed 300 g of food, for a total fluoride consumption during gestation of 66 mg. On the average, the 12.5 fetuses, weighing about 3.5 g each, of an average female fed 200 ppm fluoride in the diet had a fetal fluoride concentration 3.6 ppm higher than the fetuses of animals fed the control diet. Thus, the fetuses accumulated about 160 jug fluoride, or only 0.24% of that ingested. It seems reasonable to assume that if a form of fluoride had substantially increased capacity to cross the placenta and accumulate in the fetus, it would have been detected in the present study. On this basis, the previous findings of Stookey et al. (6), of less caries incidence in the offspring of rats fed sodium pentafluorostannite during gestation than in the offspring of those fed sodium fluoride, do not appear to have been due to any difference in placental transfer of fluoride.