The degree to which systemically administered fluoride is taken up by the enamel and dentin of the developing tooth is of great interest in relation to caries prevention. The purpose of. the present study was to compare the fluoride uptake of enamel and dentin by the various teeth of rats when known amounts of fluoride were administered during tooth development. Four groups of animals were used. Group I served as control. Group 2, 3, and 4 received 2㎎, l0㎎ and 20㎎of fluorine/㎏ body weight as NaF respectively. Fluoride was administered daily either by intraperitoneal injection or by ingestion with stomach tube. In order to study the effects of fluoride on each type of molar individually, 3 schedules for fluoride administration were followed in each experimental group.
The 1st subgroup was given fluoride from 5 to 20 day postnatally; The 2nd subgroup was given fluoride from 5 to 35 day; and the 3rd subgroup was given from 15 to 35 day. All animals were sacrificed the day following the last fluoride administration. The teeth were then dried in an oven of 100℃ for 3 days and pulverized to pass through a 200 mesh sieve. Enamel and dentin were then separated by the floatation method of Manly and Hodge as modified by Gilda. The samples were ashed at 550℃and analyzed for fluoride by fluoride electrode and ash/dry weight ratio.
In conclusion, the followings could be made;
1) The ash/dry weight ratio(%) in the enamel of control group sacrificed at 35 days postnatally was higher than that sacrificed at 20 days. The more the fluoride dose was administered, the more the ash/dry weight ratio of enamel was decreased.
2) The different route of fluoride administration did not induce any difference in the degree of fluorine uptake by enamel and dentin.
3) The fluoride concentration of dentin was 2.6 to 6.5 times as higher as that of enamel.
4) During tooth development in the rats, the degree of fluoride uptake by enamel and dentin was correlated with the dose of fluoride administered systemically.
5) When individual teeth were compared after various dose of fluoride administration from 5 to 20 day postnatally, the enamel from the 1st molar showed the highest concentration; from 5 to 35 days, the 2nd molar; from 15 to 35 days, the 3rd molars.
6) The degrre of fluoride uptake by enamel and dentin depended on the degree of tooth development, when fluoride was administered by systemic administration. The stage of the most effective fluoride uptake by enamel and dentin was from calcification to pre-eruptive stage.
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