The purpose of this study was to examine the distribution of fluoride in different surfaces and layers in the enamel. This study involved the use of 40 samples of enamel blocks sectioned into each surface from intact human permanent molars. These samples were etched away by exposure to 1.0ml of 0.5M perchloric acid for 5 and 20 seconds. Fluoride was determined by a combination fluoride electrode (ORION, 69-09) and calcium by atomic absorption spectrophotometry (HITACHI, 508 A).
The results were as follows:
The means and standard deviations of fluoride content and depth were 2086±525ppm and 1.78±0.35μm in the case of 5-second, while in the case of 20-second etching they were 2252±1173 ppm and 5.16±1.02μm, respectively.
The coefficient of variation of fluoride content in 20-second etching was about 2 times higher than in 5-second etching.
It is suggested that the distribution of fluoride varied characteristically in the layers approximately 5μm from the surface. On the other hand, the mean fluoride content of different surfaces was not statistically significant, but the fluoride content of mesio-distal surfaces was lower than that of bucco-lingual surfaces.
Microsampling from the enamel surface for chemical analyses is prerequisite to reveal in detail the properties of caries resistance in relation to fluoride in the enamel of teeth in situ.

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In relation to the caries preventive sealant developed by Takeuchi et al., in which ethyl-2-cyanoacrylate is used as liquid and poly methyl methacrylate as powder, a study was made on the degree of improvement in the adhesion to acid-etched human surface enamel by the addition of varying weight percentages of glass filler which had been treated with Silan A-174 followed by a treatment with solution polymerization with MMA of the above-mentioned powder portion of the sealant, with results as follows:
1. The adhesion against tensile strength was the highest in the case of addition of 30 wt% or less of the above-mentioned filler, and markedly lowered by the addition of 50 wt% or more.
2. Compared with the unsupplemented cases, an addition of 30 wt% or less of filler showed improvement in abrasion resistance by 2.5 times. There was no difference, however, in the Micro Brinell hardness and water absorption.
3. The marginal leakage became extremely good with the addition of 30 wt% or less filler.
4. While tag formation was good in the case of addition of 30 wt% or less than that, there were abnormal findings in the cases of addition of 50 wt% or more.
Through these findings it was concluded that the adequate amount of the above-mentioned filler was 30 wt%.

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