In 1956, a series of studies were performed by S. Yamamura, one of the present authors, in an effort to determine how to relieve the noxious effects of fluorides, while retaining its desirable action in tooth formation. In the report of these experiments, the finding was that the use of fluoride and boric acid in combination appeared to be a simple method for accomplishing this result. Later experiments confirmed that mottling of teeth was materially retarded through the use of an admixture of equal quantities of fluoride and boric acid. In the recent experiments of the authors on female mice, 0.25 per cent NaF in the quantity of 0.1 cc for each 10 grams of body weight, for one period, everyday and for another, on alternate days, two methods of introduction were used; hypodermic injection and esophagus infusion. From the careful recording of the results of these experiments, the following findings were obtained:
1. Introduction of excessive quantity of fluorides brought about miscarriage or the arresting of growth of the embryo and its ultimate absorption, with slight difference whether fluorides alone or fluorideboric acid mixtures were used.
2. Abortion and arrested growth were observed microscopically. The number of cases being less for fluoride-boric acid mixture than for fluoride alone.
3. Observation of the embryo, the new born and the suckling, disorders were uncovered, such as atrophy, degeneration and necrosis of the enamel organ cells, especially of ameroblasts, accumulation of granulated and floccule substance, formation of calco lumps, defects in the enamel caspal area, obvious appearance of Brown Striae of Retzius, accumulation of excess tissue fluid between dentigerous cell layers, degeneation and necrosis of dentigerous cells, formation of undulate dentinogenice zone and insufficient calcification of dentine.
Comparison of the frequency of these disorders showed that there were 21 such cases where fluorides were used and where the mixture of fluoride and boric acid, there were but a few cases of slight abnormality, particularly at the submaxilla.
The conclusion is that the greater part of the fluorides introduced into the experimental animals apparently accumulated at the submaxilla and that the use of boric acid with the fluoride diminishes the ill effects of the fluorides. (Authors' abstract)

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