[Reactions of fluoride with hydroxyapatite powders--especially on the formation of alkali-soluble and -insoluble fluorides].

Synthetic hydroxyapatite (HA) powders were treated for varying time (1-60 min.) with neutral sodium fluoride solution of varying concentrations (10(0)-10(4) ppm). The alkali-soluble and -insoluble fluorides formation were studied independently of each other following their separation in molar potassium hydroxide. The total fluoride uptake by HA and its alkali-soluble and/or -insoluble fluoride contents were both found to be linearly related to the logarithm of the ionic fluoride level in the treatment solution, except for the outstandingly high figures in 10(4) ppm F solution. Further, the alkali-soluble/-insoluble fluoride rates were found in the same manner above. From the present results, it was suggested that the less treatment period (e.g. 1 min.) could sufficiently be effective in the fluoride painting. Further, the usefulness of frequent application with lower fluoride concentration was also suggested.