Abstract
I chose Shodo island as aclosed system, because it is separated from other areas geographically and geologically, so that I might define the relationship between fluorine ion density and dental caries in drinking water in one area.
Shodo island has three towns, Uchinomi-cho, Ikeda-cho, and Tonosho-cho. For my research on this occasion, I had the cooperation of the three town offices, and was able to collect tap water and well water in all villages.
In the drinking water, I measured the factors that would seem to have a relation to dental caries. They are pH, fluorine ion density and chlorine ion density.
I examined the relationship between these factors and the prevalence of dental caries in elementary school children, who are the most easily influenced, by these three factors.
As a result, an obvious relation was seen between fluorine ion density and the prevalence of caries. The prvalence is the lowest when the fluorine ion density is 0.300-0.399 ppm. Chlorineion density has a tendency to increase together with flurorine ion density.
I found that both fluorine ion and chlorine ion content is large in drinking water in the western part of the island, and that this content decreases in the eastern part.
As for the pH, almost all the drinking water had a pH of less than 7.0, so that most people on this island drink acidic water.
