In the mid-1900s it was discovered that towns with a high level of fluoride in their water supply was causing the residents' teeth to have both brown spotting and a strange resistance to dental caries.
Pada pertengahan 1900-an ditemukan bahwa kota-kota dengan tingkat fluorida tinggi dalam persediaan air mereka menyebabkan gigi penduduk memiliki bintik-bintik coklat dan resistensi aneh terhadap karies gigi.