Water fluoridation
Health and dental organizations worldwide have endorsed its safety and effectiveness. Its use began in 1945, following studies of children in a region where higher levels of fluoride occur naturally in the water. Further research showed that moderate fluoridation prevents tooth decay.
Fluorine deficiency
Disputes over the essentiality of fluorine date back to the 19th century, when fluorine was observed in teeth and bones. In 1973 a trial found reduced reproduction in mice fed fluorine-deficient diets, but a subsequent investigation determined that this was due to reduced iron absorption.