The first attempts to show the correlation between mottled enamel and an elements in the water supply started at the very beginning of the 20th century, but it was 1923 that proved to be the crucial year.
Fluoride's Effect on Teeth
That year Dr. Frederick McKay traveled to Oakley in Idaho where he met with parents who had observed brown stains developing on their children's teeth after the town constructed a communal water pipeline bringing in water from a warm spring close by.
Despite not finding anything suspicious in the water, Dr. McKay advised the town to switch to another source of water. The advice worked, and within a few years the children were growing healthy adult teeth without spotting. Despite this being the confirmation he needed, Dr. McKay still could not determine what it was in the water that was causing it.
When he later traveled to Bauxite, Arkansas, with Dr. Grover Kempf from the US Public Health Service to investigate more reports of brown stained teeth, they discovered that the disorder was found among the majority of children from Bauxite, a company town which was owned by the Aluminum Company of America, but was absent in a town less than five miles away. They analyzed the water but no cause was discovered yet again.
However, this research proved crucial, as the report the two men published in 1930 caught the attention of the Aluminum Company's chief chemist, Dr. H. V. Churchill. Afraid that this discovery could adversely influence aluminum cookware safety claims, he decided to conduct the tests on the water from Bauxite and the surrounding areas himself. After several attempts using a much more precise photospectrographic analysis it was finally clear, the water had high levels of fluoride in it. The sample from Bruxite was among the highest, measuring 13.7parts per million.
With this discovery, Dr. Churchill composed a letter to Dr. McKay in January 1931, asking him for cooperation in discovering the role fluoride might play in the discoloration phenomenon. Dr. McKay accepted and within months he finally had an answer he has been searching for the majority of his life, it was high levels of water-borne fluoride that were causing the mottled enamel and brown discoloration.