The long road of discovery to find the link between mottled enamel and water-borne fluoride finally ended in the early 1930s, but that turned out to be just the beginning.
Questions Surrounding Fluoride in Water
After Doctors Churchill and McKay finally proved brown teeth stains were caused by water-borne fluoride, many more questions emerged. Public Health Service scientists jumped on the wagon and started investigating a myriad of new questions regarding water-borne fluoride. First and foremost, resources were directed towards finding out what levels of fluoride would not cause the mottling on teeth.
At the forefront of the new research was Dr. H.T. Dean, head of the National Institute of Health's Dental Hygiene Unit. He began investigating fluorosis in 1931, focusing primarily on determining the safe level of fluoride in drinking water without causing the mottling effect. Joining him in his research was Dr. Elias Elvove, a senior chemist at the institute.
Finding the Key
Dr. Elvove was given the task of finding a more precise way to determine fluoride levels in drinking water, and after two years of hard work he came back with the results. The method he presented was able to measure levels of fluoride with an astounding accuracy of 0.1 part per million, an immense improvement over previous techniques.
Having a way to properly measure fluoride, Dr. Dean started a journey across cities in the U.S. to compare fluoride levels in drinking water across the country. By the end of the decade, together with his staff, Dr. Dean was finally able to show concrete results.
In his famous report titled the “21-City Study” he established that brown spotting on teeth was exceedingly rare at fluoride levels of 1 part per million, and that only a very mild mottling effect on enamel could be noticed in a small percentage of people. The results of his work were published in 1942.