• To learn about how scientific research was conducted in the 1930s & 1940s
  • To learn about the history of dentistry
  • To understand the role of the Public Health Service in protecting Americans’ health
  • To understand both sides of the controversy over adding fluoride to America’s drinking water



Dental caries: destruction of the tooth; tooth decay, commonly referred to as “cavities”

Enamel: a smooth hard layer that protects the tooth

Epidemiology: the study of how and where diseases occur in a specific community

Fluoride, or fluorine: an element that naturally occurs in water and some foods and is used in industrial settings in metal refineries as well as in the production of glass, plastics, and ceramics.

Mottled: stained or spotted

ppm (parts per million): the unit of concentration of a substance in air or fluids



In the United States of the early 20th century, most people lost most of their teeth by the time they were 40 years old. In the 1930s, NIH (National Institute of Health) scientist Dr. H. Trendley Dean performed experiments showing that the chemical fluoride helped prevent dental carries in children’s teeth. This led to the recommendation to add fluoride to America’s drinking water, a process that began in Michigan in the 1940s and continues to this day, in the attempt to save millions of children from the pain and suffering caused by cavities, dental fillings, and teeth pulling. However, some people are concerned about the toxic effects of fluoride and prefer to drink non-fluoridated water. They object to the government adding this element—known to be dangerous when ingested at high levels—to the public drinking supply.

The story of how fluoride came to be added to drinking water is an example of how scientists looking for one thing sometimes stumble upon something completely different. It is also the story of how some chemicals commonly thought to be poison can in fact have healthful uses. The story will raise questions about individual rights in matters of public health. How far can the government go to protect us? What rights do people have to make their own health decisions? How might things have changed from the 1940s to the 2000s?



The story of fluoride and drinking water actually begins with mottled teeth. This phenomenon was first described in 1901 by dentists in both Italy and the United States. Dr. Frederick S. McKay noticed that many children living in and around the mining town of Colorado Springs had stained, spotted teeth, a condition he called “Colorado Brown Stain.” In 1909, he lured renowned dentist Dr. Greene V. Black to the area to help him study the problem.

Preliminary testing of the water, with what turned out to be inadequate tests, found no known chemical that could be blamed for the staining. However, the problem started showing up in the dental literature in other mining towns in states such as Arkansas and Idaho. When H.V. Churchill, the chief chemist at the Aluminum Company of America, read about the problem, he decided to help solve the mystery. At his disposal were tools to perform much more sophisticated tests on the water than McKay and Black had been able to do previously. The new tests turned up unusually high levels of a chemical called fluoride in the drinking water of Colorado Springs, Bauxite, Arkansas, and Oakley, Idaho. Was this a coincidence?

Children with stained teeth living in small towns out West failed to capture the attention of East-coast researchers until the late 1920s. Dental research was not well funded at the time and not many large studies took place. However, in 1928, the National Institute of Health (NIH) in Washington, D.C. began to conduct studies on tooth discoloration and cavities. In 1931, Dr. H. Trendley Dean became a one-man Dental Studies Unit and set out to solve the mystery of Colorado Brown Stain.

Dean wanted answers to many questions: Was fluoride really the only cause of mottled teeth? Why was it worse in some areas of the country? How much fluoride would need to be in the water to cause the problem? And, of course, what could be done?

The dentist went to work examining children’s teeth, taking water samples, and talking to local and state health officials in the effected areas in Colorado, Idaho, and Arkansas. He started to notice something surprising: though the mottled teeth were stained, they were otherwise healthy and in fact less prone to dental caries than the teeth in “normal” children. This discovery led Dean to ask new and unanticipated questions about fluoride. Was fluoride actually protecting teeth from cavities? Was it possible to find a level of fluoride which would protect teeth from cavities without staining and spotting? At what levels, in other words, would fluoride be helpful, and in what levels was it dangerous?

There was no accurate way to measure levels of fluoride in the water. He asked a fellow NIH Division of Chemistry scientist, Dr. Elias Elvove, to come up with a usable technique. The new method used a colorimeter. This type of test can measure the levels of a known element in water by comparing the color to a standard solution of that element. Using colorimetry, then, Dean determined that 1 ppm (part per million) of fluoride in drinking water would prevent cavities without causing stains.

A young government dentist had not only solved the mystery of Colorado Brown Stain, but was well on the way to solving the nationwide problem of dental carries in children! However, without massive testing, Dean was unsure of the large-scale and long-term results of adding fluoride to drinking water. Even in small amounts, could fluoride make people sick? Before asking state governments to add the chemical, he had to know more. In the mid-1930s, NIH dental scientists Drs. Frank McClure and Francis Arnold helped Dean to broaden the research in order to determine the effects of fluoride on the human body.

Dean also had to figure out how to remove excess fluoride from water systems in towns such as Colorado Springs. Officials in cities and towns across the country were worried about high levels of fluoride in the water causing Colorado Brown Stain in their locations. While Dean was studying how to safely add fluoride to the drinking supply, many public water boards acted to reduce the amount of fluoride in their water so as to reduce the mottled teeth experienced by their citizens. They could often easily do this by switching water sources. For those towns that could not change their water supply, Dean and his colleagues came up with a way to use manganese to reduce fluoride in water.

Fluoride research continued back in Washington. Dean’s colleagues at NIH, Drs. Henry Klein and Carroll Palmer, believed that fluoride not only protected teeth from cavities but also actively inhibited tooth decay. The scientists grew excited about the possible ramifications of their research. These studies could lead to widespread improvements in the dental health of Americans. Dean himself focused on epidemiology: he learned where in the country cavities occurred and correlated that information with statistics about the water supply on a nationwide level. Using a 26-state 1933-1934 dental survey of American schoolchildren sponsored by the American Dental Association, Dean used maps and graphs to plot the incidences of dental problems against the levels of fluoride in the drinking water. These studies solidified his belief in the correlation between healthy teeth and small levels of fluoride. He found that a level of fluoride of 2.5 ppm caused mottled teeth, while his recommended level of 1 ppm prevented cavities without staining or other problems.

In 1938, Dean proposed an epidemiological study of his own. He wanted to do a test to see if the amount of dental caries in a town would decrease when fluoride was added to a town=s drinking water. Would Dean be able to help children avoid the pain of cavities and teeth removal? Generations of Americans had dealt with dentists who knew little more than how to pull teeth, resulting in swelled gums, bloody mouths, and intense pain. Maybe this was a way out. William Randolph Hearst, the famous newspaper editor from California, sent reporters to cover the story for a waiting public.

But the public had a long time to wait. It would be ten long years until the results from this study became available. Dean had to set up his experiment with great care, to insure clean results. First, he had to prove the relationship between a bacteria that was known to cause dental caries (L. acidophilus), mottled teeth, and fluoride levels in drinking water. This time, he used surveys in 21 cities. By 1942, Dean had convinced himself that 1 ppm of fluoride would bring the best results in protecting teeth.

Next, he had to prove that adding fluoride to a town=s drinking water would cause no harm to its citizens. In the early 1940s he demonstrated, using evidence from two towns, that fluoride in drinking water at the level of 1ppm caused no ill effects. He showed that the citizens of Bartlett, Texas (which had high levels of fluoride) and Cameron, Texas (which had low levels of fluoride) demonstrated no harmful side effects from drinking water. During the same period, his NIH colleague McClure also studied the chemical fluorine=s affects on bones. Using army recruits and teenage males as his subjects, McClure showed that fluorine did not injure the bone structure, as had been feared.

By 1944, all was set to find two cities to cooperate with the government’s study. The two localities had to be places that had no previous evidence of fluoride in the drinking water. In one city, fluoride would be added. In the other city, the water would be kept free of the chemical. The scientists chose to do the study in Michigan because the state health department, in charge of all the water treatment, control, and personnel, agreed to participate with no legal obstacles. Grand Rapids, with its large and stable school population would receive the fluoride. Muskegon would serve as the control city, or the one that did not change its water supply.

Dean designed the study to answer questions about the effects of the fluoridated water on both baby teeth and permanent teeth. He wanted to learn how fluoride protected teeth from decay, and he wanted to learn more about the technicalities of artificially adding fluoride to water. Would artificially fluoridated water prove to be as effective as naturally fluoridated water in inhibiting tooth decay?

When school opened in the fall of 1944, the children were given teeth exams and saliva tests for bacterial counts. This examination would provide a base line for the study. On January 25, 1945, at 4 p.m., W.L. Harris, the chief chemist of Grand Rapids, oversaw the addition of the first fluoride to the city’s drinking water. For the first time, a city acted to add a chemical to drinking water not to treat the water, but to treat the drinker. The study had begun.

The results of the Michigan study showed that children in Grand Rapids got fewer cavities than those in Muskegon. The Public Health Service reported no harmful effects as a result of the fluoridation. Dean and his NIH colleagues had triumphed! Even before the end of the study, more and more cities began adding fluoride to their water in the hopes of protecting future generations from dental cavities. By the 1980s, about half of the public water supplies in the United States were artificially fluoridated.

However, like most scientific results, this study had its challengers. Many people believe that the Public Health Service exaggerated the claims and began to unnecessarily expose the entire population to fluoridated water for the benefit of only part of the population. Fluoridation delays tooth decay rather than prevents it, so as children get older they lose some of the beneficial effects. Also, fluoride can be naturally ingested from several foods, from pollution, and other sources, putting people well above the 1 ppm limit. In states with heavy industries such as aluminum, phosphate, and uranium enrichment, fluoride levels in the air and water are quite high. Fluoridation opponents point out that there are other ways—fluoride tablets, topical toothpastes, improved diets, improved dental hygiene—to reduce dental carries in children without exposing the rest of the public to the potential dangers and unknown properties of fluoridated water. Many countries, such as Sweden, Scotland, and Australia, have banned artificial fluoridation because of worries that adding the element to water will eventually prove to have been a toxic mistake.

Today, the National Institute of Craniofacial and Dental Research at the National Institutes of Health, together with the Centers for Disease Control, unambiguously support water fluoridation and the work of Dean and other mid-20th century researchers. However, a vocal contingent continues to question the government on this issue and support further studies on the effects of fluoride on bone density; on the levels of fluoride pollution from factories and heavy industry; and on new ways to reduce dental carries in children.


Classroom Discussion:

Dean’s fluoride-dental carries study began in 1931 and took decades to complete. Why does scientific research take so long?

If a study like the one the NIH did in Michigan were conducted today, how would the public react? What would they want to know?

What public health issues are important now, 70 years after Dean’s dental research began?


Questions for further research:

What other measures besides adding fluoride to water can decrease dental caries? What could the government have done instead of promoting fluoridation? What is done in other countries? Does the United States have lower levels of dental carries than Europe? What other measures besides adding fluoride to water can decrease dental caries? [Using fluoridated toothpaste at least twice a day, taking fluoride tablets calibrated at a dose compatible to the amount of fluoride in the water, and getting a fluoride rinse at the dentist.]

What other chemicals are added to the water supply? Why?

What are some other examples of government-funded studies using people as subjects?


Classroom Activity #1

Students will learn that fluoride helps protect teeth against decay.
Students will make observations of chemical reactions.

Fluoride solution (available from a dentist, dental supply company, or some pharmacies)
2 Hard boiled eggs
3 Clear containers
Science journals

1. Have the students take out their science journals to prepare for the experiment.
2. Place one egg into a container and pour in enough fluoride solution to cover it.
3. Let the egg soak for five minutes. Remove the egg.
4. Pour four inches of vinegar into the remaining two containers.
5. Place the treated egg into one container of vinegar, and the untreated egg in the other container.
6. Ask the students to carefully observe the reaction in either container. The bubbling in the container holding the non-treated egg is a chemical reaction between the acid in the vinegar with the calcium of the eggshell. The acid is dissolving the untreated eggshell. The fluoride treatment protects the one egg=s shell from the acid, while the acid attacks the untreated egg=s shell. Our teeth are similarly protected from the acids in our mouths with fluoride.

(Adapted from ALesson Five: Fluoride Power@ by Oral-B, www.oralb.com/learningcenter/teaching/lesson5.asp)


Classroom Activity #2

Conduct your own epidemiological study in your classroom. Have the students interview each other about where they were born and where they grew up. Then, based on the “Decayed, Missing, and Filled” chart developed at NIH in 1937, have them ask each other about their dental histories. Using charts of fluoride amounts in water, have the students compare the dental health of those raised in places with high concentrations of fluoride in the water and those with low concentrations. For Virginia fluoride levels, use www.vahealth.org/teeth/servden.htm. For other states, contact the local Department of Health. Fluoride levels for many countries can be found on the web.


Classroom Activity #3

Find out the concentration of fluoride in the water in your community. Is fluoride added to your water supply and if so, when did that start? Is there data to suggest that this decreased dental caries in your area? If fluoride is taken out of your water system because there is too much in the drinking water, find out how that procedure works. If you live in an area with no public water, how do dentists in your area give fluoride treatments? How do they figure out the proper amount of fluoride to prescribe?


Classroom Activity #4

There is much controversy about adding fluoride to drinking water. Ruth Roy Harris= book Dental Science in A New Age: A History of the NIDR (Montrose Press, Rockville, 1989) describes some of the legal battles. A search on the internet will provide many more examples of scientists and members of the public who are opposed to water fluoridation. Investigate the situation for your area: has fluoride been added to the water? If so, how was that authorized? What does each side have to say? After reading the materials, what do you believe? How do you decide the reliability of information found on the internet? Did the government do the right thing by advocating fluoridation in the 1960s? Is it the right thing to do today?


Classroom Activity #5

Use water testing kits to test the water in your school, water from childrens homes, and/or water from a stream or other natural source.

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Last updated: 16 June 2009
First published: 2 February 2005
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