© 2025 American Dental Association l 3
History of Water Fluoridation
History of Water Fluoridation
Research into the effects of fluoride began in the early 1900s. Dr. Frederick McKay, a young dentist,
opened a dental practice in Colorado Springs, Colorado, and was surprised to discover that many local
residents exhibited brown stains on their permanent teeth. Dr. McKay could find no documentation of
the condition in the dental literature and eventually convinced Dr. G.V. Black, dean of the Northwestern
University Dental School in Chicago, to join him in studying the condition. Through their research, Drs. Black
and McKay determined that mottled enamel, as Dr. Black termed the condition, resulted from developmental
imperfections in teeth. Drs. Black and McKay wrote detailed descriptions of mottled enamel.9,10
(“Mottled enamel” is a historical term. Today, this condition is called dental or enamel fluorosis).
In the 1920s, Dr. McKay, along with others, suspected that something either in or missing from the drinking
water was causing the mottled enamel. Dr. McKay wrote to the Surgeon General in 1926 indicating that
he had identified regions in Colorado, New Mexico, Arizona, California, Idaho, South Dakota, Texas, and
Virginia where cases of mottled enamel existed. Also in the late 1920s, Dr. McKay made another significant
discovery—these stained teeth were surprisingly resistant to decay.10
Following additional studies completed in the early 1930s in St. David, Arizona,11 and Bauxite, Arkansas,12
it was determined that high levels of naturally occurring fluoride in the drinking water were causing the
mottled enamel. In Arizona, researchers studied in great detail 250 residents in 39 local families and were
able to rule out hereditary factors and environmental factors, except for one—fluoride in the water that
occurred naturally at levels of 3.80 mg/L to 7.15 mg/L.11 In Bauxite, Arkansas, H.V. Churchill, chief chemist
with the Aluminum Company of America (name later changed to ALCOA), was using a new method of
spectrographic analysis in his laboratory to look at the possibility that the water from an abandoned deep
well in the area might have high levels of aluminum-containing bauxite that were causing mottled teeth.
What he found was that the water contained a high level of naturally occurring fluoride (13.7 mg/L). When
McKay learned of this new form of analysis and Churchill’s findings, he forwarded to Churchill samples of
water from areas where mottled enamel was commonplace. All the samples were found to have high levels
of fluoride when compared to waters tested from areas with no mottled enamel.10
Dr. Henry Klein, a dentist and epidemiologist in the US Public Health Service (USPHS), led a study of more
than 8,200 American Indian schoolchildren in 16 states in 1929 through 1932 and suggested that the low
caries (tooth decay) prevalence among children in the Southwest may be related to the endemic fluorosis in
that area.13 That study formed the basis for subsequent epidemiologic studies on the association between
naturally occurring fluoride levels in drinking water and children’s dental caries experience.14
During the 1930s, Dr. H. Trendley Dean, a dental officer with USPHS, and his associates conducted classic
epidemiological studies in the United States on the geographic distribution and severity of mottled enamel.15
These early studies quantified the severity of tooth decay and dental fluorosis according to fluoride levels
in the water. In so doing, it was observed that “at Aurora, Illinois where the domestic water contained
1.2 ppm of fluoride (F) and where a relatively low tooth decay prevalence was recorded, mottled enamel
as an esthetic problem was not encountered.”16 Dean and his staff had made a critical discovery. Namely,
fluoride levels of up to 1.0 ppm in drinking water did not cause dental fluorosis in most people and
caused only mild dental fluorosis in a small percentage of people.16–18
In 1939, Dr. Gerald J. Cox and his associates at the Mellon Institute evaluated the epidemiological evidence
and conducted independent laboratory studies. While the issue was being discussed in the dental research
community at the time, they were the first to publish a paper that proposed adding fluoride to drinking
water to prevent tooth decay.19 In the 1940s, four pioneering community trials were carried out to evaluate
the effects of the controlled addition of sodium fluoride to fluoride-deficient water supplies. The first
History of Water Fluoridation
History of Water Fluoridation
Research into the effects of fluoride began in the early 1900s. Dr. Frederick McKay, a young dentist,
opened a dental practice in Colorado Springs, Colorado, and was surprised to discover that many local
residents exhibited brown stains on their permanent teeth. Dr. McKay could find no documentation of
the condition in the dental literature and eventually convinced Dr. G.V. Black, dean of the Northwestern
University Dental School in Chicago, to join him in studying the condition. Through their research, Drs. Black
and McKay determined that mottled enamel, as Dr. Black termed the condition, resulted from developmental
imperfections in teeth. Drs. Black and McKay wrote detailed descriptions of mottled enamel.9,10
(“Mottled enamel” is a historical term. Today, this condition is called dental or enamel fluorosis).
In the 1920s, Dr. McKay, along with others, suspected that something either in or missing from the drinking
water was causing the mottled enamel. Dr. McKay wrote to the Surgeon General in 1926 indicating that
he had identified regions in Colorado, New Mexico, Arizona, California, Idaho, South Dakota, Texas, and
Virginia where cases of mottled enamel existed. Also in the late 1920s, Dr. McKay made another significant
discovery—these stained teeth were surprisingly resistant to decay.10
Following additional studies completed in the early 1930s in St. David, Arizona,11 and Bauxite, Arkansas,12
it was determined that high levels of naturally occurring fluoride in the drinking water were causing the
mottled enamel. In Arizona, researchers studied in great detail 250 residents in 39 local families and were
able to rule out hereditary factors and environmental factors, except for one—fluoride in the water that
occurred naturally at levels of 3.80 mg/L to 7.15 mg/L.11 In Bauxite, Arkansas, H.V. Churchill, chief chemist
with the Aluminum Company of America (name later changed to ALCOA), was using a new method of
spectrographic analysis in his laboratory to look at the possibility that the water from an abandoned deep
well in the area might have high levels of aluminum-containing bauxite that were causing mottled teeth.
What he found was that the water contained a high level of naturally occurring fluoride (13.7 mg/L). When
McKay learned of this new form of analysis and Churchill’s findings, he forwarded to Churchill samples of
water from areas where mottled enamel was commonplace. All the samples were found to have high levels
of fluoride when compared to waters tested from areas with no mottled enamel.10
Dr. Henry Klein, a dentist and epidemiologist in the US Public Health Service (USPHS), led a study of more
than 8,200 American Indian schoolchildren in 16 states in 1929 through 1932 and suggested that the low
caries (tooth decay) prevalence among children in the Southwest may be related to the endemic fluorosis in
that area.13 That study formed the basis for subsequent epidemiologic studies on the association between
naturally occurring fluoride levels in drinking water and children’s dental caries experience.14
During the 1930s, Dr. H. Trendley Dean, a dental officer with USPHS, and his associates conducted classic
epidemiological studies in the United States on the geographic distribution and severity of mottled enamel.15
These early studies quantified the severity of tooth decay and dental fluorosis according to fluoride levels
in the water. In so doing, it was observed that “at Aurora, Illinois where the domestic water contained
1.2 ppm of fluoride (F) and where a relatively low tooth decay prevalence was recorded, mottled enamel
as an esthetic problem was not encountered.”16 Dean and his staff had made a critical discovery. Namely,
fluoride levels of up to 1.0 ppm in drinking water did not cause dental fluorosis in most people and
caused only mild dental fluorosis in a small percentage of people.16–18
In 1939, Dr. Gerald J. Cox and his associates at the Mellon Institute evaluated the epidemiological evidence
and conducted independent laboratory studies. While the issue was being discussed in the dental research
community at the time, they were the first to publish a paper that proposed adding fluoride to drinking
water to prevent tooth decay.19 In the 1940s, four pioneering community trials were carried out to evaluate
the effects of the controlled addition of sodium fluoride to fluoride-deficient water supplies. The first
