Who Found the Effect of Fluoride, and How Brown Teeth Led to Water Fluoridation
The fluoride story begins with brown-stained teeth in Colorado in 1901 and reaches a water program in Grand Rapids in 1945. The early cavity numbers shrank, and the mechanism changed. Fluoride stayed a dental topic because the evidence came from teeth.
The history of fluoride starts with brown stains on children's teeth in Colorado, not with a bottle of drops. In 1901, dentists in the United States and Italy had already noticed that people with stained teeth had less tooth decay. Nobody identified the cause until 1930. Grand Rapids, Michigan, added fluoride to its public water on January 25, 1945, and CDC's timeline calls it the first city to do so ([CDC timeline](https://www.cdc.gov/fluoridation/timeline-for-community-water-fluoridation/index.html)). ## A stain the locals had already named Frederick S. McKay opened a dental practice in Colorado Springs in 1901. Residents called the stain "Colorado brown stain," and McKay spent years investigating it. After field work, he concluded that something in the public water supply probably caused it. He also noticed that affected teeth seemed less likely to decay ([CDC 1999 report](https://www.cdc.gov/mmwr/preview/mmwrhtml/mm4841a1.htm)). In 1916, McKay and G.V. Black, dean of Northwestern University's dental school, published the first of five joint papers. The first one held a paradox: "Contrary to what might be expected [mottling] does not seem to increase the susceptibility of the teeth to decay" ([CDC timeline](https://www.cdc.gov/fluoridation/timeline-for-community-water-fluoridation/index.html)). ## A chemist, a well and a new name In 1930, H.V. Churchill, a chemist with the Aluminum Company of America, tested water from an abandoned well in Bauxite, Arkansas, and found 13.7 parts per million (ppm) of fluoride ([CDC 1999 report](https://www.cdc.gov/mmwr/preview/mmwrhtml/mm4841a1.htm)). Fluoride usually occurs in water below 1.0 ppm, and McKay's own samples from affected areas ran from 2.0 to 12.0 ppm (same source). In 1931, H. Trendley Dean, a US Public Health Service officer, headed the Dental Hygiene Unit at the National Institute of Health. He renamed the condition "dental fluorosis" ([CDC timeline](https://www.cdc.gov/fluoridation/timeline-for-community-water-fluoridation/index.html)). ## From fluorosis to a cavity trial The DMFT index (decayed, missing and filled teeth) let surveys in the 1930s and 1940s compare caries across communities ([CDC 1999 report](https://www.cdc.gov/mmwr/preview/mmwrhtml/mm4841a1.htm)). In 1938 Dean found "a strong inverse relation" between fluorosis and decay among children in 26 states (same source). In 1942 he published the 21 Cities Study, which followed 7,200 children aged 12 to 14 in Colorado, Illinois, Indiana and Ohio. Children had fewer cavities in cities with more fluoride in the water, and the effect leveled off above 1.0 ppm ([CDC timeline](https://www.cdc.gov/fluoridation/timeline-for-community-water-fluoridation/index.html)). Dean concluded that 1.0 ppm lowered decay with negligible risk of fluorosis (same source). ## Grand Rapids and a trial that never quite finished Grand Rapids began fluoridating in January 1945 as part of a planned trial. Each fluoridating city had a control city of similar size, and Grand Rapids was paired with Muskegon, Michigan ([CDC timeline](https://www.cdc.gov/fluoridation/timeline-for-community-water-fluoridation/index.html)). By 1949, dental examiners in Grand Rapids, Newburgh and Brantford reported sharply fewer cavities among children starting school (same source). A 1950 review concluded that "controlled fluoridation displayed the same effects as natural fluoridation" (same source). Muskegon quit the trial in 1951 and started fluoridating its own water, so the Grand Rapids trial was "technically finished." By 1960, decay rates in the two cities were roughly equal (same source). ## The early numbers shrank, and the mechanism changed Early reports put the caries reduction from fluoridation at 50 to 70 percent. By the mid-1980s, children in fluoridated communities had mean DMFS scores (decayed, missing and filled tooth surfaces) only 18 percent lower than children elsewhere. A review of studies from 1979 to 1989 found reductions of 8 to 37 percent among adolescents, averaging 26.5 percent ([CDC 1999 report](https://www.cdc.gov/mmwr/preview/mmwrhtml/mm4841a1.htm)). CDC attributes part of the narrowing to fluoride reaching non-fluoridated areas through processed foods, beverages and toothpaste (same source). The mechanism changed too. Researchers first thought fluoride built harder enamel while the tooth formed. CDC's 1999 account says the action is mostly topical, after the tooth erupts (same source). That is why fluoride became a dental public health measure rather than a nutrient program. The evidence came from teeth, the action happens on the tooth surface, and NIH's dental unit ran the early studies (same source). ## Water, toothpaste and drops are not the same product Toothpaste works only as well as people use it. CDC says water fluoridation "reaches all residents of communities and generally is not dependent on individual behavior" ([CDC 1999 report](https://www.cdc.gov/mmwr/preview/mmwrhtml/mm4841a1.htm)). Crest, which CDC's timeline calls the world's first fluoride toothpaste, went national in 1956 ([CDC timeline](https://www.cdc.gov/fluoridation/timeline-for-community-water-fluoridation/index.html)). Supplements are a third route. According to NIH ODS, only a few supplements contain fluoride. Those that do are mostly multivitamin or trace-mineral products, and some products meant for children come as drops. The most common amount is 0.25 mg per serving ([NIH ODS](https://ods.od.nih.gov/factsheets/Fluoride-HealthProfessional/)). ODS also summarizes American Dental Association guidance: children aged 6 months to 3 years get 0.25 mg a day when their water holds less than 0.3 ppm (same source). The [folate history](/blog/history/history-of-folate-from-lucy-wills-to-fortified-bread) covers the other public health route, adding a nutrient to flour. ## Upper limits for children NIH ODS defines a tolerable upper intake level as the "maximum daily intake unlikely to cause adverse health effects." For fluoride, the limits cover all sources and rest on dental and skeletal fluorosis ([NIH ODS](https://ods.od.nih.gov/factsheets/Fluoride-HealthProfessional/)). For children they are 0.7 mg a day from birth to 6 months, 0.9 mg at 7 to 12 months, 1.3 mg at 1 to 3 years, 2.2 mg at 4 to 8 years and 10 mg at 9 to 13 years (same source). Dose warnings for minerals have their own history, and iron tablets are one example in the [iron supplements post](/blog/history/history-of-iron-supplements-and-the-ferritin-test). CDC's timeline records a uniform target of 0.7 mg per liter for community water, set in 2015 (CDC timeline, last updated May 2024). ## Next reads - [Vitamin B12 from liver cure to cobalamin](/blog/history/history-of-vitamin-b12-from-liver-cure-to-cobalamin): a clinic treatment that came more than two decades before the vitamin was crystallized. - [Calcium from shell to bone trials](/blog/history/history-of-calcium-supplements-from-chalk-to-bone-trials): the same mineral question, asked from the supplement side. ### Related reading - [copper from anemia to trace mineral](/blog/history/history-of-copper-from-anemia-to-trace-mineral) - [iodine from seaweed to iodized salt](/blog/history/history-of-iodine-from-seaweed-to-iodized-salt)