Four Decades of Fluoridated Water: How São Paulo Dramatically Reduced Tooth Decay
What 40 Years of Data Tell Us About Fluoride, Cavities, and Public Health
For decades, dental caries (tooth decay) has been one of the most common public health problems worldwide—especially among children. Sugary diets, limited access to dental care, and social inequality continue to fuel the problem. Against this backdrop, a long-running public health intervention in São Paulo, Brazil, offers a rare opportunity to see what works over the long term.
A new study published in Revista de Saúde Pública examines 40 years of community water fluoridation in São Paulo and its impact on dental caries and dental fluorosis among 12-year-old schoolchildren. The findings provide strong real-world evidence that fluoridated water has played a major role in improving oral health across the city.
Why Water Fluoridation Matters
Reducing sugar consumption at a population level has proven extremely difficult. Because of this, public health experts have long focused on protective strategies that do not depend on individual behavior. One of the most widely studied approaches is community water fluoridation—the controlled addition of fluoride to public drinking water.
This intervention is considered a classic public health measure: it reaches everyone, is low-cost, does not require lifestyle changes, and has been shown to be safe. The only known side effect, mild dental fluorosis, is generally cosmetic and does not affect tooth function.
São Paulo began fluoridating its public water supply in 1985, and the program has continued uninterrupted ever since.
What the Researchers Did
The researchers analyzed secondary epidemiological data collected between 1986 and 2023, focusing on children aged 12—the standard global indicator age for assessing dental caries.
They examined:
Caries prevalence (the proportion of children with at least one decayed, missing, or filled tooth),
The DMFT index, which measures the average number of affected permanent teeth,
Inequality in disease distribution, using the Gini coefficient,
Fluoride levels in more than 49,000 water samples collected over three decades,
Trends in dental fluorosis, assessed using internationally accepted criteria.
The analysis was framed using an Evidence-Based Public Health (EBPH) approach, which combines scientific evidence with real-world implementation and population context.
A Steep Decline in Tooth Decay
The results are striking.
In 1986, nearly 95% of 12-year-olds in São Paulo had experienced dental caries. By 2023, that figure had dropped to 46%.
Over the same period, the average DMFT score fell by 76.7%, from 6.47 affected teeth per child to just 1.51. This dramatic decline mirrors the long-term exposure to consistently fluoridated water.
These improvements occurred even as social inequalities persisted and access to dental care remained uneven—suggesting that fluoridation provided a protective baseline for the entire population.
What About Dental Fluorosis?
One common concern about fluoride exposure is dental fluorosis. The study found that fluorosis levels in São Paulo remained stable and predominantly mild over time.
Most cases fell into the “very mild” or “mild” categories, which have no functional or aesthetic impact. Moderate and severe fluorosis were extremely rare. Importantly, fluoride concentrations in the water supply stayed within recommended ranges for nearly 98% of all samples analyzed.
In short, the benefits of fluoridation were not offset by meaningful harm.
Unequal Disease, Shared Protection
While overall tooth decay declined, the study found that caries became more concentrated among a smaller group of children—a pattern known as disease polarization. This means that inequality in oral health remains a challenge.
However, the authors emphasize that fluoridation still plays a crucial role in reducing overall disease burden, particularly for children who face barriers to regular dental care.
Why This Evidence Matters Today
Water fluoridation has come under renewed debate in several countries, including Brazil. Critics often argue that improvements in oral health are due to toothpaste use, education, or broader social changes rather than fluoridated water alone.
The authors acknowledge that multiple factors are involved. However, they note that fluoridated water and fluoridated toothpaste expanded together, reinforcing each other. From an Evidence-Based Public Health perspective, the key question is not whether fluoridation acts alone—but whether it works in real-world conditions.
After four decades, the answer in São Paulo appears clear.
The Bottom Line
Forty years of continuous water fluoridation in São Paulo have been associated with a major and sustained reduction in dental caries, without causing significant harm. In a city where access to dental care remains uneven, fluoridation has functioned as a powerful, population-wide protective measure.
According to the authors, decisions to discontinue fluoridation should be based on solid scientific evidence—not ideology or misinformation. For now, São Paulo’s experience stands as one of the strongest real-world demonstrations of fluoridation’s public health value.
Original Article Reference
Narvai PC, Soares CCS, Frias AC, Antunes JLF.
Dental caries and fluorosis after 40 years of community water fluoridation in São Paulo, Brazil.
Revista de Saúde Pública. 2025;59:e47.