The Benefits of Fluoride: Addressing Public Concern and Supporting Topical Use

The introduction of fluoride in drinking water to reduce the incidence of dental caries, once hailed as a major public health success, has recently come under scrutiny. In August 2024, a monograph from the National Toxicology Program (NTP) reported that fluoride at levels above 1.5 mg/L is associated with reduced intelligence quotient (IQ) in children.¹ In September 2024, a US district judge required that the Environmental Protection Agency take action regarding the “unreasonable risk” posed by fluoride in drinking water.² In May 2025, the Food and Drug Administration initiated efforts to remove ingestible fluoride prescription products.³ Effective May and July of 2025, Utah and Florida, respectively, became the first states to ban fluoride from public drinking water. These recent policy changes warrant a review of the history of fluoride’s use for reducing caries, the evidence for fluoride in water and oral health products, the current criticism of fluoride, and the evidence for the effectiveness of fluoride alternatives.

Impact of Community Water Fluoridation

The role of fluoride in dental health was first noted in the early 20th century when residents of Colorado Springs, Colorado, with naturally high levels of fluoride in their water supply, were found to have relatively few caries lesions despite noticeable staining on their teeth. The cause of the staining was traced to naturally high levels of fluoride in the local water. This staining, later identified as dental fluorosis, prompted further investigation into the effects of fluoride. By the 1930s, researchers discovered that low levels of fluoride in water, around 1 parts per million (ppm), would not cause fluorosis. Based on knowledge of lowered rates of caries in populations with naturally occurring fluoride in their water supplies, a trial was initiated to study the benefits of community water fluoridation at 1 ppm.⁴

The original water fluoridation trial was conducted in the Grand Rapids-Muskegon study.⁵ The study evaluated the impact of water fluoridation on dental caries among school children in Grand Rapids, Michigan, over a decade. Initiated in 1945, this public health trial compared Grand Rapids, where fluoride was added to the water supply at 1 ppm, with Muskegon, a nearby city without fluoridation (naturally occurring fluoride concentration of around 0.2 ppm) during the study period. The research focused on children aged 4 to 16 who had been lifelong residents and consumed city water since birth. Around 5,000 children were examined in Grand Rapids, and slightly less than 3,000 were studied in Muskegon. Annual dental examinations revealed a significant reduction in tooth decay among children in Grand Rapids compared to those in Muskegon. For instance, after 10 years, there was a 54% reduction in decayed/extracted/filled teeth of 6-year-olds in Grand Rapids, whereas only a 25% reduction was noted in their counterparts in Muskegon. This led to the introduction of community water fluoridation.⁵

Since then, studies have continued to measure the benefit of water fluoridation. A 2024 Cochrane review analyzed prospective, controlled studies to assess the impact of community water fluoridation on dental caries rates.⁶ The review focused on changes in the number of decayed, missing, or filled teeth in children and adolescents (up to 19 years old), using the dmft index for primary teeth and the DMFT index for permanent teeth. Researchers compared dental caries rates in communities before and after the introduction of water fluoridation and also examined similar timepoints in control communities without fluoridated water. To account for broader changes in oral health practices, the analysis distinguished between studies conducted before and after 1975—the approximate start of widespread use of fluoridated toothpaste. In studies conducted before 1975, communities that introduced water fluoridation experienced a greater reduction in caries: an average decrease of 2.1 in dmft (five studies, 5,709 children) and 1.0 in DMFT (three studies, 5,623 children) scores compared to control communities. However, in studies conducted after 1975, the difference in caries reduction was smaller: only 0.24 for dmft (two studies, 2,908 children) and 0.27 for DMFT (four studies, 2,856 children). These findings suggest that while water fluoridation remains beneficial, its relative impact may have diminished in the post-1975 era due to the widespread use of other fluoride sources, particularly fluoridated toothpaste.⁶

Systemic Vs Topical Fluoride

The observed reduction in the marginal benefit of community water fluoridation following the widespread adoption of fluoride-containing toothpaste has raised questions regarding the relative contributions of systemic versus topical fluoride exposure. A growing body of evidence suggests that fluoride’s caries-preventive effect is primarily topical rather than systemic. Laboratory studies have demonstrated that fluoride incorporated into synthetic enamel during tooth development, analogous to systemic fluoride exposure from drinking water, does not significantly reduce acid solubility or inhibit demineralization of enamel.^7-9 In contrast, the presence of fluoride in the surrounding solution at concentrations as low as 1 ppm significantly decreases enamel dissolution, with progressively greater inhibition observed at higher fluoride concentrations.^7,10 These findings underscore the importance of fluoride in saliva and plaque fluid at the time of acid challenge, as opposed to fluoride integrated into the enamel matrix during development.

Epidemiological evidence supports this mechanistic understanding. In a 4-year study conducted in England, children who began receiving fluoridated water at age 12 exhibited a 27% reduction in caries incidence compared to peers in non-fluoridated areas, indicating a substantial post-eruptive benefit from fluoride exposure.¹¹ Conversely, a study involving nursing students in Okinawa found no significant difference in caries experience between those who had systemic fluoride exposure during early childhood and those who had none, suggesting minimal pre-eruptive benefit.¹² Collectively, these findings reinforce the conclusion that fluoride’s primary mode of action in preventing dental caries is topical.

As the caries-preventive benefits of fluoride are primarily attributable to its topical effects, and these benefits can be achieved through the use of fluoridated toothpaste, the necessity of community water fluoridation warrants re-examination. A reasonable justification is that water fluoridation may provide a public health benefit for individuals of lower socioeconomic status who may lack consistent access to fluoridated toothpaste, due to either financial barriers or insufficient parental supervision of oral hygiene practices. However, the aforementioned 2024 Cochrane review concluded that there was insufficient evidence to determine whether individuals from lower socioeconomic backgrounds derive greater benefit from water fluoridation. This conclusion was based on the fact that only one study included in the review stratified caries outcomes by socioeconomic status.⁶ Despite the lack of evidence, logic follows that removal of fluoride from drinking water could revert caries rates to those of the 1950s in populations without access to fluoridated oral care products.

Assessing the Current Situation

A major source of recent concern regarding fluoride in drinking water stems from the publication of a report by the NTP, which identified an association between high levels of fluoride in drinking water and reduced IQ scores in children.¹ Most of the studies included in the NTP review were conducted in regions such as Iran, China, India, and Mexico, where naturally occurring fluoride levels in drinking water ranged from 2 ppm to 9 ppm. A subsequent meta-analysis published in association with the NTP report concluded that community water fluoridation at concentrations below 1.5 ppm was not associated with reduced IQ, except when only studies assessed as low risk of bias were included.¹³ Low risk-of-bias studies were characterized by stronger control for potential confounders (eg, environmental exposures), precise measurement of fluoride exposure, and rigorous cognitive testing protocols. Notably, only three studies met these criteria. A separate meta-analysis that was focused specifically on fluoride exposures within the range used for community fluoridation found no association with IQ scores in children.¹⁴

The NTP also reviewed two Canadian studies that reported an association between prenatal fluoride exposure at recommended community fluoridation levels and lower IQ in children.^15,16 However, these findings have been criticized for methodological weaknesses, including the use of spot urine samples to assess fluoride exposure and inconsistencies in IQ testing across different study sites.^17,18

Given the concern over fluoride ingestion and the well-established benefits of topical fluoride, which is most commonly delivered via toothpaste, it is reasonable for individuals to prefer obtaining fluoride through topical means rather than systemic ingestion. Unfortunately, public discourse opposing ingested fluoride may lead to broader hesitancy, including avoidance of topical fluoride in oral health products,¹⁹ and may prompt interest in alternative remineralizing agents.

Fluoride prevents dental caries by enhancing enamel’s resistance to acid demineralization. It does so by substituting hydroxyl (–OH) groups in hydroxyapatite [Ca₁₀(PO₄)₆(OH)₂] with fluoride ions (F^_), forming fluorapatite [Ca₁₀(PO₄)₆F₂]. Due to the smaller ionic radius of fluoride compared to hydroxyl, this substitution results in a denser, more stable crystal lattice. According to Coulomb’s law, the tighter ionic packing increases electrostatic attraction within the crystal, thereby improving acid resistance.²⁰ By contrast, natural enamel is primarily composed of carbonated hydroxyapatite, in which carbonate (CO₃^2_) replaces phosphate (PO₄^3_) or hydroxyl ions, creating lattice imperfections and reducing structural stability. Fluoride-driven remineralization facilitates the replacement of these defects, resulting in purer, more acid-resistant fluorapatite.²¹

An emerging alternative to fluoride is hydroxyapatite-containing toothpaste. Three small clinical trials have compared the efficacy of hydroxyapatite to fluoride toothpaste in caries prevention. These trials, which enrolled 150, 77, and 171 participants and lasted 6, 12, and 18 months, respectively, found no significant difference in caries outcomes between the two agents.²² However, the limited sample sizes and short durations preclude strong conclusions.

Conclusion

In summary, fluoride remains the most well-studied and effective agent for the prevention of dental caries. Its primary mode of action is topical, which supports the use of fluoridated toothpaste as an alternative to fluoridated water. While ingestion of fluoride at levels above 1.5 ppm is associated with reduced IQ in some studies, there is insufficient evidence to support this association at the recommended level of 0.7 ppm used in community fluoridation. Discontinuation of water fluoridation may disproportionately impact individuals without regular access to fluoridated toothpaste. Moreover, public skepticism about fluoride in drinking water may inadvertently reduce the use of effective topical fluoride therapies. Given its unique mechanism of action and robust clinical support, fluoride remains the gold standard in caries prevention, and evidence supporting alternatives is currently limited.