In the mid-20th century, governments introduced community water fluoridation as a strategy to address the widespread issue of dental decay, which posed a major public health challenge.^[11] Observational research at the time showed that communities with naturally high fluoride levels in their water had significantly lower rates of tooth decay (dental cavities) than communities with lower levels,^[12][13][14] and subsequent experimental research confirmed the beneficial effects of water fluoridation for reducing cavities and improving dental health.^[9] This evidence supported community water fluoridation as a cost-effective measure for improving dental health across entire populations in both adults and children, offering widespread benefits regardless of an individual's income level or access to dental care.

This is a controversial question. Tooth decay is a public health problem affecting many adults and children. But the need for community water to be fluoridated is debated.^[1] There is evidence from observational research including 44,268 participants that fluoridation reduces levels of tooth decay and caries in children, compared to no fluoridation, by up to 35%. Fluoridation is linked with 15% more children with no decay in baby teeth and 14% more children with no decay in permanent teeth. However, most of this research is from before widespread use of fluoride toothpaste.^[9] There is not enough evidence to know what would occur if fluoridation were removed in the present day.

Although more research is needed to know for sure, it appears that excessive fluoride exposure is linked to poorer cognition in children; it’s important to note that community fluoridation in the United States and Canada is far below this level. A meta-analysis of 8 cross-sectional and cohort studies did not find that fluoride exposure via community water fluoridation affects IQ scores in children. However, high fluoride exposure (3.7 mg/L) from natural groundwater in certain geographical areas (e.g., parts of China and India) was associated with lower IQ when compared with lower fluoride exposure (0.7 mg/L). There was no difference in IQ between mean exposure to 0.9 mg/L fluoride when compared to 0.3 mg/L fluoride.^[2] Another meta-analysis of 26 observational studies mostly conducted in China found that high fluoride exposure from water is associated with lower intelligence compared to normal fluoride exposure.^[8] This data is limited by its observational nature and the presence of various confounding factors. For example, the impact of socio-economic status or exposure to environmental toxins was not able to be controlled.

While Western countries like the United States intentionally add a small amount of fluoride to drinking water for dental health, some geographical locations have groundwater that is naturally excessively high in fluoride, and people who live in these areas have a greater risk of developing fluoride toxicity. In some regions of India and China, geothermal and volcanic activity has led to the formation of rocks that have high levels of fluoride. When these rocks are exposed to alkalinity and heat, fluoride is released into the soil and freshwater sources, resulting in high-fluoride food crops and drinking water. Fluoride does not have a taste, odor, or color, and since groundwater is not tested often, high fluoride exposure can go undetected for a long time. It is predicted that some countries in Central Africa are also at high risk for drinking water with excessively high fluoride.^[10]

Fluoride varnish is a highly concentrated fluoride treatment applied to the surface of the teeth by dental professionals using a brush, cotton tip, or syringe-like applicator, typically 2 to 4 times per year in individuals who are at high risk of caries (dental cavities).^[15][16]

Fluoride varnishes form a temporary coating on the teeth that allows fluoride to be slowly released and absorbed into the enamel over time. This process helps reduce enamel demineralization (mineral loss) and promotes remineralization, repairing early tooth damage.^[16] More specifically, during an acid attack (in which bacteria in plaque produce acids from sugars), fluoride moves with the acid from plaque into the tooth enamel, where it reduces mineral loss by decreasing the solubility of the enamel, increasing calcium and phosphate availability, and inhibiting the diffusion of acid into the enamel. As the pH normalizes after the acid attack, fluoride combines with calcium and phosphate in the saliva to rebuild and strengthen the enamel by forming fluorapatite, a mineral that is more resistant to future acid damage.^[17] This dual action — reducing mineral loss and enhancing mineral gain — makes fluoride a powerful tool for preventing dental caries.