Water fluoridation for the prevention of dental caries.

Observational prospective before-after studies with concurrent controls evaluating initiation of fluoridation; one cessation study; participants primarily children aged 3–16 years across multiple countries; no randomized trials; caries indices used: dmf (decayed, missing, filled deciduous) and DMFT (permanent); fluorosis indices used: Dean's Index or TSIF.

Initiation of community water fluoridation by adding fluoride to public drinking water; fluoride concentrations typically around 0.7 ppm (range 0.4–1.0 ppm in initiation studies; some studies involve higher natural fluoride levels in fluorosis analyses); duration of exposure ranges from about 2 to 12 years; exposure occurs via drinking water (population-wide).

Initiation of water fluoridation is associated with lower caries in children: mean reductions of 1.81 in dmf (95% CI 1.31 to 2.31; 9 studies, 44,268 participants) and 1.16 in DMFT (95% CI 0.72 to 1.61; 10 studies, 78,764 participants); equivalent to about a 35% reduction in dmf and 26% reduction in DMFT relative to low/non-fluoridated water. Proportions of caries-free children increased by 15 percentage points for deciduous dentition and 14 percentage points for permanent dentition. For dental fluorosis, a fluoride level around 0.7 ppm is associated with approximately 12% having aesthetic concern; around 40% show fluorosis at any level. The evidence base is largely old and observational with high risk of bias, limiting confidence and applicability; data for adults are insufficient; information on disparities by socioeconomic status is limited. Policy implications depend on local oral health behaviors, other preventive measures, diet, tap water consumption, and population movement.

Evidence mainly from observational studies, many pre-1975; high risk of bias and substantial heterogeneity; limited adult data; limited data on stopping fluoridation or socioeconomic disparities; applicability to current settings remains uncertain.