Association of drinking water fluoride with dental fluorosis and caries among schoolchildren in Al-Ahsa, Saudi Arabia

Fluoride is essential for caries prevention; however, excessive exposure during enamel development increases the risk of dental fluorosis. In Saudi Arabia, fluoride concentrations vary across water sources due to environmental and treatment-related factors, yet updated regional assessments remain limited. This study examined fluoride levels in drinking-water sources in Al-Ahsa, Saudi Arabia, and assessed their association with dental fluorosis and caries among primary schoolchildren. A cross-sectional study included 568 children aged 6–12 years selected through stratified random sampling from 11 public schools across four regions of Al-Ahsa. Parents completed the Arabic WHO Oral Health Questionnaire. Dental fluorosis was assessed using Dean’s Index, and caries were recorded using DMFT/dmft indices. Fifty-five water samples from public network water, home-filtered water, and well water were analyzed using an ion-selective fluoride meter. Non-parametric tests, Spearman correlations, and generalized linear models evaluated associations between fluoride concentrations, oral-health outcomes, and sociodemographic and behavioral factors. Fluoride levels ranged from 1.01 to 2.61 ppm in filtered public-network water and 3.56–5.63 ppm in well water, with several samples exceeding the WHO maximum permissible guideline of 1.5 ppm. Although 70.2% of children showed no fluorosis, 25.5% had questionable or very mild fluorosis, and 4.2% had mild-to-moderate fluorosis. High caries experience (DMFT/dmft ≥ 6) was observed in 41.2%. Dean’s Index differed across water sources ( p = 0.024), but fluoride levels were not significantly correlated with fluorosis severity or caries indices ( p > 0.05). Caries was significantly associated with socioeconomic and behavioral factors. In this cross-sectional study using spot measurements of drinking-water fluoride in Al-Ahsa, well-water sources contained fluoride levels exceeding the WHO maximum permissible guideline of 1.5 mg/L. No statistically significant association was observed between measured water fluoride concentrations and dental fluorosis severity or dental caries experience. These findings should be interpreted cautiously given the single-point exposure measurement, group-level exposure assignment, temporal mismatch with historically relevant fluoride exposure, and absence of data on non-water fluoride sources. Caries experience was significantly associated with socioeconomic and behavioral determinants, underscoring the need for fluoride monitoring and comprehensive, multi-level preventive programs.