Fluoride in drinking water and fluorosis in an Argentine province: a spatial and epidemiologic analysis

Excessive fluoride exposure during enamel development is a major risk factor for dental fluorosis, particularly in populations relying on groundwater sources with naturally elevated fluoride concentrations. Rural regions with limited access to centralized water systems may present heterogeneous exposure patterns influenced by environmental and socioeconomic factors.

This study aimed to evaluate fluoride concentration in drinking water and the prevalence of dental fluorosis in schoolchildren from La Rioja, Argentina.

A cross-sectional ecological study was conducted including 469 schoolchildren aged 6-12 years from San Blas de los Sauces and Arauco. Only children born and continuously residing in the study area were included. Dental fluorosis was assessed using the Thylstrup and Fejerskov (T-F) index by calibrated examiners (Kappa > 0.8). Fluoride concentration was determined in 82 georeferenced groundwater samples using an ion-selective electrode. Spatial analysis included Moran's I and Local Indicators of Spatial Association (LISA). Associations between fluorosis severity and locality were evaluated using chi-square tests with Monte Carlo simulation.

The overall prevalence of dental fluorosis was 46.3% (95% CI: 40.8-49.9), with moderate fluorosis as the most frequent category. A significant association between locality and fluorosis severity was observed (p < 0.0001; Cramér's V = 0.23), with marked spatial heterogeneity. Fluoride concentrations varied across localities, with several exceeding the 1.5 mg/L threshold. Spatial analysis revealed significant clustering of high fluoride concentrations (Moran's I = 0.16; p = 0.006) and localized hotspots.

Although areas with higher fluoride concentrations and higher fluorosis severity were spatial overlapped, this was therefore interpreted as a descriptive pattern of co-occurrence, not as evidence of causality. A high prevalence of dental fluorosis with significant spatial variability was identified in the study area. The absence of a direct association between fluoride levels and fluorosis severity suggests a complex exposure pattern influenced by multiple factors.

The integration of epidemiological, environmental, and spatial data provides a useful framework for identifying high-risk areas and supporting targeted public health interventions in regions with decentralized water systems.