Dental fluorosis and associated factors in 12-year-old Thai ethnic children in Con Cuong, Nghe An, Vietnam: a cross-sectional study with water fluoride analysis

Dental fluorosis is a public health concern in areas with elevated fluoride in drinking water. Data on fluorosis among ethnic minority children in remote Vietnamese mountains are scarce. This study aimed to determine the prevalence and severity of dental fluorosis, assess fluoride concentrations in drinking water sources, and identify associated factors among 12-year-old Thai ethnic children in Con Cuong district, Nghe An province. A cross-sectional study was conducted from May to November 2023. A stratified random sample of 476 Thai ethnic children aged 12 years from nine communes was examined (sample size calculated based on an expected fluorosis prevalence of 12%, with 95% confidence and 3.5% precision). Dental fluorosis was assessed using Dean’s Fluorosis Index (WHO 2013). Drinking water samples ( n = 27) from wells, streams, and taps were collected and analyzed for fluoride content using ion-selective electrode. Structured questionnaires collected data on dietary habits, oral hygiene, and household fuel use. Bivariate and multivariable logistic regression were used to identify factors associated with fluorosis (excluding questionable cases). Significance was set at p < 0.05. The prevalence of dental fluorosis (excluding questionable) was 7.1% (34/476); including questionable cases it was 13.2% (63/476). Most cases were very mild (4.6%) or mild (2.3%); only one child (0.2%) had moderate fluorosis, and no severe cases occurred. The Community Fluorosis Index was 0.13, indicating no public health problem. Drinking water fluoride concentrations ranged from 0.21 to 0.79 mg/L (mean 0.48 ± 0.16 mg/L), with a method detection limit of 0.019 mg/L; none exceeded the WHO guideline value of 1.5 mg/L (upper limit for health protection). In multivariable logistic regression, water fluoride level ( p = 0.68), consumption of tea ( p = 0.54), use of wood for cooking ( p = 0.71), and gender ( p = 0.82) were not significantly associated with fluorosis. Caries prevalence was 14.3%. Only 1.5% of affected children reported aesthetic concerns. Dental fluorosis is not currently a public health problem among 12-year-old Thai ethnic children in Con Cuong district, based on the cross-sectional data collected. The low fluorosis prevalence is consistent with optimal fluoride levels in drinking water at the time of the study. However, causal inferences are limited by the cross-sectional design and single water sampling. The low caries prevalence suggests adequate fluoride exposure for caries prevention without fluorosis risk. Routine water fluoride monitoring and periodic oral health surveys are recommended. Longitudinal studies with repeated water sampling are needed to confirm the observed associations.