Effect of combined high iodine-fluorine water exposure on the occurrence of dental fluorosis in school-age children: a cross-sectional study from rural Jiangsu, China.

The combined impact of high iodine and high fluoride exposure has garnered increased attention. To determine whether exposure to high levels of fluoride and iodine in water has adverse effects on children's teeth. In this study, 582 children aged 8 to 12 from rural Jiangsu, China, were divided into three groups based on the concentrations of iodine and fluoride in their drinking water: a high fluoride and high iodine group (HFHI), a high fluoride group (HF), and a control group (CONTROL). We employed the ion-selective electrode method to measure fluoride levels in urine samples and used inductively coupled plasma mass spectrometry to assess urinary iodine (UI) levels. The prevalence and severity of dental fluorosis (DF) were determined using Dean's Index in accordance with WHO criteria. A logistic regression model was used to analyze factors related to dental fluorosis. The urinary fluoride (UF) regression coefficients were compared using the Z-test to assess their influence. The results indicate that the prevalence of DF was 52.5, 33.5, and 4.1% in the HFHI, HF, and CONTROL groups, respectively. There were statistically significant differences in both the prevalence and severity of DF among the groups (P < 0.001 for both). The dental fluorosis indexes (DFI) were calculated as 1.2, 0.7, and 0.1 for the HFHI, HF, and CONTROL groups, respectively. UF levels were positively associated with DF in the HFHI and HF groups, with adjusted odds ratios (OR) of 5.30 and 3.12, respectively. The Z-test results showed statistically significant differences (HFHI vs. CONTROL, P < 0.001; HF vs. CONTROL, P = 0.048; HFHI vs. HF, P < 0.001). UF levels > 1.4 mg/L and UI > 300 μg/L demonstrated a significant interaction in the HFHI group (OR = 9.62, 95% CI 2.70-18.36, P < 0.001) and Overall (OR = 9.15, 95% CI 2.71-16.58, P < 0.001). Simultaneous exposure to high iodine and high fluoride in water adversely impacts the incidence of DF in school-age children. It is recommended that monitoring of UI levels in children from high fluoride regions be enhanced.