Systemic fluoride levels in toenails as biomarkers of exposure and their association with the severity of dental fluorosis in Mexican schoolchildren – a cross-sectional study

<b>Introduction.</b> Elevated fluoride (F^-) exposure during childhood produces dental fluorosis (DF). Nails have been used for monitoring systemic F^- in relation to DF. The aim of this study was to evaluate F^- levels in toenails in association with DF severity in Mexican schoolchildren. <b>Materials and methods.</b> 120 schoolchildren from nonendemic areas (NEAs) and endemic F^- areas (EAs) were screened for DF via the Thylstrup and Fejerskov index (TFI). Toenails were collected to quantify systemic F^-. The associations between the biomarker, DF severity, tap water intake, sex, and age were analyzed. <b>Results.</b> The mean F^- in toenails in the NEAs and EAs were 0.63 ± 0.43 and 2.72 ± 1.38 mg/kg, respectively (p &lt; 0.001). A positive correlation was observed between the biomarker and DF severity (r_s = 0.755, p &lt; 0.001). Tap water consumption and the biomarker were associated with DF severity (p &lt; 0.001). Within TFI7-8 the mean F^- level was higher in those ages 10-11 than in those ages 8-9 (p &lt; 0.05). <b>Conclusion.</b> Systemic F^- levels in toenails are associated with DF severity in Mexican schoolchildren from both the NEA and the EA, which reflects the ability of the biomarker to accurately record the exposure to the compound in relation to clinical damage.