Risk assessment for dental fluorosis by analysis of human nails

Nail clippings have been suggested as appropriate biological markers of fluoride (F) exposure. However, the choice for using fingernail or toenail to this purpose is controversial. Objective: The aim of this study was to evaluate the concordance of fingernail and toenail F-concentrations as biomarkers for dental fluorosis. Methods: Three- to seven-year-old children exposed to different F-levels in the drinking water (low 0.09, optimum 0.72 and high 1.68mg/L) participated. Fingernail and toenail clippings (n=30 for low and optimum, n=15 for high F-level area) were collected, washed (interdental brush and deionized water, sonication 10min), dried, weighed, tested for F (electrode, after HMDS-facilitated diffusion) and statistically analyzed (ANOVA, Tukey, p<0.05). High risk for dental fluorosis was assumed as above 2.0mgF/kg in nails. Results: Mean (±SD, mg/kg) fingernail/toenail F-concentrations were 1.75±0.64/1.58±0.74, 2.28±1.18/2.66±1.73 and 5.95±4.03/5.49±1.76 for low, optimum and high F-level areas, respectively. Except for fingernail F-concentrations between low and optimum water F, fingernail and toenail F-concentrations were significantly different among low, optimum and high F-level areas. Percentages of children at high risk for dental fluorosis (fingernail/toenail, %) were 33.33/26.67, 46.67/60.00, 93.33/100.00 and the concordance values (matching cases in %) of fingernail and toenail were 16.67, 33.33 and 93.33, for low, optimum and high water F-level areas, respectively. Conclusion: Fingernail F-concentrations tend to classify more individuals at risk in low water F regions whereas toenail F-concentrations present a trend to include more individuals at risk for dental fluorosis in areas with optimum and high F-levels in the drinking water. Supported by FAPESP grants No. 04/15417-5 and 02/07875-8.