Nails as Biomarkers of Exposure to Fluoride from Dentifrice in 2- to 3-year-old Children: a Longitudinal Study

Objectives: To evaluate the use of fingernails and toenails as biomarkers of exposure to fluoride (F) from fluoridated dentifrice in 2-3 year-old children. Methods: Ten 2-3 year-old children used a placebo dentifrice (without F) for 28 days, fluoridated dentifrice (1,500 ppm F as MFP) for the following 28 days, and then placebo dentifrice for additional 28 days, when returned to their usual dentifrices. They were instructed to brush their teeth 3 times a day with a pea-size amount of the specified dentifrice. Fingernails and toenails were clipped every 2 weeks, during the experimental period and for additional 22 weeks, totalizing 34 weeks. Fingernail and toenail F concentrations were analyzed separately with the ion specific electrode (Orion 9409) following HMDS-facilitated diffusion. Data were analyzed by 2-way ANOVA and Tukey’s test (p<0.05). Results: Nail F concentrations ranged from 1.258 to 17.417 µg/g. There were not significant differences between fingernails and toenails F concentrations. Mean F concentrations (±SD, n=10) at the 4 first weeks and the 6 last weeks were 2.709±0.971 and 2.696±1.167 µg/g, for fingernails and toenails, respectively. Mean peak F concentrations, which occurred 16 weeks after starting the use of F dentifrice were 10.051±3.328 and 9.186±3.862 µg/g for fingernails and toenails, respectively. This indicates that F enters nails via the growth end. In addition, smaller, but statiscally significant increases in nail F concentrations were seen 4 weeks after starting the use of the fluoridated dentifrice (7.251±5.682 and 5.612±4.627 µg/g, for fingernails and toenails, respectively), which suggests that F also enters the nails through their bed. Conclusions: There seems to be no differences between fingernails and toenails F concentrations and both of them may be suitable biomarkers of exposure to F from dentifrice in small children. A lag time of 4 weeks is enough for F detection in nails of small children.