Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq)Depending on toothpaste formulation, part of the fluoride is insoluble and would not be totally absorbable in the gastrointestinal tract, thus changing dental fluorosis risk estimation. This hypothesis was tested with formulations with either all fluoride in a soluble form (NaF/SiO2-based toothpaste, 1,100 mu g F/g as labeled, 1,129.7 +/- 49.4 mu g F/g soluble fluoride as analyzed) or with around 20% of insoluble fluoride (Na2FPO3/CaCO3-based toothpaste, 1,450 mu g F/g as labeled, 1,122.4 +/- 76.4 mu g F/g soluble fluoride as analyzed). Toothpastes were evaluated either fresh or after accelerated aging, which increased insoluble fluoride to 40% in the Na2FPO3/CaCO3-based toothpaste. In a blind, crossover clinical trial conducted in five legs, 20 adult volunteers ingested 49.5 mu g of total fluoride/kg body weight from each formulation or purified water (control). Whole saliva and urine were collected as bioavailability indicators, and pharmacokinetics parameters calculated showed significantly (p < 0.05) lower fluoride bioavailability for Na2FPO3/CaCO3 toothpaste, which was reduced further after aging. A significant correlation between the amount of soluble fluoride ingested, but not total fluoride, and fluoride bioavailability was found (r = 0.57, p < 0.0001). The findings suggest that the estimated fluorosis risk as a result of ingestion of Na2FPO3/CaCO3-based toothpastes should be calculated based on the toothpaste's soluble rather than total fluoride concentration. Copyright (C) 2012 S. Karger AG, Basel473226233Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq)Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq)CNPq [130645/2010-9]