Fluoride Gastrointestinal Absorption from Na₂FPO₃/CaCO₃- and NaF/SiO₂-Based Toothpastes

Abstract

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 µg F/g as labeled, 1,129.7 ± 49.4 µg F/g soluble fluoride as analyzed) or with around 20% of insoluble fluoride (Na₂FPO₃/CaCO₃-based toothpaste, 1,450 µg F/g as labeled, 1,122.4 ± 76.4 µg 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 µg 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.

Factors associated with dental fluorosis in school children in southern Brazil: a cross-sectional study

“…It has been shown that not all ingested F from toothpaste will be absorbed, and may not be absorbed systemically. 21,24 The finding that children who initiated tooth brushing at an early age had a higher prevalence of DF may suggest that they swallowed a quantity of fluoridated toothpaste great enough to have had a negative systemic impact.…”

Estimated Fluoride Doses from Toothpastes Should be Based on Total Soluble Fluoride

“…The present data show that the dose to which children are subjected can be overestimated when total soluble fluoride (TSF) is not considered in the calculation of F intake (Table 2). Moreover, previous data demonstrate a lower degree of fluoride bioavailability in calcium-based toothpastes [9,10,11,12], which are the top selling toothpastes [20]. …”

“…The amount of bioavailable fluoride in toothpaste depends on the type of fluoride salt and abrasive used in its composition [9,10,11,12]. Due to the incompatibility of NaF, SnF 2 and even amine fluorides with calcium-based abrasives, silica (SiO 2 ) particles have been employed.…”

Effects of Low and Standard Fluoride Toothpastes on Caries and Fluorosis: Systematic Review and Meta-Analysis

“…It should be noted that the F agent of the 1,450-ppm toothpaste is a combination of sodium monofluorophosphate (Na 2 FPO 3 ) and sodium F in a calcium-based abrasive system. It has already been shown that Na 2 FPO 3 / CaCO 3 formulations containing 1,400-1,500 ppm F of total F present approximately 1,000 ppm F in a soluble form [Falcão et al, 2013]. Therefore, it is possible that part of the toothpaste used in the study by Tavener et al [2006] was not bioavailable.…”