Fluoride Bioavailability from Silica- or Calcium Carbonate-based Toothpastes

Objective: Fluoride (F) bioavailability from toothpastes is expected to be a function of the amount of soluble (bioavailable) F present in the formulation, but this has been ignored when calculating dental fluorosis risk by toothpaste ingestion. Thus, calcium-based F toothpastes, which present part of total F (TF) insoluble, could have a lower risk of causing fluorosis than silica-based toothpastes, if the same amount of total F is ingested from both. Thus F availability from calcium carbonate (CaCO₃) and silica-based toothpastes was evaluated in the present study.

Method: In a crossover, blind, in vivo study, 20 adults volunteers were orally subjected to 49.5 µg F/kg body weight from a NaF/silica toothpaste (Tandy^®, TF=1085.7±64.4, total soluble fluoride (TSF)=1091.5±33.9 ppm F) or from a MFP/CaCO₃ toothpaste (Sorriso^®, TF=1439.0±20.1, TSF=1097.1±55.0 ppm F), which differ in the amount of TF, but not in TSF. Toothpastes were dissolved in 30 mL of distilled water, and after ingestion volunteers rinsed twice with 30 mL of distilled water. Unstimulated saliva was collected for up to 3 h after ingestion to estimate bioavailable F. Saliva was used as indicator of F biovailability because there is a high correlation between F concentration in blood and saliva. F concentration in saliva was determined by a F electrode and the area under the curve (AUC) of F concentration x time ((μg F/mL X min) was calculated. Distilled water was ingested as a control and the AUC obtained in this group for each volunteer was subtracted from those obtained for the toothpaste groups, which were compared using ANOVA.

Result: The AUC (Avg±SD;n=20) was significantly lower (p<0.05) in the group ingesting the CaCO₃-based toothpaste (3.4±1.6) when compared to the NaF-based toothpaste (4.4±1.8). 

Conclusion: The results suggest that only the soluble F in toothpastes is available for absorption and this should be considered in the discussion about F toothpastes and risk of fluorosis.