Fluoride chemically soluble in toothpaste is an indicator of fluoride bioavailability when the teeth are brushed and the same should be expected systemically when toothpaste is ingested. A four-phases study was conducted, in which eight participants were subjected in each phase to one of the assigned treatment groups: Group I: fresh sample of a Na2FPO3/CaCO3 toothpaste with 1,334 μg F/g of total soluble fluoride (TSF); groups II–IV: aged samples of toothpaste presenting TSF concentrations of 1,128, 808, and 687 μg F/g, respectively. In all phases, the participants ingested an amount of toothpaste equivalent to 70.0 µg F/kg body weight, as total fluoride (TF). Blood was collected before (baseline) and up to 180 min after toothpaste ingestion as indicator of fluoride bioavailability. Total urine (24 h before and 24 h after ingestion) was collected as indicator of absorbed fluoride that was excreted. F concentration in blood plasma and urine was determined with a fluoride ion-specific electrode. The areas under the curve of F concentration vs. time (AUC=ng F/ml x min) and the peaks of fluoride concentration in blood plasma (Cmax) were calculated. The net amount of fluoride excreted (mg/day) was calculated by subtraction. A significant correlation of the amount (mg) of TSF ingested was found between the AUC (r= 0.76; p<0.01) and Cmax (r= 0.86; p<0.01) in plasma, and the fluoride excreted (r= 0.65; p<0.01). For TF no statistical correlations were found (p>0.05). Data suggest that the concentration of TSF found in Na2FPO3/CaCO3-based toothpastes is a useful predictor of how much fluoride will be systemically bioavailable when this type of formulation is ingested.

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