Fluoride bioavailability from NaF/SiO₂ and MFP/CaCO₃ -based toothpastes

Objective: NaF/SiO₂ and MFP/CaCO₃-based toothpastes are respectively the formulations most consumed in developed and developing countries. While in NaF/SiO₂-based toothpaste all fluoride is chemically available, in those MFP/CaCO₃-based a fraction of total F (TF) may be insolubilized by reaction with Ca, which increases with time, potentially reducing its bioavailability. Since F bioavailability is critical in terms of fluorosis risks when toothpaste is ingested, we evaluated F bioavailability from these toothpastes formulations, either fresh or after aging simulating one-year storage. 

Method: A crossover blind study was conducted in five steps when 20 volunteers were subjected to: purified water, NaF/SiO₂-based toothpaste (Tandy®, most consumed by Brazilian children) and MFP/CaCO₃-based toothpaste (Sorriso®, most consumed by the population), either fresh or aged. TF concentration was 1103.5±21.4 and 1400.6±65.8 ppm F for NaF/SiO₂ and MFP/CaCO₃ formulations, respectively. While in NaF/ SiO₂-based formulation all F was soluble, in MFP/CaCO₃-based the percentage of insoluble F was 19.9±2.8% and 38.8±2.7%, respectively in fresh and aged samples. Under fasting, volunteers ingested purified water or a toothpaste suspension (49.5 µg TF/kg body weight). Unstimulated saliva was collected until 3 h after ingestion and area under the curve (AUC) of salivary F concentration versus time was calculated. Urine was collected 24 h before and after ingestion and difference in F excretion was evaluated. F was determined using ion-selective electrode. Data were analyzed by two-way ANOVA.

Result: The effect of formulation was statistically significant for AUC, with lower values found for the MFP/CaCO₃ groups (p<0.05). Moreover, aging significantly reduced AUC (from 5.4±0.7 to 3.7±0.7 µg FxmL^-1xmin) and F excretion (from 1.3±0.6 to 0.8±0.4 mg F/day) for the MFP/CaCO₃ formulation (p<0.05), but not for the NaF/silica-based.

Conclusion: Regarding fluorosis risk, the findings suggest that MFP/CaCO₃-based toothpastes, even containing higher TF concentration, may be as safe as the NaF/SiO₂-based ones.