Diurnal and nocturnal salivary fluoride bioavailability following brushing with high- or regular-fluoride dentifrices.

This study evaluated salivary fluoride (F) bioavailability during diurnal and nocturnal periods after using a high-fluoride or regular dentifrice. Fifteen healthy adults participated in a double-blind crossover study, brushing with either a 1450 ppm F or 5000 ppm F dentifrice. Saliva was collected at pre-brushing, immediately after brushing, and at 5 min, 2, 4, and 8 h post-brushing in both periods. Fluoride concentrations were measured using an ion-selective electrode and analyzed with the Wilcoxon matched-pairs and Kruskal-Wallis tests (5% significance). At pre-brushing, no statistically significant differences were detected between groups. Both dentifrices increased salivary fluoride concentrations, reaching peak levels immediately after brushing. However, the high-fluoride dentifrice consistently maintained significantly higher concentrations compared with the regular formulation. During the nocturnal period, elevated fluoride levels persisted for up to 8 h with the high-fluoride dentifrice, whereas concentrations returned to pre-brushing levels within 2 h with the regular formulation. In conclusion, fluoride bioavailability was greater and more sustained during the nocturnal period than during the diurnal period, emphasizing the influence of brushing time on salivary fluoride retention. High-fluoride dentifrice further enhanced this effect across both periods.