Effect of water rinsing after toothbrushing on fluoride ingestion and absorption

This investigation was done to determine the bioavailability of fluoride (F) after toothbrushing associated with different water rinsing procedures. Eight adult subjects participated in four experiments, conducted with a randomised, crossover design: (A) 2 min brushing with an F dentifrice, followed by three quick (3 x 2 s) rinses, each with 10 ml of water; (B) brushing as in A followed by one long-lasting (1 min) rinse with 5 ml of water combined with the toothpaste-saliva mixture; (C) brushing as in A followed by expectoration but without any water rinse afterwards; and (D) ingestion of the toothpaste as a slurry with 100 ml of de-ionized water. Blood samples were collected before and frequently for 6 h after each experiment and analyzed for F content. The area under the plasma F concentration vs. time curves (AUC) was calculated and the degree of F absorption estimated. AUC values obtained in experiment D were assumed to represent 100% F bioavailability. The plasma values recorded during experiment A were not significantly greater than the baseline values, indicating almost no F absorption when 3 quick water rinses were performed after toothbrushing. The degrees of F absorption after one long-lasting water rinse (B) were 7.6 +/- 4.2% and with no water rinse after toothbrushing (C) 23.8 +/- 13.5%, respectively. The results showed that the degree of F absorption after toothbrushing using an F toothpaste is strongly related to the mode of water rinsing.