Uptake and release of fluoride from fluoride-impregnated chewing sticks (miswaks) in vitro and in vivo

The purpose was to investigate the uptake and release of fluoride (F) from F-impregnated chewing sticks (miswaks). In the first series, 3-cm-long pieces were impregnated in 1, 2, 3 and 4% NaF solutions for 3 h, 1 day and 3 days (10 pieces/test). There was a dose-response effect with respect to both impregnation time and the concentration of the F solution. In the second and third series, totally 40 miswak pieces were impregnated in 3% NaF for 1 day and 3 days; the outer layer (bark) was separated from the inner spongy part (pulp) and analyzed separately. F was released from both parts, but somewhat more was released from the bark than from the pulp; a plateau was reached at around 30 min. In vivo, 9 healthy subjects used three products for 2 min in a crossover design: (1) a miswak impregnated in 3% NaF for 1 day, (2) a miswak impregnated in 3% NaF for 3 days, and (3) 1 g of F toothpaste (containing 1,450 ppm F as NaF) on a toothbrush. The highest F concentration at the approximal area was obtained after using the miswak impregnated in 3% NaF for 3 days compared with the other products (p < 0.05 or p < 0.01). To conclude, NaF-impregnated miswaks produced a rapid release of F in vitro as well as in vivo and may be an interesting vehicle for home care use for caries prevention in countries where they are used regularly.