Assessment of Loosely-bound and Firmly-bound Fluoride Uptake by Tooth Enamel from Topically Applied Fluoride Treatments

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Abstract
The amounts of loosely-bound fluoride (F) deposited on human enamel by two topical F treatments were measured with use of a constant-composition F washing method. Enamel biopsies conducted before treatment and after the washing were used for determination of the firmly-bound F uptake. The results showed that (1) the washing system did not remove F from untreated enamel surface, (2) a four-minute application of an acidulated phosphate fluoride (APF) gel deposited 27.2 (2.4) (mean, S.E.) μg of loosely-bound Fper cm2 of enamel surface and 186 (111) ppm of firmly-bound F in the outer 10 μm of enamel, and (3) a four-minute application of a pH-2.1 dicalcium phosphate dihydrate (DCPD)-forming solution followed by APF produced 44.9 (3.1) μg/cm2 of loosely-bound F and 1280 (354) ppm of firmly-bound F in the outer 10 μm of enamel. The results showed that the DCPD pre-treatment effectively enhanced the enamel reactivity with F, so that the DCPD-APF treated enamel acquired greater amounts of both loosely-bound F and firmly-bound F than did samples treated with APF alone.