IADR Abstract Archives
Fluoride Release and Uptake into Hydroxyapatite from Experimental Dental Varnish
Fluoride releasing dental varnishes (F-varnish) typically contain 5% NaF within a resin or rosin base. The sodium fluoride concentration ([NaF]) that yields optimal fluoride enamel uptake, release, and anti-caries efficacy is unknown. Also, there is controversy on whether the release rate of fluoride into saliva is predictive of the fluoride uptake into enamel. Objectives: measure fluoride uptake (loosely- and tightly-bound) into hydroxyapatite (HAp) discs and fluoride release as a function of [NaF] in F-varnish. Methods: triplicate sets of F-varnish containing 5.0%, 2.5%, 1.25%, and 0.625% (wt/wt) NaF were prepared. 0.01-0.02g F-varnish was applied to one side of a HAp disc. Fluoride release into a continuous flow of 30mmol/L KCl at 1 mL/min was measured over 3h. The HAp discs were then cleaned and loosely-bound fluoride extracted overnight in KOH (1.0mL, 1.0mol/L). Tightly bound fluoride was extracted via serial extractions in HClO4 (1.0mL, 0.5mol/L). The extraction solutions were neutralized and analyzed via fluoride ion-selective electrode. Results: the cumulative fluoride release profile increased hyperbolically over 3h. The total fluoride released at 3h ([F]180) increased as a function of [NaF] . The time for 50% (t50) of the fluoride to be released was ≤ 32min for all varnishes. Loosely- and tightly-bound fluoride increased to 2.5% NaF and plateaued.
[NaF]% | [F] Tightly bound (µg/mL) | [F] Loosely bound (µg/mL) | [F]180 released (µgF/mgVarnish) | t50 (minutes) |
0.625 | 0.10(0.03)a | 0.09(0.05)c | 0.07(0.23)f | 4.40 |
1.25 | 0.15(0.02)a | 0.26(0.12)d | 1.87(0.86)g | 31.95 |
2.5 | 0.25(0.03)b | 1.20(0.40)e | 2.47(0.47)g | 26.10 |
5.0 | 0.19(0.05)b | 1.18(0.07)e | 3.82(0.84)h | 19.70 |
Values in the table are mean(standard error).
Superscripts indicate groups that are not significantly different in each category (ANOVA, Newman-Keuls, p<0.05).
Conclusions: In this study, optimal [NaF] is 2.5% for saturating all the available tight and loose binding sites of the HAp disc. Fluoride release into solution is not a reliable indicator of fluoride uptake. Further studies using enamel are planned.