In Vitro Evaluation of F–Release and Deposition for F-Varnishes

Fluoride releasing varnishes (F-varnish) are used in dentistry primarily for caries prevention and reduction of dentin hypersensitivity. The mechanism of action and thus the optimal parameters for this therapy is not known.  Objective: to investigate the relationship between fluoride released into the surrounding solution from an F-varnish, the fluoride taken up by an untreated hydroxyapatite (HA) disc in that solution, and the fluoride uptake by the HA disc that had the varnish applied.  Method: HA discs received a layer of F-varnish of known mass.  These disks were allowed to stand for 2min then immersed in stirred saliva-like solution (SLS) for (30, 60, 120 or 180min).  During the exposure 0.5 mL aliquots of the SLS were collected for F analysis at different time points (1 to 180min). The varnish was removed with acetone and the fluoride taken up by the disk was extracted three times in 1mL HClO₄ (0.5mol/L).  The HClO₄ extraction solutions were neutralized with NaOH/TISAB and analyzed for fluoride by fluoride ion-selective electrode (F-ISE).  The aliquots of SLS taken over time were also analyzed via F-ISE. Unvarnished disks that had been placed in the 180min solution and a blank control disk were extracted and the solutions analyzed for fluoride. These experiments were repeated in triplicate for two different NaF containing F-varnishes.  Result:   The fluoride deposited on the F-varnish treated disks was dependent on the length of time the F-varnish was on the disk.  F-varnish-A (y=0.012*time; R²=0.9996); F-varnish-B (y=0.047*time; r²=0.9584); the cumulative amount released increased asymptotically over time for both F-varnishes. The relationship between F-released and F-deposited had a positive slope but was different for the two F-varnishes. F-deposited on disks adjacent to the F-varnished disks was not measurable. Conclusion: F-released may be a good predictor of the F-deposited on the treated surface.