# Fluoride Ion Release Characteristics of Fluoride-Containing Varnishes--An In Vitro Study
## 3 Results  
The results of the Kruskal-Wallis H test indicated that there were significant, substantial differences between the studied materials for the fluoride concentration measurement at each timepoint. Excluding the control group of this statistical test also implied significant differences between the three varnishes at all measurement timepoints (Table 2). Figure 1: Setup of the present study (TISAB III: Total Ionic Strength Adjustment Buffer III, F\({}^{-}\): released fluoride ion concentration). The descriptive statistical values for almost all products (Table 3) showed a drop to a low, mostly homogeneous level after the first thermocycling from T1 to T2. This trend roughly corresponded with that for the control group, where the median fluoride concentration at baseline was 0.037 ppm at T0, dropping to 0.015 ppm at T1 after the first thermocycling, then further to 0.008 ppm at T2. When considering the overall values for the products with regard to their fluoride release, Bifluorid 12 always had the highest concentrations over all parameters and measurement times. The median values for all carrier discs with Bifluorid 12 varied between a maximum of 37.667 ppm at T1 and a minimum of 0.927 ppm at T3. At baseline, the fluoride concentration was 8.582 ppm. Fluor Protector S showed a maximum median value of 3.357 ppm at T1 and a minimum of 0.108 ppm at T2. The fluoride ion release at T3 was similar to that at T2, with a concentration of 0.114 ppm. The preliminary baseline test measurement of Fluor Protector S indicated a fluoride release of 1.455 ppm. These products were followed by Protecto CaF\({}_{2}\) Nano one step seal (T0 = 0.076 ppm, T1 = 0.085 ppm, T2 = 0.009 ppm, T3 = 0.012 ppm). The CaP discs, which served as a control group, showed the least amount of fluoride ions released into the surrounding solution at all measurement times (T0 = 0.037 ppm, T1 = 0.015 ppm, T2 = 0.008 ppm, T3 = 0,010 ppm). The control group and varnishes differed significantly from one another, as observed by pairwise comparison of independent samples (Table 4). \begin{table}
\begin{tabular}{c c c c c} \hline \hline
**With Control Group** & **T0** & **T1** & **T2** & **T3** \\ \hline Asymp. Sig. & \textless{}0.001 *** & \textless{}0.001 *** & \textless{}0.001 *** & \textless{}0.001 *** \\
**Without Control Group** & **T0** & **T1** & **T2** & **T3** \\ Asymp. Sig. & \textless{}0.001 *** & \textless{}0.001 *** & \textless{}0.001 *** & \textless{}0.001 *** \\ \hline \hline N = 40 (with control group) or N = 30 (without control group), \(n=10\) per group. T0 = preliminary test; T1 = 20 days thermocycling; T2 = 40 days thermocycling; T3 = 60 days thermocycling. *** = significance (\(p\leq 0.005\)). & \\ \end{tabular}
\end{table} 
Table 2: Kruskal-Wallis H test results for general differences between the four study groups regarding fluoride release. \begin{table}
\begin{tabular}{c c c c c} \hline \hline \multirow{2}{*}{**Material**} & \multicolumn{1}{c}{**T0**} & \multicolumn{1}{c}{**T1**} & \multicolumn{1}{c}{**T2**} & \multicolumn{1}{c}{**T3**} \\ \cline{2-5}  & **Median (ppm)** & **Median (ppm)** & **Median (ppm)** & **Median (ppm)** \\  & **(95\% CI Low-High)** & **(95\% CI Low-High)** & **(95\% CI Low-High)** & **(95\% CI Low-High)** & **(95\% CI Low-High)** \\ \hline Bifluorid 12 & 8.582 & 37.667 & 1.837 & 0.927 \\  & (8.037-10.900) & (32.167\({}^{-43}\).867) & (1.153-4.240) & (0.666-1160) \\ Fluor Protector S & 1.455 & 3.357 & 0.108 & 0.114 \\  & (1.380-1.523) & (2.923-3.713) & (0.106-0.209) & (0.089-0.278) \\ Protecto CaF\({}_{2}\) Nano & 0.076 & 0.085 & 0.009 & 0.012 \\  & (0.070-0.078) & (0.039-0.224) & (0.008-0.011) & (0.011-0.012) \\ CaP discs & 0.037 & 0.015 & 0.008 & 0.01 \\  & (0.036-0.037) & (0.012-0.023) & (0.008-0.010) & (0.010-0.011) \\ \hline \hline \end{tabular}
\end{table} 
Table 3: Descriptive statistical values of fluoride ion release (in ppm) for the tested materials at all measurement times.