# Fluoride Ion Release Characteristics of Fluoride-Containing Varnishes--An In Vitro Study
## 4 Discussion  
The enamel surface around orthodonically placed brackets is a retention site and shows increased risk of caries. In an in vitro study by [PERSON] et al. [19], it was shown that new demineralization occurred in only 7.7% of cases during the use of a fissure sealant as a bracket sealant, whereas in the control group with a conventional attachment of brackets without environmental sealing, the rate was 19.2%. Due to statistical insignificance, the authors questioned the use of varnishes to prevent white spots. In contrast, [PERSON] et al. demonstrated that tooth surfaces sealed with a fissure sealant developed 80% fewer occurrences of demineralization than the control group without sealant, and this difference was significant [20]. It has been reported that the use of fluoride-releasing materials around the bracket environment is beneficial to reducing white spot lesions in patients undergoing fixed appliance therapy [21,22]. To prevent white spot lesions, fluoride release should be prolonged [23]. This study examined fluoride ion release from different fluoride-releasing varnishes over a set time period based on an examination solution. Fluoride-free hydroxyapatite discs were used to prevent false measurements due to the fluorides that can be released from human enamel. An investigation on natural human or bovine teeth was discussed in advance during the planning of the study and was rejected because its use harbors the risk of a shift in the measured values due to fluorides that could detach from tooth enamel. The release of fluoride ions from glass ionomer cement is a diffusion process [9]. Environmental temperature changes alter the diffusion behavior of the same material and can thereby affect the fluoride ion characteristics of the varnishes [24]. To simulate extreme thermal interactions of cold and hot food intake, three runs of a thermocycling process were used. Each run consisted of 60 cycles at 5 and 55 \({}^{\circ}\)C. Thermocycling is a well-known methodology for simulating thermal alteration [25,26], and the temperatures used in this study have been advocated for the last 20 years for testing dental materials [27]. To ensure the comparability of this study with others, standardized test procedures were used. Measuring fluoride concentrations by means of a fluoride ion electrode has been described previously in several studies [18,28,29]. \begin{table}
\begin{tabular}{c c c c c} \hline \hline \multirow{2}{*}{**Group**} & \multicolumn{4}{c}{**Measurement Timepoint**} \\ \cline{2-5}  & **T0** & **T1** & **T2** & **T3** \\ \hline
1 vs. 2 & \textless{}0.001 *** & \textless{}0.001 *** & 0.052 & \textless{}0.05 ** \\
1 vs. 3 & \textless{}0.001 *** & \textless{}0.001 *** & \textless{}0.001 *** & \textless{}0.001 *** \\
1 vs. 4 & \textless{}0.001 *** & \textless{}0.001 *** & \textless{}0.001 *** & \textless{}0.001 *** \\
2 vs. 3 & \textless{}0.001 *** & \textless{}0.001 *** & \textless{}0.001 *** & \textless{}0.001 *** \\
2 vs. 4 & \textless{}0.001 *** & \textless{}0.001 *** & \textless{}0.001 *** & \textless{}0.001 *** \\
3 vs. 4 & \textless{}0.001 *** & \textless{}0.001 *** & \textless{}0.001 *** & \textless{}0.001 *** \\ control vs. varnishes & \textless{}0.001 *** & \textless{}0.001 *** & \textless{}0.001 *** & \textless{}0.001 *** \\ \hline \hline \end{tabular}  
*** = significance (\(p\leq 0.005\)) Exact Sig. [2 \(\times\) (1-tailed Sig.)]. *** = significance (\(p\leq 0.05\)) Exact Sig. [2 \(\times\) (1-tailed Sig.)]. Group classification: 1, CaF discs; 2, Protecto CaF\({}_{2}\) Nano; 3, Bifluorid 12; 4, Fluor Protector S.  
\end{table} 
Table 4: Mann–Whitney U test results for differences between groups regarding fluoride release (not corrected for ties). In the literature, no study was found that measured dissolved fluoride release using a fluoride ion electrode and also included thermal alteration of the tested products by thermocycling.