## 4 Discussion  
The current in vitro study aimed to establish the degree of dentinal tubule occlusion and mineral deposition on the dentin surface when using three different toothpastes containing n-HAp as an active ingredient. In our study none of the three n-HAp toothpastes determined complete occlusion of the dentinal tubules. Previous studies also showed partial closure of the dentinal tubules after an acid attack when using Biorepair Plus Sensitive toothpaste [32]. A study that tested n-HAp toothpaste Renamel (Sangi, Tokyo, Japan) had also demonstrated partial occlusion of dentinal tubules. Only one study reported total closure of dental tubules when an experimental pure n-HAp desensitizing toothpaste was tested [13]. Regarding the occlusion of dentinal tubules when comparing the toothpaste containing nano-HAp crystals to other products, the results of previous studies are contradictory. The toothpaste containing 1% n-HAp crystals led to a significantly higher percentage of tubule occlusion when compared to proargin technology [9]. Toothpastes containing 2 wt% n-HAp determined a reduction of DH in patients as a result of enamel surface restoration and dentinal tubule closure [21; 33; 34]. Some studies confirmed the efficacy of n-HAp denittifices in achieving tubule occlusion [35]. On the contrary, in other studies there was no statistical difference between n-HAp products (Biorepair Plus) and Pronamel (Sensodyne) regarding the protection against an acid attack [29]. It was demonstrated that polishing the dentin surface with n-HAp led to partial tubular closure, while 30% S-PRG (surface pre-reacted glass-ionomer) filler-containing paste determined complete tubular closure [36]. \begin{table}
\begin{tabular}{c c c c c c c} \hline \hline \multirow{2}{*}{**Ion Concentration**} & \multicolumn{2}{c}{**Levene Test**} & \multicolumn{2}{c}{**Kruskal-Wallis Test**} & \multicolumn{2}{c}{**Post-Hoc LSD Test**} \\ \cline{2-7}  & **Statistics** & \(p\) **Value** & **Chi-Square** & \(p\) **Value** & **Statistically Significant Results** & \(p\) **Value** \\ \hline \multirow{4}{*}{Carbon} & \multirow{4}{*}{0.855} & \multirow{4}{*}{0.473} & \multirow{4}{*}{24.464} & \multirow{4}{*}{0.000 *} & Group = 1 & Group = 3 & 0.005 * \\ \cline{5-7}  & & & & Group = 1 & Group = 4 & 0.000 * \\ \cline{5-7}  & & & & Group = 2 & Group = 3 & 0.001 * \\ \cline{5-7}  & & & & Group = 2 & Group = 4 & 0.000 * \\ \cline{5-7}  & & & & Group = 3 & Group = 4 & 0.000 * \\ \hline \multirow{4}{*}{Calcium} & \multirow{4}{*}{1.843} & \multirow{4}{*}{0.157} & \multirow{4}{*}{8.333} & \multirow{4}{*}{0.000 *} & Group = 1 & Group = 4 & 0.000 * \\ \cline{5-7}  & & & & Group = 2 & Group = 3 & 0.018 * \\ \cline{5-7}  & & & & Group = 2 & Group = 4 & 0.000 * \\ \cline{5-7}  & & & & Group = 3 & Group = 4 & 0.043 * \\ \hline \multirow{4}{*}{Phosphorous} & \multirow{4}{*}{1.364} & \multirow{4}{*}{0.269} & \multirow{4}{*}{12.665} & \multirow{4}{*}{0.000 *} & Group = 1 & Group = 3 & 0.045 * \\ \cline{5-7}  & & & & Group = 1 & Group = 4 & 0.000 * \\ \cline{5-7}  & & & & Group = 2 & Group = 3 & 0.004 * \\ \cline{5-7}  & & & & Group = 2 & Group = 4 & 0.000 * \\ \cline{5-7}  & & & & Group = 3 & Group = 4 & 0.012 * \\ \hline \multirow{4}{*}{Oxygen} & \multirow{4}{*}{1.169} & \multirow{4}{*}{0.335} & \multirow{4}{*}{9.055} & \multirow{4}{*}{0.000 *} & Group = 1 & Group = 4 & 0.000 * \\ \cline{5-7}  & & & & Group = 2 & Group = 4 & 0.000 * \\ \cline{5-7}  & & & & Group = 3 & Group = 4 & 0.004 * \\ \cline{5-7}  & & & & Group 3 & Group 4 & 0.000 * \\ \hline \hline \end{tabular} Statistical test resuls of ion concentrations and dentinal tubule occlusion score comparison between the study and control groups. * statistically significant differences between groups.  
\end{table} 
Table 4: Statistical test results when comparing the concentration of carbon, calcium, phosphorus, and oxygen ion concentration and the dentinal tubule occlusion score in groups.