## 4 Discussion  
This study assessed the influence of two etidronate-containing irrigants and EDTA on the proteolytic activity of NaOCl and its ability to remove the smear layer. We found that the effect of HEDP-containing irrigants on the tissue-dissolving ability of NaOCl was manufacturer(formulation)-dependent. ID9% and ID15% significantly decreased the proteolytic activity of NaOCl, showing no significant differences from EDTA (mixed), while the sequential use of NaOCl and EDTA and all DR concentrations significantly increased the proteolytic activity of the former. The most effective smear layer removal was observed after irrigation with NaOCl combined with EDTA or DR (all concentrations); however, in the NaOCl + EDTA and DR18% groups, it was accompanied by moderate to severe erosion. Irrigation with ID did not result in smear layer removal or dentin erosion. Although the exact compositions of the irrigants used in this study are not disclosed, it may be hypothesized that the differences in the effects of etidronates provided by different manufacturers can be explained by the differences in their formulations. This may also explain the controversy in the previous studies regarding the tissue-dissolving and smear layer-removing properties of HEDP. A number of studies have assessed the proteolytic effect of HEDP combined with NaOCl. [PERSON] et al. assessed the ability of NaOCl alone or combined with DR9% to \begin{table}
\begin{tabular}{c c c c c} \hline \hline
**Groups** & **Apical Third** & **Middle Third** & **Coronal Third** & _p-Value_1  \\ \hline NaOCl & 1 (1; 1) \({}^{\text{Aa}}\) & 1 (1; 1) \({}^{\text{Aa}}\) & 2 (2; 2) \({}^{\text{ADb}}\) & 0.000335 \\ \hline DW & 1 (1; 1) \({}^{\text{A}}\) & 1 (1; 1) \({}^{\text{A}}\) & 1 (1; 1) \({}^{\text{B}}\) & na \\ \hline NaOCl + EDTA & 3 (1.5; 3) \({}^{\text{Ba}}\) & 2 (2; 2.75) \({}^{\text{Ba}}\) & 3 (3; 3) \({}^{\text{Cb}}\) & 0.0302 \\ \hline NaOCl/DR9\% & 1.5 (1; 2) \({}^{\text{CDa}}\) & 1 (1; 1.75) \({}^{\text{Aa}}\) & 2 (2; 2) \({}^{\text{Ab}}\) & 0.000255 \\ \hline NaOCl/DR15\% & 1 (1; 1) \({}^{\text{Aa}}\) & 2 (2; 2) \({}^{\text{Bb}}\) & 2 (2; 2) \({}^{\text{Ab}}\) & \textless{}0.0001 \\ \hline NaOCl/DR18\% & 2 (1.25; 2) \({}^{\text{BCa}}\) & 3 (3; 3) \({}^{\text{Cb}}\) & 2.5 (2; 3) \({}^{\text{Db}}\) & 0.0000858 \\ \hline NaOCl/ID9\% & 1 (1; 1) \({}^{\text{AD}}\) & 1 (1; 1) \({}^{\text{A}}\) & 1 (1; 1.75) \({}^{\text{B}}\) & 0.174 \\ \hline NaOCl/ID15\% & 1 (1; 1) \({}^{\text{A}}\) & 1 (1; 1) \({}^{\text{A}}\) & 1 (1; 1) \({}^{\text{B}}\) & na \\ \hline NaOCl/ID18\% & 1 (1; 1) \({}^{\text{A}}\) & 1 (1; 1) \({}^{\text{A}}\) & 1 (1; 1) \({}^{\text{B}}\) & na \\ \hline \(p\) \({}^{\star}\) & \textless{}0.0001 & \textless{}0.0001 & \textless{}0.0001 & \\ \hline \hline \end{tabular} \({}^{\text{ABCD}}\) different letters indicate statistically significant differences between the irrigants (in the columns); \({}^{\text{ab}}\) different letters indicate statistically significant differences between the root thirds (in the rows); \({}^{\star}\) between the groups; \({}^{\text{1}}\) between the root canalirds; na—not applicable.  
\end{table} 
Table 4: The median (q1; q3) scores for the dentin erosion after irrigation with the studied solutions. dissolve shrimp tissue after immersion in the irrigants for 30 s [10]. The authors found that 9% HEDP (DR) did not hamper the tissue-dissolving ability of a 2.5% NaOCl solution. The effect of a continuous chelation protocol with the use of 18% HEDP was assessed by [PERSON] et al. In their study, a 15 min immersion in 2.25% NaOCl alone or in a mixture of 5% NaOCl with 18% HEDP provided a more prominent proteolytic activity compared to that of Na4 EDTA-NaOCl mixture and saline [71]. In a study by [PERSON] et al., the mean percentage weight reductions of specimens prepared from porcine palatal mucosa were 60.5% and 46.8% for 5% NaOCl and 5% NaOCl mixed with etidronate, respectively [44].