## 3 Results  
Figure 3 shows a backscattered electron micrograph acquired into a CH-treated tooth canal at 15,000\(\times\) magnification (Figure 3A) and the relative spot EDX spectra (Figure 3B). Based on the different gray shades of the particles visible in the micrographs and the relative  
Figure 2: (**A**) Original SEM image where measures were performed; the red square shows where the image is cropped as seen in (**B**). (**C**) Enhancement of contrast highlighting white dots corresponding to CH particles, (**D**) image after binarization. results of the EDX microanalysis, two well-distinguishable phases may be identified. The darker phase, containing high amounts of Ca, P, and O, may be identified as the tooth dentin; the bright globular phase, containing mainly Ca, S, Ba, and O, may be identified as the CH paste remnants. The presence of barium sulfate (BaSO4) in the CH paste, as reported in the safety data sheet of the Calxyl(r) radiopaque (OCO praparate GmbH, Dirmstein, Germany), added for its X-ray opacity properties, allows clearly distinguishing the CH paste residues in the BSE images, giving to the paste a much brighter contrast compared to the dentin. Table 1 reports the average values of residual calcium hydroxide measured inside the root canal's selected areas according to instrument and level. The Kruskal-Wallis test shows significant differences among groups, both considering the individual levels and the whole root canal. Irisafe and XP-endo Finisher performed significantly better at the coronal level than the conventional endodontic needle irrigation. Moreover, XP-endo Finisher performed better than Endovac at this level. All instruments removed a significantly higher amount of CH than conventional endodontic needle irrigation at the middle level; moreover, Irisafe and XP-endo Finisher performed significantly better than Endovac. At the apical level, the amount of CH removed was significantly higher in the Irisafe and XP-endo Finisher groups than conventional endodontic needle irrigation and Endovac irrigation. When the whole canal is considered, all instruments showed better performance than conventional endodontic needle irrigation in removing CH. Among the three techniques, Irisafe and XP-endo Finisher were able to remove a significantly higher amount of CH than Endovac. When results were compared within groups to measure the performance among the three levels of the root canal, the Kruskal-Wallis test highlighted significant differences only respecting the conventional endodontic needle irrigation. Compared to the middle and coronal root canal walls, more CH was detected at the apical level. Figure 4 shows \begin{table}
\begin{tabular}{c c c c c c} \hline \hline  & \multicolumn{6}{c}{**Groups**} \\ \cline{2-6}  & **CENI** & **IS** & **EV** & **XPF** & **K-W \(p\)-Value** \\ \hline Coronal & 4.83 \(\pm\) 6.0 \({}^{\circ}\) & 0.88 \(\pm\) 0.7 & 2.56 \(\pm\) 2.7 \({}^{\lx@sectionsign}\) & 0.66 \(\pm\) 0.7 & 0.002 \\ \hline Middle & 4.91 \(\pm\) 5.6 \({}^{\#}\) & 0.53 \(\pm\) 0.9 & 1.40 \(\pm\) 1.7 \({}^{\star}\) & 0.68 \(\pm\) 1.1 & \textless{}0.001 \\ \hline Apical & 11.52 \(\pm\) 8.8 \({}^{\circ,\star}\) & 0.35 \(\pm\) 0.4 & 6.39 \(\pm\) 11.0 \({}^{\star}\) & 2.30 \(\pm\) 5.0 & \textless{}0.001 \\ \hline Total & 7.09 \(\pm\) 5.9 \({}^{\#}\) & 0.59 \(\pm\) 0.5 & 3.45 \(\pm\) 4.6 \({}^{\star}\) & 1.21 \(\pm\) 2.0 & \textless{}0.001 \\ \hline \hline \end{tabular} \({}^{\star}\)versus Irisafe and XP-endo Finisher \(p<\) 0.05; \({}^{\lx@sectionsign}\) versus XP-endo Finisher \(p<\) 0.05; \({}^{\#}\) versus Irisafe, Endovac, and XP-endo Finisher \(p<\) 0.05; \({}^{\circ}\) versus coronal and middle levels \(p<\) 0.05.  
\end{table} 
Table 1: Calcium hydroxide residues % (mean \(\pm\) SD) inside the root canal measured on SEM images. Figure 3: **(A)** SEM image showing the globular aspect of CH residues; arrows indicate the areas analyzed with EDX, **(B)** EDX spectra relative to areas indicated in **(A)**. an overview of representative SEM images from the experimental groups at 2, 5, and 11 mm levels.