## 4 Discussion  
The current _ex vivo_ study was conducted to quantify and compare the amount of debris extrusion that was caused during cleaning and shaping of oval-shaped root canals using two different instrumentation systems specifically designed to perform in non-round root canals: the full sequence SAF and the XP-endo shaper plus sequence. Both instruments are made from NiTi alloy, but each using different characteristics of this unique alloy. The SAF is made from a NiTi tube which is cut to the form of a delicate lattice, with a special design that allows the instrument to be compressed from its 1.5 mm diameter to the dimensions of a #20 K file. This ability is based on the design of the lattice, combined with the high flexibility of the alloy and allows the file to adapt itself to any shape of root canal (Figure 3). It is used with pecking motion and with every inward move it goes through such compression (above) and back to its original form when moved outwards. The XP-endo shaper and finisher both use the extreme flexibility of the NiTi alloy, which in their case is formed as a wire, but they also use the thermal transformation which is unique to this alloy. These files have a more straight form at room temperature but when inserted into the canal and attaining body temperature their form changes, enhancing their envelope of motion when rotated, which allows them to enter and shape/clean irregular recesses of the root canal, such as the oval canals that were used in the present study. Evidence indicates that with any file system, dentine particles and other debris can often be packed into the apical anatomical complexities and pushed beyond the apex with/by the attempts to reach the WL [3; 14]. Both instrumentation sequences that were tested in the present study did push debris beyond the apical foramen. Apical extrusion of debris by the full SAF sequence has been recently reported and was found to be less than that extruded by ProTaper Next, followed by XP-endo finisher [3]. To the best of the authors' combined knowledge, the debris extrusion by the XP-endo shaper plus sequence is yet to be reported in the literature. In the present study, the full-sequence SAF exhibited significantly less debris extrusion compared to the XP-endo shaper plus sequence (\(p<0.001\)). Thus, the null hypothesis had to be rejected. When the SAF alone was previously compared with WaveOne as to their pushing of debris beyond the apex [14], glide path preparation was performed in both groups with #20 hand K files. Nevertheless, debris extrusion during this first stage of instrumentation was not recorded and not reported [14]. The present study took an approach similar to that of [PERSON] et al. [3], who reported that \begin{table}
\begin{tabular}{c c c c c c} \hline \hline  & **Full-Sequence** & **Full-Sequence** & **XP-Endo Shaper** & **XP-Endo Shaper** & **XP-Endo Shaper** \\  & **SAF** & **SAF** & **Plus Sequence** & **Plus Sequence** & **Plus Sequence** \\  & **Stage 1** & **Stage 2** & **Stage 1** & **Stage 2** & **Stage 3** \\ \hline Mean (SD) & 0.568 (0.434) & 0.471 (0.267) & 0.326 (0.077) & 0.788 (0.203) & 0.752 (0.197) \\ \hline Median & 0.570 & 0.425 & 0.328 & 0.815 & 0.770 \\ \hline Minimum & 0.340 & 0.310 & 0.200 & 0.110 & 0.340 \\ \hline Maximum & 1.070 & 0.650 & 0.490 & 1.040 & 1.160 \\ \hline \multirow{4}{*}{Percentiles} & 25 & 0.406 & 0.383 & 0.268 & 0.599 & 0.599 \\ \cline{2-6}  & 50 & 0.570 & 0.425 & 0.328 & 0.770 & 0.770 \\ \cline{1-1} \cline{2-6}  & 75 & 0.693 & 0.474 & 0.388 & 0.902 & 0.902 \\ \hline \hline \end{tabular}
\end{table} 
Table 1: Weight of apically extruded debris (mg). Data distribution. the contribution of the initial stage of glide path preparation to the total amount of debris extruded during the procedure may be substantial. The present results are in agreement and support this notion: the glide path preparation stage contributed 55% of the debris extrusion in the SAF group [3; 11].