n=3, IS group, n=3 and CI group, n=5) had to be replaced due to damage during the cross sectioning.

In the current study, mandibular canine teeth with oval cross-section canal were selected based on previous studies ([@ref22], [@ref23]). To ensure standardisation of the samples, the crowns of the teeth, all of which had a root size of 16 mm, were removed at the cemento-enamel junction. Obturation of the root canals using the vertical compaction technique was reported to provide a more homogeneous canal obturation than the single-cone and lateral compaction technique ([@ref23]). Thus, in the present study, the canals were obturated using the vertical compaction technique.

The gutta-percha removal processes were performed in a water bath at 37°C, with an intention to imitate the normal body temperature and allow the XP-endo Finisher to proceed the austenitic phase in the presence of heat.

Previous research has shown that using larger files during the preparation of the apical diameter of the root canal reduces the amount of obturation material remaining after the gutta-percha removal process ([@ref24]). However, excessive enlargement of root canals might reduce the amount of dentin remaining and reduce the resistance of the root canal, leading to the formation of vertical root fracture ([@ref25]). For this reason, the apical diameter of the canals was not enlarged in the present study. Solvent was not used with the NiTi rotary instruments in the present study. Along with friction, solvent softens gutta-percha and allows the files to easily reach the WL. However, as shown in a previous study, gutta-percha that is softened by solvent can easily reach to canal system complexities ([@ref26]); in this case, cleaning of the canals becomes difficult.

The repeated use of NiTi files can cause various problems, such as abrasion, distortion and microcracks in the surface of the file. As shown in previous studies ([@ref27], [@ref28]), cutting activities are reduced, and the instruments are more vulnerable to breakage. Thu