## 4 Discussion
Additionally, the safety zone was defined as the mesial area of the mesial root with a thicker dentin layer [38]. The safety zone is usually minimally instrumented with endodontic instruments. In this study, no significant difference was found between the groups in terms of the thickness of the danger zone (\(p>0.05\)). This result is consistent with the results of [PERSON] et al. 's study on the danger zone [39]. In other words, these results demonstrate the reliability of both systems when preparing mesial root canals of mandibular molars because neither system excessively removed the dentin in the furcation area. Canal transportation equals the deflection (in millimeters) of the root canal from its original axis after root canal preparation in comparison to before preparation [40]. [PERSON] et al. showed that canal transportation of \(>\)0.3 mm causes adverse effects on root canal obturuation [41]. In accordance with this, the canal transportation values obtained in all sections for all the groups in the present study were \(<\)0.3. In this study, canal transportation values were measured for all groups at distances of 2 mm, 5 mm, and 8 mm from the apical foramen. As a result of these measurements, a statistically significant difference was found among the groups in terms of canal transportation (\(p<0.05\)). According to these results, regardless of the Ni-Ti instrument system used, more transportation was observed in the CAC-OR and CAC-PU groups compared to the TAC-OR and TAC-PU groups at all levels where the canal transportation value was measured. This result was in line with [PERSON] et al. 's study, which compared the effects of traditional and conservative access cavities on shaping efficiency and transportation values in upper molars [18]. In another similar study, [PERSON] et al. reported that access cavities with an ultraconservative approach in mandibular teeth cause more transportation than traditional cavities. The reason for obtaining these results is due to the presence of coronal interferences of access cavities with conservative and ultraconservative approaches, which causes the instruments to not provide a straight entry into the canals and results in an uneven force distribution [17; 42]. In contrast, in [PERSON] et al. 's study on the shaping efficiency of traditional and conservative access cavities and the preservation of dentin tissue in mandibular and upper molar teeth, no significant difference was found in terms of transportation post-instrumentation with WaveOne Gold in the two different access cavities evaluated [39]. Additionally, [PERSON] et al. revealed that transportation and centering ability were not statistically affected by traditional versus conservative access cavities [43]. For conservative access cavities, the use of 3D imaging technology, an operating microscope, a good light source and illumination, ultrasonic tips, irrigation activation methods, and the use of new-generation Ni-Ti rotary instrument systems were found to minimize the negative effects on clinical procedures related to root canal treatment. Within the limitations of this in vitro study, the effects of TACs and CACs on the shaping efficiencies of two different Ni-Ti instrument systems were evaluated using micro-CT. In this regard, future experiments should be encouraged with larger sample sizes, the use of irrigation activation methods, the incorporation of different shaping tools with fewer expansion angles, and over long-term clinical studies.