Aims. A glide path is created prior to root canal instrumentation by nickel-titanium (NiTi) rotary files to increase the efficiency and safety of cleaning and shaping. This study aimed to assess root canal transportation in use of different glide path files in curved canals. Materials and Methods. 30 sound mesiobuccal root canals of mandibular molars with 20° to 40° curvature were selected and randomly assigned to 3 groups of EdgeGlidePath (EGP, EdgeEndo), One-G (Micro-Mega), and Neolix (Neoniti). The specimens were scanned before and after glide path creation by microcomputed tomography (micro-CT). The pre- and postoperative micro-CT scans were superimposed, and the degree of canal transportation and centering ratio were measured at 1, 3, 5, and 7 mm distances from the apical foramen. Statistical Analysis. The data were analyzed by two-way and one-way ANOVA. Results. The effects of distance from the apical foramen and instrument type and the interaction effect of the two were not significant on the centering ability of the files or canal transportation. Conclusion. EdgeGlidePath, One-G, and Neolix files fabricated from the conventional NiTi alloy or heat-treated M-Wire alloy showed similar performance regarding centering ability and canal transportation in glide path preparation in curved canals.

Background. Root canal preparation with nickel-titanium (NiTi) instruments may lead to the formation of microcracks in the root canal wall. Vertical root fractures may initiate from dentinal cracks, and eventually necessitate tooth extraction.Objectives. This study aimed to assess the effect of the instrumentation of curved root canals of mandibular molars with the 2Shape (2S) sequential rotary, EdgeFile ® X1 (EFX1) reciprocating and NeoNiTi (NN) rotational single-file systems on the formation of dentinal microcracks with the use of micro-computed tomography (micro-CT). Material and methods.Thirty curved mandibular molar root canals were instrumented with the 2S, EFX1 and NN systems (10 in each group). The teeth underwent micro-CT before and after instrumentation. Next, the pre-instrumentation and post-instrumentation cross-sectional images were evaluated and compared for the detection of dentinal microcracks. The number of microcracks in each group was calculated and reported as percentage. The data was analyzed using the McNemar's test with the IBM SPSS Statistics for Windows software, v. 25.0 (α = 0.05).Results. Out of the 29,280 cross-sectional images evaluated in this study, 11.5% showed dentinal microcracks (n = 3,362). On the post-instrumentation images, the frequency percentage of microcracks was 12.0% (n = 585) in the 2S group, 8.8% (n = 402) in the EFX1 group and 13.3% (n = 694) in the NN group. All of the microcracks detected on the post-instrumentation images were also present on the preinstrumentation images and no new microcracks were formed after root canal instrumentation with the aforementioned systems.Conclusions. Root canal instrumentation with the 2S, EFX1 and NN systems did not result in the formation of new dentinal microcracks.

Objectives: This study aimed to compare cone-beam computed tomography (CBCT) and micro-computed tomography (micro-CT) for evaluation of canal transportation and centering ratio after instrumentation of curved canals. Materials and Methods: A total of 20 mesiobuccal canals of mandibular molars were prepared by sequential rotary system. All specimens underwent CBCT and micro-CT before and after instrumentation and the magnitude of transportation and centering ratio were measured. The accuracy and the agreement between the two modalities were calculated considering the acceptable transportation of ≤ 0.15 mm. The agreement between the modalities was also assessed by calculating the intraclass correlation coefficient (ICC). Results: Transportation was detected by both modalities at all distances from the apex after instrumentation. Agreement between the two modalities in assessment of canal transportation was observed in 16 specimens at 1 mm, 17 specimens at 3 mm, and 15 specimens at 5 and 7 mm from the apex, out of 20 specimens, yielding 80%, 85%, 75% and 75% accuracy, respectively. ICC for transportation and centering ratio was much lower than 0.75 indicating poor agreement between the modalities. Conclusions: CBCT and micro-CT do not have a good agreement in assessing transportation and centering ratio. Micro-CT is still recommended for evaluating transportation in vitro, due to higher resolution and better visualization of details. Clinical relevance: CBCT is recommended for assessment of canal transportation in the clinical setting; however, it cannot replace micro-CT for in vitro studies, and micro-CT remains the modality of choice for in vitro assessments.