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Background: Eccentric instruments have been proposed as more effective and less time‐consuming for endodontic instrumentation. Aim: To compare biomechanical outcomes of different instrumentation systems and time undertaken for instrumentation in resin prototypes. Design: Sixty standardized prototypes of mandibular second primary molars were instrumented according to the following systems: K‐files, ProTaper Next (PTN), XP‐endo Shaper (XPS), XP‐endo Finisher (XPF), XP–Clean (XPC), and Sequence Baby File (SBF; n = 10/each). Irrigation was performed with saline with simultaneous aspiration, and time spent was recorded. The prototypes were micro‐CT‐scanned before and after the instrumentation, and image sets were reconstructed and registered. Non‐instrumented areas, accumulated debris, removed root material volume, and canal transportation were quantified. Data were analyzed through ANOVA, the Kruskal–Wallis test, and the Wilcoxon signed‐rank test (α = 5%). Results: K‐files and SBF resulted in more instrumentation time (p <.05). SBF, XPC and PTN removed less root dentine (p <.05), but PTN left more untouched areas (p <.05). Accumulated debris were lower for XPC and SBF (p <.05). Canal transportation was similar among the groups. Conclusion: Rotary systems reduced instrumentation time, whereas SBF and XPC resulted in more conservative instrumentation, with less debris accumulation and non‐instrumented areas. A dedicated paediatric endodontic system (SBF) outperformed eccentric instruments in terms of effectiveness. [ABSTRACT FROM AUTHOR]

Aim: The aim of this study was to investigate variations in the root canal morphology of human mandibular premolars using micro-computed tomography (micro-CT).Methods: Three-dimensional images of 150 extract mandibular premolars were obtained using micro-CT. The root canal configurations were analyzed using Vertucci´s classification, volume and area of apical segment and considering the total canal length. The root canal length and apical diameter were two- dimensionally analyzed.Results: The teeth were classified in the following Vertucci´s types: I (67.3%), V (16.7%), III (10%), IV (2.7%), VII (1.3%), and II (0.7%) with 1,3% not classifiable. The mean for the total length was 12.63 ± 2.20. The mean volume was 7.64 ± 5.68 mm³ for the total length and 0.89 ± 1.34 mm³ for the apical segment (5 mm). The area at 5 mm from the apical foramen was 10.57 ± 4.33 mm³ and the apical diameter was 1.68 ± 0.72 mm. Apical deltas were found in 4.7%. Lateral canals were observed in 8% and secondary in 14.7% of the teeth, with 4.7% having both a lateral canal and a secondary canal. Branches were found in 44% of the elements. Two-dimensional data showed that the mean of the total lengh and the apical diameters of the canals were 12.63 mm and 1.68 mm, respectively.Conclusion: There was a high prevalence of complex morphology through the canal and variations at the apical critical zone in mandibular premolars. [ABSTRACT FROM AUTHOR]