Effect of preset torque setting on torque/force generation, shaping ability and surface changes of nickel titanium rotary instrument in different root canal curvature locations: An ex vivo study.

The aim of this study was to evaluate how preset torque settings influence the torque, vertical force, and root canal-centering ability of ProGlider and ProTaper NEXT nickel-titanium rotary instruments in canals with different curvature locations. Based on micro-computed tomography, mesial roots of human mandibular molars (25°-40° curvature) were allocated to the apical curvature (apical 1-5 mm) or the middle curvature (apical 5-9 mm) groups, and mandibular incisors (curvature <5°) to the straight canal group. Each group was subjected to automated instrumentation and torque/force measurement with the preset torque of 1, 2.5, or 5 N•cm. Canal-centering ratios were determined with micro-computed tomography. Instrument fracture occurred only in the 2.5 and 5 N•cm groups in curved canals. The preset torque setting and curvature location did not influence canal shaping ability.

Comparison of Torque, Screw-in Force, and Shaping Ability of Glide Path Instruments in Continuous Rotation and Optimum Glide Path Motion.

INTRODUCTION: This study aimed to analyze torque/force generation and transportation in double-curved canals instrumented with 3 types of glide path files using optimum glide path (OGP) motion in comparison with continuous rotation. METHODS: Sixty simulated double-curved canals were prepared with #10/0.05 or #15/0.03 HyFlex EDM Glidepath files (Coltene/Whaledent, Altstätten, Switzerland) or a #13/0.04 prototype MANI Glidepath file (Tochigi, Japan) using OGP motion or continuous rotation (n = 10 each). Canals were sequentially prepared to 20 mm and 22 mm (full working length) using automated root canal instrumentation and a torque/force analyzing device. Transportation was calculated at 1-9 mm from the apex. Data were compared using 2-way analysis of variance followed by a post hoc simple main effect test with Bonferroni correction and a Kruskal-Wallis test (α = 5%). RESULTS: All #10/0.05 instruments fractured. In the 22-mm preparation, the OGP motion resulted in lower clockwise torque and screw-in force than did continuous rotation (P < .05). In the 20-mm preparation, #15/0.03 instruments recorded a lower screw-in force for OGP motion than for continuous rotation (P < .05). Comparing the 2 preparation phases, OGP motion generated no significant differences; however, continuous rotation developed higher clockwise torque and screw-in force in the 22-mm preparation than in the 20-mm preparation (P < .05). There was no significant difference among the tested groups for transportation values. CONCLUSIONS: Compared with continuous rotation, OGP motion generated less screw-in force, lower clockwise torque, and similar transportation. The #15/0.03 HyFlex EDM instrument and the #13/0.04 prototype MANI instrument performed similarly well.

Cleaning and Shaping Ability of Gentlefile, HyFlex EDM, and ProTaper Next Instruments: A Combined Micro-computed Tomographic and Scanning Electron Microscopic Study.

INTRODUCTION: This ex vivo study aimed to evaluate the cleaning and shaping ability of a unique stainless steel rotary system (Gentlefile; MedicNRG, Kibbutz Afikim, Israel) compared with 2 nickel-titanium rotary instruments. METHODS: Thirty human mandibular premolars with a 15° to 25° curvature were equally distributed into 3 groups for final instrumentation with Gentlefile Red (#23/0.04), HyFlex EDM OneFile (#25/0.08∼; Coltene/Whaledent, Altstätten, Switzerland), and ProTaper Next X2 (#25/0.06v; Dentsply Sirona, Ballaigues, Switzerland) (n = 10/each). The untouched canal area, volume changes, and transportation were evaluated on pre- and post-instrumentation micro-computed tomographic images. Five random regions of the canal wall located 1-7 mm from the apical foramen were evaluated with scanning electron microscopy for superficial debris and a smear layer via a 5-point scoring system. Data were compared using the Kruskal-Wallis test with post hoc Dunn's pairwise comparison test with Bonferroni correction and Wilcoxon signed-rank test (α = 5%). RESULTS: All instruments generated no overt procedural errors. Untouched area and volume changes did not show any significant differences among the 3 groups (P > .05). The Gentlefile exhibited less transportation at the level of 5-7 mm from the apex compared with ProTaper Next (P < .05). The Gentlefile showed a smaller debris score than ProTaper Next and better smear layer removal than the others (P < .05). Complete cleanliness was not achieved by any of the systems investigated. CONCLUSIONS: Canals instrumented with the Gentlefile exhibited less transportation at the mid-root level and better cleanliness than those instrumented with HyFlex EDM and ProTaper Next.

Comparison of torque, force generation and canal shaping ability between manual and nickel-titanium glide path instruments in rotary and optimum glide path motion.

This study aimed to analyze force/torque generation and canal volume changes of NiTi rotary glide path preparation using HyFlex EDM Glide Path File in comparison to manual stainless steel K-file instrumentation. Thirty extracted mandibular incisors with a minimally curved and narrow root canal were randomly divided into three groups (n = 10) according to the instrumentation kinematics: Optimum Glide Path motion (OGP) or continuous rotation (CR) with HyFlex EDM Glide Path Files using a custom-made automated-root-canal-preparation device and manual instrumentation with stainless steel K-files (SS) in watch-winding motion. Torque and force were monitored with a custom-made torque/force analyzing device. Canal volume changes and transportation values were measured on micro-computed tomographic images taken before and after the glide path preparation. The data were statistically evaluated using Kruskal-Wallis test and Mann-Whitney U test with Bonferroni correction, with a significance level set at 5%. Maximum upward apical force, representing the screw-in force, was lower in groups OGP and CR compared with that in group SS (P < 0.05). Group CR showed the highest maximum clockwise torque value and canal volume changes, followed by groups OGP and SS (P < 0.05). Canal transportation values at 1 and 3 mm from the apex were not significantly different among groups. Within the limitations of this study, rotary glide path preparation generated smaller screw-in force, larger torque and larger canal volume changes than manual preparation. OGP motion generated smaller torque and less canal volume changes than CR.