Effect of repetitive up-and-down movements on torque/force generation, surface defects and shaping ability of nickel-titanium rotary instruments: an ex vivo study.

Background: The screw-in effect is a tendency of a nickel-titanium (NiTi) rotary endodontic file to be pulled into the canal, which can result in a sudden increase in stress leading to instrument fracture, and over-instrumentation beyond the apex. To reduce screw-in force, repeated up-and-down movements are recommended to distribute flexural stress during instrumentation, especially in curved and constricted canals. However, there is no consensus on the optimal number of repetitions.

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.

Effect of kinematics on the torque/force generation, surface characteristics, and shaping ability of a nickel-titanium rotary glide path instrument: An ex vivo study.

Aim: To evaluate the effect of various rotational motions on the torque/force generation, surface wear, and shaping ability of the ProGlider glide path instrument (Dentsply Sirona).

Methodology: Mesiobuccal and mesiolingual canals of mandibular molars were selected based on the canal volume, length, angle of curvature (25°-40°), and radius of curvature (4-8 mm) after micro-computed tomographic scanning. The samples were randomly assigned to four groups (n = 13, each) according to movement kinematics [continuous rotation (CR; 300 rpm), optimum torque reverse motion (OTR; 180° forward and 90° reverse when torque >0.

Influence of rotational speed on torque/force generation and shaping ability during root canal instrumentation of extracted teeth with continuous rotation and optimum torque reverse motion.

Aim: To evaluate how different rotational speeds affect the torque/force generation and shaping ability of rotary root canal instrumentation using JIZAI (MANI, Utsunomiya, Japan) nickel-titanium instruments in continuous rotation and optimum torque reverse (OTR) motion.

Methodology: Mesial root canals of extracted mandibular molars were instrumented up to size 25, 0.04 taper using JIZAI instruments, and anatomically matched canals were selected based on geometric features of the canal [canal volume (mm ), surface area (mm ), length, 15°-20° curvature and radius of curvature (4-8 mm)] after micro-computed tomographic scanning.