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

Abstract

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 (mm3), surface area (mm2), length, 15°–20° curvature and radius of curvature (4–8 mm)] after micro‐computed tomographic scanning. An automated root canal instrumentation and torque/force analysing device was programmed to permit a simulated pecking motion (2 s downward and 1 s upward at 50 mm min−1). The selected canals were prepared with size 25, 0.06 taper JIZAI instruments using continuous rotation or OTR motion and further subdivided according to the rotational speed (300 or 500 rpm, n = 10 each). Real‐time clockwise/counterclockwise torque and downward/upward force were recorded using a custom‐made torque/force analysing device. Then, the registered pre‐ and post‐operative micro‐computed tomographic datasets were examined to evaluate the canal volume changes and centring ratios at 1, 3, 5 and 7 mm from the apical foramen. Data were analysed using two‐way analysis of variance or the Kruskal–Wallis test and Mann–Whitney U test with Bonferroni correction (α = 5%). Results Maximum upward force and clockwise torque were significantly smaller in 500 rpm groups than in 300 rpm groups (P < .05); however, no significant difference was found between continuous rotation and OTR motion (P > .05). OTR motion developed higher maximum counterclockwise torque than continuous rotation (P < .05). Maximum downward force, canal volume changes and centring ratios were not significantly different among all groups (P > .05). There was no file fracture in any of the groups. Conclusions Under laboratory conditions using JIZAI instruments, a rotational speed of 500 rpm generated significantly lower maximum screw‐in forces and torque values than rotational speed of 300 rpm. Continuous rotation and OTR motion performed similarly in shaping the canals.

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

“…A priori anova (fixed effects, omnibus, one‐way) was selected from the F ‐test family in G*Power 3.1.7 software (Heinrich Heine Universität). Based on an effect size of 0.6, an alpha‐type error of 0.05, and power of 85%, the findings of a previous study (Kyaw et al, 2021) required minimum sample size of 13 per group to identify significant differences between the four research groups in terms of torque and force generation.…”

“…A custom test device mentioned in our previous articles (Htun et al, 2020; Kimura et al, 2020; Kyaw et al, 2021; Nakatsukasa et al, 2021) was used to measure torque and forces during each file movement. Briefly, specimens were secured in a rigid holder attached to a load cell (LUX‐B‐ID; Kyowa Electronic) for force measurement and strain gauges (KFG‐2‐120‐D31‐11; Kyowa Electronic) for torque measurement.…”

“…OTR motion reduces torsional stress development during rotary preparation with an insufficient coronal enlargement (Kimura et al, 2020;Tokita, Ebihara, Nishijo, et al, 2017) and greater cyclic fatigue resistance than CR (Pedullà et al, 2018). However, another study reported that CR and OTR motion generated similar torque and force values, and performed similarly well in terms of transportation and volume changes (Kyaw et al, 2021).…”

Effect of Rotational Modes on Torque/Force Generation and Canal Centering Ability during Rotary Root Canal Instrumentation with Differently Heat-Treated Nickel–Titanium Instruments

“…Recently, torque-sensitive reciprocal rotation—in which the motor changes its motion from continuous rotation to a reciprocal movement only when the torque exceeds the preset value—has been developed, aimed at reducing the instrument fatigue without decreasing the cutting efficiency [ 15 ]. In the optimum torque reverse (OTR) motion installed on the TriAuto ZX2 motor (J Morita, Kyoto, Japan), the clockwise and counterclockwise rotational angles are set at 180° and 90°, respectively [ 6 , 16 ].…”

“…In the optimum torque reverse (OTR) motion installed on the TriAuto ZX2 motor (J Morita, Kyoto, Japan), the clockwise and counterclockwise rotational angles are set at 180° and 90°, respectively [ 6 , 16 ]. The OTR motion is reported to improve cyclic fatigue resistance [ 16 , 17 ], generate less vertical force and torque [ 5 , 6 ], and show a similar [ 15 ] or slightly better [ 18 ] canal centering ability compared with continuous rotation.…”