Dynamic torque and screw-in force of four different glide path instruments assessed in simulated single- and double-curved canals: An in vitro study.

Background/purpose: The glide path instruments are the introductory instruments into the canals; thus, they should be durable enough to withstand torsional stress/screw-in force. This study aimed to investigate the torque and screw-in force of TruNatomy Glider (TN), ProGLIDER (PG), Hyflex EDM (EDM) and Dent Craft RE (RE) glide path instruments in single- and double-curved canals. Materials and methods: Each instrument brand was divided into two groups (n = 7 each) according to the canal configuration. Torque and screw-in force were recorded during automated instrumentation of simulated resin canals with XSmart IQ cordless motor after the canal patency was checked with a #10 K-file. The values were statistically analyzed using the Kolmogorov-Smirnov test followed by the Kruskal Wallis test and the Mann-Whitney U test with Bonferroni correction (α = 0.05). Results: TN produced significantly higher torque than RE in single-curved canals and PG in double-curved canals (P < 0.05). EDM yielded significantly higher screw-in force than TN and RE in single-curved canals (P < 0.05), but there was no significant difference in double-curved canals (P > 0.05). A significant effect of different canal configurations was only detected for screw-in force in EDM (P < 0.05). Conclusion: TN in single-curved canals and RE in double-curved canals yielded higher torque values, while EDM exhibited greater screw-in force in both canal configurations. No effect of different canal configurations was detected for torque, but a significant impact was detected for screw-in force in EDM.

Effect of different axial speed patterns on cyclic fatigue resistance of rotary nickel-titanium instruments.

BACKGROUND: To evaluate the effect of pecking motions with faster upward speed on the dynamic cyclic fatigue resistance of nickel-titanium rotary instruments with different metallurgy. METHODS: Forty each of ProTaper Universal F3 (PTU) and ProTaper Gold F3 (PTG) instruments (size #30/.09) were equally divided into four groups. The test was performed using an 18-mm-long stainless steel artificial canal with a 5-mm radius of curvature, a 45° canal curvature and a 2-mm canal diameter. A downward speed of 100 mm/min was employed, while the upward speed was set at 100, 150, 200 or 300 mm/min. Time to failure (Tf), number of cycles to failure (Nf) and number of pecking motions to failure (Np) were recorded. Statistical analysis was performed using Kruskal Wallis and Mann-Whitney U tests for Tf, Nf, and Np (α = 0.05). RESULTS: The 100/300 mm/min group showed significantly higher Np values than the 100/100 mm/min group (p < 0.05), whereas there were no significant differences in Tf and Nf among the tested speed groups (p < 0.05) in either PTU or PTG. PTG exhibited significantly higher Tf, Nf, and Np than PTU (p < 0.05). CONCLUSIONS: Under the tested conditions, the fastest upward speed group showed significantly higher cyclic fatigue resistance, as demonstrated by larger Np, than the same speed group. PTG had significantly higher cyclic fatigue resistance than PTU in all groups.

Comparative evaluation of mechanical properties and shaping performance of heat-treated nickel titanium rotary instruments used in the single-length technique.

This study aimed to evaluate the mechanical properties of contemporary heat-treated nickel-titanium (NiTi) rotary instruments used in the single-length technique [ProTaper Next (PTN), HyFlex EDM (EDM), and JIZAI (JZ)]. Bending loads, cyclic fatigue resistance, torque/force values and canal-centering ratios were evaluated for the three instruments and a non-heat-treated experimental NiTi instrument with the same geometry as JZ (nJZ). EDM and JZ exhibited significantly lower bending load and more cycles to failure compared with nJZ and PTN (p<0.05). PTN and JZ exhibited significantly better centering ability than nJZ and EDM (p<0.05). JZ and nJZ generated significantly smaller upward force and maximum torque than PTN and EDM (p<0.05). Under the present experimental condition, JZ exhibited flexibility and cyclic fatigue resistance comparable to EDM, better maintained the canal curvature than the other instruments, and generated smaller torque and screw-in force than PTN and EDM.

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.

Effect of Optimum Torque Reverse Motion on Torque and Force Generation during Root Canal Instrumentation with Crown-down and Single-length Techniques.

INTRODUCTION: Optimum torque reverse (OTR) motion is a torque-sensitive reciprocal motion in which the motor rotates in alternating 90° counterclockwise and 180° clockwise rotation when the torque exceeds a predetermined value. This study aimed to examine whether OTR motion contributes to torque and force reduction during nickel-titanium rotary instrumentation with the crown-down or single-length technique. METHODS: Twenty-eight simulated straight canals in resin blocks were divided into 2 groups according to the type of motion (OTR or continuous rotation). The groups were further subdivided according to the preparation technique (crown-down or single-length technique, n = 7 each). Automated root canal instrumentation was performed with a torque/force analyzing device (300 rpm, up-and-down speed of 10 mm/min) and EndoWave instruments (FKG Dentaire, La-Chaux-de-Fonds, Switzerland) to size #25/0.06 taper. Maximum torque and apical force were recorded and analyzed with analysis of variance and the Bonferroni test. RESULTS: During the crown-down preparation phase (#35/0.08, #30/0.06, #25/0.06, and #20/0.06), OTR motion developed lower maximum torque and upward force (representing the screw-in force) than continuous rotation. During the apical preparation phase (#25/0.06), OTR motion generated significantly lower maximum clockwise and counterclockwise torque (P < .05) when the single-length technique was used and significantly lower maximum upward force regardless of the preparation technique (P < .05) compared with continuous rotation. CONCLUSIONS: Under the present experimental conditions, OTR motion reduced both torque and screw-in force during the crown-down preparation phase of the crown-down technique and during the apical preparation phase of the single-length technique.

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.

Enhanced root canal-centering ability and reduced screw-in force generation of reciprocating nickel-titanium instruments with a post-machining thermal treatment.

This study aimed to evaluate the influence of a post-machining thermal treatment on canal-centering ability and torque/force generation of reciprocating nickel-titanium instruments. Simulated J-shaped resin canals were prepared with reciprocating instruments sharing identical geometric architecture and with/without post-machining thermal treatment (Reciproc Blue/Reciproc, VDW, Munich, Germany). Using an original automated root canal instrumentation and torque/force analyzing device, files were operated in a combination of reciprocation and up-and-down motion, and torque/force values were monitored. Canal-centering ratios were measured after superimposition of pre- and post-instrumentation images. Compared with Reciproc, Reciproc Blue showed a significantly lower canal-centering ratio (i.e., less deviation; p<0.05) at 0-1 mm from the apex and generated a significantly smaller upward maximum vertical force (p<0.05). Under standardized conditions using the automated device, Reciproc Blue showed better canal-centering ability and reduced screw-in forces than Reciproc, indicating that the post-machining thermal treatment confers superior performance to reciprocating nickel-titanium instruments.

Assessment of mechanical properties of WaveOne Gold Primary reciprocating instruments.

This study aimed to evaluate cyclic fatigue resistance and bending properties and torque/force generation of WaveOne Gold (WOG) Primary in comparison with WaveOne (WO) Primary and Reciproc (RE) R25. A cyclic fatigue test revealed that the WOG Primary took significantly longer time to fracture compared with the WO Primary (p<0.05). The WOG Primary had the smallest load values at a deflection of 0.5 and 2 mm (p<0.05), as measured with a cantilever bending test. Torque/force measurement demonstrated that maximum upward force and maximum counterclockwise torque values in the WOG Primary were significantly lower than those in the RE R25 (p<0.05). Under the present experimental condition, the WOG Primary showed a higher cyclic fatigue resistance compared with the WO Primary, a higher flexibility compared with the WO Primary and RE R25, and generated a significantly lower maximum torque compared with the RE R25.

Effect of Different Speeds of Up-and-down Motion on Canal Centering Ability and Vertical Force and Torque Generation of Nickel-titanium Rotary Instruments.

INTRODUCTION: This study was performed to evaluate how the speed of up-and-down motion affects the canal centering ability and torque/force generation of ProTaper Next rotary instruments (Dentsply Maillefer, Ballaigues, Switzerland). METHODS: Twenty-one simulated resin canal blocks with a J-shaped canal were prepared with ProTaper Next X1, X2, and X3 instruments using an original automated root canal instrumentation and torque/force analyzing device with up-and-down speed settings of 10, 50, and 100 mm/min (low-, medium-, and high-speed groups, respectively). Pre- and postinstrumentation images were superimposed, and centering ratios were calculated at 0-3 mm from the apex. The maximum vertical force and torque were also recorded. The results were statistically analyzed using 1-way analysis of variance and the Tukey test. RESULTS: At 0, 0.5, 1, and 2 mm from the apex, the high-speed group showed the lowest centering ratio (ie, least deviation) followed by the medium-speed and low-speed groups (P < .05). Force values (downward and upward) tended to increase as the up-and-down speed increased; with the X2 and X3 instruments, the high-speed and/or medium-speed groups generated significantly larger values than the low-speed group (P < .05). With all instruments, the high-speed and/or medium-speed groups generated significantly larger clockwise torque than the low-speed group (P < .05). One and 2 X2 instruments fractured in the low- and high-speed groups, respectively. CONCLUSIONS: The up-and-down speed affected the canal centering ability and stress generation of ProTaper Next instruments. The high-speed group showed the best centering ability but tended to generate larger vertical force and torque than the medium- and low-speed groups.

Evaluation of Root Canal Anatomy of Maxillary Premolars Using Swept-Source Optical Coherence Tomography in Comparison with Dental Operating Microscope and Cone Beam Computed Tomography.

OBJECTIVE: This study aimed to evaluate the ability of swept-source optical coherence tomography (OCT) to detect internal anatomy of maxillary premolars in comparison with dental operating microscope (DOM) and cone beam computed tomography (CBCT). BACKGROUND DATA: The ability of OCT to observe the pulp horn during cavity preparation and assess the remaining dentin thickness (RDT) has been demonstrated, whereas validation of OCT in comparison with other imaging techniques seems required. METHODS: Ten extracted human maxillary premolars were sectioned perpendicular to the tooth axis from the occlusal surface at approximately 2 mm increments. OCT and DOM were performed after each cut, and microfocus X-ray computed tomography (micro-CT; reference standard) and CBCT were conducted before sectioning and after the first and second cuts. Three examiners evaluated all images for presence of the pulp horn/pulp chamber, isthmus, lateral canals, and the number of root canals. RDT was determined from OCT, micro-CT, and CBCT images. Correlations were analyzed with Pearson's correlation coefficient. RESULTS: OCT had a sensitivity and specificity of 0.90 and 0.80 in detecting the pulp horn/pulp chamber and 0.84 and 0.71 in detecting the isthmus, respectively. The three techniques showed strong correlations in detecting the number of root canals compared with micro-CT. OCT and DOM did not detect lateral canals. For RDT values, strong correlations were observed between micro-CT and CBCT, micro-CT and OCT, and CBCT and OCT (p < 0.01 for all). CONCLUSIONS: Under the present experimental condition, OCT accurately measured RDT and detected internal tooth anatomy such as the pulp horn, isthmus, and root canals.

Evaluation of selected mechanical properties of NiTi rotary glide path files manufactured from controlled memory wires.

This study aimed to investigate mechanical properties related to flexibility and fracture resistance of controlled memory wiremanufactured nickel-titanium rotary glide path files [HyFlex EDM Glide Path File (EDM) and HyFlex GPF (GPF)]. Scout RaCe (RaCe) served as control. Bending loads, torsional/cyclic fatigue resistance, and screw-in forces were measured. EDM showed a significantly larger torque at fracture, a longer time to cyclic fracture in reciprocation and a larger screw-in force compared with GPF and RaCe. GPF showed significantly lower bending loads and higher angular deflection values than EDM and RaCe, and a significantly longer time to cyclic fracture than RaCe. The time to cyclic fracture was significantly longer in reciprocation compared with continuous rotation in EDM and GPF. It can be concluded that EDM and/or GPF showed higher flexibility and cyclic/torsional fatigue resistance compared with RaCe; and that reciprocation conferred better cyclic fatigue resistance to EDM and GPF.

Dynamic Torque and Vertical Force Analysis during Nickel-titanium Rotary Root Canal Preparation with Different Modes of Reciprocal Rotation.

INTRODUCTION: The purpose of the present study was to compare 2 modes of reciprocal movement (torque-sensitive and time-dependent reciprocal rotation) with continuous rotation in terms of torque and apical force generation during nickel-titanium rotary root canal instrumentation. METHODS: A custom-made automated root canal instrumentation and torque/force analyzing device was used to prepare simulated canals in resin blocks and monitor the torque and apical force generated in the blocks during preparation. Experimental groups (n = 7, each) consisted of (1) torque-sensitive reciprocal rotation with torque-sensitive vertical movement (group TqR), (2) time-dependent reciprocal rotation with time-dependent vertical movement (group TmR), and (3) continuous rotation with time-dependent vertical movement (group CR). The canals were instrumented with TF Adaptive SM1 and SM2 rotary files (SybronEndo, Orange, CA), and the torque and apical force were measured during instrumentation with SM2. The mean and maximum torque and apical force values were statistically analyzed using 1-way analysis of variance and the Tukey test (α = 0.05). RESULTS: The recordings showed intermittent increases of upward apical force and clockwise torque, indicating the generation and release of screw-in forces. The maximum upward apical force values in group TmR were significantly smaller than those in group CR (P < .05). The maximum torque values in clockwise and counterclockwise directions in groups TqR and TmR were significantly smaller than those in group CR (P < .05). CONCLUSIONS: Under the present experimental conditions using TF Adaptive instruments, both torque-sensitive and time-dependent reciprocal rotation generated significantly lower maximum torque and may have advantages in reducing stress generation caused by screw-in forces when compared with continuous rotation.