Phase transformation behavior and mechanical properties of HyFlex EDM nickel-titanium endodontic rotary instrument: Evaluation at body temperature.

Background/purpose: Temperature-dependent phase compositional changes influence the mechanical properties of heat-treated nickel-titanium (NiTi) rotary instruments. This study evaluated the phase composition, bending properties, and cyclic fatigue resistance of HyFlex EDM NiTi rotary instruments against differently heat-treated and non-heat-treated NiTi instruments at body temperature (BT). Materials and methods: HyFlex EDM OneFile (EDM) instruments, heat-treated HyFlex CM (CM) and Twisted File (TF) instruments, and non-heat-treated K3 instruments (size #25/.08) were subjected to differential scanning calorimetry, and the martensitic, R-phase, and reverse transformation starting and finishing temperatures were determined. A cantilever bending test and a cyclic fatigue test were conducted at BT (37 °C ± 1.0 °C), and the bending load and number of cycles to failure (NCF) were recorded. Statistical analysis was performed using Kruskal-Wallis and Mann-Whitney U tests (α = 0.05). Results: TF and K3 had reverse transformation finishing temperatures lower than BT, while those for EDM and CM were higher than BT. The bending loads at a 0.5 mm deflection were in the order of EDM < TF < CM < K3 (P < 0.05), and those at a 2.0 mm deflection were EDM < CM and TF < K3 (P < 0.05). EDM had the highest NCF among the four instruments (P < 0.05). Conclusion: The EDM instrument had a reverse transformation finishing temperature higher than BT indicating its martensite/R-phase composition at BT. The EDM instrument had superior flexibility and greater resistance to cyclic fatigue than the CM, TF, and K3 instruments at BT.

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.

Phase transformation and mechanical properties of heat-treated nickel-titanium rotary endodontic instruments at room and body temperatures.

BACKGROUND: The aim of this study was to evaluate the phase composition, phase transformation temperatures, bending property, and cyclic fatigue resistance of different heat-treated nickel-titanium (NiTi) rotary instruments with the same tip diameter and taper at room (RT; 25 ± 1 °C) and body (BT; 37 ± 1 °C) temperatures. METHODS: Five heat-treated NiTi rotary instruments, HyFlex EDM (EDM), HyFlex CM (CM), Vortex Blue (VB), RE file CT (RE) and JIZAI, and a non-heat-treated NiTi rotary instrument (Mtwo) with a size 40, 0.04 taper were investigated. Temperature-dependent phase transformation was examined with differential scanning calorimetry (DSC). The bending loads of the instruments at RT and BT were evaluated using a cantilever-bending test. Cyclic fatigue resistance at RT and BT was measured using a dynamic test, during which the instruments were rotated in combination with a 2-mm back-and-forth motion in an artificial curved canal, and the number of cycles to failure (NCF) was determined. The results were analyzed using two-way repeated measures analysis of variance, a simple main effect test, and the Bonferroni test (α = 0.05). RESULTS: DSC results indicated that EDM and Mtwo were primarily composed of martensite/R-phase and austenite, respectively, while the other heat-treated instruments were composed of a mix of martensite/R-phase and austenite at the tested temperatures. Regardless of the temperature setting, the bending loads of heat-treated instruments were significantly lower than those of Mtwo (p < 0.05). EDM showed the lowest bending loads and highest NCF at both temperatures (p < 0.05). CM, VB, and JIZAI showed significantly higher bending loads at BT than at RT (p < 0.05). The NCF of all the heat-treated instruments, except VB, was lower at BT than at RT (p < 0.05). At BT, the NCF of CM, VB, RE, and JIZAI were not significantly higher than that of Mtwo (p > 0.05). CONCLUSIONS: Heat-treated NiTi instruments exhibited lower bending loads and higher NCF values than Mtwo. However, this tendency was less pronounced at BT than at RT, especially in the NCF values of instruments with a mixture of martensite/R-phase and austenite phases at the tested temperatures.

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.

Influence of different kinematics on stationary and dynamic torsional behavior of JIZAI nickel-titanium rotary instruments: An in vitro study.

Background/purpose: Using conventional approach to examine stationary torque of nickel-titanium rotary instruments contradicts the clinical condition, and its validity for motions involving clockwise and counterclockwise rotations is questionable. This study aimed to examine the effect of different kinematics on the torsional behavior using a JIZAI instrument (#25/.04) under stationary/dynamic test conditions using clinical torque limit settings. Materials and methods: In the stationary test, the 5-mm tip of JIZAI was fixed in a cylinder-shaped vise and rotated in continuous rotation (CR) with auto-torque-reverse, optimum-torque-reverse (OTR), or reciprocation (REC) until fracture (n = 10, each). In the dynamic test, straight and severe curved canals were instrumented with JIZAI using the single-length technique with CR, OTR, or REC (n = 10, each). The stationary torque at fracture, time to fracture (Tf), dynamic torque, and screw-in force were recorded using automated-shaping-device with torque/force measuring unit. One-way ANOVA or Kruskal-Wallis test and Mann-Whitney U test with Bonferroni correction were used for statistical analysis (⍺ = 0.05). Results: The kinematics did not influence the stationary or dynamic torques (P > 0.05); however, did influence the screw-in force in straight canals (P < 0.05). REC had significantly longer Tf, and severe curved canals yielded significantly greater torque and screw-in force in CR (P < 0.05). Conclusion: Under the present experimental conditions, parameters other than torque showed significant effects on different kinematics. The dynamic torque and screw-in force of OTR were similar to the other rotational modes and not influenced by the canal curvature.

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.

Mechanical Properties and Root Canal Shaping Ability of a Nickel-Titanium Rotary System for Minimally Invasive Endodontic Treatment: A Comparative In Vitro Study.

Selection of an appropriate nickel−titanium (NiTi) rotary system is important for minimally invasive endodontic treatment, which aims to preserve as much root canal dentin as possible. This study aimed to evaluate selected mechanical properties and the root canal shaping ability of TruNatomy (TRN), a NiTi rotary system designed for minimally invasive endodontic shaping, in comparison with existing instruments: HyFlex EDM (HEDM), ProTaper Next (PTN), and WaveOne Gold (WOG). Load values measured with a cantilever bending test were ranked as TRN < HEDM < WOG < PTN (p < 0.05). A dynamic cyclic fatigue test revealed that the number of cycles to fracture was ranked as HEDM > WOG > TRN > PTN (p < 0.05). Torque and vertical force generated during instrumentation of J-shaped artificial resin canals were measured using an automated instrumentation device connected to a torque and vertical force measuring system; TRN exhibited smaller torque and vertical force values in most comparisons with the other instruments. The canal centering ratio for TRN was smaller than or comparable to that for the other instruments except for WOG at the apex level. Under the present experimental conditions, TRN showed higher flexibility and lower torque and vertical force values than the other instruments.

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

This study aimed to evaluate how various rotational modes influence the torque/force production and shaping ability of ProTaper Universal (PTU; non-heat-treated) and ProTaper Gold (PTG; heat-treated) nickel−titanium instruments. J-shaped resin canals were instrumented with PTU or PTG using an automated instrumentation device operated with reciprocating rotation [150° clockwise and 30° counterclockwise (R150/30) or 240° clockwise and 120° counterclockwise (R240/120)], optimum torque reverse motion (OTR), or continuous rotation (CR) (n = 10 each). Maximum force and torque were recorded, and canal centering ratios were calculated. Statistical analysis was performed with two-way ANOVA and a Bonferroni test (α = 0.05). The results were considered with reference to previous studies on the microstructure of the instruments. The upward force generated by R240/120 and OTR was smaller than that generated by R150/30 and CR in PTG (p < 0.05). The clockwise torque produced by OTR was lower than that produced by R150/30 in PTU and R240/120 and CR in PTG (p < 0.05). R240/120 and OTR induced less canal deviation compared to CR in PTU at 0 mm from the apex (p < 0.05). In conclusion, R240/120 and OTR reduced the screw-in force in PTG and improved the canal centering ability in PTU, which may be associated with the heat treatment-induced microstructural difference of the two instruments.

Effect of Different Downward Loads on Canal Centering Ability, Vertical Force, and Torque Generation during Nickel-Titanium Rotary Instrumentation.

This study aimed to examine how downward loads influence the torque/force and shaping outcome of ProTaper NEXT (PTN) rotary instrumentation. PTN X1, X2, and X3 were used to prepare J-shaped resin canals employing a load-controlled automated instrumentation and torque/force measuring device. Depending on the torque values, the handpiece was programmed to move as follows: up and down; downward at a preset downward load of 1 N, 2 N or 3 N (Group 1N, 2N, and 3N, respectively; each n = 10); or upward. The torque/force values and instrumentation time were recorded, and the canal centering ratio was calculated. The results were analyzed using a two-way or one-way analysis of variance and the Tukey test (α = 0.05). At the apex level, Group 3N exhibited the least canal deviation among the three groups (p < 0.05). The downward force was Group 3N > Group 2N > Group 1N (p < 0.05). The upward force, representing the screw-in force, was Group 3N > Group 1N (p < 0.05). The total instrumentation time was Group 1N > Group 3N (p < 0.05). In conclusion, increasing the downward load during PTN rotary instrumentation improved the canal centering ability, reduced the instrumentation time, and increased the upward force.

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 >0.4 N cm), time-dependent reciprocal motion (TmR; 180° forward and 90° reverse), and optimal glide path motion (OGP; a combination of 90° forward, 90° reverse, 90° forward, and 120° reverse)]. Instrumentation was performed with an automated root canal instrument and torque/force analysing device. Maximum torque/force values, canal volume changes, and canal-centring ratios at 1, 3, 5, and 7 mm were evaluated. Surface defects (pits, grooves, microcracks, blunt cutting edges, and disruption of cutting edges) and spiral distortion on the ProGlider instrument were scored at the tip and 5 mm short of the tip before and after five consecutive uses with scanning electron microscopy. The Kruskal-Wallis test followed by Dunn's post-test with Bonferroni correction and Wilcoxon signed-rank test were used to analyse the data (α = 0.05). RESULTS: Optimal glide path motion generated significantly less clockwise torque and greater upward force than other groups (p < .05). OGP resulted in significantly fewer surface defects than CR (p < .05). In OGP and CR, the tip exhibited more surface defects than 5 mm short of the tip (p < .05). CR resulted in greater volume changes than OGP and TmR (p < .05) and greater centring ratios (i.e., more deviation) than OGP at 1 mm and OTR at 3 mm (p < .05). CONCLUSIONS: Under laboratory conditions using the ProGlider instrument, OGP generated significantly less clockwise torque and greater upward force than the other rotatory motions. OGP generated fewer superficial defects than CR, and the three modes of reciprocal rotation better maintained the apical curvature of root canals than CR with the ProGlider instrument.

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.

Cyclic Fatigue Resistance of Rotary and Reciprocating Nickel-Titanium Instruments Subjected to Static and Dynamic Tests.

INTRODUCTION: This study compared the static and dynamic cyclic fatigue resistance of contemporary nickel-titanium instruments with different kinematic, metallurgic, and design features to establish whether the fatigue-reducing effect of the pecking motion differs among different nickel-titanium instruments. METHODS: ProTaper Gold (PTG), Hyflex EDM (EDM), Reciproc Blue (RPB), and WaveOne Gold (WOG) files were divided into 2 groups of 10 for the static and dynamic cyclic fatigue resistance tests. A stainless steel artificial canal with 1.5-mm inner diameter, 60° angulation, and 3-mm radius of curvature was used. In the dynamic cyclic fatigue resistance test, speeds were set at 100 and 200 mm/min for the descending and ascending motion, respectively. The number of cycles to fracture (NCF) was calculated, the fractured lengths were recorded, and fractographic analysis of the fractured surfaces was carried out by scanning electron microscopy. Data were analyzed statistically with the Kruskal-Wallis test with Bonferroni correction (alpha = 0.05). RESULTS: The RPB and EDM showed significantly higher NCF in the static and dynamic cyclic fatigue resistance tests (P < .05). The dynamic cyclic fatigue resistance test showed significantly higher NCF than the static cyclic fatigue resistance test in the PTG and EDM (P < .05). There was no significant difference between the RPB and WOG (P > .05). CONCLUSIONS: In the experimental condition where the ascending speed was higher than the descending speed, the dynamic cyclic fatigue resistance was significantly higher than the static cyclic fatigue resistance in continuous rotary instruments, but not in reciprocating instruments.

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.

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.

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.

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.