Bending resistance and cyclic fatigue resistance of WaveOne Gold, Reciproc Blue, and HyFlex EDM instruments

Comparative evaluation of the remaining dentin volume following instrumentation with rotary, reciprocating, and hand files during root canal treatment in primary molars: An ex vivo study

Background/purpose

The effectiveness of root canal treatments with different file systems in primary teeth is important in terms of clinical practice and the use of file systems that work with different principles in primary tooth pulpectomy is becoming widespread. The amount of remaining dentin in the coronal region of the root is important in terms of the prognosis of the tooth and the long-term success of the treatment in teeth that have undergone root canal treatment. The aim of this study was to evaluate the remaining dentin volume in the coronal part of the root after the use of rotary, reciprocating, and conventional hand files in primary tooth pulpectomy.

Materials and methods

A total of 30 primary molars were divided into three groups. In each group, the preparations were made with three different file types: WaveOne Gold, which works with reciprocating motion; TruNatomy, which works with rotational motion; and conventional hand files. The three-dimensional images were evaluated for remaining dentin volume in the 2-mm coronal part of the root. Group means were compared using one-way analysis of variance, and post hoc analyses were performed with the Tukey test.

Results

There was no statistically significant difference between the groups in terms of preoperative and postoperative dentin volume (P > 0.05). The mean difference after preparation was observed the most in the WaveOne Gold group and the least in the TruNatomy group. When the mean percentage differences were evaluated, it was observed that statistically significantly more dentin volume was preserved after the preparation with TruNatomy than with WaveOne Gold (P = 0.021).

Conclusion

In primary tooth pulpectomy, file systems working with rotational motion can be preferred over file systems working with reciprocating motion in preserving the amount of dentin in the 2-mm coronal part of the root.

Evaluation of Cyclic Fatigue Resistance of Novel Replica-Like Instruments in Static Test Model

Introduction

The aim of our study is to comparatively analyze the canal cyclic fatigue resistance of widely used rotary file systems, including EndoArt Touch Gold (ETG), Perfect MTF Plus Gold (PPG), Fanta V-Taper Gold (FVG), and ProTaper Next (PTN).

Methods

Stainless steel canals with a 60° angle and a 3-mm curvature radius were specially prepared. The canals were shaped with each rotary file system and tested for resistance using a cyclic fatigue testing apparatus. The number of fracture cycles (NFC; K file tip separation) was measured. Data were analysed by one-way ANOVA and post hoc LSD tests.

Results

PTN and PPG rotary file systems exhibited the highest NFC. The NFC value for PTN was 589 ± 63, and for PPG, it was 507 ± 51.

Conclusion

The results of this study demonstrate that rotary file systems such as PTN and PPG exhibit higher cyclic fatigue resistance. ETG and FVG rotary file systems also possess generally acceptable cyclic fatigue resistance levels.

Phase Transformation and Mechanical Behaviour of Different Heat-Treated Nickel-Titanium Rotary Instruments

OBJECTIVES

This study evaluated the phase composition, phase transformation behaviour, and mechanical properties of five heat-treated NiTi instruments.

METHODS

ProTaper NEXT (M-wire, PTN), ProTaper Gold (Gold-wire, PTG), One Curve (C-wire, OC), EdgeTaper Platinum (Fire-wire, ETP), NeoNiTi (electrical discharge machining-wire, NNA), and ProTaper Universal (conventional wire, PTU, control) with #25-tip size were tested (n = 12/group) for cyclic fatigue resistance (number of cycles to failure; NCF) and torsional resistance (angle of rotation to fracture and maximum torque at fracture [ultimate torsional strength]). The geometry and fracture surfaces of the tested instruments were examined by scanning electron microscopy. The phase transformation temperature and phase composition of the instruments were evaluated using differential scanning calorimetry and X-ray diffraction. Data were statistically analysed using one-way ANOVA and Tukey's post hoc test, with the significance level set at 5%.

RESULTS

PTG showed the highest NCF (P < .05) at 37°C, while ETP exhibited the highest angle of rotation to fracture, ultimate torsional strength, and stiffness (P < .05). Scanning electron microscopy demonstrated typical clusters of fatigue striations and numerous cracks after cyclic fatigue fracture, whereas there was a concentric abrasion pattern with a dimple and microvoids at the centre after torsional fracture. In differential scanning calorimetry curves, austenite-finishing temperatures of heat-treated instruments were higher than 37°C, whereas that of PTU was lower than 37°C. PTU showed strong peaks of austenite at 25 and 37°C, whereas ETP showed a strong peak of R-phase at 25°C, but mostly austenite phase at 37°C in X-ray diffraction.

CONCLUSIONS

Geometry, alloy type, and phase transformation temperatures of NiTi instruments affected their mechanical behaviour.

CLINICAL RELEVANCE

PTG showed the highest NCF, suitable for markedly curved canals. ETP had the highest torsional resistance, appropriate for narrow and constricted canals.

Screw-in force, torque generation, and performance of glide-path files with three rotation kinetics

We aimed to evaluate the screw-in force, torque generation, and performance of three nickel-titanium (NiTi) glide-path files with different rotational kinetics. ProTaper Ultimate Slider (PULS) and HyFlex EDM Glide-path (HEDG) files were used for canal shaping with constant rotation (CON) or the alternative rotation technique (ART). In the ART mode, the NiTi file was periodically rotated at a speed of 1.5 times faster than that in the CON mode. WaveOne Gold Glider was used with reciprocating motion (WOGG_RCP). Sixty J-shaped resin blocks were assigned to five groups: PULS_CON, PULS_ART, HEDG_CON, HEDG_ART, and WOGG_RCP (n = 12). Glide-path preparation was performed using an automated pecking device. During glide-path preparation, the screw-in force and clockwise and counterclockwise torques were recorded and the number of pecking motions required to reach the working length was determined. The centering ratio was calculated after glide-path preparation using stereomicroscopic images. Data were analyzed using one-way analysis of variance with the Games-Howell post hoc test and the Kruskal-Wallis test with Bonferroni correction. PULS_ART generated a lower maximum screw-in force than PULS_CON. The average number of pecking motions required to reach the working length by HEDG_ART was lower than that by HEDG_CON. The mean centering ratios of PULS_CON and HEDG_CON were - 0.04 and - 0.06, respectively, while those of PULS_ART, HEDG_ART, and WOGG_RCP were 0.09, 0.01, and 0.08, respectively. The ART mode reduced the screw-in force of PULS and enabled faster glide-path preparation with the HEDG file.

Evaluation of cyclic fatigue behavior of RACE EVO rotary Files: In-vitro comparative study

Introduction

Comparative evaluation of the newly introduced; RACE EVO file system to the currently well-performing file systems like HyFlex EDM OneFile, Vortex Blue, ProTaper Gold (PTG) with regards to the cyclic fatigue resistance.

Materials

&Methods.The endodontic rotary files under evaluation were segregated into four groups as follows:; RACE EVO, PTG, Vortex Blue, and HyFlex EDM OneFile. A detailed physical analysis of the cyclic fatigue resistance was performed in 15 files of each type (n = 60). Under the test conditions of 37 °C the test samples were subjected to continuous motion at the manufacturer recommended speed within an artificial curved canal until it fractured. For all the test samples, with the recording of time of fracture, calculation was done for number of cycles to fracture (NCF). In addition, the length of the fractured segment was determined. The fractured surface was further evaluated with scanning electron microscopic (SEM) images.

Results

Highest significance for NCF was seen in HyFlex EDM OneFile followed by the Vortex Blue, PTG, and; RACE EVO (p < 0.05) by analyzing the data statistically. Significant differences among the lengths of the fractured segments were evident among tested files, ranging between 4.73 and 6.3 mm (p < 0.05) with HyFlex EDM OneFile uniquely differentiating from the others showing the fracture at 6.3 mm. The common features of cyclic fatigue failure was further substantiated by SEM images.

Conclusions

Compared to the HyFlex EDM OneFile, Vortex Blue, and PTG files; RACE EVO demonstrated significantly lower resistance to cyclic fatigue.

Cyclic Fatigue Resistance of Rotary versus Reciprocating Endodontic Files: A Systematic Review and Meta-Analysis

(1) Background: The failure of nickel-titanium (NiTi) rotary files is a complication related to endodontic instruments. The aim of this study was to compare the resistance to cyclic fatigue between rotary and reciprocating file systems. (2) Methods: Specific PICO: Population (P): artificial root canals; Interventions (I): instrumentation with NiTi rotary and reciprocating files; Comparison (C): rotary versus reciprocating files; Outcome (O): cyclic fatigue resistance. Studies were identified through bibliographic research using electronic databases (Medline, Embase, Scopus, SciELO, and WOS). The studies were combined using a random effects model by the inverse variance method. The effect size was the mean of the time to fracture (TTF) and number of cycles to fracture (NCF). Heterogeneity was assessed using the p value of the Q test for heterogeneity and the I2. (3) Results: TTF for rotary files was determined in 474.5 s and 839.1 for reciprocating without statistically significant differences. NCF for rotary systems was determined in 1444.2 and for reciprocating file systems in 4155.9 with statistically significant differences (p = 0.035), making reciprocating files more resistant. (4) Conclusions: Reciprocating files have better resistance to cyclic fatigue than rotary files. When tested in double curvature canals, reciprocating files also showed higher resistance.

Effect of NaOCl on cyclic fatigue resistance

The impact of 5.25 percent NaOCL on the resistance offered by TruNatomy, Hero Gold and ProtaperGold against cyclic fracture as against the treatment of NiTi rotary files with distilled water is of interest to dentists. Inside the stainless steel blocks, man-made canals were created for the purpose of testing the cyclic fatigue. 60 endodontic files were taken as study specimens. It was observed that values of number of cycles to fracture in NaOCl among three file systems were in the order of TruNatomy (1053.50 ± 134.81)>Hero Gold (652.66 ± 58.66) > ProtaperGold (494.50 ± 47.69). The TruNatomy file system reflected greatest cyclic fatigue resistance. It was also found that cyclic fatigue resistance in NiTi rotary files studied here is not hampered by 5.25% NaOCl.

Influence of endodontic motors on the behaviour of root canal shaping instruments: an in vitro comparative study

AIMS

The endodontic literature reports a lot of comparative study on endodontic instruments, concerning as well their geometry, instrumental dynamics, material, mechanical behavior or heat treatment. However, to our knowledge, no study has focused on the influence of endodontic motors on the shaping abilities of endodontic instruments. Thus, the aim of this study was to analyze the influence of the endodontic motors on root canal shaping instruments.

METHOD

Dual Move (MICRO-MEGA, Besançon, France), Canal Pro CL2i (COLTENE, Alstätten, Suisse), Canal Pro Jeni Motor (COLTENE, Alstätten, Suisse), Ai Motor (WOODPECKER, Guilin, China), Wave One motor (VDW, Postfach, Munich) and Smart A (WOODPECKER, Guilin, China) were pre-clinically compared in continuous rotation and reciprocating motion on a traction/compression bench using resin blocks. Canal shaping in continuous rotation and reciprocating motion were performed with One Curve and One RECI instruments (MICRO-MEGA, Besançon, France), respectively. The penetration/removal forces, making it possible to objectify the cutting effect and screwing effect of the instruments during root canal shaping, were analyzed.

RESULTS

The results showed (i) that endodontic motors influence the mechanical behavior of endodontic instruments, (ii) that the influence of the motors is essentially felt during reciprocating motion and (iii) that the reciprocating angles influence the mechanical behavior of endodontic instruments.

CONCLUSION

Only endodontic instruments are widely studied in literature while endodontic motors have a direct influence on root canal treatment. This study analyzes the influence of the endodontic motors on root canal shaping instruments. This study tends to demonstrate that Jeni Motor could optimize the mechanical behavior of endodontic instruments.

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.

Experimental Analysis of the Influence of Heat Treatments on the Flexibility of NiTi Alloy for Endodontic Instruments Manufacturing

The flexibility of NiTi based endodontic files is improved by heat treatment, leading to lower risk of failure, ledges, and canal transportation during the preparation of curved root canals. The aim of this study is to investigate and clearly highlight the influence of every parameter of heat treatment on the flexibility of NiTi wires and thus of endodontic instruments. A full factorial Design of Experiment (DoE) and a designed bending-torsion bench following the ISO 3630-1 standard were used for this investigation. Temperature, holding time, and cooling method were selected as contributing factors, while maximum bending moment, hysteresis size, and stiffness during martensitic transformation were selected as outputs. Regression analysis was performed to estimate the relationship between contributing and output variables to assess how the experimentation fits with the model. The experimental results showed that wires heated at 425 °C for 30 min are more flexible. Moreover, heat treatment temperature is the most critical factor influencing the flexibility and hysteresis size of the NiTi wire followed by the holding time, while the cooling method has a negligible effect. The regression analysis showed that the model is effective at predicting the relationship between contributing factors, bending moment response, and hysteresis size.

Characterization of the file-specific heat-treated ProTaper Ultimate rotary system

AIM

To compare design, metallurgy and mechanical performance of the ProTaper (PT) Ultimate system with instruments of similar dimensions from the ProGlider, PT Gold and PT Universal systems.

METHODOLOGY

New PT Ultimate instruments (n = 248) were compared with instruments of similar dimensions from ProGlider (n = 31), PT Gold (n = 155) and PT Universal (n = 155) systems regarding their number of spirals, helical angle, blade symmetry, tip geometry, surface finishing, nickel/titanium ratio, phase transformation temperatures and mechanical performance. One-way anova and nonparametric Mood's median tests were used for statistical comparison (α = 5%).

RESULTS

All instruments had symmetrical blades without radial lands or flat sides, similar surface finishing and an almost equiatomic nickel/titanium ratio, whilst the number of spirals, helical angles and the tip geometry were different. PT Ultimate instruments showed 3 distinct heat treatments that matched with the colour of their metal wire. Slider and ProGlider instruments had similar R-phase start (Rs) and R-phase finish (Rf) temperatures. SX, F1, F2, F3 and Shaper instruments showed equivalent heat treatments (Rs ~45.6°C and Rf ~28.3°C) that were similar to their PT Gold counterparts (Rs ~47.9°C and Rf ~28.2°C), but completely distinct to the PT Universal ones (Rs ~16.2°C and Rf ~-18.2°C). Amongst the PT Ultimate instruments, the lowest maximum torques were observed in the SX (0.44 N cm), Slider (0.45 N cm) and Shaper (0.60 N cm) instruments, whilst the highest was noted in the FXL (4.90 N cm). PT Ultimate Slider and ProGlider had similar torsional (~0.40 N cm) and bending loads (~145.0 gf) (p = 1.000), whilst the other PT Ultimate instruments showed statistically significantly lower maximum torque, higher angle of rotation and lower bending load (higher flexibility) than their counterparts of the PT Universal and PT Gold systems.

CONCLUSIONS

The PT Ultimate system comprises instruments with 3 distinct heat treatments that showed similar phase transformation temperatures to their heat-treated analogues. PT Ultimate instruments presented lower torsional strength and superior flexibility than their counterparts, whilst maximum torque, angle of rotation and bending loads progressively increased with their sizes.

Mechanical and Metallurgical Characterization of Nickel-Titanium Wire Types for Rotary Endodontic Instrument Manufacture

This study aimed to evaluate and compare the effects of ambient temperature and post-manufacture heat-treatment on the mechanical behavior of nickel-titanium (NiTi) wires. Four types of commercial NiTi variants (Stock NiTi, heat treated "Blue", "Gold", "Superflex", all Dentsply Maillefer, Ballaigues, Switzerland) were stressed in a tensile testing machine in a temperature-controlled water bath at three different temperatures. Stress and strain values were extrapolated from the raw data, and 2-way ANOVA and Tukey's test for multiple comparisons were performed to compare the differences of the mechanical constants. Differential scanning calorimetry (DSC) tests established the martensitic transformation starting (M_s), finishing (M_f) and austenitic (reverse-martensitic) starting (A_s) and finishing (A_f) points. Austenitic modulus of elasticity and transformation stress values increased with temperature for all NiTi groups. The martensitic modulus of elasticity, maximum transformation strain and ultimate tensile stress were not significantly affected by temperature changes. Stock NiTi and Gold wire samples presented with clearly delineated austenitic and martensitic transformations in the DSC experiments. Differences in manufacturing/heat treatment conditions and ambient temperature affect the mechanical behavior of nickel-titanium and may have clinical implications. Further improvements to the experimental setup could be considered to provide more accurate measurements of strain.

Evaluation of design, mechanical properties, and torque/force generation of heat-treated NiTi glide path instruments

BACKGROUND

Recently, various kinds of heat-treated nickel-titanium (NiTi) glide path instruments have been manufactured. This study aimed to investigate design, phase transformation behavior, mechanical properties of TruNatomy Glider (#17/02), V Taper 2H (#14/03), and HyFlex EDM (#15/03) and compare torque/force generated during simulated glide path preparation with them.

METHODS

The designs and phase-transformation behaviors of the instruments were examined via scanning electron microscopy (n = 3) and differential scanning calorimetry (n = 2). Their bending (n = 15), torsional (n = 15), and cyclic fatigue resistances (n = 15) were tested. The ultimate strength and distortion angle were obtained from torsional resistance test. The number of cycles to failure (NCF) was calculated from cyclic fatigue resistance test. The preparation of the glide path was simulated using a double-curved artificial canal (n = 15), and the maximum torque and screw-in forces were measured. Data except NCF was compared between brands with one-way ANOVA with Tukey's honestly significant difference test. NCF was analyzed via Kruskal-Wallis and Mann-Whitney U tests.

RESULTS

TruNatomy Glider had the greatest number of threads. TruNatomy Glider showed progressive taper, while V Taper 2H and HyFlex EDM had constant taper. The austenitic transformation-finish temperatures of all the instruments were above body temperature. V Taper 2H demonstrated significantly lower ultimate strength, higher distortion angle, and a higher number of cycles to failure compared with HyFlex EDM and TruNatomy Glider (p < 0.05). The maximum torque generated during preparing glide path was lowest for V Taper 2H, and the maximum screw-in force was lowest for HyFlex EDM (p < 0.05). TruNatomy Glider generated the highest torque and screw-in force during the apical preparation.

CONCLUSIONS

V Taper 2H #14/03 showed superior cyclic fatigue resistance and lower ultimate strength. TruNatomy Glider generated greater clockwise torque and screw-in force during apical preparation. The mechanical properties, torque, and screw-force was affected by design of heat-treated glide path instruments. Cervical pre-flaring prior to glide path instrument is recommended.

A comparative study of cyclic fatigue of 6 endodontic systems. An in vitro study

Background

Mechanical preparation and the formation of space for adequate obturation are included in root canal shaping, but the complex root canal anatomy may be affect it. Manufacturers have created different alloys like M-Wire, Blue-Wire, Gold-Wire or R-phase. Objective: This investigation was performed to verify the null hypothesis that there were not significant differences between size 25 instruments ESP Files Thermoflex, Protaper Ultimate, Protaper Next, Blueshaper, One Curve and 2Shape about cyclic fatigue and length of broken fragments.

Material and Methods

180 new size 25 files of the systems investigated were selected (n=30). Files were used with Endo Mate DT endo motor with speed and torque recommended by manufacturers, holding the instruments with clamping mechanism, with passive adjustment, glycerine and without pressure in a stainless-steel block. The time was calculated in seconds until fracture. Number of fatigue cycles was determined as (Resistance (s) x Speed)/60. Separated fragment lengths were calculated with digital Vernier caliper. Statistical analysis was carried out with the SPSS 18 programme at a 95% confidence level, using Levene´s Test to compare variances, Welch’s Test to compare means, and Games-Howell´s Test to reveal differences between groups.

Results

Levene’s Test determined no equal variances (P<0.05). Welch’s Test and ANOVA (P<0.05) showed significant differences in cyclic fatigue and separated fragment lengths. Games-Howell’s and Bonferroni´s Test established significant differences in multiple comparisons (P<0.05).

Conclusions

ESP Files Thermoflex was superior in cyclic fatigue. About separated fragment lengths, ESP Files Thermoflex, Protaper Ultimate and Blueshaper obtained longer lengths.

Key words:Cyclic fatigue, continuous movement, separated fragment lengths, rotary systems.

Mechanical Properties of the New Generation RACE EVO and R-Motion Nickel-Titanium Instruments

This study aimed to evaluate and compare the dynamic cyclic fatigue, torsional and bending resistance of two novel RACE EVO (FKG Dentaire SA, La Chaux de Fonds, Switzerland) and R-Motion (FKG) nickel−titanium instruments with traditional RaCe (FKG) instruments. RACE EVO, R-Motion and RaCe instruments with a size of 25 and taper of 0.06 were used. A dynamic cyclic fatigue test was used to assess the time to fracture. The fractured surfaces were further analyzed using scanning electron microscopy at ×350 and ×3000 magnifications. A torsional resistance test was performed to measure the maximum torsional strength and angle of rotation. Phase transformations with temperature were evaluated using differential scanning calorimetry. The results were statistically analyzed with a Kruskal−Wallis test at a 5% significance level. R-Motion had the highest time to fracture and the lowest torsional and bending resistance, whereas RaCe had the lowest time to fracture and the highest torsional and bending resistance (p < 0.05). In relation to the angle of rotation, RACE EVO instruments had the highest deformation capacity followed by R-Motion and RaCe instruments (p < 0.05). The greater cyclic fatigue resistance and lower torsional and bending resistance results indicate that the novel R-Motion and RACE EVO instruments are less rigid and more flexible than RaCe instruments.

Comparative Assessment of the Shaping Ability of Reciproc Blue, WaveOne Gold, and ProTaper Gold in Simulated Root Canals

Maintaining the original trajectory of the root canal is a major challenge in endodontic therapy, especially in narrow and curved root canals. The present study aims to assess the shaping capacity of three endodontic systems made of different nickel−titanium alloys on simulated curved root canals. Thirty-six endodontic resin blocks (Ref. V040245, VDW) divided into three groups, each of twelve blocks (n = 12), were shaped, photographed, and analyzed: Group 1-Protaper Gold (PTG) (Dentsply Maillefer, Ballaigues, Switzerland) F2 25/08; Group 2-Reciproc Blue (RB), RB 25/08 (VDW, Munich, Germany); Group 3-WaveOne Gold (WOG) (Dentsply Maillefer), WOG 25/07. Each block was standardized and photographed before and after shaping in the same position, with the foramen oriented to the left. Post-shaping images were superimposed onto the initial ones. Thirteen measurement points were used for evaluation, spaced with 1 mm distance from one another, from level 0, apical foramen, to level 12, coronal orifice. The amount of removed resin from inner (X1) and outer (X2) walls, the direction of transportation (X1 − X2), and the centering ability (X1 − X2)/Y were measured, calculated, and comparatively analyzed. Statistical differences (p < 0.05) were observed between the shaping capacity of the considered systems in the middle and coronal thirds. PTG had a better centering ability than WOG and RB in the coronal third, while RB was more centered in the middle third in comparison to both WOG and PTG. In the apical third, the centering capacity of WOG was higher, without being statistically significant. WOG 25/07 and PTG 25/08 tend to cut more on the inner wall of the root canals, and RB 25/08 on the external one.

Evaluation of Cyclic Fatigue and Bending Resistance of Coronal Preflaring NiTi File Manufactured with Different Heat Treatments

Coronal preflaring NiTi files should possess proper hardness, resistance to fracture and flexibility. This study compared the bending resistance and cyclic fatigue resistance of three orifice preflaring NiTi files. HyFlex EDM Orifice opener (#25/12), HyFlex CM (#25/08) and One Flare (#25/09) were tested (n = 46/instrument). Bending resistance was assessed with the stress when perpendicular displacement was applied to a 3 mm point from the file tip, and was performed at either room temperature (RT, n = 10) or body temperature (BT, n = 10). Cyclic fatigue resistance was tested with an artificial ceramic root canal at RT (n = 10) and BT (n = 10), and the number of cycles to failure (NCF) was obtained. The bending resistance and the NCF results were analyzed by two-way ANOVA and Tukey’s test. Differential scanning calorimetry (DSC) and X-ray diffraction (XRD) analyses were performed (n = 3, respectively). HyFlex EDM exhibited the highest bending resistance, followed by One Flare and HyFlex CM (p < 0.05), irrespective of the tested temperature. At RT, HyFlex CM demonstrated the highest NCF (p = 0.001), while HyFlex EDM had the highest NCF at BT (p < 0.001). The tested NiTi files were composed of austenite and martensite according to the DSC and XRD results. HyFlex EDM had the highest bending resistance and NCF measured at BT.