Controlled Memory Wire Research Articles

Hyflex CM and EDM from Shape Memory to Control Memory.

The new era in endodontics has been established with the introduction of nickel titanium (NiTi) alloys, and later on the automation of mechanical preparation. By changing the phase transformation temperatures of NiTi alloy, the manufacturers alter the phase composition to have a NiTi with new mechanical properties. These mechanical properties can be achieved either by thermal, mechanical treatments or both. Moreover, many machining procedures (e.g. twisting, electrical discharge machining), were developed. The higher flexibility of thermomechanically treated NiTi alloys was found as the main advantages of these alloys with the improvement of cyclic fatigue resistance when compared to conventional NiTi. Austenitic alloys have superelastic properties due to stress-induced martensite transformation and consequently try to springback to their original shape after distortion. In contrast, the martensitic instruments have ability to reorientation of martensite variants when heated. So these instruments easily deformed and show a shape memory effect. Moreover, the use of martensitic alloy results in more flexible files, with an increased cyclic fatigue resistance compared with austenitic alloy. So, continued development in the manufacturing treatment of NiTi alloys has resulted in the producing of controlled memory (CM) wire. These materials do not possess superelastic properties at neither room nor body temperature. This article reviews the development process, features and properties of Hyflex file and Hyflex EDM file made from CM wire. Keywords: NiTi alloy, CM wire, Hyflex EDM, Heat treated NiTi

Cyclic fatigue resistance for six types of nickel titanium instruments at artificial canals with different angles and radii of curvature.

This study evaluated the cyclic fatigue resistance for six types of 25# NiTi instruments. A traditional manufacturing instrument, an M wire instrument, a gold treatment instrument, a controlled memory (CM) wire instrument, a CM wire instrument with electrical discharge machining (EDM), and an R-phase heat treatment instrument, were operated in the different curved artificial canals. The fracture time (FT) and number of cycles to fracture (NCF) of the NiTi instruments were higher at 45° angles and double-curvature canals than at 60° angles. Except for the instruments with gold technology and EDM technology, others showed the longest FT and the highest NCF at an 8 mm radius of curvature. Morphological characteristics of cyclic fatigue were exhibited on the cross-section and lateral view of fracture fragments. The use of M-wire, R-phase wire, CM-wire, gold technology, EDM technology, and reciprocating movement were beneficial to enhance the cyclic fatigue resistance of NiTi files.

CYCLIC FATIGUE RESISTANCE OF NEWLY INTRODUCED SURFACE AND THERMAL TREATED NICKEL-TITANIUM ROTARY FILES

Objectives The main objective of the present study invitro was to evaluate the cyclic fatigue resistance and metallurgic properties of newly thermal treated (CM wire) rotary Ni-Ti files with different surface treatments.Materials and Methods: A total of one hundred and twenty rotary files were used from three different rotary systems with the same thermomechanical treatment – controlled memory wire (CM Wire) and different surface treatment technique using rotation motion. Groups were set as Group 1: M3 Pro Gold (United Dental, Shanghai, China) (CM Wire) size (25/0.04), Group 2: AF F One Blue (Fanta Dental Material Co., Shanghai, China) [controlled memory wire (CM Wire)] size (25/0.04) and Group 3: Hyflex EDM (25/ 0.04). These files were tested for cyclic fatigue resistance using a custom-made static cyclic fatigue testing apparatus with various angles and radius (angle 60 radius 2.5mm and 5mm radius and angle 90 radius 2.5mm and 5mm). Each rotary file was coated with EDTA after its attachment in handpiece supported in stainless steel cylinder apparatus. M3 Pro Gold rotary files, AF F one blue and Hyflex EDM rotary files were rotated at 500rpm 2.5N/cm torque according to manufacture instructions. Digital watch was used to record the time taken until file fracture in seconds and the (NCF) number of cycles till fracture were calculated. Scanning electron microscope SEM image of the fractured surface were taken. Statistical analysis was performed using one-way analysis of variance and Tukey’s test at the 95% confidence level (P = 0.05). Results: After comparing the cyclic fatigue resistance of AF F One Blue and M3 Pro Gold by recording time till the file fracture was ranged between 670s to 1180s in all groups at angle 60 degree with different radius and 10s to 815s in all groups at angle 90 degree with different radius. There were no significant differences between the M3 Pro Gold and AF F One Blue rotary files at angle 60 degree and 90 degree in both radius 2.5mm and 5mm ( P> 0.05), while there were significant differences between the Hyflex EDM and M3 Pro Gold and AF F One Blue rotary files at angle 60 degree, radius 2.5mm ( P> 0.05). Hyflex EDM have the highly significant differences M3 Pro Gold and AF F One Blue rotary files at angle 90 degree, radius 2.5mm (P < 0.001). Conclusions: All new thermomechanical treatment technique - controlled memory CM-Wire rotary systems represented great performance and remarkable enhancement in cyclic fatigue resistance but the Hyflex EDM rotary files had the highest cyclic fatigue resistance among the M3 Pro Gold and AF F one Blue rotary files. Also surface treatment of the rotary files enhancing the cyclic fatigue resistance by decreases surface micro cracks and the tendency to fracture.

Comparison of the cyclic fatigue resistance of nickel-titanium rotary instruments manufactured using controlled memory wire

Comparison of the cyclic fatigue resistance of nickel-titanium rotary instruments manufactured using controlled memory wire

Effect of deep cryogenic treatment on cyclic fatigue resistance of controlled memory wire nickel-titanium rotary instruments

Cryogenic methods have been used to increase the wear, abrasion, corrosion resistance and to improve the strength of metals. The aim of this study was to evaluate the effect of cryogenic treatment on the cyclic fatigue resistance of rotary nickel-titanium (NiTi) instruments. In this in vitro study, 20 Hyflex (Coltene, Altstätten, Switzerland) nickel-titanium instruments, size 25, 0.06 taper, were randomly divided into two groups as follows: untreated NiTi rotary files (Group A) and cryotreated NiTi rotary files (Group B). The instruments of Group A were completely immersed in a cryocan containing liquid nitrogen (-196°C) for 24 h. After 24 h, the instruments were removed from the bath and were allowed to return to room temperature gradually. All files were used (at a speed of 500 rpm and a torque of 2.5 Ncm) in an artificial canal with a 60° curvature until fracture. Time to failure was recorded with a stopwatch in seconds and subsequently converted to number of cycles to fracture (NCF). Groups were compared using the independent-samples t-test. The level of statistical significance was set at 0.05. Mean NFCs in Group A and B were 1576 and 1395, respectively. However, statistical analysis showed that there was no significant difference between the groups (P = 0.2). Deep cryotherapy of NiTi endodontic files cannot improve the cyclic fatigue resistance of HyFlex files, but further studies are required to evaluate these cryogenically treated NiTi files clinically.

Surface topography and cutting efficiency study of a preheated controlled memory wire machined endodontic file after exposure to different irrigants: An in vitro study

Aim: To examine the effect of seven irrigants on surface topography and cutting efficiency of Mpro files when files are immersed for 10 min. Materials and Methods: This was an in vitro study; sixty-three MPro files were used divided into seven groups (nine each). Groups were immersed in irrigants for 10 min: Group 1 Saline, Group II Curcumin, Group III EDTA 17%, Group IV Lycopene, Group V Chitosan 0.3%, Group VI Chitosan 0.5% and Group VII sodium hypochlorite. Files were inspected by scanning electron microscope and all photomicrographs were reviewed and scored according to the defects found. All previously immersed files were used to prepare plastic blocks with simulative canals to assess cutting efficiency by weight loss technique Data were analyzed using chi-square, one-way analysis of variance (ANOVA)/Tukey’s test and linear regression. Results: Groups I, V, and VI showed no defects. Group II showed pitting, fretting blunting, and disruption of cutting edge and residues. Group III showed pitting, blunting, and disruption of cutting edges. Group IV showed pitting, blunt cutting edges, and residues. Group VII showed fretting blunt and disruption of cutting edges, micro fractures, and metal flash. None of groups showed corrosion. Results for the cutting efficiency study showed a significant difference between all groups among which the highest mean of debris cut was recorded by Group V chitosan 0.3%Conclusion: Chitosan 0.3 and 0.5% did not affect the surface topography of Mpro file. Chitosan 0.3% enhanced the file’s cutting efficiency, so can be recommended to be used as irrigation.

Torsional and Bending Properties of V Taper 2H, ProTaper NEXT, NRT, and One Shape.

Nickel-titanium (NiTi) rotary files have enabled efficient root canal preparations that maintain the canal center with fewer aberrations compared to hand files. However, NiTi rotary files are susceptible to fracture, which can thereby compromise root canal treatment. Therefore, NiTi files have been developed to enhance fracture resistance by modifying design and thermal treatment. The objective of this study was to compare the torsional fatigue resistance and bending resistance of NiTi files manufactured from different alloys and treatments. ProTaper NEXT X2 (PTN; M-wire), V taper 2H (V2H; controlled memory wire), NRT (heat-treated), and One Shape (OS; conventional alloy) instruments of tip size #25 were compared. Torsional fatigue was evaluated by embedding the 3 mm tip of each instrument (N = 10/brand) in resin and the repetitive application of torsional stress (300 rpm, 1.0 N·cm) by an endodontic motor with autostop when the file fractured. The number of loading cycles to fracture was recorded and analyzed by Kruskal–Wallis and Mann–Whitney U tests with Bonferroni's correction. Bending resistance of the instruments was tested using a cantilever bending test to the 3 mm point from the tip (N = 10/brand). The stress was measured when deflection of 3 mm was subjected and statistically analyzed with a one-way analysis of variance and Tukey's honest significance difference test (α = 0.05). V2H withstood the highest number of load applications during torsional fatigue testing (p < 0.05), followed by NRT, PTN, and OS, where the differences between NRT and PTN (p=0.035) and between PTN and OS (p=0.143) were not statistically significant. V2H showed the lowest bending stiffness, followed by NRT, PTN, and OS (p < 0.001). Thermal treatment of NiTi wire resulted in improved mechanical properties, and controlled memory wire provided improved flexibility and torsional fatigue resistance.

Influence of heat treatment on torsional resistance and surface roughness of nickel-titanium instruments.

To evaluate the influence of controlled memory (CM) thermal treatment on the torsional resistance and surface roughness of nickel-titanium instruments with identical geometric and dimensional characteristics. The influence of environmental temperature on torsional resistance was also evaluated. A sample of 25 conventional NiTi alloy and 25 CM thermal-treated NiTi instruments, with an identical geometric design and a nominal size of 0.25mm at D0 and a nominal taper of .06mmmm-1 were selected. The torsional strength and the angle of rotation of the instruments were tested following ISO 3630-1 at two temperatures: 21 and 35°C. The fracture surfaces of all tested instruments were verified with a scanning electron microscope. The surface roughness of the blades of conventional NiTi alloy and CM wire files was evaluated by using a New View 7100 Profilometer. Statistical analysis was performed using Student's t-test and paired t-test to analyse the torsional resistance and surface roughness at a significance level of P<0.05. The torsional strength of thermally-treated instruments was significantly lower than nontreated instruments (P<0.05). However, thermally-treated instruments had significantly greater angular rotation to fracture than nontreated instruments (P<0.05). Temperature did not influence the torsional strength (P>0.05) and the angular rotation (P>0.05) of the instruments. Regarding the roughness measurements, groove depth was lower at the surface of thermally-treated instruments when compared to nontreated instruments (P<0.05). Thermal treatment influenced the torsional resistance and surface roughness of NiTi instruments with identical geometric and dimensional characteristics. Temperature did not affect torsional behaviour.

EFFECT OF HEAT TREATMENT ON CYCLIC FATIGUE, FLEXIBILITY AND PHASE TRANSFORMATION OF TWO CONTROLLED MEMORY NITI ROTARY INSTRUMENTS

Aim: The aim of this study the effect of heat treatment on flexibility, cyclic fatigue and of OneCurve nickel-titanium (Ni-Ti) rotary file (OC) and compare them with those of EdgeFile (EF) NiTi file as both files manufactured from a controlled memory wire. Methods: A sample of 45 instruments with tip size of 25 and 0.06 taper from both OC and EF were selected for the current study. The cyclic fatigue testing was performed using dynamic mode. The bending resistance was tested using the universal testing machine and files were bent until reach 45°. In addition, dispersive scanning calorimetric analysis (DSC) was carried out for identification of Af transformation temperature. An independent t-test was used in the statistical analysis and significance difference was set at p-value 0.05. Results: The EF files showed significantly greater resistance to cyclic fatigue (p<0.05). As well as, the EF exhibited less bending resistance than OC (p<0.5). The DSC analysis showed that the OC has an Af near 54°C, while the EF was near 57°C. Conclusions: The EdgeFile NiTi rotary instruments have high flexibility and high resistant to cyclic fatigue than OneCurve does when tested in dynamic mode and both have a close has an Af temperature exceeding 50˚C

Influence of proper or reciprocating optimum torque reverse kinematics on cyclic fatigue of four single files.

The aim of the present study was to evaluate the resistance to cyclic fatigue of heat-treated single files used in proper or in reciprocating optimum torque reverse motions. Ninety-six HyFlex electrical discharge machining (EDM), Reciproc R25 (Rec), WaveOne Primary (WO), and WaveOne Gold (WOG) Primary were used. Resistance to cyclic fatigue was determined by recording time to fracture in a stainless steel artificial canal. Differential scanning calorimetric analysis was performed. Data were analyzed by two-way analysis of variance and Bonferroni post-hoc tests at 0.05. In both movements, HyFlex EDM showed higher time to fracture than other files (P<0.0001). Rec showed higher time to fracture than WO (P<0.0001), while WOG showed higher cyclic fatigue resistance than Rec and WO with both movements (P<0.005). Reciprocating optimum torque reverse motion improved significantly cyclic fatigue resistance of gold and controlled memory wire single files.

Construction and mechanical analysis of finite element model for bending property of controlled memory wire nickel-titanium rotary file

To construct a model for a controlled memory (CM) nickel-titanium (NiTi) file and another M-wire NiTi file with the same geometry by using finite element analysis. To evaluate the flexibility of a CM NiTi file by using three dimensional finite element method and to compare its mechanical responses with that M-wire NiTi. Based on the reverse engineering, the 21 mm long, 25#/08 taper Hyflex NT NiTi file and Hyflex CM NiTi file were fixed by the cantilever bending model at a distance of 9.5 mm from the tip of the file. The mechanical tester's indenter was loaded/unloaded at a distance of 3 mm from the tip of the file. The maximum displacement was 3 mm, the load displacement curve was obtained. Subsequently, by using a micro-CT to scan (layer spacing of 8 μm) NiTi files, and ABAQUS (6.10) was introduced to construct a geometric model. Hyflex NT was considered as a shapememory alloy constitutive model, Hyflex CM was considered as a power-hardening plastic constitutive model, respectively. Comparing the load-displacement curve of cantilever bending in the three-dimensional finite element model with the load-displacement curve in the experiment. Two tetrahedral element models were constructed, the total number of nodes was 99 353 and the total number of cells was 63 744. When the loading displacement was 1 mm, the stress distribution of the cross section at 6.1 mm from the tip of the file was observed. The upper and lower surfaces were subjected to the maximum bending stress and entered the phase transformation yield stage. The finite element simulation could clearly show the deformation of the file. Various information such as deformation characteristics and stress distribution in the process were well fitted to the actual experimental curve. The constitutive behavior of the material has a significant effect on the mechanical behavior of NiTi file. The finite element model established for the NiTi file of the CM wire can accurately capture the characteristics of various deformation processes of the NiTi root canal file, and it has a good fit with the actual experimental curve. The finite element model can be used for study on bending properties of CM wire.

Nickel-Titanium Rotary File Systems: What's New?

Ever since their introduction, nickel–titanium (NiTi) alloys have continued to revolutionize the field of endodontics. They have considerable advantages over the conventional stainless steel file in terms of mechanical properties. However, despite of their superior mechanical properties, NiTi alloys still pose some risk of fracture. Consequently, there has been considerable research conducted to investigate the mechanisms behind the occurrence of these procedural errors. Since the last decade, different proprietary processing procedures have been introduced to further improve the mechanical properties of NiTi alloys. These treatments include thermal, mechanical, electropolishing, and recently introduced electric discharge machining. The main purpose of these treatments is to impart a more martensitic phase into the files at normal body temperature, so that the maximum advantage of flexibility can be obtained. These heat-treated instruments also possess improved cyclic fatigue resistance when compared to conventional NiTi alloys. NiTi alloys can be subclassified as the instruments mainly containing austenitic phase (conventional NiTi, M-wire, R-phase), and those containing martensitic phase (controlled memory wire, ProTaper Gold, and Vortex Blue). Instruments based on austenitic alloys possess superelastic properties due to the stress-induced martensitic transformation. Contrary to this, martensitic alloys can easily be deformed due to phase transformation, and they can demonstrate the shape memory effect when heated. This review discusses the different phase transformations and heat treatments that the NiTi instruments undergo.

Cyclic Fatigue Resistance of Novel Rotary Files Manufactured from Different Thermal Treated Nickel-Titanium Wires in Artificial Canals.

The aim of this in vitro study was to compare the static cyclic fatigue resistance of thermal treated rotary files with a conventional nickel-titanium (NiTi) rotary file. Four groups of 60 rotary files with similar file dimensions, geometries, and motion were selected. Groups were set as HyFlex Group [controlled memory wire (CM-Wire)], ProfileVortex Group (M-Wire), Twisted File Group (R-Phase Wire), and OneShape Group (conventional NiTi wire)] and tested using a custom-made static cyclic fatigue testing apparatus. The fracture time and fragment length of the each file was also recorded. Statistical analysis was performed using one-way analysis of variance and Tukey's test at the 95% confidence level (P = 0.05). The HyFlex group had a significantly higher mean cyclic fatigue resistance than the other three groups (P < 0.001). The OneShape groups had the least fatigue resistance. CM-Wire alloy represented the best performance in cyclic fatigue resistance, and NiTi alloy in R-Phase had the second highest fatigue resistance. CM and R-Phase manufacturing technology processed to the conventional NiTi alloy enhance the cyclic fatigue resistance of files that have similar design and size. M-wire alloy did not show any superiority in cyclic fatigue resistance when compared with conventional NiTi wire.

Torsional fatigue resistance of pathfinding instruments manufactured from several nickel-titanium alloys.

To evaluate the torsional properties of pathfinding nickel-titanium (NiTi) rotary instruments manufactured from several NiTi alloys, ProGlider (M-wire), Hyflex GPF (conventional NiTi Wire and controlled memory wire), Logic (conventional NiTi wire and controlled memory wire) and Mtwo (conventional NiTi wire). A total of 56 NiTi instruments from Glidepath rotary systems (n=8) were used: Logic (size 25, .01 taper), Logic CM (size 25, .01 taper), ProGlider (size 16, .02 taper), Hyflex GPF (size 15, .01 taper), Hyflex GPF CM (size 15, .02 taper; size 20, .02 taper) and Mtwo (size 10, .04 taper). The torsion tests were performed based on ISO 3630-1 (1992). Three millimetres of each instrument tip was clamped to a small load cell by a lever arm linked to the torsion axis. Data were analysed using a one-way analysis of variance (anova) and Tukey test with a significance level at a=5%. The Logic size 25, .01 taper had significantly higher torsional strength values (P<0.05). The ProGlider was significantly different when compared with Hyflex GPF size 15, .01 taper and size 15, .02 taper (P<0.05). The Logic CM size 25, .01 taper had significantly higher torsional strength than Hyflex GPF size 15, .01 taper and size 15, .02 taper (P<0.05). No difference was found amongst Mtwo size 10, .04 taper and Hyflex GPF groups (size 15, .01 taper; size 15, .02 taper; size 20, .02 taper). In relation to the angle of rotation, Logic CM size 25, .01 taper and Hyflex GPF size 15, .01 taper had the highest angle values (P<0.05). The ProGlider had the lowest angle values in comparison with all the groups (P<0.05) followed by Mtwo size 10, .04 taper. The Logic size 25, .01 taper had significantly higher angle of rotation values than ProGlider and Mtwo size 10, .04 taper (P<0.05). The Logic size 25, .01 taper instrument made of conventional NiTi alloy had the highest torsional strength of all instruments tested. In addition, the ProGlider instrument manufactured from M-Wire alloy had the lowest angle of rotation to fracture in comparison with the other instruments.

A new torquemeter to measure the influence of heat-treatment on torsional resistance of NiTi endodontic instruments

Abstract NiTi endodontic rotary instruments have increased flexibility and strength compared with stainless steel instruments, but they seem to be vulnerable to fracture in clinical situations. Heat treatment (thermal processing) is one of the most fundamental approaches toward adjusting the transition temperatures of NiTi alloys and affecting the fatigue and torsional resistance of NiTi endodontic files. In recent years, novel thermo-mechanical processing and manufacturing technologies such as controlled memory wire (CM-wire), M-Wire and electrical discharge machining (EDM) have been developed to optimize the microstructure of NiTi alloys and their mechanical properties. Aim of this work was to investigate the torsional resistance (maximum torque load, and angular rotation) of NiTi instruments made by different thermo-mechanical and manufacturing processes. For this purpose, a torque device able to perform static and dynamic tests of Ni-Ti instruments for root canal treatment was designed and realized, by performing this device through the design and optimization of the single components and on the system globally.

Comparison of the Cyclic Fatigue Resistance of Nickel-Titanium Rotary Instruments Manufactured using Controlled Memory Wire

Comparison of the Cyclic Fatigue Resistance of Nickel-Titanium Rotary Instruments Manufactured using Controlled Memory Wire

Effect of irrigation on surface roughness and fatigue resistance of controlled memory wire nickel-titanium instruments.

To investigate the effect of irrigation on the surface roughness and fatigue resistance of HyFlex and M3 controlled memory (CM) wire nickel-titanium instruments. Two new files of each brand were analysed by atomic force microscopy (AFM). Then, the instruments were dynamically immersed in either 5.25% sodium hypochlorite (NaOCl) or 17% ethylene diamine tetraacetic acid (EDTA) solution for 10min, followed by AFM analysis. The roughness average (Ra) and root mean square (RMS) values were analysed statistically using an independent sample t-test. Then, 36 files of each brand were randomly assigned to three groups (n=12). Group 1 (the control group) was composed of new instruments. Groups 2 and 3 were dynamically immersed in 5.25% NaOCl and 17% EDTA solutions for 10min, respectively. The number of rotations to failure for various groups was analysed using the one-way analysis of variance software. For M3 files, the Ra and RMS values significantly increased (P<0.05) after the immersion. For the HyFlex file, the Ra and RMS values significantly increased (P<0.05) only in EDTA, but not (P>0.05) NaOCl. The resistance to cyclic fatigue of both HyFlex and M3 files did not significantly decrease (P>0.05) by immersing in 5.25% NaOCl and 17% EDTA solutions. Except the HyFlex files immersed in NaOCl, the surface roughness of other files exposed to irrigants increased. However, a change in the surface tomography of CM wire instruments caused by contact with irrigants for 10min did not trigger a decrease in cyclic fatigue resistance.

Influence of heat-treatment on torsional resistance to fracture of nickel-titanium endodontic instruments

Over the past 3 decades, Nickel-Titanium (NiTi) instruments have become an important part of the armamentarium for shaping phase of root canal treatment. NiTi endodontic files have increased flexibility and strength compared with stainless steel instruments, but they seem to be vulnerable to fracture in clinical situations. Many variables might contribute to file separation, but the 2 main causes are cyclic fatigue and torsional stress. Heat treatment (thermal processing) is one of the most fundamental approaches toward adjusting the transition temperatures of NiTi alloys and affecting the fatigue and torsional resistance of NiTi endodontic files. In recent years, novel thermo-mechanical processing and manufacturing technologies such as controlled memory wire (CM-wire), M-Wire and electrical discharge machining (EDM) have been developed to optimize the microstructure of NiTi alloys and their mechanical properties. Aim of this work was to investigate the torsional resistance (maximum torque load, and angular rotation) of NiTi instruments made by different thermo-mechanical and manufacturing processes.One-hundred new Hyflex EDM One- File (#25/0.08, CM-wire and EDM process), WaveOne Primary (#25/0.08, M-wire), ProTaper Next X2 (#25/0.06, M-wire), Hyflex CM (#25/0.06, CM-wire) and F6 SkyTaper(#25/0.06, conventional NiTi) files were used. Torque and angle of rotation at failure of new instruments (n = 20) were measured using a torsiometer according to ISO 3630-1 for each brand. Data were analyzed using the analysis of variance test and the Student- Newman-Keuls test for multiple comparisons. The fracture surface of each fragment was examined with a scanning electron microscope.Files made by CM wire size #25, 0.06 taper (Hyflex CM) showed same torque load and angular rotation to fracture than conventional NiTi (F6 SkyTaper) (P > .05); instead CM files (manufacturing by grinding or EDM process) recorded lower maximum torque load (P < .05) but significantly higher angular rotation (P < .0001) to fracture than M-wire for both instruments size #25, 0.06 taper and size #25, 0.08 taper (Hyflex EDM OneFile/WaveOne Primary; Hyflex CM/ProTaper Next X2). Conventional (F6 SkyTaper) NiTi files showed same torque load (P > .05) but significantly higher angular rotation (P < .05) to fracture than M-wire instruments size #25, 0.06 taper (ProTaper Next).Hyflex EDM One-File and Hyflex CM have same torque load and angular rotation to fracture than F6 SkyTaper due to the higher flexibility and cross-sectional area of CM files tested than conventional NiTi one.Moreover CM files showed lower torque load and higher angular rotation to fracture than M-wire instruments due to the flexibility of CM alloy. M-wire instruments showed same torque load but significantly lower angular rotation than conventional NiTi files due to the same flexibility and higher cross-sectional area of the files tested.

Torsional and Cyclic Fatigue Resistance of a New Nickel-Titanium Instrument Manufactured by Electrical Discharge Machining

IntroductionThe purpose of this study was to evaluate the torsional and cyclic fatigue resistance of the new Hyflex EDM OneFile (Coltene/Whaledent AG, Altstatten, Switzerland) manufactured by electrical discharge machining and compare the findings with the ones of Reciproc R25 (VDW, Munich, Germany) and WaveOne Primary (Dentsply Maillefer, Ballaigues, Switzerland). MethodsOne hundred-twenty new Hyflex EDM OneFile (#25/0.08), Reciproc R25, and WaveOne Primary files were used. Torque and angle of rotation at failure of new instruments (n = 20) were measured according to ISO 3630-1 for each brand. Cyclic fatigue resistance was tested measuring the number of cycles to failure in an artificial stainless steel canal with a 60° angle and a 3-mm radius of curvature. Data were analyzed using the analysis of variance test and the Student-Newman-Keuls test for multiple comparisons. The fracture surface of each fragment was examined with a scanning electron microscope. ResultsThe cyclic fatigue of Hyflex EDM was significantly higher than the one of Reciproc R25 and WaveOne Primary (P < .05 and P < .001, respectively). Hyflex EDM showed a lower maximum torque load (P < .05) but a significantly higher angular rotation (P < .0001) to fracture than Reciproc R25 and WaveOne Primary. No significant difference was found comparing the maximum torque load, angular rotation, and cyclic fatigue of Reciproc R25 and WaveOne Primary (P > .05). ConclusionsThe new Hyflex EDM instruments (controlled memory wire) have higher cyclic fatigue resistance and angle of rotation to fracture but lower torque to failure than Reciproc R25 and WaveOne Primary files (M-wire for both files).

Comparison of the Cyclic Fatigue Resistance of 5 Different Rotary Pathfinding Instruments Made of Conventional Nickel-Titanium Wire, M-wire, and Controlled Memory Wire

IntroductionThis study compared the cyclic fatigue resistance of current nickel-titanium rotary path-finding instruments. MethodsFive types of nickel-titanium rotary pathfinding instruments were used in steel canals with a 90° curvature and a curvature radius of 3 mm (n = 10) and 5 mm (n = 10). The cyclic fatigue of the following instruments was tested at 4 mm from the tip: PathFile (#16 and a .02 taper; Dentsply Maillefer, Ballaigues, Switzerland), G-File (#12 and a .03 taper; Micro-Mega, Besançon Cedex, France), Scout Race (#15 and a .02 taper; FKG Dentaire, La Chaux-de-Fonds, Switzerland), HyFlex GPF (#15 and a .02 taper; Coltene-Whaledent, Allstetten, Switzerland), and ProGlider (#16 with a mean taper of .04125 and a .02 at the first 4 mm from the tip, Dentsply Maillefer). The length of the fractured parts was measured, and the number of cycles to fracture (NCF) was calculated. The data were statistically analyzed using Kruskal-Wallis and Mann-Whitney tests (α = .05). After Bonferroni correction, the new P value was set as .005. ResultsThe difference in the cyclic fatigue of all the files at both curvatures was statistically significant (P values from .0035 to less than .0001). The ranking of the instruments from the highest to the lowest NCF was as follows: HyFlex GPF, G files, ProGlider, PathFile, and Scout Race. The length of the fractured part of the instruments was similar in all the groups (P > .05). All the tested instruments had a lower NCF at a curvature radius of 3 mm when compared with a curvature radius of 5 mm (P < .0001). ConclusionsWithin the limitations of this study, the cyclic fatigue resistance of the HyFlex GPF instrument was the highest, and the curvature radius had a significant effect on the fatigue resistance.