Differences in Cyclic Fatigue Resistance between ProTaper Next and ProTaper Universal Instruments at Different Levels

Investigation of four nickel titanium endodontic instruments, with cyclic fatigue resistance, scanning electron microscopy, and energy dispersive x-ray spectroscopy

The aim of this study was to compare of four different nickel-titanium (Ni-Ti) endodontic files and evaluate in terms of cyclic fatigue resistance and metallurgical properties. Four different type Ni-Ti root canal files Protaper Next X2 (PTN) (Dentsply Maillefer, Ballaigues, Switzerland), One Curve (OC) #25.06 (Micro Mega, Besancon, France), EndoPlus Flex Plus Gold X2 (EPG) (Turkuaz Dental, Denizli, Turkey), and EndoPlus Flex Plus Blue #25.06 (EPB) (Turkuaz Dental, Denizli, Turkey) files were tested for cyclic fatigue resistance (n = 20). During experiments artificial zirconia block canal was used. The artificial canal designed with curvature 60° and 5-mm radius. The number of cyclic to fracture (NCF) was noted. Fractured length (FL) parts of Ni-Ti files were recorded to assessment of fracture volumetric point. All fractured surfaces of Ni-Ti files were assessed by scanning electron microscope (SEM) to confirm the type of fractures. Descriptive evaluation become accomplished for the fundamental composition of units with the aid of using energy-dispersive x-ray spectroscopy (EDX). NCF data were evaluated via Bonferroni test with post hoc multiple comparison method. OC showed the highest NCF values (p < .05). The standardization of the study was confirmed as the FL of files was statistically similar in length (p > .05). SEM analysis confirmed that all scanned samples were fractured due to cyclic fatigue. EDX analysis confirmed that EPB established the poorest Ni content file. RESEARCH HIGHLIGHTS: The cyclic fatigue-related failure of One Curve was significantly more resistant than Protaper Next and EndoPlus files. Scanning electron microscopy images showed that One Curve and Protaper Next have round tips Energy dispersive x-ray spectroscopy showed that all four endodontic instruments mainly have Nickel and Titanium elements.

Root Canal Instrumentation: Current Trends and Future Perspectives

The evolution of root canal instrumentation techniques has significantly impacted the field of endodontics, enhancing both the efficiency and outcomes of treatments. This review outlines the transition from manual to mechanical and rotary instruments, highlighting the role of nickel-titanium (NiTi) alloys and smart technologies in advancing procedural precision and reducing patient discomfort. Key historical developments and technological innovations, such as digital imaging and navigation systems, are explored for their contributions to improved clinical outcomes and patient satisfaction. Additionally, the review addresses the challenges presented by the complex anatomy of the root canal system and the advent of current instrumentation techniques. The potential of emerging trends, including artificial intelligence and advances in materials science, is discussed in the context of future endodontic practices. Despite the progress, challenges related to using advanced instrumentation methods, ethical considerations, and the cost factor of new technologies persist. The present review underscores the ongoing need for research and development to further refine root canal instrumentation techniques, ensuring that advancements in endodontic care remain patient-centered and accessible.

Advancing Nitinol: From heat treatment to surface functionalization for nickel–titanium (NiTi) instruments in endodontics

Nickel-titanium (NiTi) alloy has been extensively researched in endodontics, particularly in cleaning and shaping the root canal system. Research advances have primarily focused on the design, shape, and geometry of the NiTi files as well as metallurgy and mechanical properties. So far, extensive investigations have been made surrounding surface and thermomechanical treatments, however, limited work has been done in the realm of surface functionalization to augment its performance in endodontics. This review summarizes the unique characteristics, current use, and latest developments in thermomechanically treated NiTi endodontic files. It discusses recent improvements in nano-engineering and the possibility of customizing the NiTi file surface for added functionalization. Whilst clinical translation of this technology has yet to be fully realized, future research direction will lie in the use of nanotechnology.

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Nitinol (Nickel Titanium alloy) is widely used to clean/shape root canal system in endodontics.

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To enhance its performance, various thermo-mechanical and nano-engineering modifications have been performed.

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This comprehensive review summarizes the latest advances and future trends relating to functionalized NiTi endodontic files.

Analysis of the Importance of the Motion Used in the Resistance of Different Mechanical Instrumentation Systems in Endodontics: A Comparative Study

Aim: The aim of this study was to compare the cyclic fatigue strength of different reciprocating rotary systems depending on the movement used. Methods: Four study groups were analyzed (n = 30): (1) Reciproc®, (2) Reciproc Blue®, (3) Wave One Gold® and (4) Procodile®. Each group was divided into three subgroups according to the motion used: (A) Reflex Dynamic® (n = 10), (B) ReFlex Smart® (n = 10) and (C) conventional reciprocating motion (n = 10). They were used in a dynamic cyclic fatigue prototype until their fracture, and the time was measured in seconds. The results obtained were analyzed with the ANOVA method, and for two-to-two comparisons, the Tukey method and Weibull statistics were used. Results: Procodile ReFlex Smart had the longest time to failure, and statistically significant differences were found between Procodile ReFlex Smart and the other files and motions (p < 0.05). Conclusion: Smart motions increase cyclic fatigue strength. ReFlex Smart® motion increases the cyclic fatigue strength of reciprocating rotary systems, and Procodile® ReFlex Smart was the most resistant system file.

An Investigation of the Metal Fatigue of Different Nickel-Titanium Rotary Instruments After Prolonged Use

Objective:This study aimed to compare the cyclic fatigue (CF) resistance of nickel-titanium (Ni-Ti) endodontic instruments from ProTaper (PTU), ProTaper Next (PTN), Wave One (WO), and Reciproc (RPC). Materials and Methods:In our study, PTU, PTN, WO, and RPC rotary files were divided into the experimental and control groups containing an equal number of samples. The experimental group files were used in the shaping of 80 extracted human lower premolar and lower molar teeth. The experimental and control group kits were then placed in the test apparatus and observed until they fractured. Fracture times were recorded and statistically evaluated. Results:In the one-to-one comparisons of the experimental and control group files, while the differences between the fracture times of the experimental and control group files were found to be statistically insignificant in RPC, WO, PTU, and PTN X1 files (p>0.05), fracture time differences were statistically significant in all PTN X2 files (p0.05). Conclusion:The files used with reciprocal movement were found to be safer in terms of metal fatigue when compared to the other files used with rotational movement after the preparation.

Influence of Sodium Hypochlorite and Chlorhexidine on the Dynamic Cyclic Fatigue Resistance of XP Endo Shaper Instruments

Objective  This study evaluated the dynamic cyclic fatigue resistance of the XP-Endo Shaper (XPS), associated with chlorhexidine digluconate (CHX) or sodium hypochlorite (NaOCl) in two different formulations: gel (G) or liquid (L).

Materials and Methods  Sixty XPS were used in an artificial stainless-steel canal, and the files were fully immersed in the irrigating solution throughout the experiment until the fracture. The files were divided into six groups ( n  = 10) based on the irrigation solution used: NaOCl(L), NaOCl(G), CHX(L), CHX(G), natrosol gel (NAT) (control), and lubricating oil (LO) (control). The artificial canal was manufactured 1.5 mm wide, 20 mm long, and, 3.5 mm deep with a straight cervical segment measuring 14.29 mm; an apical segment of 4.71 mm with 3 mm radius; and 90 degrees of curvature apical 1 mm long straight segment. Resistance to cyclic fatigue was determined by recording the number of cycles to fracture (NCF).

Results  The CHX(G), CHX(L), and OIL (LO) groups showed no significant difference between them and presented longer time to fracture ( p  > 0.05). NaOCl(L) shows the lowest NCF without significant differences between NaOCl(G) and NAT. The NCF of the NaOCl(G) was statistically similar to the CHX(L) and statistically lower than the CHX(G) and OIL groups. NAT did not present a statistical difference of the NaOCl(L), NaOCl(G), and presented a significantly lower NCF than the CHX(G) ( p  < 0.01).

Conclusion  The use of CHX(G) resulted in increased cyclic fatigue resistance of the XPS instruments compared to NaOCl or LO.

A comparative investigation between ProTaper Next, Hyflex CM, 2Shape, and TF-Adaptive file systems concerning cyclic fatigue resistance

Background. This study aimed to compare the cyclic fatigue resistance of ProTaper Next, Hyflex CM, 2Shape, and TF-Adaptive nickel-titanium endodontic file systems with various alloy properties and production methods and investigate the fractured cross-sectional surface of files due to cyclic fatigue by scanning electron microscopy (SEM).

Methods. A total of 120 instruments were used (n=30). For standardization, #25/.06 apical diameter and taper angle were selected for each file system. The experiment of files was subjected to a static cyclic fatigue model. The time for files’ failure was recorded with a digital chronometer and multiplied by the rotation speed to calculate the number of cycles. Kolmogorov-Smirnov, one-way ANOVA, and post hoc Bonferroni analysis were used for statistical analysis. Statistical significance was set at P < 0.05.

Results. The number of cycles for the failure of files was compared between the groups, and significant differences were found (P < 0.05). The number of cycles for instrument failure was recorded from the highest to the lowest as follows: Hyflex CM, TF-Adaptive, ProTaper Next, and 2Shape.

Conclusion. The files were fractured at different average numbers of cycles in an artificial canal in all the groups. The Hyflex CM demonstrated better cyclic fatigue resistance than TF Adaptive, ProTaper Next, and 2Shape file systems. Factors such as production patterns, alloy properties, and the phase in which the files were produced might affect the lifespan of file systems.

Comparative evaluation of dentin volume removal and centralization of the root canal after shaping with the ProTaper Universal, ProTaper Gold, and One-Curve instruments using micro-CT

Background. The main goal of our study was to assess the volume of dentin removed and transportation in root canals using ProTaper Universal (PTU), ProTaper Gold (PTG) and One-Curve (OC). Ni-Ti rotary instruments in extracted human teeth using by micro-CT.

Methods: Thirty human upper 1st premolar teeth with two separate root canals and sturdy, mature root tips were used in the present study. Specimens were decoronated and root length was standardized for micro CT scanning before root canal preparation done. The teeth were randomly separated into three categories (n = 10) according to the rotary NiTi system used for canal instrumentation, i.e., PTU (Dentsply, Maillefer), PTG (Dentsply, Maillefer), and OC (Micro-Mega SA). After root canal preparation, samples were scanned again on micro-CT by the same scanning parameters. Surface area, canal volume, structure model index (SMI), percentage of uninstrumented area and transportation parameters were obtained for each sample before and after micro-CT analyse.

Results: No significant differences between the PTG and PTU in terms of the total volume of removed dentin, surface area and percentage of uninstrumented areas were found. However, regarding to parameters above, OC showed a lower efficacy than PTG and PTU in coronal section. Regarding canal transportation, PTG and OC showed lower mean transportation values at all levels.

Conclusion: This paper demonstrated the root canal shaping abilities of the PTU, PTG, and OC NiTi file systems. The PTG and OC systems were associated less canal transportation and a better ability to preserve dentinal walls than PTU. There was no significance different between all rotary file systems for SMI values however, PTU and PTG showed greater canal volume and surface area change than OC file systems in coronal section.

The Influence of NiTi Alloy on the Cyclic Fatigue Resistance of Endodontic Files

Background: The aim of this study was to analyze the influence of NiTi alloy in endodontic rotary instruments on cyclic fatigue resistance. Methods: One hundred and sixty-four (164) sterile endodontic rotary files were selected and distributed into the following study groups: A: 25.08 F2 ProTaper Universal (PTU) (n = 41); B: 25.06 X2 ProTaper Next (PTN) (n = 41); C: 25.08 F2 ProTaper Gold (PTG) (n = 41), and D: 25.06 ProFile Vortex Blue (PVB) (n = 41). A cyclic fatigue device was designed to conduct the static cyclic fatigue tests with stainless steel artificial root canals systems with 250 µm apical diameter, 60° curvature angle, 5 mm radius of curvature, 20 mm length, and 6% (25.06) and 8% taper (25.08). Failure of the endodontic rotary instrument was detected by a single operator through direct observation and was also filmed to allow measurement of the exact time to failure. Results were analyzed using the ANOVA test and Weibull statistical analysis. Results: All pairwise comparisons presented statistically significant differences between the time to failure for the NiTi alloy study groups (p < 0.001), except between the PTN and PVB study groups (p = 0.379). In addition, statistically significant differences between the number of cycles to failure for the NiTi alloy study groups (p < 0.001) were also observed. Conclusions: The NiTi CM-Gold wire alloy of the ProTaper Gold endodontic rotary files resulted in greater resistance to cyclic fatigue than ProFile Vortex Blue, ProTaper Next, and ProTaper Universal endodontic rotary files.

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.

A comparative study of root canal shaping using protaper universal and protaper next rotary files in preclinical dental education

BACKGROUND

Dentistry has undergone an evolution in endodontics practice caused by the advancement of rotary techniques for root canal preparation and their subsequent incorporation into the teaching of dentistry undergraduates. This research aimed to evaluate the shaping ability of third-year dental students as their first experience in rotary instrumentation using ProTaper Universal (PTU) and ProTaper Next (PTN) (Dentsply Maillefer) rotary instruments in simulated curved canals.

METHODS

Forty students instrumented 200 simulated canals with a 40° curvature in resin blocks according to the manufacturer's instructions with PTU and 39 students and 195 canals with PTN files. The canals were prepared at a speed of 300 rpm using a 16:1 reduction hand-piece powered by an electric motor (Xsmart; Dentsply Maillefer). The final apical preparation was set to F2 for the PTU and X2 for the PTN group. The change in canal curvature was evaluated based on Schneider technique using the AutoCAD 2007 software on post-digital photographs. The incidence of instrument fracture and deformation, the incidence of ledge, the change in working length (WL), and the working time were noted. The data were analyzed with Student's t-test and Chi-Square test at a significance level of 0.05 using SPSS.

RESULTS

PTN maintained the original canal curvature better, resulting in fewer fractures and ledges, and shaped the canals faster than the PTU (P < 0.05). The mean curves of the resin canals after the instrumentation for the PTU and PTN groups were 24.03° ± 3.14° and 25.64° ± 2.72°, respectively. Thirty-three (17.4%) PTU and 18 (9.3%) PTN files fractured (p < 0.05). Nine (4.5%) PTU and 2 (2.6%) PTN deformed (p > 0.05). The change in WL after instrumentation was 0.97 mm ± 0.95 mm in PTU and 0.96 mm ± 0.80 mm in PTN (p < 0.05). The mean times were 627 s ± 18 s for PTU and 379 s ± 18 s for PTN (p < 0.000).

DISCUSSION

PTN can be recommended in severely curved root canals in terms of maintenance of the original canal curvature, superior instrument fracture and fewer ledges. Even if training before preparation provides an acceptable level of canal shaping for preclinical students, the use of NiTi rotary instruments should be included in the undergraduate dental curriculum, contributing to an increase in the quality of root canal shaping and, consequently, to an improvement of the clinical experience of students.

Structural Characteristics and Torsional Resistance Evaluation of WaveOne and WaveOne Gold Instruments after Simulated Clinical Use

INTRODUCTION

The aim of this study was to compare 2 reciprocating nickel-titanium systems with different manufacturing characteristics and to evaluate the influence of simulated clinical use on their torsional resistance.

METHODS

New 25/.08 WaveOne Primary (WO; Dentsply Sirona, York, PA) and 25/.07 WaveOne Gold Primary (Dentsply Sirona) files were used in this study. The diameter and cross-sectional area at 3 mm from the tip were measured using image analyses. The alloy microstructure was evaluated by X-ray diffraction and the phase transformation temperatures by differential scanning calorimetry analyses. Forty files were divided into 4 groups: control group 1 and control group 2, which were submitted to torsion tests until rupture, and experimental group 1 and experimental group 2, in which instruments were used to shape 2 mesial canals of an extracted mandibular molar and then submitted to torsion tests until rupture.

RESULTS

WO had higher values of diameter and area at 3 mm from the tip. X-ray diffraction analysis presented R-phase and austenite for both systems. Austenite finish temperatures, determined by differential scanning calorimetry, were above room temperature. WO showed higher values of torque until rupture, and WaveOne Gold showed higher values of angular deflexion (P > .05). No differences were found between the same type of instrument in the control and experimental groups.

CONCLUSIONS

The higher torsional resistance of WO can be attributed to geometric characteristics. The use in 1 tooth with curved canals is safe and does not affect the torsional resistance of the instruments analyzed.

Comparative analysis of torque and apical force to assess the cutting behaviour of ProTaper Next and ProTaper Universal endodontic instruments

This study assessed the cutting properties of two Nickel Titanium file systems with different designs and manufacturing materials. ProTaper Next X1 and X2 (PTN; Dentsply Sirona) and ProTaper Universal S2 and F1 (PTU; Dentsply Sirona) instruments were employed. The cutting parameters, that is torque and apical forces, were determined using a specially designed bench-testing machine. Dimensional and geometric parameters were considered to evaluate the results. The average maximum torque values showed statistically significant differences (P < 0.05) among all instruments. Apical force for PTN X2 and PTU F1 instruments initially decreased and then experienced a rapid increase in the last 2 mm of the canal. For PTN X1 and PTU S2, apical force increased during the entire test. When compared to PTU files, PTN required higher torque and apical forces during the shaping procedure. The results lead us to conclude that PTN instruments demonstrated a lower cutting efficiency than PTU.

Fracture and deformation of ProTaper Next instruments after clinical use

Background

The aim of this study was to evaluate the fracture and defects observed in ProTaper Next files discarded after a normal clinical use.

Material and Methods

571 ProTaper Next rotary instruments were collected after clinical use from the clinic of endodontics over 12 months. The length of the files was measured using a digital caliper to determine any fracture, later all the files were evaluated under a stereomicroscope to observe defects such as unwinding, curving or fracture. The data obtained were analyzed using a chi-square and z test.

Results

13.83% of the discarded files showed defects, the most frequent defect was fracture (7.53%). The highest rate of fracture was observed in the X1 (17.04) files (19.87%). The presence of deformations without fracture was also more frequent in the 17.04 file (11.8%).

Conclusions

Because of the relatively high incidence of deformation of smaller files, these instruments should be considered as a single use. It is important not to exceed the maximum uses recommended by the manufacturer to reduce the risk of cyclic fatigue, the main cause of fracture of the files (79.07%). It is also important to observe each file after use to discard small defects or fractures.

Key words:Clinical use, deformation, fracture, M-Wire, ProTaper Next.

Cyclic fatigue resistance of 2Shape, Twisted File and EndoSequence Xpress nickel-titanium rotary files at intracanal temperature

Background. The aim of this study was to compare the cyclic fatigue resistance of 2Shape, Twisted File (TF) and EndoSequence Xpress (ESX) nickel-titanium rotary files at intracanal temperature (35°C).

Methods. Twenty 2Shape TS1 (25/.04), 20 TF (25/.04) and 20 ESX (25/.04) files were tested for cyclic fatigue at intracanal temperature (35°C). All the instruments were rotated in artificial canals which were made of stainless steel with an inner diameter of 1.5 mm, 60° angle of curvature and a radius curvature of 5 mm until fracture occurred; the time to fracture was recorded in seconds using a digital chronometer and the number of cycles to fracture (NCF) for each file was calculated. Kruskal-Wallis test with Bonferroni correction was performed to statistically analyze data using SPSS 21.0. Statistical significance was set at P<0.05.

Results. NCF values revealed that the 2Shape had significantly the highest cyclic fatigue resistance, followed by TF and ESX at intracanal temperature (P<0.05). The difference was significant between the TF and ESX groups (P<0.05). There was no significant difference among the 2Shape, TF and ESX files with respect to the lengths of the fractured file fragments (P>0.05).

Conclusion. Within the limitations of present study, it was concluded that the cyclic fatigue resistance of 2Shape files at the intracanal temperature is higher than that of TF and ESX files.

Impact of a modified motion on the fatigue life of NiTi reciprocating instruments: a Weibull analysis

OBJECTIVES

To evaluate the impact of a modified motion on the fatigue life of four brands of nickel-titanium (NiTi) reciprocating instruments.

MATERIALS AND METHODS

Cyclic fatigue (CF) resistance of 160 instruments was evaluated in an artificial stainless-steel canal (90° angle, 5-mm radius of curvature). WaveOne and WaveOne Gold (Denstply Maillefer, Baillagues, Switzerland) and Reciproc and Reciproc Blue (VDW, Munich, Germany) were tested with two different motions: (1) X-Smart Plus (Denstply Maillefer) endodontic motor and (2) a 4:1 contra-angle with an experimental motion (EVO) with different rotation angles and based on a sinusoidal acceleration. Motions with X-Smart Plus and EVO were recorded and analyzed at a reduced speed with VLC Media Player software for a more accurate analysis. Mean half-life, beta, and eta Weibull parameters were determined and compared.

RESULTS

Reciproc Blue resulted the most resistant instruments either with EVO or X-Smart. WaveOne Gold lasted significantly longer than WaveOne with EVO (probability of 91%) while no significant differences were found with X-Smart. Considering NCF, Reciproc, WaveOne Gold, and Reciproc Blue lasted significantly longer with EVO (probabilities of 66%, 80%, and 89% respectively). WaveOne Gold showed the highest beta parameter.

CONCLUSIONS

The experimental motion was found to have a positive impact on fatigue lifetime of reciprocating instruments.

CLINICAL RELEVANCE

Current findings provide insight for future improvements in the clinical use of reciprocating files. Experimental motions may be considered when searching for additional strategies in order to increase the safer use of NiTi files during endodontic procedures.

An in vitro cyclic fatigue resistance comparison of conventional and new generation nickel-titanium rotary files

Background

New designs and processing of Niquel-Titanium (NiTi) have been introduced to increase resistance to cyclic fatigue. The purpose of this study was to compare the cyclic fatigue resistance of 3 NiTi rotary instruments, ProTaper Next (PTN; Dentsply Maillefer, Ballaigues, Switzerland), Profile Vortex Blue (PVB; Dentsply Tulsa Dental, Tulsa, OK, USA) and ProTaper Universal (PTU; Dentsply Maillefer, Ballaigues, Switzerland).

Material and Methods

A cyclic fatigue test was conducted operating instruments from ProTaper Next X2, Profile Vortex Blue 25.06 and ProTaper F2. A total of 234 instruments were rotated in 2 simulated stainless steel curved canals with different angles of curvature (45º and 60°) and 5-mm radius of curvature. The number of cycles to fracture (NCF) was calculated. Data were compared using 2-way analysis of variance and post-hoc Bonferroni test in software (SPSS 15.0, Chicago, IL). Statistical significance was set at P<0.05.

Results

Profile Vortex Blue showed higher resistance to cyclic fatigue in both curved canals than ProTaper Next and ProTaper Universal (P<0.001). ProTaper Universal obtained the lowest resistance to cyclic fatigue in both canals (P<0.001).

Conclusions

Profile Vortex Blue was the most resistant to cyclic fatigue failure, followed by ProTaper Next and ProTaper Universal. Anatomical complexity (angle of curvature) and manufacturing process of NiTi are important factors for resistance to cyclic fatigue.

Key words:Cyclic fatigue, M-Wire, Protaper Next, ProTaper Universal, Profile Vortex Blue.

Influence of Continuous or Reciprocating Optimum Torque Reverse Motion on Cyclic Fatigue Resistance of Two Single-File Nickel-Titanium Rotary Instruments

Objective:

Different single-file instruments and kinematics have been introduced on the market. It is important to know the cyclic fatigue performance of these instruments in these new kinematics such as reciprocation of Optimum Torque Reverse (OTR) motion. The aim of this study was to evaluate the resistance to cyclic fatigue of F6 SkyTaper and OneShape used in continuous rotation (proper rotation) or in reciprocating OTR motion.

Methods:

A total of forty-eight nickel-titanium files were tested. Twenty-four instruments of both brands were divided into two groups (n=12) on the basis of the motion tested: continuous rotation (group 1) or reciprocating OTR motion (group 2). Resistance to cyclic fatigue was determined by recording time to fracture (TtF) in a stainless steel artificial canal with a 60° angle of curvature and 5 mm radius of curvature. Data were analysed by two-way analysis of variance and post-hoc Bonferroni tests for multiple comparisons with P<0.05 as the level of significance.

Results:

F6 SkyTaper showed higher TtF compared with OneShape, both in continuous and in OTR motion (P<0.0001). The two tested instruments showed higher cyclic fatigue resistance in reciprocating OTR motion than continuous rotation (P<0.0001).

Conclusion:

OTR motion significantly improves cyclic fatigue resistance of the tested instruments. In addition, F6 SkyTaper showed higher cyclic fatigue resistance than OneShape in both motions.

Wear of the Primary WaveOne single file when shaping vestibular root canals of first maxillary molar

Background

It is very important for a clinician to know the increased wear of mechanized files when establishing endodontic therapy. The aim of this study was to check the wear of the Primary WaveOne file upon shaping two, four and six maxillary molar vestibular canals.

Material and Methods

The deterioration of 40 files, divided into four groups, was evaluated microscopically: group 1, control (unused); group 2, two canals; group 3, four canals; and group 4, six canals. After instrumentation, the files were embedded in resin and sectioned at their apical third into three equal parts. To analyze the wear of edges in the different sections, AutoCAD software was used and analysis of variance (ANOVA) was then performed to compare the mean rake angles.

Results

The files with two and four uses showed slight wear, whereas those with six applications showed significant wear (p<0.05).

Conclusions

Primary WaveOne files can be used in up to four root canals without their edges losing effectiveness.

Key words:Files wear, reciprocating motion, shaping capacity, WaveOne.

The geometric effect of an off-centered cross-section on nickel-titanium rotary instruments: A finite element analysis study

Background/purpose

Geometric design dictates the mechanical performance of nickel–titanium rotary instruments. Using finite element (FE) analysis, this study evaluated the effects of an off-centered cross-sectional design on the stiffness and stress distribution of nickel–titanium rotary instruments.

Materials and methods

We constructed three-dimensional FE models, using ProTaper-NEXT type design (PTN) as well as three other virtual instruments with varied cross-sectional aspect ratios but all with the same cross-sectional area. The cross-sectional aspect ratio of the PTN was 0.75, while others were assigned to have ratios of 1.0 (square), 1.5 (rectangle), and 2.215 (centered-rectangle). The PTN center of the cross-section was ‘k’, while others were designed to have 0.9992k, 0.7k, and 0 for the square, rectangle, and centered-rectangle models, respectively. To compare the stiffness of the four FE models, we numerically analyzed their mechanical response under bending and torque.

Results

Under the bending condition, the square model was found to be the stiffest, followed by the PTN, rectangle, and then the centered-rectangle model. Under the torsion, the square model had the smallest distortion angle, while the rectangular model had the highest distortion angle.

Conclusion

Under the limitation of this study, the PTN type off-centered cross-sectional design appeared the most optimal configuration among the tested designs for high bending stiffness with cutting efficiency while rotational stiffness remained similar with the other designs.

Alternating versus continuous rotation: Root canal transportation and centering ratio with the ProTaper Next

Background:

The technique of alternating rotation has been used with NiTi rotary instruments to increase the resistance to fracture compared with conventional continuous rotation. However, it is still not clear what type of instrumentation could provide better results in the preservation of the original canal anatomy.

Aim:

The aim of this study is to determine the influence of the type of rotation on canal transportation and centering ability using cone-beam computed tomography (CBCT) imaging.

Materials and Methods:

In total, 50 mesial canals of mandibular molars with curvatures between 30° and 60° were divided into two experimental groups (n = 25 each) according to the type of movement employed with the ProTaper Next (PTN) instruments: Group A (alternating rotation) and Group B (continuous rotation). Canals were scanned before and after instrumentation using a CBCT scanner to evaluate root canal transportation and the centering ratio at 3, 5, and 7 mm from the apex. Data were analyzed statistically using Student's t-test; the significance level was set at P < 0.05.

Results:

There was no significant difference between the groups in canal transportation or the centering ratio at any of the three studied cross sections (3, 5, and 7 mm).

Conclusions:

PTN instruments promoted minimal apical transportation and remained relatively centered within the root canal, with no significant difference between alternating and continuous rotation.

Comparative evaluation of the shaping ability of two different nickel-titanium rotary files in curved root canals of extracted human molar teeth

AIM

The aim of the present study was to compare the shaping ability of two different nickel-titanium rotary files in the curved root canals of extracted human molar teeth.

METHODS

Thirty root canals of 17 extracted human molars teeth were randomly assigned to two experimental groups (n = 15): ProTaper Next and ProTaper Universal (PTU), on the basis of the rotary files system used. The final size of all apical foramina was 0.25 mm in diameter. Standardized digital radiographs were taken before and after instrumentation in both clinical and proximal views, with a size 10 K-file inserted into the canal for the determination of the angle of curvature and apical transportation. Preparation time and fractured or deformed instruments were also recorded. The unpaired Student's t-test was used to compare results.

RESULTS

There was no significant difference between the two instruments with respect to canal straightening and apical transportation before and after instrumentation (P > 0.05). The use of both instruments resulted in a significant reduction in the angle of curvature after instrumentation (P < 0.05). Instrumentation time was significantly greater for PTU (P < 0.05).

CONCLUSIONS

The ProTaper Universal and ProTaper Next systems performed similarly with regard to the straightening of curved root canals and apical transportation. ProTaper Next was significantly faster than ProTaper Universal.

An in vitro analysis of separation of multi-use ProTaper Universal and ProTaper Next instruments in extracted mandibular molar teeth

This study investigated the separation incidence of reused ProTaper Universal and ProTaper Next rotary instruments and identified the location of separated fragments. The root canals of extracted human mandibular molars were prepared with 10 assorted sets of ProTaper Universal and ProTaper Next instruments. After each preparation, instrument sets were autoclaved. This arrangement was repeated until an instrument fractured. The number of prepared teeth until fracture occurred was recorded for each instrument set. Teeth in which the instruments fractured were analyzed to determine the separation grade, apical relation, and coronal position. Fracture surfaces of the instruments were examined with scanning electron microscope. ProTaper Universal instruments fractured after application to a mean of 7.3 teeth, and ProTaper Next instruments after application to a mean of 5.7 teeth (p > 0.05). In the ProTaper Universal and ProTaper Next groups, F2 and X1 were the most commonly fractured instruments, respectively. Torsional and cyclic failures were evenly distributed in both the groups. The mean lengths of the fractured fragments of the instruments showed no statistically significant difference. The distance between the tip of the fractured instruments and apical constriction was similar (p > 0.05). However, the mean distance between the root canal orifice and coronal part of the fractured instrument was shorter in the ProTaper Next group (p < 0.05). The life span of ProTaper Universal and ProTaper Next instruments was the same for preparation of mandibular molar teeth. None of the instruments were fractured in the first usage.

A review of instrumentation kinematics of engine-driven nickel-titanium instruments

Over the years, NiTi alloys have become indispensable materials in endodontic treatment. With technological advancements in metallurgy, manufacturers have attempted to produce instruments with enhanced features. In parallel with these developments, endodontic motors have undergone improvements in terms of torque control and kinematics that are adjustable in different directions. This review presents an overview of the advancements in instrumentation kinematics and the effect of instrumentation kinematics on root canal shaping procedures and instrument performance. The literature search for this narrative review was conducted in Google Scholar, Scopus, PubMed and Web of Science using the keywords 'kinematics and endodontics' and 'reciprocation and endodontics'. In addition, historical literature was searched using the keyword 'nickel-titanium and endodontics'. Overall, 143 articles were included up to 2015.