Nickel-titanium Endodontic Instruments Research Articles

A SEM/EDS evaluation of debris removal of used rotary Ni-Ti endodontic files by four different cleaning solutions

PurposeThe aim of this study was to compare the efficacies levels of four cleaning solutions for removing debris from rotary Nickel-Titanium (Ni–Ti) endodontic instruments. Materials and methodsTwelve instruments that fractured during ex vivo instrumentation were used. Fractured surfaces were investigated by SEM before and after 3, 6 and 9 min of ultrasonic cleaning in 17 % EDTA.3NaOH (Group A), 2.5 % NaOCl (Group B), Dentasept 3H Rapide (Group C) and ZymeX™ (Group D) solutions. EDS analyses of selected files from all four groups of untreated and ultrasonically cleaned samples were performed to assess the elemental composition of the alloy surfaces. ResultsSEM analysis revealed that after 9 min of ultrasonic agitation, all four investigated solutions had cleaned fractured surfaces. However, some low-atomic-number regions exhibited random distributions on the fractured surfaces. EDS analyses indicated that only C was retained on surface after 9 min of ultrasonic cleaning. This finding was common in all tested groups. ConclusionsAll four investigated solutions substantially removed debris from the surfaces of the Ni–Ti files and were considered appropriate for clinical practice.

Comprehensive Assessment of Cyclic Fatigue Strength in Five Multiple-File Nickel-Titanium Endodontic Systems.

The resistance of nickel-titanium endodontic instruments against cyclic fatigue failure remains a significant concern in clinical settings. This study aimed to assess the cyclic fatigue strength of five nickel-titanium rotary systems, while correlating the results with the instruments' geometric and metallurgical characteristics. A total of 250 new instruments (sizes S1/A1, S2/A2, F1/B1, F2/B2, F3/B3) from ProTaper Gold, ProTaper Universal, Premium Taper Gold, Go-Taper Flex, and U-Files systems underwent mechanical testing. Prior to experimental procedures, all instruments were meticulously inspected to identify irregularities that could affect the investigation. Using a stereomicroscope, design characteristics such as the number of spirals, length, spirals per millimeter, and average helical angle of the active blade were determined. The surface finishing characteristics of the instruments were examined using a scanning electron microscope. Differential scanning calorimetry was employed to establish the instruments' phase transformation temperatures, while energy-dispersive X-ray spectroscopy was utilized to analyze the elemental composition of the alloy. The instruments were subjected to cyclic fatigue testing within a stainless steel non-tapered artificial canal featuring a 6 mm radius and 86 degrees of curvature. Appropriate statistical tests were applied to compare groups, considering a significance level of 0.05. The assessed design characteristics varied depending on the instrument type. The least irregular surface finishing was observed in U-Files and Premium Taper Gold files, while the most irregular surface was noted in Go-Taper Flex. All instruments exhibited near-equiatomic proportions of nickel and titanium elements, whereas ProTaper Universal and U-Files instruments demonstrated lower phase transformation temperatures compared to their counterparts. Larger-sized instruments, as well as ProTaper Universal and U-Files, tended to display lower cyclic fatigue strength results. Overall, the design, metallurgical, and cyclic fatigue outcomes varied among instruments and systems. Understanding these outcomes may assist clinicians in making more informed decisions regarding instrument selection.

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

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

A critical evaluation of physical and manufacturing properties of genuine and counterfeit rotary nickel-titanium endodontic instruments.

Rotary nickel-titanium (NiTi) instruments are made to exacting standards and are costly to manufacture, and quality control is paramount. Consequently, unauthorized factories make counterfeit instruments that are less expensive and may therefore be attractive to dentists. Little information exists about the metallurgy and manufacturing quality of such instruments. There is the potential for counterfeit instruments to be at higher risk of fracture during treatment, thereby compromising clinical outcomes. The aim of this study was to evaluate physical and manufacturing properties of genuine and counterfeit ProTaper Next™ and Mtwo® rotary NiTi instruments. This study investigated the metallurgical properties, manufacturing quality, microhardness and number of cycles to failure of two commonly used rotary NiTi systems and compared them with counterfeit products purporting to be genuine articles. Counterfeit instruments were found to be inferior in manufacturing standards and were less resistant to cyclic fatigue when compared to genuine instruments. Counterfeit rotary NiTi instruments may be less efficient at preparing root canals and may be at higher risk of fracture during endodontic treatment. Dentists must be aware that, although less expensive, counterfeit instruments may be of dubious manufacturing quality and at higher risk of fracture if used in patients. © 2023 Australian Dental Association.

Unveiling the Performance of Nickel-Titanium Endodontic Instruments through Multimethod Research: A Review

This article aims to explore the importance of multimethod research in assessing the performance of nickel-titanium (NiTi) endodontic instruments. The review highlights the limitations of relying solely on measurements obtained through a narrow set of mechanical tests and acknowledges the challenge of replicating real-world working conditions in controlled laboratory settings. While achieving a perfect simulation may be difficult, the focus should be on developing research strategies that provide a superior understanding of outcomes. The multimethod research, which combines qualitative and quantitative methodologies, offers a promising solution to address this challenge effectively. By integrating nonquantifiable data with quantitative measurements, researchers may overcome the limitations of individual methodologies and gain deeper and more comprehensive insights into instrument performance. This multimethod approach enables a more accurate interpretation of results, enhancing the validity of the methodology. Therefore, conducting a comprehensive analysis of various competencies displayed by NiTi systems is essential for a comprehensive understanding of their characteristics, including cyclic fatigue, torsional and bending resistance, cutting efficiency, microhardness, design analysis, element composition, phase transformation temperatures, shaping ability, and additional methodologies that can address specific inquiries. By combining qualitative and quantitative methodologies in a multimethod approach, researchers can enhance their ability to answer research questions and provide valuable insights for clinical practice.

Comparative Analysis of Stress Distribution through Finite-Element Models of 3 NiTi Endodontic Instruments while Operating in Different Canal Types.

Distribution of stress along endodontic instruments determines their fracture resistance during instrumentation of root canals. The cross-sectional design of instruments and root canal anatomy are of the most important factors affecting the stress distribution. The purpose of this study was to evaluate the stress distribution in different cross-sectional design of nickel-titanium (NiTi) endodontic instruments operating in different canal anatomies using finite element analysis (FEA). In this original finite element analysis study, 3-dimensional models of convex triangle (CT), S-type (S), and triple-helix (TH) cross-sectional designs with the size of 25/04 simulated rotational movements through 45ᵒ and 60ᵒ angled root canals with 2- and 5-mm radii using ABAQUS software. The stress distribution was evaluated by the means of FEA. CT showed the lowest stress values followed by the TH and S ones. The most stress concentration was detected in the CT apical third while, TH revealed better stress distribution all along its length. 45ᵒ curvature angle and 5-mm radius applied the lowest stress to the instruments. Higher value of radius and smaller curvature angle apply lower stress values to the instrument. CT design shows the lowest stress level with the most stress concentration in its apical third while the triple-helix design has a better stress distribution. Thus, it is safer to use convex triangular cross-section mostly for coronal and middle thirds in initial steps of shaping and triple-helix for the apical third in final steps.

Effect of autoclave sterilization on the cyclic fatigue resistance of EdgeFile X7, 2Shape, and F-one nickel-titanium endodontic instruments.

Rotary nickel-titanium files have become the most commonly used engine-powered endodontic instruments due to their improvement in fatigue resistance and flexibility. The autoclaving is the most commonly used method for sterilization. However, the risk of instrument fracture, mainly due to cyclic fatigue during rotation within a curved canal, is still a matter of critical concern. This study aimed to measure and compares the cyclic fatigue resistance of EdgeFile X7, 2Shape, and F-One files in a single curved simulated canal before and after autoclave sterilization. Twenty-four files each of EdgeFile X7, 2Shape, and F-One files were used in this study. They were grouped as group A: EdgeFile X7, group B: 2Shape, and group C: F-One files. Then, each group was subdivided into two, sterilized and nonsterilized, subgroups. The files were tested using a custom-made artificial canal. The number of cycles to fracture (NCF) was calculated. One-way analysis of variance, post hoc Tukey's test, and independent t-test were used. In nonsterilized instruments, the NCF of the EdgeFile X7 group was significantly higher than that in the other groups (P < 0.05). In sterilized instruments, there was a nonsignificant difference in NCF between EdgeFile X7 and F-One files (P > 0.05). The NCF of 2Shape was significantly lower than other files (P ≤ 0.05) in sterilized and nonsterilized groups. The autoclaving significantly decreased (P ≤ 0.05) the cyclic fatigue resistance of the tested files. EdgeFile X7 was the most fatigue resistant. Autoclaving reduced the cyclic fatigue resistance of the tested files.

Mechanical properties analysis of medical endodontic instruments based on parameterization

To study the relationship between structural parameters and mechanical properties of endodontic instruments, the T02004B25 nickel-titanium endodontic instrument was selected for bending and torsion tests and finite element simulation analysis, which demonstrated the feasibility of simulation analysis method. Then based on the idea of parametric design, the models of the endodontic instruments with different structural parameters (cross-section, pitch, taper) were established, and the bending-torsion performance simulation analysis was completed. The results showed that the mechanical properties of endodontic instruments with different structural parameters are different. It is necessary to find the optimal parameters for different structure parameters of endodontic instruments to maximize their service life.

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&amp;gt;0.05), fracture time differences were statistically significant in all PTN X2 files (p&amp;lt;0.05). As a result of the pairwise comparison of the experimental and control groups, the difference between the experimental and control groups of the WO and RPC files used with reciprocal movement was found to be statistically insignificant (p&amp;gt;0.05). 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.

Research of the major clinical findings of the use of reciprocant files: a systematic review

Introduction: In the context of root canal treatments, nickel-titanium endodontic rotary instruments fracture due to torsional overload or cyclic fatigue. Channels with bends located closer to the channel orifice and channels with double bends (S-shaped channels) have been shown to increase the risk of fatigue failure of rotating instruments. Thus, Yared was the first to report the use and effectiveness of reciprocating motions for rotary files, as he demonstrated that a single reciprocating file was sufficient to replace several files used in continuous rotation. Objective: A concise systematic review was carried out on the main results of clinical studies on the use of reciprocating files, to externalize the scientific evidence of these files to files used in continuous rotations. Methods: The present study followed the model of systematic literature review (PRISMA). The research was carried out from January 2022 to March 2022 and was developed based on Google Scholar, Scopus, PubMed, Scielo, and the Cochrane Library. The quality of scientific evidence of the studies was based on the GRADE instrument. The risk of bias was analyzed according to the Cochrane instrument. Results and Conclusion: A total of 85 articles were found. After the process of analyzing the quality of scientific evidence, 32 articles were selected. After analyzing the risk of bias, 8 recent clinical studies, from 2019 to 2022, were selected to compose this systematic review. Based on the clinical studies presented in the present study, it was evidenced that there is a significant statistical difference in the number of cycles in and out movement and wear time to failure between reciprocating and continuous rotary files. Furthermore, an endodontic treatment combining a single reciprocating file with a single cone showed similar clinical efficacy to treatment with hand file instrumentation and lateral compaction obturation. However, randomized clinical studies have shown that reciprocating instruments have less resistance to cyclic fatigue when operated in canals with curvatures in the coronal and middle thirds when compared with curvatures in the apical thirds.

Effect of body temperature on the cyclic fatigue resistance of the nickel-titanium endodontic instruments: A systematic review and meta-analysis of in vitro studies.

Aim:The aim of this systematic review was to compare the effect of body temperature (I) on the cyclic fatigue resistance (O) of nickel–titanium (NiTi) endodontic instruments (P) to that of room temperature (C).Methods:The study was registered in the PROSPERO database (CRD42020204286). A systematic search in PubMed, Scopus, Web of Science, Google Scholar, and OpenGrey was conducted in English until December 31, 2021. In vitro studies comparing the cyclic fatigue resistance of NiTi instruments at the body (35°C ± 2°C) and room temperature (20°C–25°C) were included. Eligible studies were evaluated for risk of bias and meta-analyzed to estimate the effects.Results:Twenty-one studies out of 347 met the criteria for inclusion. The meta-analysis included six studies (n = 215) with comparative study parameters. The overall effect sizes (5.49; 95% confidence interval [CI]: 4.04–6.93) were significantly different (P < 0.001), indicating that the mean values at room temperature were significantly (P < 0.001) higher. The effect sizes for full rotary motion (standardized mean difference [SMD]: 4.80; 95% CI: 3.04–6.56) and reciprocating motion (SMD: 6.37; 95% CI: 3.63–9.11) were not significantly different (P = 0.346). Heterogeneity was high (I2 = 94%). Sensitivity analysis revealed that the SMD values were not significantly different (P > 0.05) from the overall effect size, indicating that none of the studies had an effect on the overall effect size.Conclusions:Within the limitation of the study, the cyclic fatigue resistance of heat-treated NiTi endodontic files is significantly reduced at body temperature when compared to room temperature. Cyclic fatigue testing should be conducted at simulated body temperature.

Effects of sodium hypochlorite on corrosion of the rotary nickel-titanium endodontic instruments - SEM analysis

Introduction/Objective. of this study is to use scanning electron microscopy (SEM) analysis to examine surfaces of new and same sets of Ni-Ti instruments after canal preparations, to check their suspectability to corrosion. Methods. In this study, we used five different endodontic Ni-Ti instruments: K3, Mtwo, ProTaper Universal, HyFlex and BioRaCe. Instruments were analyzed before and after preparation of canals of different curvature, using SEM (150?2000 ?). Results. Corrosion of the working part was observed in 5.5% of new Ni-Ti instruments of the K3 system (apical and middle segment), in 5.5% of Mtwo instruments (apical third), and in 11.1% of ProTaper Universal systems (apical and middle third). Corrosion was not observed on the new instruments of the HyFlex and BioRaCe kits. After instrumentation, disinfection, and sterilization, corrosion was observed in all sets of K3 and ProTaper Universal systems and in all HyFlex instruments of the first group. Corrosion was observed in the HyFlex system in the second group in 16.7% of instruments (apical and middle third) and in the third 83.3% in the apical and 66.7% in the middle segment. In the Mtwo set, corrosion was observed in 16.7% of instruments in the first (apical and middle third), in the second group in 33.3% of instruments in the apical part and 50% in the middle third, while in the third group, corrosion was observed in 16.7% of instruments in the middle third of instruments. Conclusion. Rotary Ni-Ti instruments K3 and ProTaper Universal are susceptible to corrosion in a very high percentage. Ni-Ti systems with post-heat treatment of the working part (HyFlex) are somewhat more resistant to corrosion, while in Ni-Ti systems with electropolished surface (BioRaCe), corrosion is not observed.

The analysis of research methods and results on resistance of nickel-titanium endodontic instruments to torsion load: the systematic review

Relevance. The objective of this study was to analyze current data concerning research methods and results on resistance of nickel-titanium endodontic instruments to torsion load in order to minimize complications of dental root canal treatment. The use of the nickel -titanium endodontic instruments is a special importance to ensure high-quality dental root canal treatment; it prevents the further contamination of the canals with microorganisms. However, these instruments can form a fracture under torsional load which leads to further complications.Aim. The analysis of research methods and results on resistance of nickel-titanium endodontic instruments to torsion load for minimization complications.Materials and methods. A series of publications in the electronic databases such as Google Scholar, Pub Med was analyzed in the course of a systematic review of the literature. The articles dealing with nickel-titanium endodontic instruments and torsion load that directly influences the quality of dental root canal treatment were included in the paper.Results. 73 articles were viewed during the review. Having analyzed the literature for inclusion criteria, the total number of publications has become 51. There were 16 main methods which demonstrated the influence of torsion load on endodontic instruments. These methods were summarized in the Table 1.Conclusions. As regards literature data, there are a various number of methods which converge to one conclusion: nickel-titanium instruments cannot fully resist torsion load. Fracture is caused approximately in 0,5-5% of cases.

Heat Treatment and Surface Treatment of Nickel–Titanium Endodontic Instruments

Knowledge and thorough understanding of the characteristics of endodontic nickel–titanium (NiTi) files is paramount for dentists performing root canal treatments to patients. Understanding the behavior of the NiTi files guides the clinicians in choosing the correct instruments for different clinical and anatomical situations. This review focuses on the metallurgical properties of endodontic NiTi files, with a special emphasis on recent developments and improvements in metallurgy and the effects of heat treatment and surface treatment. In this study, the impact that such developments have on the properties of endodontic NiTi files is discussed.

Effect of Core Mass and Alloy on Cyclic Fatigue Resistance of Different Nickel-Titanium Endodontic Instruments in Matching Artificial Canals.

Instrument failure during root canal preparation is still a concern among endodontists. However, it remains unclear whether the use of more martensitic alloys or the cross-sectional design parameters (i.e., core mass) significantly improve fracture resistance. The aim of the study was to evaluate the impact of core mass and alloy on dynamic cyclic fatigue resistance of nickel-titanium endodontic instruments in matching artificial canals at body temperature. Two groups were tested. (A) taper 0.04: F360 (Komet, Lemgo, Germany), Twisted file (Sybron Endo, Glendora, CA, USA) (=TF), JIZAI (Mani, Tochigi, Japan) (=J_04) (all size #25) and the variable tapered TruNatomy (Dentsply, Ballaigues, Switzerland) (size #26) (=TN). (B) size #25; taper 0.06: (Mtwo (VDW, Munich, Germany), JIZAI (Mani) (=J_06), and variable tapered Hyflex EDM OneFile (Coltene Whaledent, Altstätten, Switzerland) (=HF). Time, number of cycles to fracture (NCF), and number and length of fractured fragments were recorded and statistically analysed using ANOVA Student-Newman-Keuls, Kruskal–Wallis or Chi-square test (significance level = 0.05). (A) TN showed the significantly shortest time until fracture, followed by TF, F360 and J_04 which also differed significantly, while NCF showed the following order: F360 < TN < TF < J_04 (p < 0.05). Only one J_04 but all instruments of the other groups fractured within the test-limit of 10 min. (B) Mtwo was significantly inferior concerning time until fracture and NCF, compared to J_06 and HF (p < 0.05), which did not differ significantly (p > 0.05). While all Mtwo instruments fractured, only four instruments failed in the other groups (p < 0.05). Within the limitations of this study, alloy and cross-sectional design (i.e., core mass) were critical factors regarding instrument failure, but none of these factors could be determined as a main parameter for increased or decreased time, and cycles to fracture. Rather, it seemed to be the interaction of multiple factors (e.g., longitudinal and cross-sectional design, alloy, and rotational speed) that was responsible for differences in the time and cycles to fracture. Nonetheless, all instruments had lifetimes that allow safe clinical use. However, the superiority or inferiority of an instrument with regard to cyclic fatigue based on laboratory results—even when identical trajectories are guaranteed—may be considered questionable, as the characteristics and design parameters of the instruments vary considerably, and the experimental setups lack additional clinical parameters and thus clinical relevance.

Evaluation of the Shaping Ability of Three Thermally Treated Nickel–Titanium Endodontic Instruments on Standardized 3D-printed Dental Replicas Using Cone-Beam Computed Tomography

Background and Objectives: The aim of the present study is to compare the efficacy of three root canal preparation systems in the shaping of 3D-printed root canal replicas of single rooted teeth. Materials and Methods: Sixty 3D-printed root canal replicas were produced and divided into three groups, each consisting of twenty samples. Each group was shaped with a different instrument: Reciproc Blue R25/08 (VDW GmbH, Munich, Gemany), WaveOne Gold Primary 25/07 (Dentsply Sirona, Ballaigues, Switzerland), and ProTaper Gold F2 25/08 (Denstply Sirona). To ensure the reproducibility of pre- and post-operative CBCT images of the root canals, the endodontic printed replicas were placed in a mould of silicon impression material. A cone-beam computed tomography (CBCT) software was used to compare pre- and post-instrumentation images collected at three levels of the root canal length: 3, 6, and 9 mm from the apical foramen. The amount of transportation, centring ability, and curvature angle after shaping were evaluated for each system. The results were statistically analysed and compared using one-way analysis of variance (ANOVA). Results: Regarding the transportation of the root canal after shaping, significant differences between groups at 3 mm (p = 0.010721) and 6 mm (p = 0.000046) were recorded in the mesio-distal direction, while in the bucco-lingual significant differences were only observed at 6 mm (p = 0.000554). Reciproc Blue removed more dentin from the mesial and buccal wall of the root canal. When evaluating the centring ability of the three systems, significant differences were observed between the groups at the level of 9 mm (p = 0.037258) in the mesio-distal direction, and at the level of 6 mm (p = 0.038197) in the bucco-lingual direction. Significant differences of the canal curvature angle after shaping were also observed between groups (p = 0.000001). Reciproc Blue straightened the curvature the most, while ProTaper Gold the least. Conclusions: All systems produced minor root canal transportation. No instrument was able to achieve a perfect centring preparation of the root canal. All systems produced a small degree of root canal straightening.

Experimental Study of the Effects of Torsional Loading on Three Types of Nickel-Titanium Endodontic Instruments

In modern endodontics, nickel-titanium (NiTi) rotary instruments are used on a large scale for root canal shaping. Nevertheless, the separation of an instrument is a serious concern during shaping. The aim of this study is to determine and compare the torsional fracture characteristics of three types of NiTi endodontic instruments, each with different cross-section designs and movements performed during root canal shaping: Endostar E3 (Endostar, Poldent Co. Ltd., Warsaw, Poland); Reciproc R25 (VDW, Munich, Germany); and Protaper Next X2 (Dentsply Maillefer, Ballaigues, Switzerland). Fifteen instruments are used in this study, divided in three groups (n = 5): Group Endostar, Group Reciproc and Group Protaper. For testing, each instrument is used to shape five simulated root canals, following which its torsional stress to failure is measured. The fracture lengths of all three groups are roughly between 2 and 3 mm from the tip. Higher values of the moment of torsion in fracture, and smaller values of the maximum twisting angle are observed for Group Endostar, as well as closer to circular cross-sections. However, the values of the shear tension are similar for all three groups, because the disadvantage given by the fracture section shape for Groups Reciproc and Protaper is compensated either by size or by intrinsic properties of the instrument material. For the shear tension the Endostar values are insignificantly increased (Kruskal–Wallis test, p = 0.207), and in the case of the maximum twist angle the Protaper values are insignificantly increased (Kruskal–Wallis test, p = 0.287). Because of the instruments shape and conicity, the analysis had to be carried out separately with regard to the length of the fractured tip. Rules-of-thumb are extracted from the study for current practice: if a blockage of the first 2 to 3 mm part of the tip can be anticipated (by the excessive curving of the instrument), the handpiece must be adjusted to torque values that do not exceed 1.5 to 2.5 N · cm for Endostar and 1 to 2 N · cm for Reciproc and Protaper instruments.

Current technology in endodontic instrumentation: advances in metallurgy and manufacture

Since the introduction of nickel-titanium endodontic instruments, there have been a myriad of developments which can be confusing and sometimes contradictory. This article seeks to review and articulate these advances, and allow the reader to better understand the benefits and the limitations of the systems available. Ultimately, this helps clinicians to engage more confidently with trade and have a more informed choice of the most appropriate file to use for each individual endodontic case. All this should facilitate more predictable endodontic outcomes.

Microstructural, microchemical, and mechanical changes associated with the clinical reuse of two nickel–titanium endodontic instruments

Nickel-titanium (NiTi) instruments have represented a great technological development that enabled endodontists conforming irregular-shaped root canals. Notwithstanding, the repeated use of these instruments may lead to the fracture without any prior visible warning signs. This study aimed to evaluate how multiple clinical instrumentation/sterilization cycles of two NiTi mechanized instruments can affect their microstructural, microchemical, and mechanical characteristics. In this observational descriptive study, a total of 140 NiTi instruments, 70 ProTaper Gold® (PTG) and 70 WaveOne Gold® (WOG) were analyzed. For each brand system, instruments were evaluated in the as-received condition (n = 10) and after one (n = 20), two (n = 20), and three (n = 20) instrumentation/sterilization cycles. Intraoperative instrumentation parameters were recorded for all used instruments. Afterward, the files were examined using scanning electron microscopy and energy-dispersive X-ray microanalysis. All of the instruments were tensile-fatigue tested until rupture in order to calculate the mechanical tensile strength and the maximum elongation percentage for the samples. Statistical analysis was completed using Chi-square, Kruskal-Wallis H-, or Mann-Whitney U-tests with a statistical significance set at P < 0.05. Significant increasing changes in surface topography (P < 0.05, Chi-square test) and chemical composition (P < 0.05, Kruskal-Wallis H-test) in both brand systems through instrumentation/sterilization cycles were detected. In addition, values of mechanical tensile strength and maximum elongation percentage increased significantly through instrumentation/sterilization cycles in the PTG group, whereas only the median values of mechanical tensile strength increased significantly in the WOG group (all P < 0.01, Kruskal-Wallis H-test). Although multiple instrumentation/sterilization cycles may render NiTi instruments more flexible and fatigue resistant, the significant changes detected in their surface topography and chemical composition should preclude their repeated clinical use in the routine endodontic practice as prevention for breakage.

Advancement of Mechanical Properties of Nickel-Titanium Rotary Endodontic Instruments by Spring Machining on the File Shaft

Nickel-titanium (NiTi) endodontic rotary instruments are used extensively in root canal procedures by both general dentists and specialists. However, their vulnerability to fracture is the major reason for clinicians’ concern regarding their use. The objective of this study was to investigate the potential effects of spring machining of the file shaft on the fatigue and torsional resistances of NiTi rotary instruments. Three types of NiTi rotary systems with (S) and without (NS) spring machining were used in this study (n = 15 each): a spring file (SPR; #25/.06, SPR-S, SPR-NS), a ProTaper Next X2 (PTN; #25/variable taper, PTN-S, PTN-NS), and a ProTaper Gold F2 (PTG; #25/variable taper, PTG-S, PTG-NS). Spring machining was adjusted on the 6 mm of each file system’s shaft via a laser cutting process. The number of rotation cycles until fracture (i.e., cyclic fatigue resistance), ultimate torsional strength, the distortion angle, and the toughness of each subgroup were estimated with specially designed devices. The results were analyzed using a paired t-test at a significance level of 95%. NiTi rotary instruments with spring machining exhibited a higher cyclic fatigue resistance than instruments without spring machining. The groups with spring machining exhibited a higher toughness and larger distortion angle than the groups without it (p < 0.05). In conclusion, spring machining on the shank of NiTi instruments may provide a stress-bearing area and attenuate the torsional and cyclic fatigue of NiTi rotary instruments.