No full-text available
To read the full-text of this research,
you can request a copy directly from the authors.
Metallurgical Characterization of Controlled Memory Wire Nickel-Titanium Rotary Instruments
Abstract
To improve the fracture resistance of nickel-titanium (NiTi) files, manufacturers have introduced new alloys and developed new manufacturing processes for the fabrication of NiTi files. This study aimed to examine the phase transformation behavior and microstructure of NiTi instruments from a novel controlled memory NiTi wire (CM wire).
Instruments of EndoSequence (ES), ProFile (PF), ProFile Vortex (Vortex), Twisted Files (TF), Typhoon (TYP), and Typhoon™ CM (TYP CM), all size 25/.04, were examined by differential scanning calorimetry (DSC) and x-ray diffraction (XRD). Microstructures of etched instruments were observed by optical microscopy and scanning electron microscopy with x-ray energy-dispersive spectrometric (EDS) analyses.
The DSC analyses showed that each segment of the TYP CM and Vortex instruments had an austenite transformation completion or austenite-finish (A(f)) temperature exceeding 37°C, whereas the NiTi instruments made from conventional superelastic NiTi wire (ES, PF, and TYP) and TF had A(f) temperatures substantially below mouth temperature. The higher A(f) temperature of TYP CM instruments was consistent with a mixture of austenite and martensite structure, which was observed at room temperature with XRD. All NiTi instruments had room temperature martensite microstructures consisting of colonies of lenticular features with substantial twinning. EDS analysis indicated that the precipitates in all NiTi instruments were titanium-rich, with an approximate composition of Ti(2)Ni.
The TYP CM and Vortex instruments with heat treatment contribute to increase austenite transformation temperature. The CM instrument has significant changes in the phase transformation behavior, compared with conventional superelastic NiTi instruments.
... During root canal preparation, the normal and shear stresses due to the curvature of the canal and the cutting process induce a martensitic transformation with a reversible strain increasing the flexibility of the instrument. However, this flexibility can be insufficient to correctly follow the severely curved canals leading to premature instrumental fracture [1,25,26]. The increase of transformation temperatures (M s , M f , A s and A f ) of NiTi results in a more martensite phase at clinically relevant temperatures [25,27,28], which makes heat-treated NiTi instruments more flexible and more resistant to fatigue than conventional NiTi instruments. ...
... However, this flexibility can be insufficient to correctly follow the severely curved canals leading to premature instrumental fracture [1,25,26]. The increase of transformation temperatures (M s , M f , A s and A f ) of NiTi results in a more martensite phase at clinically relevant temperatures [25,27,28], which makes heat-treated NiTi instruments more flexible and more resistant to fatigue than conventional NiTi instruments. ...
... Near-equiatomic NiTi SMAs contain three microstructural phases which are austenite, martensite, and R-phase. The relative proportions and characteristics of each phase determine the mechanical properties of SMAs [15,21,25]. Conventional superelastic NiTi SMAs have an austenite structure at room temperature and clinical use. ...
The flexibility of NiTi based endodontic files is improved by heat treatment, leading to lower risk of failure, ledges, and canal transportation during the preparation of curved root canals. The aim of this study is to investigate and clearly highlight the influence of every parameter of heat treatment on the flexibility of NiTi wires and thus of endodontic instruments. A full factorial Design of Experiment (DoE) and a designed bending–torsion bench following the ISO 3630-1 standard were used for this investigation. Temperature, holding time, and cooling method were selected as contributing factors, while maximum bending moment, hysteresis size, and stiffness during martensitic transformation were selected as outputs. Regression analysis was performed to estimate the relationship between contributing and output variables to assess how the experimentation fits with the model. The experimental results showed that wires heated at 425 °C for 30 min are more flexible. Moreover, heat treatment temperature is the most critical factor influencing the flexibility and hysteresis size of the NiTi wire followed by the holding time, while the cooling method has a negligible effect. The regression analysis showed that the model is effective at predicting the relationship between contributing factors, bending moment response, and hysteresis size.
... Traditional NiTi alloy instruments conventionally exist in the austenite phase at room and body temperature; however, this limits their use in severely curved canals due to their stiffness and low resistance to fatigue [77,78]. Heat treatment releases the internal strain of NiTi and increases the phase transformation resulting in more martensitic phase at clinically relevant temperatures potentially modifying the instrument's fatigue resistance (torsional or cyclic fatigue) [77,79,80]. ...
... Traditional NiTi alloy instruments conventionally exist in the austenite phase at room and body temperature; however, this limits their use in severely curved canals due to their stiffness and low resistance to fatigue [77,78]. Heat treatment releases the internal strain of NiTi and increases the phase transformation resulting in more martensitic phase at clinically relevant temperatures potentially modifying the instrument's fatigue resistance (torsional or cyclic fatigue) [77,79,80]. ...
... CM-wire contains a lower percentage of Ni (52% wt.) compared with conventional NiTi alloy due to the proprietary thermomechanical processing of the NiTi wire [103]. CM-wire contains mainly stable martensite phase and does not have the superelastic properties of conventional NiTi, as the Af temperature is above body temperature [77]. This controlled memory effect allows the endodontic instrument to maintain the shape of the canal even when it has been removed from the canal, similar to Vortex Blue. ...
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.
... In the so-called gold heat-treated endodontic instruments, the surface layer is also responsible for the characteristic color [415]. After such heat treatment, the nitinol matrix is predominantly the R phase or B19 martensite, whereby the alloy is more flexible [413] and has significantly improved fatigue life [416][417][418], conventionally treated nitinol with austenitic B2 matrix. ...
... The use of thermomechanical treatment for nitinol, first used in 2007 by Sportswire LLC (Langley, OK, USA) to the so-called M-Wire bars [135,442] containing 55.8 ± 1.5 wt.% Ni, 44.2 ± 1.5% Ti and <1 wt.% trace elements [443]. This alloy is characterized by a higher temperature A f = 43-50 • C than in the case of conventional nitinol [278,416,[444][445][446], which results, at human body temperature, in the structure B2 + B19 + R of the austenite mixture with a relatively small share of martensite and R phases [278,444,446]. This phase composition provides a superelastic state [447] and increased flexibility compared to conventional nitinol [278,421,448,449]. ...
... A similar structure of the B2 + B19 + R mixture of austenite and martensite with a relatively small proportion of the R phase at room temperature is shown by CM Wire [273,416,453], which was introduced in 2010. The structure of unused Hyflex CM tools provides a temperature of A f = 32-37 • C, and after use, it rises to A f = 54-61 • C, when the intracanal temperature is lower, i.e., 47-55 • C [273,416,453]. ...
A very extensive literature review presents the possibilities and needs of using, in endodontics, the alloys commonly known as nitinol. Nitinol, as the most modern group of engineering materials used to develop root canals, is equilibrium nickel and titanium alloys in terms of the elements’ atomic concentration, or very similar. The main audience of this paper is engineers, tool designers and manufacturers, PhD students, and students of materials and manufacturing engineering but this article can also certainly be used by dentists. The paper aims to present a full material science characterization of the structure and properties of nitinol alloys and to discuss all structural phenomena that determine the performance properties of these alloys, including those applied to manufacture the endodontic tools. The paper presents the selection of these alloys’ chemical composition and processing conditions and their importance in the endodontic treatment of teeth. The results of laboratory studies on the analysis of changes during the sterilization of endodontic instruments made of nitinol alloys are also included. The summary of all the literature analyses is an SWOT analysis of strengths, weaknesses, opportunities, and threats, and is a forecast of the development strategy of this material in a specific application such as endodontics.
... The relative proportions and properties of the microstructural phases govern the mechanical behavior of NiTi alloy. Heat treatment (thermal processing) has been reported to influence the fatigue resistance of NiTi instruments and is one of the most common methods for adjusting NiTi alloy transition temperatures (7)(8)(9)(10). ...
... The goal of heat treatments is to change the transition temperatures of NiTi alloys and, as a result, modify fatigue resistance. Superelastic conventional NiTi instruments existed in the austenite phase at room and body temperatures, which limited their usage in severely curved canals due to the stiffness of the instrument and low fatigue resistance (7,27). The heat treatment process releases the internal strain of NiTi alloy and increases the phase transformation temperature of NiTi, resulting in more martensite phase at clinically relevant temperatures (7, 10), which makes heat-treated NiTi instruments higher flexibility and fatigue resistance than those of conventional NiTi instruments (Figure 2). ...
... In comparison to conventional superelastic NiTi rotary instruments, heat-treated NiTi instruments have greater flexibility and cyclic fatigue resistance (7). It can be assumed that the cutting efficiency of the comparatively soft and flexible NiTi instruments is lower than that of the relatively stiff NiTi 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.
... Bhagchandani et al. 2014 [16] Yes N/A Yes Yes Yes Yes Yes Yes Bhalekar et al. 2019 [17] Yes N/A Yes Yes Yes Yes Yes Yes Grygier et al. 2018 [18] Yes [19] Yes N/A Yes Yes Yes Yes Yes Yes Freitas et al. 2011 [20] Yes Yes Yes Yes Yes Yes Yes Yes Gravina et al. 2014 [21] Yes Yes Yes Yes Yes Yes Yes Yes Łępicka et al. 2015 [22] Yes N/A Yes Yes Yes Yes Yes Yes Mesquita et al. 2018 [23] Yes N/A Yes Yes Yes Yes Yes Yes Mohammadi et al. 2014 [24] Yes N/A Yes N/A Yes Yes Yes Yes Muguruma et al. 2010 [25] Yes N/A Yes Yes Yes Yes Yes Ntasi et al. 2013 [26] Yes N/A Yes Yes Yes Yes Yes Sestini et al. 2006 [27] Yes N/A Yes Yes Yes Yes Yes Yes Sharma et al. 2017 [28] Yes N/A Yes Yes Yes Yes Yes Yes Shen et al. 2011 [29] Yes Yes Yes Yes Yes Yes Yes Tian et al. 2017 [30] Yes N/A Yes Yes Yes Yes Yes Yes Vijayalakshmi et al. 2009 [31] Yes The forces necessary to move the incisor, premolar, and molar teeth, however, differ from one another. It is well known that a wire must have a structural gradient along its length to be subject to various actuating forces. ...
... The study's conclusion was that manufacturing companies and extended time intervals have a significant impact on nickel release from simulated fixed orthodontic appliances. Shen et al. 2011 [29] In vitro study This research sought to investigate the microstructure and phase transition behavior of NiTi instruments made from a new controlled memory NiTi wire (CM wire). Differential scanning calorimetry (DSC) and x-ray diffraction were used in this work to investigate instruments of the brands EndoSequence ( It was assessed that the austenite transition temperature is raised by the heat-treated TYP CM and Vortex instruments, and when compared to traditional superelastic NiTi instruments, the phase transformation behavior of the CM instrument has undergone considerable alterations. ...
A variety of metals and alloys are employed in the field of orthodontics, primary of which happen to be the construction of wires. Through this systematic review, we aimed to assess the various metallurgical characteristics of the said metals and alloys. Four hundred and eighty-two documents in total were found after a thorough search of the online journals, and 169 of the papers were initially chosen. Ultimately, 16 documents were selected that satisfied the necessary inclusion and exclusion criteria, primarily in vitro studies, literature reviews, and comparative analyses. NiTi alloy was found to be the most commonly used alloy in construction of orthodontic wires across all the studies that we had selected for our review. It also had better performance and consistency in terms of its usage as depicted by the meta-analysis performed, with stainless steel wires being a close second primarily due to its lesser cost compared to the former. Metallurgy and orthodontics are inextricably linked with one another. The various components of orthodontics such as wires, pliers, and other instruments utilize the metallurgical characteristics of metals and alloys that are specially prepared for the challenges of this field.
PROSPERO Registration Number: CRD42022378444.
... The onset and endset transformation temperatures were obtained from the intersection between extrapolations of the baseline and maximum gradient line of the lambda-type DSC curve. 76,77 . Four main points were determined: martensitic transformation starting (Ms) and finishing (Mf) points, and austenitic (reverse-martensitic) starting (As) and finishing (Af) points. ...
... DSC data for some NiTi alloy types have previously been reported, and the results from the present study are comparable to prior investigations for Untreated 75,76,80,81 , Gold 82,83 and Blue 75,80,84,85 NiTi alloys. The Untreated NiTi alloy behaves the most differently of the four NiTi types examined, with considerably lower transition temperatures for both the austenitic and martensitic phases. ...
Nickel-titanium (NiTi) rotary endodontic instruments are a critical component in cleaning and shaping of the root canal system in clinical dentistry. Currently, these instruments are available to clinicians in a plethora of complex geometrical designs and specifications. Modifications to the metallurgical types of these instruments have been introduced in successive iterations. Despite this, mechanical failure, often via cyclic fatigue, can lead to instrument fracture, and this in turn may result in adverse treatment outcomes.
Finite element analysis (FEA) is a numerical method for conducting simulations of experimental designs. Among many applications, FEA has been used to test the effect of different boundary and load conditions on rotary NiTi endodontic instruments. In the first chapter of the present work, a review of the current literature on FEA for studying the performance of NiTi instruments is presented. The use of this approach has been sparse, but has risen in frequency in the last decade. Despite greater complexity in both experimental and FEA studies of cyclic fatigue resistance of instruments, existing work lacks a standardised approach and a robust framework for predicting the cyclic fatigue life of rotary endodontic instruments.
In the second chapter of this thesis, different types of NiTi types in the form of small wire blanks were subjected to differential scanning calorimetry (DSC) and microtensile tests to establish their mechanical properties and limits. A purpose-built experimental setup was used for the tensile tests to allow for the variable of temperature to be explored, an aspect that was missing from prior work. Samples were immersed in a temperature-controlled water bath. The values for the martensitic elastic moduli were not significantly different among the four NiTi tested, however values for austenitic elastic moduli and transformation stress were significantly different between the untreated and heat-treated specimen groups. The values for the austenitic elastic moduli and transformation stress were also affected by the temperature of the fluid medium.
The third chapter investigated a proposed cyclic fatigue test rig for its suitability for the inclusion in the ISO 3630-1 norm. Two instruments with identical geometry but different metallurgical properties were tested, and both satisfied the strain limits proposed for the norm, and were therefore considered viable as a standardised test device for future studies.
The fourth chapter used a finite-element version of the test method described in the third chapter, within which instruments comprised of the materials tested in the second chapter were evaluated. Mechanical data extracted from the results of the second chapter were applied to user-defined material subroutines in FEA in a 2-step method. FEA results showed the stress locations and values during the insertion and rotation process, but the prediction of fatigue life required the presence of a fatigue failure criterion.
Overall, the findings from the thesis show that thermo-mechanically treated NiTi samples have distinctly different mechanical properties, and that extracted data from mechanical testing is suitable as input data for FEA platforms for exploring these instruments in silico. Further research into fatigue criteria for failure analysis will provide a better model for the prediction of the fatigue life of rotary endodontic instruments.
... All DSC data were analyzed using STARe Evaluation software (Mettler Toledo). The onset and endset transformation temperatures were obtained from the intersection between extrapolations of the baseline and maximum gradient line of the lambda-type DSC curve [12,13], with four main points determined: martensitic transformation starting (M s ), finishing (M f ) and austenitic (reverse-martensitic) starting (A s ) and finishing (A f ). ...
... The DSC results of the present study are comparable to those reported in prior investigations for Stock [11,12,16,17], Gold [18,19] and Blue [11,16,20,21] NiTi alloys. The Stock NiTi alloy samples behave overall differently compared to the three heat-treated NiTi samples examined, with considerably lower transition temperatures for both the austenitic and martensitic phases. ...
This study aimed to evaluate and compare the effects of ambient temperature and post-manufacture heat-treatment on the mechanical behavior of nickel-titanium (NiTi) wires. Four types of commercial NiTi variants (Stock NiTi, heat treated “Blue”, “Gold”, “Superflex”, all Dentsply Maillefer, Ballaigues, Switzerland) were stressed in a tensile testing machine in a temperature-controlled water bath at three different temperatures. Stress and strain values were extrapolated from the raw data, and 2-way ANOVA and Tukey’s test for multiple comparisons were performed to compare the differences of the mechanical constants. Differential scanning calorimetry (DSC) tests established the martensitic transformation starting (Ms), finishing (Mf) and austenitic (reverse-martensitic) starting (As) and finishing (Af) points. Austenitic modulus of elasticity and transformation stress values increased with temperature for all NiTi groups. The martensitic modulus of elasticity, maximum transformation strain and ultimate tensile stress were not significantly affected by temperature changes. Stock NiTi and Gold wire samples presented with clearly delineated austenitic and martensitic transformations in the DSC experiments. Differences in manufacturing/heat treatment conditions and ambient temperature affect the mechanical behavior of nickel-titanium and may have clinical implications. Further improvements to the experimental setup could be considered to provide more accurate measurements of strain.
... HyFlex CM is a NiTi rotary system made from specific NiTi alloy that has a lower percent in weight of nickel (52.1 wt%) than conventional NiTi alloys composed of 54.5e57 wt% Ni. 11 Moreover, a unique sequence of thermal treatments was used during the manufacturing process, which improved the mechanical properties of the alloy. 25 The austenite/martensite transition temperature of HCM system is approximately 50 C; thus, a stable martensitic microstructure is present at room temperature. ...
... 26 Previous studies have shown that HCM instruments provide superior flexibility and higher fatigue resistance during instrumentation than other conventional NiTi instruments that are purely austenitic. 11,27 Mandibular incisors with a single canal were used in this study. Wolf et al. reported that more than 50% of the physiological foramen of lower incisors are oval. ...
Background/purpose
Canal instrumentation with rotary nickel-titanium (NiTi) instruments might weaken the dentinal wall. This study aims to investigate the apical root defects during canal instrumentation with two NiTi rotary systems by using optical coherence tomography (OCT) scans.
Materials and methods
Twenty mandibular incisors were selected and divided into two groups instrumented using HyFlex CM (HCM) and ProTaper Universal (PTU) systems. OCT scans were taken immediately after canal instrumentation with file #25, #30 and #40. Each cross-sectional reconstructed image of 1, 2 and 3 mm from the apex was examined, root cracks were scored, and dentin thickness was measured at 12 sites. The risk sites with dentin thickness less than 0.30 mm were recorded.
Results
In HCM group, no cracks were observed after instrumentation with file #30/.06, while in PTU group, root cracks were found in 6 teeth with a total score of 9 after using F3 (#30/.09) (P < 0.05). After file #40, 8 teeth with cracks had a score of 14 in PTU group, while one tooth was observed crack with a score of 1 in HCM group (P < 0.05). The number of risk sites in PTU group was 49 (13.16%), which was significantly more than the 28 (7.78%) in HCM group (P < 0.05) when canals were instrumented with file #30.
Conclusion
Within the limitations of this study, when the canals of mandibular incisors were instrumented with size #30 and #40 files, OCT scans showed less root defects in HCM group.
... Once the separation occurs, the removal of the fragment is critical or impossible, worsening the prognosis of the treatment. To overcome this problem, different designs and NiTi alloys have been proposed aiming to increase flexibility, fatigue resistance, canal centering ability and cutting efficiency (Thompson, 2000;Shen et al., 2011;Silva et al., 2018). In addition to these modifications, changes in the activation kinematics, such as reciprocating motion has been shown to extend the life span and resistance to fatigue of NiTi instruments when compared to continuous rotary motion (Silva et al., 2018). ...
... 2021 region without undesirable wear (Lopes et al., 2012). Endodontic instruments with improved flexibility might reduce trans-operatory accidents such as canal transportation 8 and also improve instrument cyclic fatigue resistance (Shen et al., 2011;Silva et al., 2018;Plotino et al., 2014;De-Deus et al., 2017;Gündogăr & Özyürek, 2017;Rodrigues et al., 2019). The buckling resistance is defined as the elastic lateral deformation of an endodontic instrument when subjected to a compressive load applied in the longitudinal direction of the file axis (Lopes et al., 2012). ...
... Among the multiple advances achieved in recent years, we can highlight the thermal treatment of NiTi alloys, new NiTi alloys [7][8][9][10], the addition of new movements to instrumentation systems [11,12], and innovations in instrument design [13]. Changes available, both rotary and reciprocating, has greater resistance to cyclic fatigue, with a null hypothesis (H0) postulating that there would be no difference between reciprocating and rotary endodontic files with regard to cyclic fatigue resistance, as well as an alternative hypothesis (H1) to demonstrate that the use of reciprocating movement has greater resistance to cyclic fatigue. ...
(1) Background: The failure of nickel–titanium (NiTi) rotary files is a complication related to endodontic instruments. The aim of this study was to compare the resistance to cyclic fatigue between rotary and reciprocating file systems. (2) Methods: Specific PICO: Population (P): artificial root canals; Interventions (I): instrumentation with NiTi rotary and reciprocating files; Comparison (C): rotary versus reciprocating files; Outcome (O): cyclic fatigue resistance. Studies were identified through bibliographic research using electronic databases (Medline, Embase, Scopus, SciELO, and WOS). The studies were combined using a random effects model by the inverse variance method. The effect size was the mean of the time to fracture (TTF) and number of cycles to fracture (NCF). Heterogeneity was assessed using the p value of the Q test for heterogeneity and the I2. (3) Results: TTF for rotary files was determined in 474.5 s and 839.1 for reciprocating without statistically significant differences. NCF for rotary systems was determined in 1444.2 and for reciprocating file systems in 4155.9 with statistically significant differences (p = 0.035), making reciprocating files more resistant. (4) Conclusions: Reciprocating files have better resistance to cyclic fatigue than rotary files. When tested in double curvature canals, reciprocating files also showed higher resistance.
... 5,6 Isıl işlem görmüş NiTi eğelerin esnekliği ve döngüsel yorulma direncinin, geleneksel NiTi eğelere kıyasla daha fazla olduğu bildirilmiştir. [7][8][9][10] Son yıllarda kanal preparasyon teknikleri oldukça gelişmiş olup; bu teknolojik gelişmeleri takiben klinik ortamda hekimlere daha esnek, kırılma direnci yüksek, farklı hareket tiplerinde çalışan NiTİ eğelerle çalışma olanağı sunulmuştur. 11 Reciproc Blue (RB; VDW, Münih, Almanya), resiprokal hareketle çalışan döner alet sistemleri arasında en çok tercih edilen eğelerden birisidir. ...
... This instrument was made from NiTi wire that had undergone patented Thermomechanical treatment to raise the austenite temperature to more than 37 °C, at working temperature, keeping the NiTi file in the twinned martensitic phase compared to the CM method. In general, this thermal treatment was known to improve the crystal structure arrangement, thus leading to flexibility raising (Shen et al, 2011). ...
Background Nickel-titanium (NiTi) alloy was improved in endodontic treatments in the last ten years. Many processing techniques were developed to increase the mechanical features of NiTi endodontic instruments. A single-file approach was used in the reciprocating system that shapes and cleans the canal in less time while using a less antimicrobial solution with low apical pressure. Objectives to describe the reciprocating NiTi instruments with an overview of the comparison studies of these instruments in different subjects including; root canal cleaning and shaping, debris compaction and apical extrusion, dentin defects, and cyclic fatigue resistance. Materials and Methods the data was collected from 160 papers from the PubMed, Google Scholar, and Science Direct databases in the English language, without date restriction. Following the inclusion and exclusion criteria application, topic papers were critically appraised using the Critical Appraisal Skills Program to identify the most relevant papers. This review of 82 papers included the related studies after excluding 78 unrelated papers. Results the reciprocating motion was shown to have fewer tendencies to canal transportation. It was discovered that the reciprocating instruments had decreased apical debris extrusion. The reciprocating instruments produced a lower risk of fracture during the preparation. Conclusion the reciprocation motion maintained the anatomical canal pathway and enhanced an instrument›s fracture resistance with less apical debris extrusion.
... They are made of M-wire technology which undergoes a proprietary thermomechanical procedure with a special titanium oxide coating (the reason for the blue color after the heat treatment) [36] which provides superior flexibility for the file. Due to the property of controlled memory of the martensitic phase during the complex heating-cooling treatment, these files have a greater resistance to cyclic fatigue, better cutting efficiency, and canal centering ability and also allow intentional deformation with shape memory only when heated [35,[37][38][39][40]. The taper is variably variable (taper varies from 4% to 8% at different sections of the flute length) and has a 16 mm file length with a 12 mm flute, which makes it unique among its competitors in the field of pediatric endodontics. ...
Successful outcome of pulp therapy depends on good chemomechanical preparation of the canals. This is completed with the help of various upcoming rotary and hand files. However, during this preparation, there might be an apical extrusion of the debris which may result in postoperative complications. The aim of this study was to evaluate and compare the number of debris apically extruded during canal preparation using two different pediatric rotary file systems and conventional hand file systems in primary teeth. 60 primary maxillary central incisors that were extracted due to trauma or untreated dental caries with no signs of resorption were taken. Canal preparation was executed using three different file systems: Group A: Group A hand K file system, Group B Kedo S Plus, Group C Kedo SG Blue. For each of these files using the Myers and Montgomery model, the pre- and post-weight of the eppendorf tube was assessed to quantify the number of apical debris. The maximum extrusion of apical debris was noticed with the Hand K-file system. The least debris was noticed in the Kedo S Plus file system. Statistical analysis revealed that there were highly significant differences in apical extrusion and debris when comparing hand files and rotary files and also between the two rotary files used. Apical debris collection is an unavoidable outcome of canal instrumentation. Among the file systems compared, rotary files had lesser extrusion when compared to hand files. Among the rotary files, Kedo S plus showed normal extrusion compared to SG Blue.
... (e.g., twisting, electrical discharge machining), specific thermomechanical treatments such as controlled memory wire (CM wire), memory wire (M-wire), electrical discharge machining (EDM), and surface finishing techniques. [8][9][10] ProTaper Next (PN, Dentsply Sirona Balligues, Switzerland) was introduced as an off-center rectangular file with multiple progressive and regressive taper concepts. Taper variation reduces the connection between the file and the dentin, lowering screw impression and undesirable taper lock. ...
Preparation of the root canal system is a crucial step in root canal treatment. Endodontically treated teeth differ structurally from healthy, untreated teeth. This can lead to root cracking by creating pressure on the canal wall, reducing the fracture resistance of the tooth. Different designs, including cross-sectional shape, tip, taper, flute, radial land, helix angle, rake angle, and pitch, can influence the outcome of the root canal preparation and the risk of root fracture. The purpose of this study was to evaluate the fracture resistance of teeth after root canal preparation using three different NiTi rotary files: ProTaper Next (PN), ProTaper Gold (PG), and HyFlex CM (HC). Thirty premolars with a single and straight root canal were decoronated at the cementoenamel junction, leaving 14 mm of the root. The subjects were divided into 3 groups. Group 1 (n = 10) was prepared using PN, group 2 (n = 10) was prepared using PG, and group 3 (n = 10) was prepared using HC. After instrumentation and irrigation, the specimens were subjected to a continuous vertical compressive force (crosshead-speed of 2.28 mm/sec) in order to record the force (in newtons) until root fracture. To describe the surface characteristic of the dentinal root after the preparation, a section fragment from the apical third of the specimens was observed using a scanning electron microscope (SEM) at 2500x magnification. The micrographs were analyzed according to the Hulsman’s method. The results demonstrated that there was a statistically significant difference in root fracture resistance among the three groups. (p = 0.043). The LSD post hoc test indicated that HC showed a higher root fracture resistance (p < 0.05) compared to both PN and PG. In conclusion, the different file systems of PN, PG, and HC instruments generate different root fracture resistance of teeth. In comparison to PN and PG, HC instruments tend to result in increased fracture resistance.
... This system tends to reduce the canal straightening effect due to its controlled memory effect. [23] In addition to this controlled memory property, rotary files of the Kedo system have an additional blue titanium oxide coating. [24] Aun et al. (2016) [25] Figure 3: CBCT images of dentin thickness after canal preparation at coronal, middle, and apical thirds. ...
Background:
The complex root canal anatomy of primary root canals is considered to be most challenging. The quality of the root canal preparation plays a significant role in the success of endodontic treatment. Now, there are very few root canal instruments that are capable of cleaning the canal three dimensionally. To evaluate the efficacy of root canal instruments, various technologies have been used; one of the most reliable strategies was cone-beam computed tomography (CBCT).
Aim:
The aim of this study is to compare the centralization ability and canal transportation of three commercially available pediatric rotary file systems using CBCT analysis.
Materials and methods:
Thirty-three extracted human primary teeth with a minimum 7 mm root length were randomly divided into three groups (group I - Kedo-SG Blue, group II - Kedo-S Square, and group III - Pro AF Baby Gold). Biomechanical preparation was done according to the manufacturers instructions. Pre- and postinstrumentation CBCT images were taken for each group to evaluate the remaining dentin thickness thereby assessing the centering ability and the canal transportation ability of different file systems.
Results:
Significant difference was noticed in canal transportation and centering ability between the three tested groups. Mesiodistal canal transportation was significant at all three levels, whereas buccolingual canal transportation was significant only at the apical third of the root. However, Kedo-SG Blue and Pro AF Baby Gold showed lesser canal transportation compared to Kedo-S Square rotary file system. Mesiodistal centering ability was significant at cervical and apical thirds of the root with Kedo-S Square rotary file system maintaining less canal centricity.
Conclusions:
All three file systems tested in the study were effective in removing the radicular dentin. However, Kedo-SG Blue and Pro AF Baby Gold rotary file systems showed comparatively less canal transportation and more centering ability than Kedo-S Square rotary file system.
... Challenging root canal anatomy is the norm rather than the exception and this adds more challenges to the instrumentation preventing proper disinfection and causing procedural errors such as instrument separation, transportation, ledges, or perforations [3]. Thermal treatment of NiTi by adjusting its transition temperature, while controlling the microstructure to produce an alloy mainly formed of Rphase or martensite contributed to a significant increase in flexibility and cyclic fatigue resistance [4][5][6]. ...
This study aimed to compare the shaping ability of ProTaper Gold (PTG) and the newly developed ProTaper Ultimate (PTU) systems in artificial S-shaped canals. Both files are manufactured via gold thermal treatment methods and have variable taper along their working part. Thirty-Two S-shaped canals in clear resin blocks were prepared up to an apical size of 25 using PTU and PTG instruments (n = 16 canals/group). Resin blocks were filled with ink and photographed before & after instrumentation to develop composite images by superimposition. The amount of removed resin was measured perpendicularly to the canal surface in 18 points, in addition to the canal transportation and centering ratio. Statistical analysis was performed by using Manne-Whitney U-test (α = 0.05). No broken files or aberrations were recorded during instrumentation. PTG significantly removed a higher amount of resin at 4, 6, 8, and 9 mm from the apex, but at 1 mm PTU significantly cut a higher amount (p < 0.05). Concerning transportation & centering ability, both files deviated from the center and at 3 mm PTU yielded significantly higher deviation, while at 4 mm PTG recorded a higher value (p < 0.05). In conclusion, PTU produced more conservative preparation than PTG especially in the coronal third, while for maintaining the original canal curve, PTG caused lesser deviation at the beginning of the apical curvature.
... Scanning electron microscope was chosen as the method for the evaluation of superficial defects before and after each use. This method has been used in other studies (10,11,12) and has been accepted for the accurate evaluation of deformation of instruments (13). ...
... The austenitic phase of the NiTi alloy is relatively stiff, hard and has limited flexibility. When stress is applied to this type of instrument, a transformation from the austenitic to the martensitic crystallographic arrangement may occur in a process named stress-induced martensitic transformation This atomic reorganization leads to a feature known as superelasticity, characterized by a form rearrangement that may spring back the instrument to its original form without any definitive deformation when the induced stress is stopped or reduced (Shen et al., 2011), meaning that its lower elastic modulus, compared with stainless-steel instruments, provides superior flexibility (Zupanc et al., 2018). The austenitic form, and its superelasticity features, characterizes the NiTi conventional alloy that has been used in systems such as the ProTaper Universal tested in this study. ...
Aim:
To compare design, metallurgy, and mechanical performance of the ProTaper (PT) Ultimate system with instruments of similar dimensions from the ProGlider, PT Gold and PT Universal systems.
Methodology:
New PT Ultimate instruments (n=248) were compared with instruments of similar dimensions from ProGlider (n=31), PT Gold (n=155) and PT Universal (n=155) systems regarding their number of spirals, helical angle, blade symmetry, tip geometry, surface finishing, nickel/titanium ratio, phase transformation temperatures, and mechanical performance. One-way ANOVA and nonparametric Mood's median tests were used for statistical comparison (α=5%).
Results:
All instruments had symmetrical blades without radial lands or flat sides, similar surface finishing, and an almost equiatomic nickel/titanium ratio, while the number of spirals, helical angles, and the tip geometry were different. PT Ultimate instruments showed 3 distinct heat treatments that matched with the colour of their metal wire. Slider and ProGlider instruments had similar R-phase start (Rs) and R-phase finish (Rf) temperatures. SX, F1, F2, F3 and Shaper instruments showed equivalent heat treatments (Rs ⁓45.6 °C and Rf ⁓28.3 °C) that were similar to their PT Gold counterparts (Rs ⁓47.9 °C and Rf ⁓28.2 °C), but completely distinct to the PT Universal ones (Rs ⁓16.2 °C and Rf ⁓ -18.2 °C). Amongst the PT Ultimate instruments, the lowest maximum torques were observed in the SX (0.44 N.cm), Slider (0.45 N.cm) and Shaper (0.60 N.cm) instruments, while the highest was noted in the FXL (4.90 N.cm). PT Ultimate Slider and ProGlider had similar torsional (~0.40 N.cm) and bending loads (~145.0 gf) (p = 1.000), while the other PT Ultimate instruments showed statistically significantly lower maximum torque, higher angle of rotation and lower bending load (higher flexibility) than their counterparts of the PT Universal and PT Gold systems.
Conclusions:
The PT Ultimate system comprises instruments with 3 distinct heat treatments that showed similar phase transformation temperatures to their heat-treated analogues. PT Ultimate instruments presented lower torsional strength and superior flexibility than their counterparts, while maximum torque, angle of rotation, and bending loads progressively increased with their sizes.
... The controlled memory (CM) wire, introduced in 2010, was the first thermomechanically treated NiTi endodontic alloy with reduced super-elasticity [4]. NiTi files with CM wire contain martensite, whereas conventional NiTi files contain austenite at body temperature [5]. CM wire instruments have a lower tendency to straighten curved root canals during preparation, thereby resulting in less transportation [6]. ...
We evaluated the mechanical properties and torque/force generated during canal shaping by four NiTi files with innovative designs. Each of the 52 TruNatomy Prime, XP-endo Shaper, Spring Endo files with unheated finish (Spring Endo), and Spring Endo files with heated finish (Spring H) were subjected to bending, buckling, cyclic fatigue, and torsional resistance tests (n = 10 per NiTi file type). Canal shaping was simulated with J-shaped resin blocks (n = 10). Phase transformation behavior was investigated using differential scanning calorimetry (n = 2). Statistical analysis was performed by one-way ANOVA and the Games–Howell test. Spring Endo and Spring H files showed higher bending and buckling resistances, ultimate torsional strength, and elastic modulus than TruNatomy and XP-endo Shaper (p < 0.05). XP-endo Shaper demonstrated the highest cyclic fatigue resistance and angle of rotation to fracture (p < 0.05). The elastic modulus increased in the order of XP-endo Shaper, TruNatomy Prime, Spring H, and Spring Endo. During simulated canal shaping, XP-endo Shaper generated greater clockwise torque and less screw-in force compared to Spring Endo files, with superior cutting ability. TruNatomy Prime generated the least clockwise torque and screw-in force. At room temperature, TruNatomy and XP-endo Shaper files consisted of mixed phases of austenite, martensite, and R-phase; Spring H files consisted of martensite; and Spring Endo files consisted of austenite.
... The soft and ductile properties of martensite play an important role in preventing fracture of NiTi files [20]. The martensitic phase also has excellent damping characteristics owing to the energy absorption abilities of its twinned phase structure [21]. The NiTi files made using heat treatment, which possess martensite at room temperature, demonstrated superior resistance to cyclic fatigue and torsional fracture, which has also been reported in previous studies [22,23]. ...
ABSTRACT
Adult Background/purpose: NiTi files have been manufactured with various designs and heat treatments. This study aimed to determine the effects of design and heat treatment on the mechanical properties of NiTi instruments.
Materials and methods: ProFile, Profa File Gold, ProTaper Universal,
ProTaper Gold, Profa Taper Gold, and ExactTaper H (n=44/brand) were
subjected to bending, buckling, cyclic fatigue and torsional resistance tests (n=10/brand/test). Instrument surfaces were examined with scanning electron microscopy (SEM) (n=2/brand), and phase transformation behavior studied by differential scanning calorimetry (DSC) (n=2).
Results: ProFile and Profa File Gold showed a concave triangular crosssection with radial lands, while other NiTi files had a convex triangular crosssectional design. DSC curves revealed that austenitic transformationfinishing temperature of Profa File Gold, ProTaper Gold, Profa Taper Gold and ExactTaper H were above 37℃. ProTaper Universal, Profa Taper Gold, and ExactTaper H presented the highest bending resistance. ProTaper Universal showed the highest buckling resistance, elastic modulus, and the lowest cyclic fatigue resistance. ExactTaper H exhibited the highest cyclic fatigue resistance and ultimate torsional strength. ProTaper Gold and ExactTaper H showed the greatest angle of rotation until fracture and consisted of mainly R-phase at room temperature.
Conclusion: NiTi instrument’s mechanical properties were affected
significantly by both design and heat treatment.
... This is related to the relative amount of the martensitic phase of the file, which seems to determine the NCF. From a metallurgic perspective, the austenite start (As) and austenite finish (Af) temperatures (which indicate the temperatures at which the change in the file's metal structure from martensite to austenite starts and completes, respectively) are increased by heat treatments [59]. When the temperature is between (As) and (Af), the alloy consists of both austenite and martensite phases, exhibiting a higher fatigue resistance [60]. ...
The aim of the present systematic review was to perform a qualitative synthesis of in vitro studies that assess the cyclic fatigue resistance of rotary glide path (GP) files of endodontic applications. Systematic electronic searches were performed in the Medline, Embase, Scopus, SciELO, and Web of Science databases on 15 February 2022, and were last updated on 1 April In vitro studies that evaluated and compared the cyclic fatigue resistance of at least one rotary GP file system with another rotary GP file system were included. A total of 25 studies were included in the qualitative synthesis. All studies assessing the difference in the cyclic fatigue resistance between continuous and reciprocating rotation in rotary glide path files found that the latter resulted in a significantly higher cyclic fatigue resistance, as evidenced by a higher number of cycles until fracture and/or time until fracture. Within the limitations of this review and the in vitro nature of the included studies, the results indicate that the cyclic fatigue resistance of rotary GP files may be influenced by several intrinsic factors of the files, such as their taper, cross-sectional design, alloy properties, kinematics, and external factors, such as the curvature and radius at which the file is activated, the irrigation or lubricant used, and the temperature.
... They have an off-centered rectangular design with progressive and regressive tapers on a single file. The off-centered rectangular d esign decreases the screw effect, prevents taper lock, and torque on the file by having two-point contact between the file and the dentin 21,22 Pro Taper Next file in sequence of X1, (size 17, 0.04 taper), X2 (size 25, 0.06 taper) full WL at 300 rpm and 4 N/cm torque was used for cleaning and shaping files for second group. Group 3: ProTaper Gold instruments with a torque-controlled endodontic motor (X-Smart, Dentsply Maillefer) was used for cleaning and shaping of group 3. Protaper Gold files has identical geometric features like the Protaper universal system but presents more flexibility and more fatigue resistance, due to heat treatment process 23 . ...
Comparative evaluation of dentinal crack formation after root canal preparation using
Pro Taper universal, Pro Taper Next and Pro Taper Gold
... Modern technological processes of the development of machine files are based on the knowledge that the mechanical properties of equiatomic NiTi alloy depend on the phase transformation caused by stress and the fact that these microstructural changes can be controlled by thermomechanical treatments 14 . It has also been confirmed that the metallurgical characteristics of NiTi alloy (composition, microstructure, and phase constitution) significantly affect the basic performance of files 11,15,16 . ...
... Estos instrumentos se crearon mediante una transformación de estructura de un alambre de NiTi puro en fase austenita a fase R mediante un proceso térmico de calentamiento y enfriamiento (22,55,56). En fase R, el NiTi no puede ser fresado, pero sí trenzado (twisted), por lo que se somete a este proceso junto a repetidos ciclos de calentamiento/enfriamiento para mantener su nueva forma (R-phase twisted) y volver de nuevo a la estructura austenítica (30,55,57). En la fase R la aleación muestra sus características de superelasticidad y memoria de forma, por lo que una lima fabricada de este modo debe ser más flexible que todos los sistemas anteriores (48, 56) . ...
El objetivo del presente estudio es comparar la resistencia a la fractura lpor fatiga cíclica entre los dos sistemas rotatorios de Níquel-Titanio para crear el glidepath: los instrumentos Pathfile y ProGlider, en D4 y D8, y discutir su relevancia clínica.
... However, it mainly contains the austenite phase and remains superelastic [15]. CM-Wire is a mixture of austenite and martensite with small amounts of R-phase at room temperature, [21,34,35]. The alloy mainly contains martensite and would seem to have greater flexibility than M-Wire and conventional NiTi instruments [22,[36][37][38][39][40][41]. ...
Objectives:
This study compared the cyclic fatigue resistance of One Curve (C wire) and F6 Skytaper (conventional austenite nickel-titanium [NiTi]), and 2 instruments with thermo-mechanically treated NiTi: Protaper Next X2 (M wire) and Hyflex CM (CM wire).
Materials and methods:
Ten new instruments of each group (size: 0.25 mm, 6% taper in the 3 mm tip region) were tested using a rotary bending machine with a 60° curvature angle and a 5 mm curvature radius, at room temperature. The number of cycles until fracture was recorded. The length of the fractured instruments was measured. The fracture surface of each fragment was examined with a scanning electron microscope (SEM). The data were analyzed using one-way analysis of variance and the post hoc Tukey test. The significance level was set at 0.05.
Results:
At 60°, One Curve, F6 Skytaper and Hyflex CM had significantly longer fatigue lives than Protaper Next X2 (p < 0.05). No statistically significant differences were found in the cyclic fatigue lives of One Curve, F6 Skytaper, and Hyflex CM (p > 0.05). SEM images of the fracture surfaces of the different instruments showed typical features of fatigue failure.
Conclusions:
Within the conditions of this study, at 60° and with a 5 mm curvature radius, the cyclic fatigue life of One Curve was not significantly different from those of F6 Skytaper and Hyflex CM. The cyclic fatigue lives of these 3 instruments were statistically significantly longer than that of Protaper Next.
... Although instruments of comparable diameter and taper were used for final canal preparation in the present study, there were some differences in their respective designs and alloy construction that could have influenced their shaping ability. 21 Additional factors that can affect the shaping ability of an instrument include the cross-sectional design of the file, operator technique, and canal system anatomy. 22,23 In this study a single operator instrumented all the mesiobuccal canals with similar curvatures using glide path and analogous shaping files in the same motor, according to the manufacturer's instructions. ...
The aim of this study was to evaluate and compare canalcentering ability and transportation of three analogous reciprocating shaping instruments after glide path preparation. Radiographs were used to select sixty untreated mesiobuccal canals with curvatures of 25° to 35° from extracted, human, mandibular molars. The canals were randomly divided into three groups for glide path preparation and shaping (n = 20): Group TWOG (WaveOne Gold Glider + Primary WaveOne Gold); Group TEF (Edge GlidePath + Primary EdgeOne Fire); and Group TOFG (One File G Reciprocating Glide Path File + Primary Shaping file). Pre- and post-preparation micro-CT scans were compared at levels 7 mm (coronal), 5 mm (midroot), and 3 mm (apical) from the apex to evaluate transportation and centering ratios. There were no significant differences in centering ratios at the coronal and midroot levels (P > 0.05). Transportation values were similar at the coronal level and for the combined mean values (P > 0.05). Transportation values for TEF and TWOG were similar (P = 0.98) at the midroot level but significantly lower than TOFG (P = 0.04). Apically, TEF remained significantly more centered with significantly lower transportation values than TWOG and TOFG (P < 0.05). Combined results showed that TEF was significantly more centered than TWOG but similar to TOFG (P = 0.017). Centering ratios and transportation values were more favorable in the apical region after use of TEF. All three groups evaluated in this study proved to be safe for the preparation of moderately curved root canals.
... 8,9 A new M-Wire NiTi alloy and reciprocating movement had a markedly positive influence on the resistance to cyclic fatigue. 11 The M-Wire NiTi instruments represent an innovation in the manufacturing of NiTi instruments, 24 leading to improvements in the overall physical and mechanical properties, such as fatigue resistance. 25 Previous studies analyzed the effect of reciprocating movement on cyclic fatigue life of the NiTi files and observed that files used under reciprocation movement showed an increase in their resistance to cyclic fatigue. ...
Objectives:
The aim of this cross-sectional retrospective study was to evaluate radiographically the technical quality of root canal treatment performed by undergraduate students using reciprocating NiTi instrumentation and single-cone obturation.
Methods:
Endodontic treatment on 1102 teeth performed by undergraduate students from the School of Dentistry of the University of Santa Cecilia (Brazil) was evaluated. All root canal preparations were performed using Reciproc files and were irrigated with 1% NaOCl. The root canal was filled with gutta-percha, along with AH Plus sealer, using the single-cone obturation technique. The technical quality of the root canal treatment was evaluated based on immediate postoperative radiographs. Distance between the end of the filling and the radiographic apex, the filling density, and the taper of the root filling was assessed. Inter-examiner agreement statistic (Kappa) and Chi-square statistic test were used for statistical evaluation of the results. Differences were considered statistically significant when p < 0.05.
Results:
Anterior teeth, maxillary premolars, and molars presented better results than mandibular premolars and molars (p < 0.05). Mandibular premolars presented a high incidence of a short length of obturation (33.34%) and mandibular molars presented a high incidence of overfilling (6.55%). The majority of the treatment analyzed (62.46%) fulfilled all the criteria showing acceptable working length, taper, and density of obturation. Instrument fractures occurred in eighteen root canals (0.81%).
Conclusions:
The use of NiTi reciprocating instruments with the single-cone obturation technique provided an acceptable quality of endodontic treatment in the majority of the cases performed by undergraduate students.
... CM Wire files have a significantly improved resistance to cyclic failure than conventional and M-Wire NiTi instruments [34], which might be attributed to the failure of a deflection angle is lower than conventional and M-Wire NiTi [35]. ...
Background
Various systems of nickel-titanium (NiTi) instrument have long been commercially available. However, the preparation of narrow and curved root canals has always been challenging. The purpose of this study was to compare the shaping ability of two NiTi systems (2Shape and NeoNiTi) in severely curved root canals with different morphological patterns using micro-computed tomography (Micro-CT).
Methods
A total of 22 human extracted permanent teeth of mandibular first molars, with the exact mesial angle of curvature of 25 and 35 degrees, according to Schneider’s technique, were distributed randomly into two groups (group I: 2Shape, group II: NeoNiTi) based on the rotary system used (n = 22). The groups were subdivided into two subgroups corresponding to the angle of canal curvature (25° and 35°) (n = 11). Canals were scanned using Micro-CT pre- and post-preparation to assess the volume of dentin removed; canal transportation; and canal centering ratio at 3, 6, and 9 mm from the apex. The Mann–Whitney U test was utilized to determine any significant differences between the two systems. The level of statistical significance was set at p < 0.05.
Results
There was no significant difference between the two groups in volume of dentin removed; canal transportation; and centering ability for 25° and 35° canal curvatures at 3, 6, and 9 mm from the apex (coronal, middle, and apical) thirds ( p > 0.05). At the middle third, the NeoNiTi group demonstrated a statistically significant increase in volume of dentin removed for 35° canal curvatures compared to the 2Shape group.
Conclusion
Within the limitation of our in vitro study, 2Shape and NeoNiTi systems with severely curved canals were confirmed to be relatively safe in preparation and to respect original canal anatomy. Nevertheless, NeoNiTi instruments produced more centered preparation and minimal canal deviation compared to the 2Shape system.
... That is, the heat-treated NiTi alloy mainly contains R-phase or martensite, which is more flexible, while the conventional NiTi alloy contains austenite [3,4]. It has been reported that heat-treated NiTi files have significantly increased flexibility and cyclic fatigue resistance compared to conventional NiTi files [5][6][7]. ...
Abstract Background In root canal preparations, it is important to maintain the original canal shape. However, it is difficult to accomplish this, especially due to the complex canal anatomy. This study aimed to compare the shaping ability of the ProTaper GOLD, WaveOne GOLD, and newly developed TruNatomy in simulated S-shaped canals. Methods The root canals of 60 S-shaped resin blocks were dyed using ink and photographed. The blocks were then randomly divided into three groups: group ProTaper GOLD (n = 20), WaveOne GOLD (n = 20), and TruNatomy (n = 20). The simulated canals were instrumented according to the NiTi file system and photographed again after being dyed with red ink. The pre- and post-preparation images were superimposed, and the amount of resin removed from both the mesial and distal sides of the canal measured up to 9 mm from the apical terminus, with a 1 mm increment. The preparation time was also calculated. A paired t-test was used to determine the degree of deviation at different levels within the groups. To compare the degree of transportation at different levels between the groups, one-way ANOVA and Kruskal–Wallis tests were performed according to the normality. Results TruNatomy showed a significant deviation between the mesial and distal sides of the canal only in the coronal area at 6, 7, 8, and 9 mm levels of the canal (p
... The martensitic phase is softer than the austenite phase due to the low Young's modulus, and the CM-wire file is mostly in the martensitic phase. 26 Many studies have reported that the HCM is more flexible and exhibits higher cyclic fatigue resistance than other files with different properties and metallurgies. 27,28 Topcuoğlu et al 29 evaluated the cyclic fatigue resistance of HCM, ProTaper Universal (Dentsply Tulsa Dental Specialities, Tulsa, OK), PTN, and OneShape (Micro Mega, Besancon, France) file systems in an artificial canal with two curvature angels and reported that PTN and HCM file systems were more durable in the apical curvature than other groups. ...
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.
The introduction of nickel-titanium (NiTi) mechanical instruments dramatically changed clinical endodontics over the last few decades. Before NiTi, it was necessary to use more instruments to create an ideal root canal shape, and many approaches, sequences and techniques were developed over the years. Recently, NiTi endodontic instruments have undergone a series of changes brought about by modifications in design, surface treatments, and thermal treatments to improve their root canal preparation outcomes and reduce associated canal preparation risks during root canal treatment. Heat treatment is one of the most fundamental approaches to improving the fatigue resistance and flexibility of NiTi endodontic instruments. In addition, new kinematics have been developed to offer greater safety and efficiency. This narrative review describes the general properties and manufacturing of NiTi instruments, and the mechanical system evolution of NiTi instruments.
Purpose: The aim of this study was to evaluate the impacts of cyclic fatigue resistance of four heat-treated nickel-titanium (NiTi) rotary instruments after immersion and sterilization in sodium hypochlorite (NaOCl). Materials and Procedures: In simulated canals, the cyclic fatigue resistance of 320 new nickel-titanium endodontic files was examined. A total of four subgroups (n = 20) of 25/.06 TruNatomy (TN; Dentsply Sirona, Maillefer, Ballaigues, Switzerland), 25/.06 Hyflex CM (Coltene Whaledent, Cuyahoga Falls, OH), 25/.06 Hyflex EDM (Coltene, Whaledent Pvt Ltd), and 25/.06 EdgeFile X3 (EdgeEndo, Albuquerque, NM, USA) files were created for The new instruments in Subgroup 1 (the control group) were not autoclave sterilized or submerged in NaOCl. Instruments in subgroup 2 were dynamically submerged in 5.25% NaOCl solution for 3 minutes. Instruments in subgroup 3 received three rounds of autoclave sterilization at 121°C with 15 pressure for fifteen minutes. Subgroup 4 enlisted instruments that underwent three cycles of autoclave sterilization and a round of dynamic immersion in NaOCl solution. Every file was rotated until a crack developed. ANOVA with the post-hoc Games Howell test was used to compute and statistically assess the means and standard deviations of the number of cycles to failure (NCF). (P < .001). Results: A statistically significant difference in NCF was found when the four instruments under investigation were compared (P >.001). In all the subgroups, EdgeFile X3 files demonstrated the highest cycle fatigue resistance, followed by Hyflex EDM files, Hyflex CM files, and TruNatomy with the lowest resistance. When comparing the instruments with regard to the four treatment procedures, there was also a statistically significant difference (P<.001) (subgroups). The cyclic fatigue of the NiTi files tested was affected by the instruments' dynamic immersion in NaOCl solution for three minutes, followed by three cycles of autoclave sterilization. All four of the heat-treated instruments significantly outperformed the control group in terms of cyclic fatigue resistance. Conclusions: Within the constraints of this study, the EdgeFile X3 group, Hyflex EDM group, Hyflex CM group, and TruNatomy group had the strongest fracture resistance to cyclic fatigue. Instruments that underwent three minutes of dynamic immersion in NaOCl solution followed by three cycles of autoclave sterilization had an impact.
Introduction:
The rotary systems have found a common application in the clinical practice for the endodontic therapies. Hence, we compared three recent endodontic systems for the comparison of the dentine removal and the apical transportation particularly in the curved canals.
Methods:
Oneshape, Pro Taper Next, and Edgefile X3 were the three systems that were compared. Thirty maxillary mesio buccal canals of the human permanent teeth were compared due to its curved nature. The volume of dentin removed and apical transportation (mm) were measured using micro-computed tomographic imaging (mm). Both the coronal section and the entire canal length had their dentin removed in accordance with measurements. Total dentine removed, coronal dentine removed, and the canal transportations were compared for the three rotary file systems. The values were compared with appropriate statistical tests for evaluating the significance.
Results:
There was no statistically significant difference between the three file systems for the dentin removed. The mean canal transportation was 0.33 ± 0.12, 0.21 ± 0.25, and 0.23 ± 0.21 mm, respectively, for Oneshape, Pro Taper Next, and Typhoon CM. In terms of statistics, there were no appreciable variations among the three rotary tools for apical transfer.
Conclusions:
The three rotary systems were comparable for the apical transportation and the dentine removal. Despite variations in the magnitude of apical enlargements, none of the instrumentation methods detected apical transportation.
Although nickel–titanium (NiTi) rotary files are invaluable tools in dentistry, the relationship between their properties and performance has not been elucidated. Herein, the performance of gold heat-treated (ProTaper Gold and ProfaTaper Gold), controlled memory (CM)-wire (HyFlex CM and V Taper 2H), T-wire (2Shape), and R-phase heat-treated (K3XF) NiTi files was evaluated; the non-heat-treated ProFile was used as the control. The bending, buckling, cyclic fatigue, and torsional resistances of the NiTi files were determined, and their phase transformation behavior was studied through differential scanning calorimetry (DSC). The angle of rotation until fracture (ARF), ultimate torsional strength (UTS), and stiffness were evaluated via torsional resistance testing. One-way analysis of variance (ANOVA) and post hoc analyses were conducted using the Games–Howell test and Tukey’s test. ProFile displayed the highest buckling resistance (8 N), CM-wire NiTi files exhibited the lowest bending resistance (0.660–0.758 N cm), and HyFlex CM displayed the highest cyclic fatigue resistance. ProTaper Gold exhibited high UTS and low ARF. K3XF demonstrated high bending resistance and the lowest cyclic fatigue resistance. The CM-wire NiTi files were the most suitable for use in curved canals, while the gold-wire NiTi files were ideal for constricted canals. ProFile was recommended for use in re-treatment cases.
Introduction:
We aim to evaluate the cyclic and torsional fatigue resistance of two rotary instruments, Hyflex CM 25/0.06 (HCM) (Coletene-Whaledent, Allstetten, Switzerland) and Aurum Blue (AB) 25/0.06 (Meta-Biomed, Republic of Korea).
Methods and materials:
Forty rotary instruments, HCM 25/0.06 and AB 25/0.06 (n=20 each) were used. The instruments were rotated in an artificial stainless steel canal with a 60° angle and a 5-mm radius of curvature (n=10) at body temperature (35°±1°C). The torsional test evaluated the torque and angle of rotation at failure of new instruments (n=10) in the portion 3 mm from the tip according to ISO 3630-1. The fractured surface of each fragment was observed by scanning electron microscopy. The data were analyzed using unpaired student's t- test, and the level of significance was set at 5%.
Results:
AB 25/0.06 had significantly greater number of cycles to failure than HCM 25/0.06 (P<0.05). The torsional test showed there were no significant differences in the torsional strength and angular rotation to fracture between the groups (P>0.05).
Conclusion:
Based on this in vitro study, AB 25/0.06 instrument was more resistant to cyclic fatigue than the HCM 25/0.06 instrument, suggested that these instruments are safer than HCM 25/0.06 for the preparation of severely curved canals. However; there was no significant difference in the torsional properties of the two instruments then appear to have similar performance during constricted canal preparation.
Abstract Background Recently, various kinds of heat-treated nickel-titanium (NiTi) glide path instruments have been manufactured. This study aimed to investigate design, phase transformation behavior, mechanical properties of TruNatomy Glider (#17/02), V Taper 2H (#14/03), and HyFlex EDM (#15/03) and compare torque/force generated during simulated glide path preparation with them. Methods The designs and phase-transformation behaviors of the instruments were examined via scanning electron microscopy (n = 3) and differential scanning calorimetry (n = 2). Their bending (n = 15), torsional (n = 15), and cyclic fatigue resistances (n = 15) were tested. The ultimate strength and distortion angle were obtained from torsional resistance test. The number of cycles to failure (NCF) was calculated from cyclic fatigue resistance test. The preparation of the glide path was simulated using a double-curved artificial canal (n = 15), and the maximum torque and screw-in forces were measured. Data except NCF was compared between brands with one-way ANOVA with Tukey’s honestly significant difference test. NCF was analyzed via Kruskal–Wallis and Mann–Whitney U tests. Results TruNatomy Glider had the greatest number of threads. TruNatomy Glider showed progressive taper, while V Taper 2H and HyFlex EDM had constant taper. The austenitic transformation-finish temperatures of all the instruments were above body temperature. V Taper 2H demonstrated significantly lower ultimate strength, higher distortion angle, and a higher number of cycles to failure compared with HyFlex EDM and TruNatomy Glider (p
Aim: To comparatively evaluate in vitro the cyclic fatigue resistance of different file systems based on different manufacturing technologies after exposure to NaOCl and multiple sterilization cycles.
Materials and Methods: Sixty new Nickel − Titanium (NiTi) rotary files were selected and divided into five groups (n = 12) based on different manufacturing technology. These groups were: Protaper Universal (GPT) (DentsplyMaillefer, Ballaigues, Switzerland) Protaper Next (GPTN) (Dentsply, Tulsa, OK, USA), Twisted files (GTF) (Sybron Endo, Orange, CA, USA), Neoniti (GNL) (Neolix, France), and Hyflex CM (GHCM) (Coltene/whaledent inc., 235 Ascort Parkway, Cuyahoga falls, OH, USA). Files were sterilized in an autoclave at 121°C at 15 psi for 15 min and exposed to 5.0% NaOCl solution for 30 s before cyclic fatigue testing till instrument fracture using a standardized grooved block assembly with the artificial canal at 90° angle of curvature using a 16:1 reduction hand-piece powered by a torque-controlled motor. This whole procedure of autoclaving, immersion in sodium hypochlorite solution and rotating in a stainless steel assembly was repeated again and again until the file fractured.
Results: The highest mean for the number of cycles before fracture was observed with Neoniti (GNL) and lowest for Hyflex CM (GHCM). The difference between GPT vs GTF, GPTvs GNL, GNLvs GHCM; GPTNvs GTF, GPTNvs GNL, GPTNvs GHCM; GTFvs GNL, GTFvs GHCM and GNL VS GHCM was statistically significant, whereas the difference between GPTvs GPTN was statistically nonsignificant.
Conclusion: Neoniti and twisted file systems resisted the maximum number of cycles to fracture at 90° angle of curvature after exposure to 5% sodium hypochlorite solution and multiple autoclaving cycles. Hyflex CM showed the least resistance in the similar conditions.
This chapter summarises the metallurgical properties of nickel‐titanium (NiTi) endodontic instruments, with a special focus on the latest generation of NiTi instruments. NiTi alloy has special characteristics of superelasticity and shape memory. The differences in mechanical properties between NiTi endodontic instruments lie in the properties of the phases that exist in the alloy. The austenite phase exists at higher temperatures and is stronger and stiffer than the martensite phase, which exists at lower temperatures and is softer and more flexible. Surface enhancement of NiTi instruments minimises inherent defects and increases surface hardness and flexibility resistance to fatigue and cutting efficiency. Thermal treatments have been shown to have an impact on some of the mechanical properties and transformation characteristics of NiTi shape memory alloy depending on their thermomechanical history. The process of heat treatment would be performed before the machining of the instrument to decrease the work hardening of the alloy.
According to the Global Burden of Disease (GBD) 2015, around 3.5 billion people suffer from dental diseases. The treatment of these disease requires either a specific dental device or a material which are usually subjected to stress and corrosion of the oral environment due to varying temperature, pH, occlusion, and masticatory forces. Various smart materials have emerged in the biomedical field because of their superior properties compared to conventional alloys. However, Nickel-Titanium (Ni-Ti) alloys with nearly equi-atomic composition have a long-standing history of successful use in dentistry because of their shape memory (SM) and superelastic (SE) properties with excellent cytocompatibility and corrosion resistance. The SM property offers preferable control of the transition temperature range (TTR) near the oral temperature providing multiple actuation. The SE property has revolutionized orthodontic treatment by delivering light and continuous physiological forces to the teeth, thereby improving patient comfort. The SE property of Ni-Ti alloy has been extensively used to produce orthodontic archwires and endodontic files as they exhibit higher flexibility compared to conventional stainless-steel alloy. However, the duration and type of heat treatment performed on these devices have been reported to modify their thermo-mechanical properties, producing adverse effects. Besides this, the devices are also subjected to short-term cooling or heating, sterilization, and disinfection protocols that creates a corrosive environment. Thus, thermo-mechanical properties and the influence of oral environment on various commercially available Ni-Ti alloy dental devices have been briefly explored and discussed. Besides orthodontic archwire and endodontic files, other Ni-Ti alloy-based dental devices are also reviewed, such as Shape memory Ni-Ti alloy sleeve for Abutment System, SM Ni-Ti alloy palatal expander, and SM Ni-Ti alloy porous dental implant. Thus, this manuscript aims to provide a concise assessment of the properties of SE and SM Ni-Ti alloys and their evolution in the field of dentistry.
Aim: To assess impact of elemental composition, core metal mass and phase transformation behaviour on the dynamic cyclic fatigue resistance of three Ni-Ti rotary files at room and body temperatures.
Methods: Twenty instruments of each system were tested for dynamic cyclic fatigue resistance in a simulated root canal with a 90˚ angle of curvature and a 5-mm radius of curvature at room and body temperature. The core metal mass at the fractured surface of each instrument was calculated by Image J software analysis of SEM images. The energy dispersive X-ray analysis was used to assess file composition. Scanning calorimetry was used to assess the structural phase state and the transformation temperature. One-way analysis of variance (ANOVA) was performed to determine any statistical difference amongst groups. For inter-group comparison, the unpaired t-test was used.
Results: HEDM showed significantly higher TtF and NCF values than AFBS and ZB-F6 instruments, at both temperatures tested. The mean core metal mass was smallest in HEDM followed by AFBS with no statistical difference between them, while ZB-F6 had the significantly largest metal core. EDX analysis showed that all the instruments were mainly composed by nickel and titanium. DSC analysis revealed that HEDM and AFBS exhibited a martensitic phase at body (37˚C) and room temperature (25˚C), whereas ZB-F6 revealed an austenitic phase at body temperature.
Conclusions: Dynamic cyclic fatigue resistance increased when the instruments had less cross-sectional metal mass, less Ni (wt%), a thermally treated surface, and a martensite phase at body temperature.
The objective of this study was to evaluate the cyclic fatigue resistance of novel NiTi files (subjected to heat treatment) using the in vitro model (artificial canal). Twelve ProDesign Logic instruments - PDL 25/.06 (Easy Equipamentos Odontológicos, Belo Horizonte, Brazil) and 12 Protaper Next X2 instruments - PTN (tip 25) were included in this research. The Static cyclic fatigue test was performed with a grooved stainless steel block simulating a canal of 1,5 mm diameters, a 60o angle of curvature and 5 mm radius. The files were positioned inside the artificial canal and rotated until the fracture occurred. Using the time until fracture (seconds) and the number of rotations per minute (RPM), the number of cycles until fracture (NCF) was calculated and the length of ruptured fragments was registered. Three samples from each group were analyzed in Scanning Electronic Microscopy (SEM) to characterize the metal rupture. Data were analyzed using the Mann-Whitney non-parametric test and the level of significance considered was p<0.05. PDL obtained a mean value of 956,0 NCF (352,0 - SD) and PTN achieved 391,0 NCF (36.7 - SD) with statistical significance between the groups (p < 0.001). There was no statistical difference on fragment length (p > 0.05). SEM analysis showed features compatible with ductile fracture. ProDesign LOGIC files showed higher NCF than Protaper Next X2. There was no difference between groups considering the length of the ruptured fragment.
This article reviews the historical development, properties, and trends of nickel titanium rotary instrumentation use for the veterinary endodontist.
NiTi endodontic instruments are used for root canal treatment, but can sometimes fracture due to bending cyclic fatigue. Three comparable instruments (X2 Protaper Next®, Race® and F6 Skytaper®) were tested under bending (at a 45° angle) and cyclic rotary bending fatigue (at 30°, 45° and 60° angles). Experimental (differential scanning calorimetry (DSC) and scanning electronic microscopy) and numerical approaches were used to investigate the parameters determining their bending behavior and their cyclic fatigue fracture. The results showed that Race® was the stiffer instrument under bending and presented a significant difference compared to the two other instruments at 60° fatigue test. There was a significant difference among all instruments at 45°. These results could be partly explained by the geometry of the instruments and the phase-transition temperatures (DSC). The microscopic observations showed that, in the case of Protaper Next® and F6 Skytaper® instruments, the fracture could come from surface defects resulting from their manufacturing process. This was confirmed by the finite-element analysis on these instruments which revealed a mismatch between the simulated area of maximum bending stress and the experimental fracture zone. Thus, the geometry, alloy and surface condition have an influence on the bending behavior and cyclic fatigue life.
Introduction:
One of the disadvantages of stainless steel instruments used for root canal preparation is the lack of flexibility and shape memory. The invention of rotary instruments has been successful in overcoming these problems to a greater extent; however, some drawbacks still remain, one of which is vertical root fracture and the cause for it is microcracks formation in dentin, which in turn causes vertical root fracture. There are enough studies for microcracks using different rotary systems and this study compared microcracks with single as well as reciprocating files followed by final finishing with XP endo finisher. Apart from other studies, we used conefocal laser scanning microscope to assess microcrack propagation before and after instrumentation with each rotary system.
Aim:
To evaluate microcrack propagation in mandibular molars after root canal preparation with continuous and reciprocating file systems followed by final finishing with XP Endo finisher.
Materials and methods:
Thirty mandibular molars indicated for the extraction due to periodontal causes were selected for this study. They were divided into three groups based on rotary systems used: Group A: ProTaper universal; Group B: ProTaper gold; and Group C: Waveone gold. All specimens were subjected to scanning before instrumentation to assess the presence of any existing cracks. Cone focal laser microscopic scanning is again repeated for each specimen after instrumentation with each rotary system and also after final finishing with XP Endo finisher.
Statistical analysis:
One-way ANOVA is used.
Results:
Crack propagation is the highest with ProTaper universal and least with waveone gold. After final finishing of canals with XP Endo finisher, crack propagation observed was negligible.
Conclusion:
The success of root canal treatment depends on effective disinfection of root canal system. XP Endo finisher can be used as a final finishing file by considering its advantageous properties, moreover crack propagation with XP Endo finisher in an previously instrumented canal is negligible.
Since there are no reviews of the literature on this theme, the aim of this narrative review is to summarize the metallurgical tests used in endodontics, pointing out their functional use and their pros and cons and giving readers a user-friendly guide to serve as an orientation aid in the plethora of metallurgical tests. With this purpose, a literature search for articles published between January 2001 and December 2021 was conducted, using the electronic database PubMed to collect all published articles regarding the metallurgical tests used in endodontics for the evaluation of NiTi rotary instruments. The search was conducted using the following keywords: “metallurgy”, “differential scanning calorimetry” (DSC), “X-ray diffraction” (XRD), “atomic force microscopy” (AFM), “energy-dispersive X-ray spectroscopy” (EDS), “focused ion beam analysis” (FIB) and “Auger electron spectroscopy” (AES) combined with the term “endodontics” or “NiTi rotary instruments”. Considering the inclusion and exclusion criteria, of the 248 articles found, only 81 were included in the narrative review. According to the results, more than 50% of the selected articles were published in one of the two most relevant journals in endodontics: International Endodontic Journal (22.2%) and Journal of Endodontics (29.6%). The most popular metallurgical test was DSC, with 43 related articles, followed by EDS (33 articles), AFM (22 articles) and XRD (21 articles). Few studies were conducted using other tests such as FIB (2 articles), micro-Raman spectroscopy (4 articles), metallographic analysis (7 articles) and Auger electron spectroscopy (2 articles).
The aim of this study was to evaluate surface wear, presence of microcracks and surface irregularities of WaveOne (WO) and WaveOne Gold (WOG) instruments before and after multiple uses. Eight Primary instruments of the WO and WOG systems were evaluated, each one was used to prepare six mesial canals of extracted human mandibular molars. The surface of the instruments was evaluated before use (T0), after instrumentation of three (T1) and six (T2) root canals. Surface wear was analyzed using a three-dimensional optical profiler and the presence of microcracks and surface irregularities were evaluated using a tabletop scanning electron microscopy. The Friedman test was used to assess surface wear and Kruskal-Wallis test to evaluate the presence of microcracks and surface irregularities, with a 5% significance level. There was a significant increase in wear in both groups at T2, compared to T0 (p=0.0003). The surface wear after instrumentation of six canals (T2-T0) was statistically greater in the WOG group, than in the WO group (p=0.02), where the presence of microcracks was significantly greater and increased after multiple uses (p<0.05). The presence of surface irregularities in the cutting blade before and after use was statistically greater in the WOG group than WO group (p<0.05). Wear of the cutting blade, microcracks and surface irregularities were observed on the surface topography of all the instruments after multiple uses. These surface changes may affect the cutting efficiency of WOG files and increase the risk of fracture of WO files.
The effectiveness of endodontic file preparation depends, among others, on the material, geometric shape, and the drive system. This study aimed to analyze the effect of cross-sectional, pitch, and rotational speed on cyclic fatigue and deflection of NiTi files using finite element analyses. A total of 18 NiTi endodontic rotary instruments ProTaper Gold F2 #25.08 and Hyflex CM #25.04 (n=9) modeling were designed using Autodesk software. Subjects were divided into two groups, the design group of square and convex triangles. Static simulation was then carried out to each group with force on the instrument’s tip by 1N, 2N, and 3N. The file’s cycling fatigue was analyzed at rotating speeds of 200 rpm, 300 rpm, and 400. The data were analyzed by using the three-way Analysis of variance (ANOVA) test followed by LSD (p< 0.05). The results showed the cross-sectional shape and force effect on the deflection value and cyclic fatigue received by the endodontic files (p< 0.05). The convex triangle design presented the lowest cyclic fatigue than square. The convex triangular cross-section design showed a higher deflection value than the square cross-section design.
There has been considerable development in the endodontic instruments, which has resulted in better root canal instruments with the increased success of the endodontic treatment. The fundamental biomaterials for endodontic treatment include carbon steel (CS), stainless steel (SS), and nickel-titanium (NiTi) alloy. NiTi instruments are increasingly used due to flexibility and shape memory effect. In contrast, CS and SS instruments are more laborious and stiffer with less flexibility than NiTi alloy. Recent developments in NiTi rotary instruments include controlled memory (CM) wire and R-phase wire with improved flexibility and fatigue resistance, and surface improvements. The advantages of these technologies bring faster and more efficient instrumentation with resistance to cyclic fatigue, cutting efficiency, and decrease canal transportation and ledging. The clinician should be familiar with different endodontic instruments as new instruments are introduced regularly. This chapter focuses on the biomechanics of endodontic instruments and presents recent developments in various alloys for endodontic instruments.
Keywords: Biomechanics, Carbon steel, Endodontic files, Endodontic instruments, Hand instruments, NiTi alloy, Surface modifications, Stainless steel.
The aim of the present study was to investigate whether cyclic fatigue resistance is increased for nickel-titanium instruments manufactured by using new processes. This was evaluated by comparing instruments produced by using the twisted method (TF; SybronEndo, Orange, CA) and those using the M-wire alloy (GTX; Dentsply Tulsa-Dental Specialties, Tulsa, OK) with instruments produced by a traditional NiTi grinding process (K3, SybronEndo). Tests were performed with a specific cyclic fatigue device that evaluated cycles to failure of rotary instruments inside curved artificial canals. Results indicated that size 06-25 TF instruments showed a significant increase (p < 0.05) in the mean number of cycles to failure when compared with size 06-25 K3 files. Size 06-20 K3 instruments showed no significant increase (p > 0.05) in the mean number of cycles to failure when compared with size 06-20 GT series X instruments. The new manufacturing process produced nickel-titanium rotary files (TF) significantly more resistant to fatigue than instruments produced with the traditional NiTi grinding process. Instruments produced with M-wire (GTX) were not found to be more resistant to fatigue than instruments produced with the traditional NiTi grinding process.
Fractured rotary nickel-titanium (NiTi) instruments have been classified into those that fail as a result of cyclic flexural fatigue or torsional failure or a combination of both. Clinically, NiTi rotary instruments are subjected to both torsional load and cyclic fatigue, and ongoing research aims to clarify the relative contributions of both factors to instrument separation.
To date, there is no specification or international standard to test cyclic fatigue resistance of endodontic rotary instruments. As a consequence, several devices and methods have been used to investigate in vitro cyclic fatigue fracture resistance of NiTi rotary endodontic instruments. In nearly all studies reported in the endodontic literature, the rotating instrument was either confined in a glass or metal tube, in a grooved block-and-rod assembly, or in a sloped metal block.
There has been no mention of the "fit" of the instrument in the tube or groove. As the instrument is likely to be fitting loosely, the description of the radius of curvature in those studies is likely to be overstated (ie, the file was actually bent less severely than reported, adding a variability in the amount of flexural stress).
This review analyzed several devices that have been used in endodontic literature for cyclic fatigue testing and found that differences in the methodology affected the fatigue behavior of rotary instruments and, consequently, the outcome of these studies. An international standard for cyclic fatigue testing of NiTi rotary instruments is required to ensure uniformity of methodology and comparable results.
The 400°C aged Ti49Ni51 alloy can exhibit the transformation sequence of B2 →r premartensite R-phase →r martensite. In the early aging stage, only the premartensitic transformation is observed due to the Ms point being deeply depressed by the coherent stress of Ti11Ni14 precipitates. In the later aging stage, internal friction peaks associated with premartensitic and martensitic transformations are all observed on both heating and cooling. The sharp peaks associated premartensitic transformation on heating is believed to be related to the "bias" effect of the coherent stress induced by the Ti11Ni14 precipitates. The serrations of internal friction appearing significantly in the temperature around -30 to -80°C are found to be caused by the stress induced accomodation of R-phase or martensite variants, and are not associated with the transformation. The Ti11Ni14 precipitates can enhance the amount of martensite formed by unit of temperature or time during the martensitic transformation.
To improve the fracture resistance of nickel-titanium (NiTi) files, manufacturers have introduced new alloys to manufacture NiTi files and developed new manufacturing processes. This study was aimed to examine the fatigue behavior of NiTi instruments from a novel controlled memory NiTi wire (CM Wire).
Instruments of ProFile, Typhoon (TYP), Typhoon CM (TYP CM), DS-SS0250425NEYY (NEYY), and DS-SS0250425NEYY CM (NEYY CM) (DS Dental, Johnson City, TN) all size 25/.04 were subjected to rotational bending at the curvature of 35° and 45° in air at the temperature of 23° ± 2°C, and the number of revolutions to fracture (N(f)) was recorded. The fracture surface of all fragments was examined by a scanning electron microscope. The crack-initiation sites, the percentage of dimple area to the whole fracture cross-section, and the surface strain amplitude (ε(a)) were noted.
The new alloy yielded an improvement of over three to eight times in N(f) of CM files than that of conventional NiTi files (P < .05). The vast majority of CM instruments (50%-92%) showed multiple crack origins, whereas most instruments made from conventional NiTi wire (58%-100%) had one crack origin. The values of the fraction area occupied by the dimple region were significantly smaller on CM NiTi instruments compared with conventional NiTi instruments (P < .01). The square (NEYY CM) versus the triangular (TYP CM) configuration showed a significantly different lifetime on CM wire at both curvatures (P < .01).
The material property had a substantial impact on fatigue lifetime. Instruments made from CM Wire had a significantly higher N(f) and lower surface strain amplitude than the conventional NiTi wire files with identical design.
To investigate the relationship between phase transformation behaviour and bending property of nickel-titanium endodontic instruments manufactured by a twisting process.
The phase transformation behaviour and bending property of Twisted Files (TF; SybronEndo, Orange, CA, USA) and K3 (SybronEndo) with.06 taper and size 30 tip were investigated. K3 was used as control group. Phase transformation behaviour was estimated by differential scanning calorimetry (DSC). Transformation temperatures were calculated from the DSC curve. Bending load of the instruments was measured by cantilever-bending test at 37°C. Data were analysed by Student's t-test and Mann-Whitney U-test.
The phase transformation temperatures of TF were significantly higher (P<0.05) than those of K3. The bending load values were significantly lower for TF than that of K3 (P<0.05), both in the elastic and super-elastic ranges.
The new method of manufacturing NiTi instruments by twisting coupled with heat treatment might contribute to the increased phase transformation temperatures and superior flexibility.
This in vitro study compared the cyclic fatigue resistance of ProFile Vortex rotary instruments (DENTSPLY Tulsa Dental, Tulsa, OK) made of two different raw materials: M-Wire and regular superelastic wire (SE-wire) at two different rotational speeds. Two rotary-based Profile Vortex instruments with taper 0.04 and 0.06 (25 mm in length and #30 in size) were compared.
Cyclic fatigue testing was performed by rotating instruments in an artificially constructed stainless steel canal with a 5-mm radius and a 90 degrees angle of curvature at two different test frequencies: 300 and 500 rpm. The time to failure was recorded, and the total number of cycles to failure was calculated and compared for a total of 160 samples. Statistical analysis was performed with one-way analysis of variance and the Tukey test for individual comparisons (confidence level of p < 0.05). Fracture surfaces of broken instruments were also observed under scanning electron microscopy. Over 50% of broken files made of SE-wire exhibited multiple crack initiation sites compared with the single crack initiation on files made of M-Wire.
Overall, there were significant differences in rotary instruments made of different materials (p < 0.001). However, for rotary instruments made from the same material (either M-Wire or SE-wire), there was no significant difference (p > 0.05) of cyclic fatigue life under different rotational speeds (300 and 500 rpm).
ProFile Vortex files made of M-Wire exhibited superior cyclic fatigue resistance (approximately 150% longer in fatigue life) compared with those made of regular SE-wire at two test frequencies (300 and 500 rpm).
To assess the failure mechanism of rotary NiTi instruments by chemical, structural and morphological analyses to provide a rational explanation of the effects of surface and bulk treatments on their resistance to fatigue fracture.
Thermal treatment (350-500 °C) was performed on electropolished (EP) and non-electropolished (Non-EP) NiTi endodontic instruments. Bulk and surface chemical composition and crystallographic structures were determined by energy-dispersive X-ray spectroscopy, X-ray photoelectron spectroscopy (XPS) and X-ray diffraction (XRD) to evaluate the effects of thermal treatment and electropolishing on the NiTi alloy. Fatigue tests of all instruments were performed. Surface morphology before and after the tests, and fractured section were analysed using scanning electron microscopy to determine crack extensions. Results were analysed statistically using analysis of variance (anova) and post hoc Student-Newman-Keuls test.
Before thermal treatment, significant differences (P < 0.05) in fatigue resistance between EP and Non-EP instruments (the number of revolutions to failure, N(f) , was 385 and 160, respectively) were attributed to differences in the surface morphology of the instruments. SEM analysis of the fracture surfaces indicated that flexural fatigue fractures occurred in two steps: first by a slow growth of initial cracks and then rapid rupture of the remaining material. Thermal treatment did not affect the surface morphology but resulted in significant changes in the instrument bulk with the appearance of an R-phase and an improved fatigue resistance; indeed after treatment at 500 °C, N(f) increased up to 829 and 474 for EP and Non-EP instruments, respectively.
Both thermal treatment and electropolishing improved the resistance of NiTi rotary instruments against fatigue fracture.
In the oral environment, orthodontic wires will be subject to thermal fluctuations. The purpose of this study was to investigate the effect of thermocycling on nickel-titanium (NiTi) wire phase transformations.
Straight segments from single 27 and 35 degrees C copper NiTi (Ormco), Sentalloy (GAC), and Nitinol Heat Activated (3M Unitek) archwires were sectioned into 5mm segments (n=20). A control group consisted of five randomly selected non-thermocycled segments. The remaining segments were thermocycled between 5 and 55 degrees C with five randomly selected segments analyzed with differential scanning calorimetry (DSC; -100<-->150 degrees C at 10 degrees C/min) after 1000, 5000, and 10,000 cycles. Thermal peaks were evaluated with results analyzed via ANOVA (alpha=0.05).
Nitinol HA and Sentalloy did not demonstrate qualitative or quantitative phase transformation behavior differences. Significant differences were observed in some of the copper NiTi transformation temperatures, as well as the heating enthalpy with the 27 degrees C copper NiTi wires (p<0.05). Qualitatively, with increased thermocycling the extent of R-phase in the heating peaks decreased in the 35 degrees C copper NiTi, and an austenite to martensite peak shoulder developed during cooling in the 27 degrees C copper NiTi.
Repeated temperature fluctuations may contribute to qualitative and quantitative phase transformation changes in some NiTi wires.
A novel thermomechanical processing procedure has been developed that yields a superelastic (SE) nickel-titanium (NiTi) wire (M-Wire) that laboratory testing shows has improved mechanical properties compared with conventional SE austenitic NiTi wires used for manufacture of rotary instruments. The objective of this study was to determine the origin of the improved mechanical properties.
Specimens from 2 batches of M-Wire prepared under different processing conditions and from 1 batch of standard-processed SE wire for rotary instruments were examined by scanning transmission electron microscopy, temperature-modulated differential scanning calorimetry, micro-x-ray diffraction, and scanning electron microscopy with x-ray energy-dispersive spectrometric analyses.
The processing for M-Wire yields a microstructure containing martensite, that the proportions of NiTi phases depend on processing conditions, and that the microstructure exhibits pronounced evidence of alloy strengthening.
The presence of Ti(2)Ni precipitates in both microstructures indicates that M-Wire and the conventional SE wire for rotary instruments are titanium-rich.
Previous micro-computed tomography analyses of root canal preparation provided data that were usually averaged over canal length. The aim of this study was to compare preparation effects on apical root canal geometry.
Sixty extracted maxillary molars (180 canals) used in prior studies were reevaluated for analyses of the apical 4 mm. Teeth were scanned by using micro-computed tomography before and after canal shaping with FlexMaster, GT-Rotary, Lightspeed, ProFile, ProTaper, instruments or nickel-titanium K-files for hand instrumentation. Apical preparation was to a size #40 in mesiobuccal and distobuccal and #45 in palatal canals except for GT (#20) and ProTaper (#25 in mesiobuccal and distobuccal and #30 in palatal canals, respectively). Data for canal volume changes, the structure model index (quantifying canal cross sections), and untreated surface area were contrasted by using analysis of variance and Scheffé tests.
Mean mesiobuccal, distobuccal, and palatal canal volumes increased after preparation (P < .05), but differences were noted for preparation techniques. GT rendered the smallest (0.20 +/- 0.14 mm(3)); K-files and ProFile showed the largest volume increases (0.51 +/- 0.20 mm(3) and 0.45 +/- 021 mm(3), P < .05). All canals were slightly rounder in the apical 4 mm after preparation indicated by nonsignificant increases in structure model index. Untreated areas ranged from 4%-100% and were larger in mesiobuccal and palatal canals than in distobuccal ones. Preparation with GT left significantly larger untreated areas in all canal types (P < .05); among root canal types, distobuccal canals had the least amounts of untreated surface areas.
Apical canal geometry was affected differently by 6 preparation techniques; preparations with GT instruments to an apical size #20 left more canal surface untouched, which might affect the ability to disinfect root canals in maxillary molars.
Employ Micro-X-ray diffraction and temperature-modulated differential scanning calorimetry to investigate microstructural phases, phase transformations, and effects of heat treatment for rotary nickel-titanium instruments.
Representative as-received and clinically used ProFile GT and ProTaper instruments were principally studied. Micro-XRD analyses (Cu Kalpha X-rays) were performed at 25 degrees C on areas of approximately 50 microm diameter near the tip and up to 9 mm from the tip. TMDSC analyses were performed from -80 to 100 degrees C and back to -80 degrees C on segments cut from instruments, using a linear heating and cooling rate of 2 degrees C/min, sinusoidal oscillation of 0.318 degrees C, and period of 60s. Instruments were also heat treated 15 min in a nitrogen atmosphere at 400, 500, 600 and 850 degrees C, and analyzed.
At all Micro-XRD analysis regions the strongest peak occurred near 42 degrees , indicating that instruments were mostly austenite, with perhaps some R-phase and martensite. Tip and adjacent regions had smallest peak intensities, indicative of greater work hardening, and the intensity at other sites depended on the instrument. TMDSC heating and cooling curves had single peaks for transformations between martensite and austenite. Austenite-finish (A(f)) temperatures and enthalpy changes were similar for as-received and used instruments. Heat treatments at 400, 500 and 600 degrees C raised the A(f) temperature to 45-50 degrees C, and heat treatment at 850 degrees C caused drastic changes in transformation behavior.
Micro-XRD provides novel information about NiTi phases at different positions on instruments. TMDSC indicates that heat treatment might yield instruments with substantial martensite and improved clinical performance.
To investigate the effect of heat treatment on the bending properties of nickel-titanium endodontic instruments in relation to their transformation behaviour.
Nickel-titanium super-elastic alloy wire (1.00 mm Ø) was processed into a conical shape with a 0.30 mm diameter tip and 0.06 taper. The heat treatment temperature was set at 440 or 500 degrees C for a period of 10 or 30 min. Nonheat-treated specimens were used as controls. The phase transformation behaviour was examined using differential scanning calorimetry. A cantilever-bending test was used to evaluate the bending properties of the specimens. Data were analyzed by ANOVA and the Tukey-Kramer test (P = 0.05).
The transformation temperature was higher for each heat treatment condition compared with the control. Two clear thermal peaks were observed for the heat treatment at 440 degrees C. The specimen heated at 440 degrees C for 30 min exhibited the highest temperatures for M(s) and A(f), with subsequently lower temperatures observed for specimens heated at 440 degrees C for 10 min, 500 degrees C for 30 min, 500 degrees C for 10 min, and control specimens. The sample heated at 440 degrees C for 30 min had the lowest bending load values (P < 0.05), both in the elastic range (0.5 mm deflection) and in the super-elastic range (2.0 mm deflection). The influence of heat treatment time was less than that of heat treatment temperature.
Change in the transformation behaviour by heat treatment may be effective in increasing the flexibility of nickel-titanium endodontic instruments.
The purpose of this study was to investigate the mode of failure of three brands of nickel-titanium (NiTi) instruments (ProTaper [Dentsply Maillefer, Ballaigues, Switzerland], ProTaper for Hand Use [Dentsply Maillefer], and K3 [SybronEndo, Orange, CA]) that separated during clinical use. A total of 79 fractured instruments were collected from three endodontic clinics over 16 months. The fracture surface of each fragment was examined by scanning electron microscope. Most of the rotary instruments (78% of K3 and 66% of ProTaper) failed because of fatigue fracture, whereas 91% of NiTi hand instruments failed as a result of shear (p < 0.01). The fracture mode of shaping files in rotary ProTaper was different between two different clinics (p < 0.05). All surfaces with fatigue fracture (n = 47) revealed the presence of either one or two crack origins. The vast majority (86%) of K3 fatigue failure had two crack origins that could be found not only at the cutting edge but also at various places along the flute compared with only 28% of ProTaper showing multiple crack origins (p < 0.01). The latter showed one crack origin in 81% of the fatigued shaping files but only 37% for finishing files (p < 0.01). The results of this study indicated that the failure mode of NiTi instruments is related to preparation technique.
Root canal files in size #15 and triagular cross-sections were fabricated from 0.020-inch diameter arch wires of Nitinol, a nickel-titanium orthodontic alloy with a very low modulus of elasticity. A unique manufacturing process was used in which the fluted structure of a K-type file was machined directly on the starting wire blanks. The Nitinol files were found to have two to three times more elastic flexibility in bending and torsion, as well as superior resistance to torsional fracture, compared with size #15 stainless steel files manufactured by the same process. The fracture surfaces for clockwise and counterclockwise torsion were observed with the scanning electron microscope and exhibited a largely flat morphology for files of both alloy types and torsional testing modes. It was possible to permanently precurve the Nitinol files in the manner often used by clinicians with stainless steel files. These results suggest that the Nitinol files may be promising for the instrumentation of curved canals, and evaluations of mechanical properties and in vitro cutting efficiency are in progress for size #35 instruments.
Superelastic mechanical behavior of nitinol alloy orthodontic wires is thought to be the result of a stress induced crystallographic transformation from austenite to martensite. The purpose of the study was to compare the SE mechanical behavior of nitinol wires to stress-induced phase changes. Eight nitinol arch wires having rectangular cross-sections were strained from 0% to 10% in tension with a mechanical testing machine. Load/extension plots were subjectively ranked for SE behavior. X-ray diffraction patterns were collected with and without 6% strain. Without strain, nitinol wires were found to be predominantly austenite with some wires containing a small amount of martensite. When strained 6%, superelastic wires demonstrated a phase transformation from austenite to martensite. XRD patterns were ranked for percent transformation and 110 peak width. Product rankings of the degree of superelasticity were positively correlated with the rank of martensitic transformation (p < 0.05). Superelasticity ranks were negatively correlated with XRD peak width ranks (p < 0.01). Increased peak width indicates greater cold work. A range of superelastic mechanical behavior and martensitic transformation is exhibited by wires currently on the market. Cold work and heat treatments are important variables to be controlled during the manufacture of nitinol products.
The development of superelastic nickel-titanium archwires has simplified the alignment phase of orthodontic treatment by permitting the use of highly flexible, resilient archwires and avoiding the need for complex loops. The majority of these archwires appear undistorted when removed from the mouth after use. This feature, coupled with the disadvantage of relatively high cost has led to sterilization and recycling of these wires by some clinicians. This study was designed to examine the effects of currently used infection control procedures on the mechanical properties of superelastic nickel-titanium alloy (SENTA) archwires. One-hundred-and-forty lengths of a SENTA wire were subjected to various sterilization and disinfection procedures. These included cold disinfection in 2 per cent glutaraldehyde solution for 3- and 24-hour cycles, and steam autoclaving. Single and double cycles were used. The properties investigated were the 0.1 per cent yield strength, the ultimate tensile strength, and the flexural rigidity. No statistically significant differences were found between the groups or against an untreated control.
The purpose of this study was to analyze the type and frequency of defects in nickel-titanium rotary endodontic files after routine clinical use, and to draw conclusions regarding the reasons for failure. All of the files (total: 378, Quantec Series 2000) discarded after normal use from a specialist endodontic practice over 6 months were analyzed. Almost 50% of the files showed some visible defect; 21% were fractured and 28% showed other defects without fracture. Fractured files could be divided into two groups according to the characteristics of the defects observed. Torsional fracture occurred in 55.7% of all fractured files, whereas flexural fatigue occurred in 44.3%. The results indicated that torsional failure, which may be caused by using too much apical force during instrumentation, occurred more frequently than flexural fatigue, which may result from use in curved canals.
An overview of nickel–titanium alloys used in dentistry. International Endodontic Journal, 33, 297–310, 2000.
The nickel–titanium alloy Nitinol has been used in the manufacture of endodontic instruments in recent years. Nitinol alloys have greater strength and a lower modulus of elasticity compared with stainless steel alloys. The super-elastic behaviour of Nitinol wires means that on unloading they return to their original shape following deformation. These properties are of interest in endodontology as they allow construction of root canal instruments that utilize these favourable characteristics to provide an advantage when preparing curved canals. This review aims to provide an overview of Nitinol alloys used in dentistry in order for its unique characteristics to be appreciated.
The phase transformation behavior in three commercial nickel-titanium orthodontic wires having different transformation temperatures was studied by micro X-ray diffraction (micro-XRD). Micro-XRD spectra were obtained at three different included bending angles (135 degrees, 146 degrees and 157 degrees) and three different temperatures (25 degrees C, 37 degrees C and 60 degrees C). The regions analyzed by micro-XRD were within the separate areas of a given wire specimen that experienced only tensile or compressive strain. The intensity ratio (M002/A110) between the 002 peak for martensitic NiTi and the 110 peak for austenitic NiTi was employed as the index to the proportions of the martensite and austenite phases. The ratio of martensite to austenite increased in all three nickel-titanium wires with decreasing included bending angle (greater permanent bending deformation), and was lower within the compression area for all wires at all bending angles than within the tension area. Micro-XRD provides an effective method for quantitative evaluation of the proportions of these two phases in nickel-titanium orthodontic wires, even though considerable preferred crystallographic orientation exists because of the wire drawing process.
Differential scanning calorimetric (DSC) analyses were performed between -130 degrees and 100 degrees C on specimens prepared from nickel-titanium (NiTi) rotary endodontic instruments: ProFile (n = 5), Lightspeed (n = 4), and Quantec (n = 3). The ProFile and Lightspeed instruments were in the as-received condition, whereas the Quantec instruments were randomly selected from a dental clinic and had unknown history. The DSC plots showed that the ProFile and Lightspeed instruments analyzed had the superelastic NiTi property, with an austenite-finish (Af) temperature of approximately 25 degrees C. Differences in DSC plots for the ProFile instruments and the starting wire blanks (n = 2) were attributed to the manufacturing process. The phase transformation behavior when the specimens were heated and cooled between -130 degrees and 100 degrees C, the temperature ranges for the phase transformations, and the resulting enthalpy changes were similar to those previously reported for nickel-titanium orthodontic wires having superelastic characteristics or shape memory behavior in the oral environment. The experiments demonstrated that DSC is a powerful tool for materials characterization of these rotary instruments, providing direct information not readily available from other analytical techniques about the NiTi phases present, which are fundamentally responsible for their clinical behavior.
Shape memory alloys are increasingly used in superelastic conditions under complex cyclic deformation situations. In these applications, it is very difficult to predict the service life based on the theoretical law. In the present work, fatigue properties of NiTi engine-driven rotary files have been characterized by using differential scanning calorimetry (DSC) and mechanical testing (bending). The DSC technique was used to measure precise transformation. The degree of deformation by bending was studied with combined DSC and mechanical property measurements. In these cold-worked files, the high dislocation density influences the reorientation processes and the crack growth. Some thermal treatments are involved in promoting some changes in the mechanical properties and transformation characteristics. Annealing around 400 degrees C shows good results; the recovery allows a compromise between an adequate density for the R-Phase germination and a low density to limit the brittleness of these instruments. In clinical usage, it is important to consider different canal shapes. It could be proposed that only few cycles of use is safe for very curved canals but to follow the manufacturer's advise for straight canals.
Differential scanning calorimetric (DSC) analyses have been performed between -130 degrees and 100 degrees C on single-segment specimens obtained from ProFile and Lightspeed nickel-titanium rotary endodontic instruments in the as-received condition and after one, three, and six periods of simulated clinical use in extracted teeth. The DSC analyses showed that both brands of instruments were always in the superelastic condition, although the enthalpy values for the transformation from martensitic NiTi to austenitic NiTi were much smaller for the Lightspeed instruments. Simulated clinical use had no evident effect upon this transformation for both brands, which is attributed to insufficient mechanical deformation of the instruments. There were substantial differences in the enthalpy change associated with the transformation from martensitic NiTi to austenitic NiTi for test segments from different positions along the shafts of the instruments and for as-received instruments from two different batches that were analyzed in this study and a previous study. These differences are attributed to variations in work hardening along the shaft during instrument fabrication and to processing differences during production of the two batches of each instrument brand.
The purpose of this study was to compare the incidence and mode of instrument separation of the two nickel-titanium (NiTi) rotary systems that were used according to a predefined schedule of clinical use by the same group of operators. A total of 166 ProFile and 325 ProTaper instruments, discarded from this endodontic clinic over 17 months, was analyzed. The incidences of instrument separation were 7% for ProFile and 14% for ProTaper (p < 0.05). The proportion of unwinding defects was 5% in ProFile and 0.3% in ProTaper instruments (p < 0.01). Flexural fatigue was implicated in the majority of separations in both groups. The results of this study indicated that while ProTaper was more likely to separate without warning, ProFile tended to exhibit unwinding of flutes more frequently.
The purpose of this study was to determine the effect of various thermal treatments on the fatigue resistance of a nickel-titanium (NiTi) engine-driven endodontic file.
Fifteen groups of 5 files each of ISO 30 and taper .04 were tested in this study. The cutting tip (5 mm from the end) of files from 14 groups were heat treated for 30 minutes in temperatures 250 degrees C, 300 degrees C, 350 degrees C, 375 degrees C, 400 degrees C, 410 degrees C, 420 degrees C, 425 degrees C, 430 degrees C, 440 degrees C, 450 degrees C, 475 degrees C, 500 degrees C, and 550 degrees C, respectively, while 1 group was used as reference. The files were placed in a device that allowed the instruments to be tested for rotating bending fatigue inside an artificial root canal. The number of rotations to breakage was recorded for each file. The mean values of all groups were statistically analyzed using 1-way analysis of variance and Student Newman Keuls multiple comparison test at alpha = .05.
The 430 degrees C and 440 degrees C groups showed the highest values, with fatigue resistance decreasing for thermal treatment at lower and higher temperatures. This may be the result of metallurgical changes during annealing.
Within the limitations of the low sample size and the specific instrument size tested, it appears that the appropriate thermal treatment may significantly increase the fatigue resistance of the NiTi file tested.
X-ray diffraction of nitinol orthodontic arch wires Micro-XRD and temperature-modulated DSC investigation of nickel-titanium rotary endodontic instruments
- Ta Thayer
- Md Bagby
- Rn Moore
- Deangelis
- Sb Alapati
- Brantley
- Wa
- M Iijima
Thayer TA, Bagby MD, Moore RN, DeAngelis RJ. X-ray diffraction of nitinol orthodontic arch wires. Am J Orthod Dentofacial Orthop 1995;107:604–12. 22. Alapati SB, Brantley WA, Iijima M, et al. Micro-XRD and temperature-modulated DSC investigation of nickel-titanium rotary endodontic instruments. Dent Mater 2009;25: 1221–9.
Fractography: observing, measuring and interpreting fracture surface topography.
- Hull D.
Hull D. Fractography: observing, measuring and interpreting fracture surface topog-raphy. Cambridge, UK: Cambridge University Press; 1999.
Twisted Files (TF) (lot 021004339; SybronEndo, Orange, CA), Typhoon (TYP) (lot 040510002; Clinician's Choice Dental Products), and TyphoonÔ CM (TYP CM) (lot 04051003; Clinician's Choice Dental Products), all size 25
- Dentsply Specialties
- Tulsa
- Ok
Dentsply Tulsa Dental Specialties, Tulsa, OK), Twisted Files (TF) (lot 021004339; SybronEndo, Orange, CA), Typhoon (TYP) (lot 040510002; Clinician's Choice Dental Products), and TyphoonÔ CM (TYP CM) (lot 04051003; Clinician's Choice Dental Products), all size 25/.04, were evaluated. Test specimens were carefully cut from References