• Austenite
• X-ray diffraction
• differential scanning calorimetry
• martensite
• metallurgy
• nickel-titanium
• phase-transformation
• thermomechanical treatment

• Cyclic fatigue resistance
• nickel-titanium file
• side flattening
• torsional resistance

• Equipment Failure
• Nickel
• Titanium
• Root Canal Preparation/instrumentation
• Torsion, Mechanical
• Materials Testing
• Equipment Design
• Torque
• Microscopy, Electron, Scanning
• Dental Instruments
• Dental Alloys/chemistry

• cyclic fatigue
• differential scanning calorimetry
• endodontics
• energy-dispersive X-ray spectroscopy
• root canal treatment

• Surface Properties
• Titanium/chemistry
• Nickel/chemistry
• Microscopy, Atomic Force
• Materials Testing
• Root Canal Preparation/instrumentation

• Finite element analysis
• GUM
• Graphene
• NiTi
• Stress analysis

• Stress, Mechanical
• Graphite
• Finite Element Analysis
• Nickel
• Titanium
• Root Canal Preparation
• Materials Testing
• Metals
• Equipment Design

• NiTi alloy
• NiTi files
• cyclic fatigue resistance
• endodontic instruments
• fatigue properties
• stress fracture
• stress resistance

• Dental instruments
• fracture strength
• heat treatment
• nickel-titanium alloy

• Humans
• Dental Alloys
• Root Canal Preparation/methods
• Nickel
• Titanium
• Equipment Design
• Materials Testing
• Dental Instruments

• Root Canal Preparation
• Equipment Failure
• Rotation
• Spectrum Analysis
• Titanium/chemistry
• Magnetic Phenomena
• Equipment Design
• Dental Alloys
• Materials Testing

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).

• endodontic rotary instruments
• endodontics
• metallurgy
• nickel–titanium alloy
• root canal treatment

The aim of this study was to compare the influence of two novel reciprocating movements on the cyclic fatigue resistance of endodontic reciprocating files.

30 Procodile® (Komet Medical, Lemgo, Germany) files were selected in this study and distributed according to the following study groups depending on the movements to be performed: ReFlex Dynamic (n = 10), ReFlex Smart (n = 10) and Reciproc (n = 10) reciprocating movement. These files were fixed to a specific dynamic cyclic fatigue device designed and manufactured by 3D impression to simulate the pecking motion performed by the operator. The time to failure and the number of cycles of in-and-out of the endodontic files was registered. The results were analyzed by ANOVA and Weibull statistics.

Statistically significant differences were found when the number of cycles of in-and-out movement and the time to failure of ReFlex Dynamic and Reciproc reciprocating movement (p < 0.001) and between ReFlex Smart and Reciproc reciprocating movement (p < 0.001) were compared in pairs. However, no statistically significant differences were observed between time to failure and number of cycles of in-and-out movement of ReFlex Dynamic and ReFlex Smart reciprocating movement (p = 0.253).

The ReFlex Smart reciprocating movement increased the cyclic fatigue resistance of endodontic reciprocating files compared with traditional reciprocating movement.

• Cyclic fatigue
• Endodontics
• Nitinol
• Reciprocating movement

• NiTi instruments
• apparatus and instruments
• cyclic fatigue
• device
• endodontics
• torsional load

Purpose: To analyze the influence of the pecking motion frequency on the cyclic fatigue resistance of endodontic rotary files. Material and Methods: Sixty PlexV 25.06 endodontic rotary files were selected and distributed into three groups: 30 movements/min (n = 20), 60 movements/min (n = 20), and 120 movements/min (n = 20). A dynamic cyclic fatigue device was designed using Computer Aided Design/ Computer Aided Engineering (CAD/CAE) technology and manufactured by 3D impressions to simulate the pecking motion performed by an operator. Failures of the endodontic rotary files were detected by a Light-Emitting Diode (LED)/Light-Dependent Resistor (LDR) system controlled by an Arduino-Driver complex and management software. Endodontic rotary files were tested on an artificial root canal manufactured by wire electrical discharge machining (EDM), with similar dimensions to those of the instrument under examination. Endodontic rotary files were used following the manufacturer’s recommendations. The results were analyzed by ANOVA and Weibull statistics. Results: All pairwise comparisons revealed statistically significant differences in all three variables, except for the difference in the number of cycles between the groups with 60 and 120 movements/min (p = 0.298). The scale distribution parameter of Weibull statistics showed statistically significant differences in all three variables, except for the differences in the number of cycles between groups with 30 and 60 movements/min (p = 0.0722). No statistically significant differences in the three variables were observed for the shape distribution parameter. Conclusion: A low frequency of pecking motion is recommended to reduce the risk of failure of endodontic rotary files associated with cyclic fatigue.

• NiTi rotary files
• cyclic fatigue
• endodontic rotary files
• endodontics
• pecking motion

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

• Cyclic fatigue
• HyFlex EDM
• Protaper Universal
• WaveOne Gold
• XP Shaper

The aim of this retrospective clinical study was to evaluate the incidence of ProTaper Universal System instrument fractures, associated with observation of the arch, group of teeth, and root thirds in which these fractures occurred.

From analysis of charts, clinical record cards and radiographs of endodontic treatments performed by postgraduate students using the ProTaper Universal System at a reference center, a total of 1031 teeth and 2355 canals were analyzed. The general incidence of instrument fractures and their frequency, considering the group of teeth, arch and root thirds, were cataloged and the data obtained were statistically analyzed (Exact Fischer test, with level of significance of 1%).

The general percentage of fractures, considering the number of teeth and number of root canals evaluated was 4.4% and 1.9%, respectively. Instrument fractures occurred more frequently in the mandibular first (8.8%) and second (9.6%) molars, however, without statistically significant difference between them (P=0.81). In the first and second maxillary molars, the incidence of fracture was 4.7% and 5.1%, respectively, also without significant difference (P=0.81). Considering the dental arches (maxillary and mandibular), the fractures occurred with significantly higher frequency in the mandibular arch (66.7%), in comparison with the maxillary arch (33.3%) (P<0.01). A significantly higher percentage of fractures occurred in the apical third (84.4%) compared with the middle third (15.6%) (P<0.01).

The general percentage of fractures, considering the number of teeth and number of root canals evaluated was 4.4% and 1.9%, respectively. However, the arch (mandibular) and root third (apical) had a significant effect on the incidence of instrument fractures.

• Fracture
• ProTaper universal
• endodontic files
• nickel-titanium instruments

One of the major innovations in endodontics has been the introduction of nickel-titanium (NiTi) alloy. This study evaluated the surface topographical changes of two different surface treatments rotary instrument after instrumentation and sterilization.

240 Extracted teeth were included in this study. 90 new AlphaKite and Revo-S NiTi rotary instruments were selected and divided into two groups (Group A 45 AlphaKite and group B 45 Revo-S). Each group were divided into three subgroups: (A1, B1) n=5 files were used as a control, (A2,B2) n=20 files were used to prepare three root canals using endodontic rotary motor then sterilized by autoclave for one cycle under 121°C at 15 psi for 30 minutes and (A3,B3) n=20 files were used to prepare nine root canals using the same rotary system then sterilized by autoclave for three cycles under 121°C at 15 psi for 30 minutes. Files were examined under scanning electron microscopy.

On examining the AlphaKite, A1 revealed gross machining grooves on their surface with no pits, A2 showed disruption of cutting and A3 showed microcracks and deepening of the machining grooves. B1 showed a smoother surface with few machining grooves, B2 showed dulling and blunting of the cutting edges was predominant and B3 files showed plastic deformation in the form of unwinding of the flutes.

The defects were less distributed along the electropolished Revo-S files than the physical vapor deposition AlphaKite.

Key words:Endodontic instruments, electropolished, rotary, sterilization.

• Autoclave
• canal curvature
• cyclic fatigue
• sodium hypochlorite

Many new rotary files systems have been introduced, however, limited research has been conducted related to the surface irregularities of these files and if these have any effects on the files themselves. Hence, the aim of the present study was to analyze surface irregularities of the ProTaper® Universal rotary files (PTU) and the ProTaper Next™ rotary files (PTN) before and after instrumentation in curved canals. The main objective was to investigate the nature of these irregularities and how they might influence the use and fracture of rotary files during root-canal treatments.

The files were examined pre-operatively using a stereomicroscope and scanning electron microscopy(SEM) to analyze surface imperfections and the presence of particles. Mesial roots of forty extracted mandibular molars were selected. Each instrument was used to prepare one of the mesial canals. The files were then rinsed with alcohol, and autoclaved and analyzed again.

Of the 80 files used in this study, five files fractured, five files unwound and seven files were curved or bent and they all belonged to the PTU group. Irregularities and debris could be visualized with the SEM on both unused PTU and PTN files. Most of the debris was found associated with deeper milling grooves and defects on the surface of the metal. Surface analysis of the files that were used and sterilized were performed and the SEM images demonstrated organic debris, metal flash, and crack formation and initiation of fractures for both file types. All files showed machining grooves, metal flash, debris, and defects on cutting edges.

These irregularities appear to be critical in the accumulation of debris and initiation of fatigue and crack propagation within the NiTi alloy. The accumulation of debris could be a concern due to the potential exchange of organic debris between patients.

Key words:ProTaper® Universal, ProTaper Next™, surface characteristics, SEM.

Intracanal instrument fracture is an unpredictable and problematic occurrence that can prevent adequate cleaning and shaping procedures and influence the prognosis of endodontic treatment. The prevalence of instrument fracture is reported to range between 0.28% and 16.2%. This article presents an overview of the prevention and management of instruments fractured during endodontic therapy on the basis of literature retrieved from PubMed and selected journal searches. Instrument fracture occurs because of reduced metal fatigue and/or torsional resistance. The reasons include canal morphology and curvature, manufacturing processes and instrument design, instrument use times and technique, rotational speeds and operator experience. With the development of various equipment and techniques, most of the retained instrument separations can be removed safely. However, in canals without associated periapical disease not every fractured separation should be removed from difficult locations because of the increased risk for root perforation and fracture. In difficult cases, either retain or bypass the fragment in the root canal and ensure regular follow-up reviews. Fractured instruments retained in the presence of periapical disease reduce significantly the prognosis of endodontically treated teeth, indicating a greater need to attempt the removal or bypass of the file separations. Apical surgery might be required in some instances, emphasizing the importance of preventing instrument fracture.

• Endodontics
• Instrument fracture
• Root canal preparation
• Prevention
• Management

• OneShape
• WaveOne
• atomic force microscopy
• glide path

• Dental Pulp Cavity/ultrastructure
• Humans
• Microscopy, Atomic Force
• Molar
• Root Canal Preparation/instrumentation
• Root Canal Preparation/methods
• Surface Properties

• M-wire nickel-titanium
• metal defects
• metallurgical properties
• reciprocating instruments
• surface wear

• Dental Instruments
• Materials Testing
• Microscopy, Atomic Force
• Microscopy, Electron, Scanning
• Root Canal Preparation/instrumentation
• Spectrometry, X-Ray Emission
• Stress, Mechanical
• Surface Properties

• atomic force microscope
• endodontics
• reciprocal motion
• rotary motion

Efforts to improve the performance of rotary NiTi instruments by enhancing the properties of NiTi alloy, or their manufacturing processes rather than changes in instrument geometries have been reported. The aim of this study was to compare in-vitro the shaping ability of three different rotary nickel-titanium instruments produced by different manufacturing methods.

Thirty simulated root canals with a curvature of 35˚ in resin blocks were prepared with three different rotary NiTi systems: AK- AlphaKite (Gebr. Brasseler, Germany), GTX- GT^® Series X (Dentsply, Germany) and TF- Twisted Files (SybronEndo, USA).

The canals were prepared according to the manufacturers’ instructions. Pre- and post-instrumentation images were recorded and assessment of canal curvature modifications was carried out with an image analysis program (GSA, Germany).

The preparation time and incidence of procedural errors were recorded. Instruments were evaluated under a microscope with 15 × magnifications (Carl Zeiss OPMI Pro Ergo, Germany) for signs of deformation. The Data were statistically analyzed using SPSS (Wilcoxon and Mann–Whitney U-tests, at a confidence interval of 95%).

Less canal transportation was produced by TF apically, although the difference among the groups was not statistically significant. GTX removed the greatest amount of resin from the middle and coronal parts of the canal and the difference among the groups was statistically significant (p < 0.05). The shortest preparation time was registered with TF (444 s) and the longest with GTX (714 s), the difference among the groups was statistically significant (p < 0.05). During the preparation of the canals no instrument fractured. Eleven instruments of TF and one of AK were deformed.

Under the conditions of this study, all rotary NiTi instruments maintained the working length and prepared a well-shaped root canal. The least canal transportation was produced by AK. GTX displayed the greatest cutting efficiency. TF prepared the canals faster than the other two systems.

To develop analytical models and analyse the stress distribution and flexibility of nickel–titanium (NiTi) instruments subject to bending forces.

The analytical method was used to analyse the behaviours of NiTi instruments under bending forces. Two NiTi instruments (RaCe and Mani NRT) with different cross-sections and geometries were considered. Analytical results were derived using Euler–Bernoulli nonlinear differential equations that took into account the screw pitch variation of these NiTi instruments. In addition, the nonlinear deformation analysis based on the analytical model and the finite element nonlinear analysis was carried out. Numerical results are obtained by carrying out a finite element method.

According to analytical results, the maximum curvature of the instrument occurs near the instrument tip. Results of the finite element analysis revealed that the position of maximum von Mises stress was near the instrument tip. Therefore, the proposed analytical model can be used to predict the position of maximum curvature in the instrument where fracture may occur. Finally, results of analytical and numerical models were compatible.

The proposed analytical model was validated by numerical results in analysing bending deformation of NiTi instruments. The analytical model is useful in the design and analysis of instruments. The proposed theoretical model is effective in studying the flexibility of NiTi instruments. Compared with the finite element method, the analytical model can deal conveniently and effectively with the subject of bending behaviour of rotary NiTi endodontic instruments.