Comparative evaluation of the cyclic fatigue resistance of four Ni-Ti instruments in simulated root canal curvatures using CAD/CAM technology

Abstract

Background

This study aimed to evaluate and compare the cyclic fatigue resistance of new generation nickel-titanium file systems in simulated single and double curvature ceramic root canals.

Methods

A total of 80 Nickel–Titanium (Ni-Ti) instruments—TruNatomy (TN) (26/0.04), WaveOne Gold (WOG) (25/0.07), Reciproc Blue (RecB) (25/0.08), and One Curve (OC) (25/0.04)—were tested under simulated intracanal thermal conditions (35 ± 0.1 °C). The instruments were evaluated within custom-designed artificial canals fabricated from ceramic blocks, incorporating either a single curvature (SC; 60° angle, 5 mm radius) or a double curvature configuration (DC; coronal bend: 60°, 5 mm radius; apical bend: 60°, 2 mm radius). For each instrument, the time until fracture occurred was recorded, and the number of cycles to failure (NCF) was calculated accordingly. Fragment lengths (FLs) were measured using a digital microcaliper, and the topography of the fracture surfaces was analyzed through scanning electron microscopy (SEM). Data were statistically assessed using non-parametric Kruskal–Wallis and Mann–Whitney U tests, with significance defined at the p-value threshold of < 0.05.

Results

RecB files demonstrated the highest NCF in the SC group (p < 0.05). TN and OC had significantly lower NCF than RecB (p < 0.05) but were statistically similar (p > 0.05). WOG recorded the lowest NCF in SC (p < 0.05). In the DC group, WOG also showed the lowest NCF (p < 0.05), with no significant differences among the other three files (p > 0.05). SEM analysis revealed that nearly all fractured instruments exhibited a ductile fracture pattern, characterized by the presence of microcavities and pits, which are typically associated with cyclic fatigue failure.

Conclusions

Selecting Ni-Ti file systems based on canal anatomy is essential for minimizing fatigue-related failures. RecB exhibited superior resistance in SC canals, while WOG showed consistently lower performance in both configurations, warranting cautious use in curved canals. These findings underscore the importance of matching instrument selection to canal morphology and mechanical demands to ensure safe and predictable clinical outcomes.

Introduction

Successful endodontic treatment necessitates thorough cleaning and shaping of the root canal system while preserving its original anatomy, followed by an apical-to-coronal tapering and a hermetic seal [1]. The introduction of flexible Nickel-Titanium (Ni-Ti) rotary instruments has been pivotal in maintaining original canal anatomy by minimizing procedural alterations [2]. Consequently, the use of Ni-Ti instruments has significantly reduced the incidence of iatrogenic events, such as apical blockage, step formation, transportation, and perforation, while also shortening preparation times [3, 4]. Despite these advantages, a primary concern with Ni-Ti rotary instruments is their propensity for sudden fracture during clinical use, often without any prior signs of permanent deformation [5]. Although Ni-Ti files exhibit enhanced durability, studies report their susceptibility to structural failure from cyclic fatigue during root canal instrumentation [6, 7]. To enhance the cyclic fatigue resistance of these instruments, recent strategies have focused on developing heat-treated alloys, modified cross-sectional designs, and surface electropolishing protocols [8]. As a result, a wide variety of Ni-Ti files are clinically available, distinguished by different operational principles and proprietary heat treatments [9–15].

TruNatomy (TN; Dentsply Sirona, Maillefer, Ballaigues, Switzerland), system is a rotation-based file manufactured using a proprietary heat treatment process. A distinguishing feature of these files is their fabrication from a slender 0.8 mm Ni-Ti wire, in contrast to the larger 1.2 mm diameter wire used for most conventional instruments [9, 14].

Introduced in 2015, WaveOne Gold (WOG; Dentsply Sirona, Maillefer, Ballaigues, Switzerland) is a reciprocating file system produced with advanced ‘Gold-Wire’ metallurgy. This specific thermal treatment, which involves multiple heating and cooling cycles, imparts a characteristic gold color and enhances the file’s mechanical properties compared to its predecessor [11, 12, 16, 17].

Reciproc Blue (RecB; VDW, Munich, Germany) is a next-generation, single-file reciprocating instrument featuring an S-shaped cross-section and a non-cutting tip [13]. Its distinct properties are derived from the proprietary ‘Blue Wire’ thermal processing, which alters the alloy’s crystalline structure to improve its mechanical performance. The system operates with a specific counter-clockwise and clockwise reciprocating motion [13, 18].

One Curve (OC; Micro Mega, Besancon, France) is a single-file Ni-Ti system that operates in continuous rotation. It is manufactured with ‘C-Wire’ technology, a heat treatment that provides the alloy with controlled shape memory. A key design feature is its variable cross-section: the apical portion exhibits three distinct cutting edges, while the coronal section features a dual-edge configuration [10, 15].

Previous investigations into the cyclic fatigue resistance of rotary instruments have utilized various testing models, including extracted human teeth and stainless-steel blocks [19–21]. For superior standardization, however, recent studies have increasingly employed artificial canals fabricated via computer-aided design/computer-aided manufacturing (CAD/CAM). This technology facilitates the production of highly precise and reproducible ceramic models with excellent strength and hardness, owing to manufacturing tolerances measured in microns [22].

To date, the literature lacks a direct, simultaneous comparison of the TN, WOG, RecB, and OC file systems. Therefore, the present study aimed to evaluate the cyclic fatigue resistance of these four Ni-Ti instruments using CAD/CAM-fabricated ceramic canals with both single and double curvatures under simulated intracanal temperature conditions. The null hypothesis postulated that there would be no significant differences in cyclic fatigue resistance among the four file systems or between the different canal curvatures.

Materials and methods

The experimental model was collaboratively developed by the Faculty of Dentistry and the Department of Mechanical Engineering at Sivas Cumhuriyet University (Fig. 1a). Ethical approval was obtained from the Non-Interventional Clinical Research Ethics Committee of Sivas Cumhuriyet University (Decision No: 2020-09/23, dated September 23, 2020).

Fig. 1.

The cyclic fatigue test setup (a). The temperature control system (b). Image of fracture in video recording taken under magnification (c)

Following the methodology described by Pruett et al. [5], canal geometries were generated using SolidWorks CAD software (DS SolidWorks Corp., Waltham, MA) based on the respective dimensions and tapers of the instruments. To reduce friction and allow free rotation, canal diameters were uniformly designed to be 0.1 mm wider than the instrument diameter along the entire working length [23, 24] (Fig. 2a and b). Designs were exported in.stl format for CAM processing (Fig. 2c and d). A total of four artificial ceramic root canals were fabricated by milling two zirconium oxide discs (UPCERA, China) using a high-precision CNC unit (K5, VHF, Germany). Each artificial canal measured 16 mm in length and was carved as a tapered groove into the zirconium oxide blocks (Fig. 2e and f).

Fig. 2.

Schematic drawings of single and double curvatures (a and b). The.stl forms of the schematic drawings of the prepared single and double curvatures (c and d). Zirconium oxide blocks prepared with CAD/CAM (e and f)

Two distinct canal geometries were created: one with a single curvature (SC) (60° angle, 5 mm radius) and another with a double curvature (DC) configuration—comprising a coronal curve (60°, 5 mm radius) and an apical curve (60°, 2 mm radius). For the TN and OC file groups, the canal design started with an apical diameter of 0.35 mm and followed a 0.06 taper, reaching a coronal diameter of 1.31 mm [25]. For the WOG and RecB file groups, the canal block featured the same apical diameter of 0.35 mm, with a 0.08 taper, ending at a coronal diameter of 1.63 mm. The same curvature specifications were used for both sets of canal blocks to ensure standardization.

An experimental setup was established at the Department of Mechanical Engineering, Sivas Cumhuriyet University, to simulate intracanal temperature conditions (Fig. 1a). A slot was created using elastomeric impression material to securely position the ceramic block containing the artificial canals within a 6 × 6 × 6 cm glass container. This design enabled a reproducible test environment by facilitating easy replacement of the ceramic block for successive tests. Both the glass container and the artificial canals were filled with distilled water to ensure complete immersion of the samples. To maintain a constant temperature, a custom-built thermal regulation system was assembled, comprising a heating plate, power supply, W1209 temperature controller, and a thermocouple (Fig. 1b). This system maintained the distilled water temperature at 35 ± 0.1 °C, with an accuracy of 0.1 °C. To fix the glass container to the heating plate and the endodontic motor to an adjustable magnetic holder, customized plastic fixtures were designed using SolidWorks software and produced with a 3D printer. The magnetic holder enabled three-dimensional positioning of the endodontic motor via detachable components. The endodontic motor, secured to the holder, was aligned parallel to the axis of the artificial canals within the ceramic block. This configuration ensured consistent instrument alignment and allowed free rotation under uniform pressure throughout the experimental procedures [26, 27].

The study consisted of four main groups—TN (26/0.04), WOG (25/0.07), RecB (25/0.08), and OC (25/0.04)— with 20 instruments in each group. Each group was divided into two subgroups (n = 10) according to canal curvature: SC and DC. A comprehensive overview of these systems is presented in Table 1. Sample size was determined via a power analysis (G*Power 3.1; Heinrich Heine University, Düsseldorf, Germany) [12], which indicated a minimum of 10 instruments per subgroup was required for adequate statistical power. All instruments were 25 mm in length and underwent pre-test inspection under a stereomicroscope (Stemi DV4; Carl Zeiss, Göttingen, Germany). No surface defects or structural deformations were observed, and all instruments were therefore included in the study.

Table 1.

The metallurgical characteristics and manufacturer-provided data for the files evaluated in our study

Ni-Ti File System	Lot Number	Manufacturing Types	Size	Company
TruNatomy	1,557,969	Special Heat Treatment	26/0.04	Dentsply Sirona
WaveOne Gold	1,649,429	Gold Wire	25/0.07	Dentsply Sirona
Reciproc Blue	277,773	Blue Wire	25/0.08	VDW
One Curve	96,435,016	C Wire	25/0.04	Micro Mega

Procedures were performed using torque-controlled endodontic motors—Silver Reciproc (VDW) and X-Smart Plus (Dentsply Sirona)—according to the manufacturers’ protocols. TN was operated at 500 rpm with a torque of 1.5 N·cm, and OC at 350 rpm with a torque of 2.5 N·cm, both using the X-Smart Plus endodontic motor. In contrast, RecB and WOG were activated using the “RECIPROC ALL” and “WAVEONE ALL” preset programs, respectively. Each instrument was operated until fracture. The entire procedure was recorded in slow motion using an optical lens at 60x magnification. The precise time to failure for each instrument was subsequently determined through detailed analysis of the video recordings (Fig. 1c). The primary outcome, the Number of Cycles to Failure (NCF), was calculated for each instrument using the following formula:

As a complementary assessment, the apical fragment length (FL) was measured with a digital microcaliper (Mitutoyo, Tokyo, Japan) offering a precision of 0.01 mm. The mean FL values were documented to confirm the standardized positioning of the instruments within the canal curvature and to validate the homogeneity of stress distribution among all specimens.

Scanning electron microscopic analysis

The fractured instruments were ultrasonically cleaned in an alcohol bath to remove surface contaminants and expose fracture morphology. To evaluate fracture characteristics, 24 fractured segments—three from each experimental subgroup—were examined under a scanning electron microscope (TESCAN Mira 3). Two blinded, independent observers then analyzed the SEM images, captured at multiple magnifications, to characterize fracture surface topography.

Statistical analysis

The normality of data distribution was assessed using the Kolmogorov–Smirnov test. As the data for both the NCF and FL were not normally distributed, the non-parametric Kruskal–Wallis and Mann–Whitney U tests were employed for intergroup comparisons.

All analyses were performed using IBM SPSS Statistics, Version 22.0 (IBM Corp., Armonk, NY, USA), with the level of statistical significance set at p < 0.05.

Results

Descriptive statistics, including the mean and standard deviation for NCF and FL across all experimental groups, are presented in Table 2. In the SC group, the RecB file system exhibited the highest NCF values, whereas the WOG system demonstrated the lowest (p < 0.05). Although TN and OC showed significantly lower NCF values than RecB (p < 0.05), no statistically significant difference was observed between these two systems (p > 0.05).

Table 2.

The number of cycles to failure and length (in millimeter) of fractured fragments of instruments during Cyclic fatigue testing in single and double curvature

		SC		DC
Group	n	NCF	FL	NCF	FL
TN	10	954.12 ± 162.29 a	5.14 ± 0.42 a	247.79 ± 56.88 a	1.61 ± 0.28 a
		%95 CI (854.1–1086.3)	%95 CI (4.8–5.4)	%95 CI (207.3–288.7)	%95 CI (1.4–1.8)
WOG	10	593.68 ± 194.72 b	6.23 ± 0.60 b	218.95 ± 38.17 b	2.52 ± 1.35 b
		%95 CI (529.2–807.8)	%95 CI (5.8–6.7)	%95 CI (174.1–228.7)	%95 CI (1.5–3.5)
RecB	10	1837.45 ± 393.89 c	5.92 ± 1.06 b	224.42 ± 64.76 a	2.30 ± 0.30 b
		%95 CI (1548.6–2112.1)	%95 CI (5.2–6.7)	%95 CI (190.7–283.3)	%95 CI (2.1–2.5)
OC	10	1104.55 ± 212.07 a	4.49 ± 0.64 c	278.37 ± 64.93 a	1.76 ± 0.44 a
		%95 CI (968.9–1272.3)	%95 CI (4.0–5.0)	%95 CI (227.8–320.8)	%95 CI (1.4–2.1)

Abbreviations: SC single curvature, DC double curvature, TN TruNatomy, WOG WaveOne Gold, RecB Reciproc Blue, OC One Curve, NCF number of cycles to failure, FL fragment length, CI confidence interval

*Kruskal-Wallis H test, Mann-Whitney U test

^a-cNo significant difference was observed between columns denoted by the same letter

Similarly, in the DC group, WOG exhibited the lowest NCF value (p < 0.05), while the other three file systems showed no significant differences among one another (p > 0.05).

In both the SC and DC groups, the average FL for WOG and RecB files was greater than that of the other files. In the SC group, the lowest FL value was observed in the OC file system (p < 0.05); whereas in the DC group, the TN and OC file systems demonstrated the lowest FL values (p < 0.05). Furthermore, no significant difference was observed between TN and OC (p > 0.05).

The SEM analysis revealed topographical features characteristic of ductile fracture across all instrument groups, including surface roughness, microporosity, and distinct fatigue striations originating from an initiation site. These findings, indicative of a failure mechanism driven by cyclic fatigue, are illustrated in Figs. 3 and 4, which display representative photomicrographs for each file system in the SC and DC canals, respectively. A key finding from the high-magnification images was the consistent presence of micro-pits and voids near the fracture origin across all experimental groups, confirming a shared failure pattern rooted in fatigue.

Fig. 3.

SEM images of TN, WOG, RecB and OC files after cyclic fatigue testing in the SC canal. The upper line shows the low magnification of the fracture surface in the single curvature (SC) canal of TN (a), WOG (b), RecB (c), and OC (d), respectively. The lower line shows a high magnification of the surface of breakage in the SC canal of TN (e), WOG (f), RecB (g), and OC (h), respectively. Fractured surfaces typically exhibit features consistent with ductile failure, including microvoid coalescence and fatigue striations. Arrowheads indicate crack initiation sites and radial propagation patterns. The presence of dimples and conical depressions in the fracture topography suggests a progressive fatigue mechanism influenced by canal curvature and file design

Fig. 4.

SEM images of TN, WOG, RecB, and OC files after cyclic fatigue testing in the DC canal. The upper line shows the low magnification of the fracture surface in the double curvature (DC) canal of TN (a), WOG (b), RecB (c), and OC (d), respectively. The lower line shows a high magnification of the surface of breakage in the DC canal of TN (e), WOG (f), RecB (g), and OC (h), respectively. Fractured surfaces typically exhibit features consistent with ductile failure, including microvoid coalescence and fatigue striations. Arrowheads indicate crack initiation sites and radial propagation patterns. The presence of dimples and conical depressions in the fracture topography suggests a progressive fatigue mechanism influenced by canal curvature and file design

Discussion

The present study investigated the cyclic fatigue resistance of four next-generation Ni-Ti file systems within CAD/CAM-fabricated ceramic canals featuring both single and double curvatures under controlled intracanal temperature conditions. The results demonstrated statistically significant differences in fatigue resistance among the experimental groups. Therefore, the null hypothesis—which postulated that no differences would exist among the tested instruments—was rejected.

Instrument fracture remains one of the primary concerns during root canal preparation [28], with cyclic fatigue identified as a leading cause. This phenomenon is specifically defined as material failure induced by repeated tensile-compressive stress cycles within curved canals [29]. Although several studies have evaluated the fatigue resistance of various Ni-Ti instruments, direct comparisons of their performance in single versus double curvatures are scarce. To the best of our knowledge, no previous study has comprehensively assessed the TN, WOG, RecB, and OC systems within a single, standardized experimental framework—representing a critical gap that the present study sought to address.

Cyclic fatigue arises from repeated tensile and compressive stress encountered by the instrument during canal shaping, particularly within curved root canals [29, 30]. For this reason, fatigue testing is conventionally performed in canals that feature curvature. Although DC canals are often perceived as rare, their clinical prevalence is notable—reported in 30–40% of distobuccal roots of maxillary molars and in 35–59% of mesial roots of mandibular molars [31]. Despite this clear clinical relevance, the vast majority of in vitro fatigue studies have utilized artificial canals with only an SC [25, 32–36], and studies evaluating fatigue resistance in DC configurations remain relatively scarce.

In the present study, both SC and DC canals were employed to evaluate the cyclic fatigue resistance of Ni-Ti instruments under differing anatomical complexities.

Consistent with previous studies, which have shown that DC canals subject instruments to greater mechanical stress than SC canals—thereby accelerating fatigue failure [37–40]—the current results demonstrated significantly higher fatigue resistance for all tested instruments in SC canals compared to DC canals.

Two primary methodologies are commonly employed to assess the cyclic fatigue of Ni-Ti instruments: static and dynamic models. In static testing, the instrument is continuously rotated at a fixed position within a curved canal until fracture occurs [41]. In contrast, dynamic models aim to replicate clinical conditions more closely by incorporating axial movements, such as pecking motions [42]. However, despite their clinical relevance, the standardization of dynamic motion parameters is inherently subjective [43], which may compromise the reproducibility and consistency of the results. By comparison, static models offer a controlled, fixed motion trajectory, yielding more objective and reproducible data [44, 45]. Accordingly, the present study adopted a static testing model to enhance the reliability and validity of the findings.

Standardization of the testing setup is critical for the reliable and reproducible assessment of cyclic fatigue resistance. Although early studies often utilized extracted human teeth to better simulate clinical conditions [19, 46], natural variability in canal anatomy and the organic-inorganic composition of dentin introduce significant inconsistencies across specimens. Moreover, the complex geometry of natural teeth makes it difficult to isolate cyclic fatigue from other failure mechanisms, such as torsional stress, thereby complicating the interpretation of fracture etiology. To overcome these limitations, the present study employed standardized artificial canals, specifically designed using SolidWorks CAD software to match the geometries of the tested instruments. The canals were milled from zirconium oxide discs and sintered to ensure high structural integrity. This methodology provided precise control over canal dimensions and curvature while offering excellent resistance to corrosion within the temperature-regulated aqueous environment. Thus, this approach established a highly reliable and reproducible framework for evaluating instrument fatigue under controlled conditions.

Recent research has identified temperature as a critical factor influencing the cyclic fatigue resistance of Ni-Ti instruments. In particular, ambient temperature has been shown to directly affect the performance of thermomechanically treated Ni-Ti alloys [20, 21, 47, 48]. In an in vivo study by de Hemptinne et al. [49], it was demonstrated that solutions introduced into the root canal quickly equilibrate to the intracanal temperature (35 ± 1 °C). Accordingly, in the present study, fatigue testing was conducted under simulated intracanal temperature conditions (35 ± 0.1 °C) using a non-conductive ceramic canal model immersed in distilled water within a glass container. This approach was designed to closely replicate clinical thermal conditions and enhance the physiological relevance of the experimental model.

Studies investigating the effects of reciprocating versus continuous rotational kinematics have consistently demonstrated that motion dynamics significantly influence the cyclic fatigue behavior—and therefore the longevity—of Ni-Ti instruments [50, 51]. A growing body of evidence suggests that reciprocating systems offer superior fatigue resistance compared to their continuously rotating counterparts [52–55]. Consistent with these findings, the present study observed that in SC artificial canals, RecB files operating with reciprocating motion exhibited higher cyclic fatigue resistance than TN and OC files, which utilize continuous rotation. This difference is likely attributed to the biomechanical advantage of reciprocating motion. This motion subjects the instrument to reduced cumulative stress, which in turn increases its NCF and enhances overall durability [53, 54].

Ni-Ti instruments with a triangular cross-section or S-shaped typically exhibit reduced metal mass, resulting in enhanced flexibility and improved resistance to cyclic fatigue compared to square or parallelogram-shaped designs. Among the systems evaluated in this study, RecB (S-shaped cross-section), TN (parallelogram-shaped, derived from 0.8 mm wire), WOG (parallelogram-shaped), and OC (a hybrid of triangular and S-shaped geometries) each featured distinct cross-sectional configurations that likely influenced their stress distribution under fatigue loading. The consistently lower cyclic fatigue resistance observed in the WOG system across both canal configurations may be partly attributed to its larger core mass and parallelogram geometry, which can lead to greater stress concentration during rotation in severely curved canals.

Standardized cyclic fatigue testing setups are designed to produce consistent stress concentrations and comparable FLs across different instruments [56]. However, variations in alloy composition and cross-sectional geometry can significantly influence the bending behavior of Ni-Ti files, potentially shifting the point of maximum stress accumulation. These structural differences may result in variations in FLs depending on the instrument type [57–59]. For instance, the consistently greater FLs of the WOG and RecB files in this study suggest that their specific alloy properties and cross-sectional geometries shifted the point of maximum stress accumulation more coronally. In contrast, the shorter fragments produced by the TN and OC files indicate a more apical concentration of stress for these instruments. These findings support the notion that instrument-specific design features play a critical role in determining fracture behavior, even under standardized testing conditions.

Fractographic analysis is a well-established method for identifying fracture mechanisms and distinguishing between fracture types. In this context, brittle fractures are typically characterized by cleavage facets, whereas ductile fractures exhibit micro-voids and dimples indicative of plastic deformation under stress. These surface features are directly linked to the micromechanics of failure and are therefore fundamental to the interpretation of fracture patterns. According to fracture mechanics theory, structural failure initiates from pre-existing flaws or microcracks that propagate when the applied stress exceeds the material’s cohesive strength [60]. In the present study, nearly all fractured instruments displayed crack propagation patterns consistent with ductile failure—characterized by the presence of micro-pits and voids at the initiation site. These features suggest that cyclic fatigue was likely the predominant cause of fracture.

A potential limitation of the present study is the use of artificial ceramic blocks, which do not accurately replicate the microhardness and surface characteristics of natural teeth. However, due to the inability to achieve standardization in experimental setups involving natural teeth, artificial canals were employed to ensure consistency.

Another limitation is the absence of a detailed pre-evaluation of the dimensional and metallurgical characteristics of the tested Ni-Ti instruments. This may have introduced variability in how each file system interacted with the standardized artificial canals—particularly given the differences in tip size, taper design, and alloy properties. Although a uniform canal design was used to standardize the testing environment, it may not have fully accounted for the unique geometries of each instrument. Future studies should consider conducting comprehensive pre-test analyses—such as SEM imaging or cross-sectional profiling—to better align canal configurations with instrument specifications and improve the validity of comparative fatigue resistance assessments.

Additionally, the use of a static testing model represents a further limitation. While dynamic cyclic fatigue models more closely mimic clinical conditions by incorporating in-and-out motions like pecking, brushing, and stroking observed during endodontic instrumentation, a static model was deliberately chosen in the current study to enhance standardization, reproducibility, and control over experimental variables. Nevertheless, it should be acknowledged that static models do not fully replicate the complex mechanical stresses encountered in vivo. Accordingly, the findings should be interpreted with caution when extrapolating to clinical scenarios, and future research employing dynamic testing protocols is recommended to validate these results under more clinically relevant conditions.

Conclusions

In this study, the findings suggest that the cyclic fatigue resistance of Ni-Ti instruments is influenced by several interrelated factors, including metallurgical properties, cross-sectional geometry, motion kinematics, and the anatomical complexity of the root canal—particularly the curvature type and severity. Instrument performance differed depending on canal configuration, with RecB demonstrating the highest resistance in SC canals. Based on these results, RecB may be considered a favorable option for canals with SC anatomy. In contrast, WOG exhibited the lowest fatigue resistance across both canal types, indicating that its use in severely curved or DC canals should be approached with caution. Therefore, clinicians should prioritize instrument systems with superior flexibility and fatigue resistance—such as RecB—when treating canals with challenging curvature profiles to reduce the risk of instrument fracture and improve procedural safety. This study provides clinically relevant insights that may aid practitioners in selecting Ni-Ti systems best suited to the biomechanical demands of different root canal configurations.

Abbreviations

TN

TruNatomy

WOG

WaveOne Gold

RecB

Reciproc Blue

OC

One Curve

NCF

Number of Cycles to Failure

SEM

Scanning Electron Microscopy

Ni-Ti

Nickel-Titanium

CAD/CAM

Computer-Aided Design/Computer-Aided Manufacturing

SC

Single Curvature

DC

Double Curvature

FL

Fragment Length

Authors’ contributions

T.Y: participated in the design of the study, writing the manuscript, collection, and interpretation of data, and revised the manuscript. R.Z: participated in the design of the study, writing the discussion, and editing the text. The final draft was read and approved by all authors.

Funding

This study has been funded by the Scientific Research Projects Unit of Sivas Cumhuriyet University under the project code DIS-262.

Data availability

Data availability the datasets used in the current study are available through the corresponding author upon justifiable request.

Declarations

Ethics approval and consent to participate

This study was approved by the Sivas Cumhuriyet University Non-Interventional Clinical Research Ethics Committee with the decision number 2020-09/23 on 23.09.2020.

Consent for publication

Not applicable.

Competing interests

The authors declare no competing interests.