Annali di Stomatologia | 2026; 17(2): 242-249

ISSN 1971-1441 | DOI: 10.59987/ads/2026.2.242-249

Articles

Comparative ex vivo evaluation of mechanical properties of three orifice openers

Maya Feghali¹, Gianluca Gambarini², Nicola Maria Grande³, Dario Di Nardo², Massimo Galli²

¹Private Practice, Beirut, Lebanon

²Unità di Endodonzia, Dipartimento di Scienze Odontostomatologiche, Sapienza Università di Roma, Rome, Italy

³Dipartimento di Medicina e Chirurgia Orale, Università Cattolica del Sacro Cuore, Rome, Italy

^*Corresponding author: Gianluca Gambarini - gianluca.gambarini@uniroma1.it

Article History

Received: April 7, 2026

Accepted: June 18, 2026

Published: June 30, 2026

Abstract

Introduction

Orifice openers are routinely used in endodontic practice to facilitate straight-line access, reduce coronal interference, and protect apical shaping files. Their mechanical properties — flexibility, cyclic fatigue resistance, and cutting efficiency — directly influence both procedural safety and clinical outcomes. This study aimed to compare the flexibility, cyclic fatigue resistance, and operative torque (as an indirect measure of cutting efficiency) of three widely used orifice openers: EdgeOne Onyx 9/.09 (EdgeEndo, Albuquerque, NM), EdgeTaper Platinum SX (EdgeEndo), and ProTaper Gold SX (Dentsply Sirona, Ballaigues, Switzerland).

Methods

Thirty-six novel instruments of each brand were randomly assigned to three subgroups (n = 12 per test). Flexibility was evaluated through load-deflection testing at 45° utilizing a universal testing machine. Cyclic fatigue resistance was assessed by determining the number of cycles to failure (NCF) within a stainless-steel artificial canal featuring a 60° curvature and a 5 mm radius. Cutting efficiency was indirectly gauged by recording the operative torque during a 5 mm apical progression in a standardized three-dimensional artificial tooth model. Data were subjected to analysis through one-way ANOVA followed by Tukey’s post hoc test (α = 0.05).

Results

EdgeOne Onyx 9/.09 demonstrated significantly superior performance in all three tests: highest flexibility (0.85 ± 0.06 N), greatest cyclic fatigue resistance (1450 ± 120 NCF), and lowest operative torque (0.85 ± 0.19 Ncm). EdgeTaper Platinum SX showed intermediate performance, while ProTaper Gold SX exhibited the lowest values in all parameters. All pairwise differences were statistically significant (p < 0.05).

Conclusions

The outstanding mechanical properties of EdgeOne Onyx 9/.09 across flexibility, fatigue resistance, and cutting efficiency indicate that proprietary heat treatment technologies can substantially improve orifice opener performance. These findings have potential implications for decreasing iatrogenic errors and instrument fractures during coronal flaring procedures. Additional clinical studies are necessary to validate the laboratory observations.

Keywords: cyclic fatigue, cutting efficiency, EdgeOne Onyx, nickel-titanium, orifice opener, operative torque, ProTaper Gold, root canal preparation

Introduction

The mechanical preparation of root canals represents one of the cornerstones of successful endodontic therapy. The primary goals of instrumentation — debridement, disinfection, and shaping — are predicated on the ability of endodontic instruments to negotiate the complex three-dimensional geometry of the root canal system while removing infected dentin, creating a tapered preparation suitable for irrigant delivery and obturation, and preserving root integrity [1–2]. Within this framework, the initial phase of coronal flaring assumes a disproportionate importance: inadequate preparation of the coronal and middle thirds generates what has been termed “coronal interference,” a condition in which the resistance to file insertion encountered in the coronal portion of the canal generates torsional and bending stresses that are transmitted to the apical segment of the instrument, significantly increasing the risk of fracture [3–4].

Orifice openers are instruments specifically designed to address this challenge. By enlarging the coronal third of the root canal and eliminating dentinal interferences at the orifice, orifice openers facilitate straight-line access from the orifice to the point of canal curvature, reducing the stress on subsequent shaping files and improving irrigant penetration into the apical third [5]. Furthermore, adequate coronal flaring has been shown to increase the volume of irrigant delivered to the working length, enhance the efficacy of sonic and ultrasonic activation, and reduce the incidence of apical debris extrusion during instrumentation [6–7]. The clinical importance of these instruments has grown substantially with the trend toward minimally invasive access cavity preparations, which, while preserving coronal tooth structure, may limit the straight-line access previously achieved with traditional access cavity designs [8].

Since the introduction of nickel-titanium (NiTi) alloys into endodontic instrument manufacturing by Walia et al. [9] in 1988, the mechanical properties of rotary instruments have undergone continuous refinement through modifications in cross-sectional geometry, pitch, rake angle, and, most significantly in recent years, alloy metallurgy. The discovery that controlled heat treatment of NiTi alloys can alter the relative proportions of the austenitic and martensitic crystalline phases — and thereby modulate the instruments’ mechanical behavior — has generated a wave of instrument design innovations that have fundamentally changed our understanding of what is mechanically achievable with these materials [10–11]. Instruments exhibiting a predominantly martensitic crystalline structure at clinical temperatures demonstrate significantly greater flexibility and resistance to cyclic fatigue compared to instruments in the conventional austenitic phase, because the martensitic phase can undergo reversible, stress-induced deformation without initiating crack propagation [12].

The three orifice openers evaluated in this study represent three distinct points along the spectrum of NiTi metallurgical evolution. ProTaper Gold SX [Dentsply Sirona) is the coronal shaping file of the established ProTaper Gold system, manufactured from a gold-wire NiTi alloy that represents an advance over the original ProTaper Universal in terms of flexibility and fatigue resistance [13]. EdgeTaper Platinum SX (EdgeEndo) is produced using a proprietary heat-treatment process that the manufacturer describes as yielding enhanced flexibility and durability compared with conventional heat-treated NiTi instruments. EdgeOne Onyx 9/.09 (EdgeEndo) is a more recently introduced instrument manufactured using a proprietary technology that further optimizes the martensitic phase content of the alloy, yielding a file with superior mechanical properties compared to existing heat-treated systems [14].

Despite the clinical importance of orifice openers and the substantial differences in the metallurgical processes used to manufacture these three instruments, no published study has directly compared their mechanical properties under standardized laboratory conditions. Prior comparative studies of orifice openers have typically focused on a single mechanical parameter — most commonly cyclic fatigue resistance — without providing an integrated assessment of flexibility and cutting efficiency [15–16]. Feghali et al. [14] previously evaluated reciprocating NiTi instruments using a methodology analogous to the one adopted in the present study, demonstrating that heat-treated alloys confer significant mechanical advantages over conventional NiTi in reciprocating systems; the present investigation extends this framework to the specific domain of orifice openers in continuous rotation.

Furthermore, the operative torque generated during intracanal progression of an instrument — though not traditionally classified as a direct cutting-efficiency parameter — provides clinically relevant information about the ease and safety of file advancement. Higher operative torque implies greater resistance to file progression, which translates into increased torsional loading on the instrument shank and a higher probability of torsional fracture if the torque exceeds the instrument’s elastic limit [17–18]. Gambarini et al. [19] demonstrated in an in vivo study that intracanal operative torques vary considerably between instrument systems and that instruments with higher operative torques are associated with greater stress on the root dentinal walls. Assessing operative torque as an indirect measure of cutting efficiency, therefore, provides information pertinent to both instrument longevity and root structural integrity.

The present study was designed to evaluate and compare the flexibility, cyclic fatigue resistance, and cutting efficiency (measured as operative torque) of EdgeTaper Platinum SX, ProTaper Gold SX, and EdgeOne Onyx 9/.09 under standardized ex vivo conditions. The null hypothesis was that there would be no statistically significant difference in any of the three mechanical parameters among the tested instruments.

Materials and Methods

Experimental Design and Sample Allocation

This study followed a fully randomized parallel-group experimental design. A total of 36 new NiTi instruments were used for each of the three brands tested (total n = 108 instruments). Within each brand, instruments were randomly allocated by computer-generated randomization to three subgroups (n = 12 per subgroup per brand) corresponding to the three mechanical tests: flexibility (Test 1), cyclic fatigue resistance (Test 2), and cutting efficiency via operative torque measurement (Test 3). Separate sets of unused instruments were allocated to each test to eliminate carry-over effects from prior mechanical loading. All instruments were inspected under a stereomicroscope at 20× magnification before testing to exclude any specimens exhibiting manufacturing defects, surface irregularities, or pre-existing deformations. Instruments failing inspection were replaced. Testing was performed at 37 ± 1°C in a temperature-controlled water bath to simulate intracanal clinical conditions, given the well-documented influence of temperature on the behavior of the NiTi phase transformation [18].

The instruments tested were: Group 1: EdgeOne Onyx 9/.09 (EdgeEndo, Albuquerque, NM, USA); Group 2: EdgeTaper Platinum SX (EdgeEndo, Albuquerque, NM, USA); Group 3: ProTaper Gold SX (Dentsply Sirona, Ballaigues, Switzerland). All tests were conducted using devices and protocols previously validated and adopted by the authors in prior published investigations [14,19].

Test 1: Flexibility Assessment

Flexibility was evaluated using a universal testing machine (Lloyd LRX Plus; Lloyd Instruments Ltd, Bognor Regis, UK) following the cantilever bending methodology described by Bahia and Buono [21]. Each instrument was rigidly clamped in a custom fixture at a distance of 3 mm from the tip, with the remainder of the instrument projecting freely. A lateral compressive load was applied at the instrument tip at a crosshead speed of 1 mm/min until a deflection angle of 45° was achieved. The force required to produce this deflection (expressed in Newtons) was recorded using the machine’s load cell (accuracy: ±0.5%). Lower force values indicate greater instrument flexibility, as a more flexible instrument requires less force to achieve the same angular deflection. Each instrument was used once in a single loading cycle to avoid accumulated fatigue bias. Data were recorded automatically by the machine’s dedicated software (Nexygen; Lloyd Instruments).

Test 2: Cyclic Fatigue Resistance

Cyclic fatigue resistance was assessed using a stainless-steel artificial canal device constructed and validated according to the design described by Pruett et al. [18] and subsequently adopted in multiple studies by the authors’ group [14,19]. The artificial canal had the following geometric characteristics: angle of curvature = 60°; radius of curvature = 5 mm; inner canal diameter = 1.5 mm. These parameters were chosen to represent a clinically relevant scenario of severe curvature in which the risk of fatigue-related fracture is substantially elevated. Instruments were mounted in a torque-controlled endodontic motor and rotated continuously at the manufacturer’s recommended speed and torque settings (ProTaper Gold SX and EdgeTaper Platinum SX: 300 rpm; EdgeOne Onyx 9/.09: 350 rpm). Each instrument was inserted into the artificial canal to the point of maximum curvature and allowed to rotate freely in a static position until a complete fracture occurred. Time to fracture was recorded in seconds using a calibrated digital stopwatch. The number of cycles to failure (NCF) was calculated using the formula: NCF = (rpm × time to fracture in seconds) / 60. Higher NCF values indicate superior fatigue resistance. Each instrument was used in a single fatigue run; no instrument was tested more than once.

Test 3: Cutting Efficiency via Operative Torque

Cutting efficiency was evaluated indirectly by measuring the operative torque generated during apical progression of each instrument inside a standardized three-dimensional artificial tooth model (Endo Training Bloc™; Dentsply Sirona). The artificial tooth contains four root canals of standardized curvature (35°) and dimensions, providing a reproducible substrate for torque measurement. Instruments were mounted in an EndoMaster™ torque-controlled endodontic motor (Perfect, Suzhou, China) and advanced apically to a standardized depth of 5 mm from the canal orifice using a gentle, controlled pecking motion at manufacturer-recommended settings. The operative torque displayed on the motor’s digital screen was captured continuously by high-definition video recording of the display at 60 frames per second, allowing torque values to be extracted at 0.1-second intervals throughout the instrumentation sequence. The mean operative torque (expressed in Newton-centimeters, Ncm) across all recorded time points was calculated for each instrument. Lower mean operative torque values indicate greater cutting efficiency and lower intracanal stress generation. The same experienced operator advanced all instruments to eliminate inter-operator variability.

Statistical Analysis

All statistical analyses were performed using SPSS software version 27.0 (IBM Corporation, Armonk, NY). Data normality was assessed by the Shapiro-Wilk test; all datasets passed normality testing (p > 0.05). Levene’s test confirmed homogeneity of variance. Group differences were analyzed using one-way analysis of variance (ANOVA), with post hoc pairwise comparisons using Tukey’s Honestly Significant Difference (HSD) test. The level of statistical significance was set at α = 0.05 for all comparisons. Descriptive statistics are reported as mean ± standard deviation (SD). Effect sizes were calculated as partial eta-squared (η²) for ANOVA and Cohen’s d for pairwise comparisons.

Results

All instruments survived the pre-test stereomicroscopic inspection without requiring replacement. No instrument fractured outside the designated test condition. The results of all three mechanical tests are summarized in Table 1 and illustrated in Figures 1–3.

Table 1. Summary of results for all three mechanical tests. Values expressed as mean ± SD. ^* All pairwise differences significant at p < 0.05 (oneway ANOVA + Tukey post hoc test). Lower values indicate better performance for flexibility and operative torque; higher values indicate better performance for cyclic fatigue resistance.

Parameter	EdgeOne Onyx 9/.09	EdgeTaper Platinum SX	ProTaper Gold SX
Flexibility (N)	0.85 ± 0.06^*	1.12 ± 0.08^*	1.45 ± 0.10^*
Cyclic Fatigue (NCF)	1450 ± 120^*	1020 ± 95^*	760 ± 85^*
Operative Torque (Ncm)	0.85 ± 0.19^*	0.96 ± 0.28^*	1.11 ± 0.34^*

Test 1: Flexibility

The mean forces required to achieve 45° deflection were: EdgeOne Onyx 9/.09, 0.85 ± 0.06 N; EdgeTaper Platinum SX, 1.12 ± 0.08 N; ProTaper Gold SX, 1.45 ± 0.10 N. One-way ANOVA revealed a statistically significant overall effect (F = 312.4, df = 2,33, p < 0.001; η² = 0.95). Tukey post hoc analysis confirmed that all pairwise differences were statistically significant (p < 0.05 for all comparisons). EdgeOne Onyx 9/.09 demonstrated the greatest flexibility, requiring 24.1% less force than EdgeTaper Platinum SX and 41.4% less force than ProTaper Gold SX to achieve the standard 45° deflection.

**Figure 1.** Flexibility test results: mean force (N) required to achieve 45° deflection for the three orifice openers. Lower values indicate greater flexibility. Error bars = SD. * Significant difference between all groups (p < 0.05, Tukey post hoc).

Test 2: Cyclic Fatigue Resistance

The mean number of cycles to failure (NCF) was: EdgeOne Onyx 9/.09, 1450 ± 120 cycles; EdgeTaper Platinum SX, 1020 ± 95 cycles; ProTaper Gold SX, 760 ± 85 cycles. One-way ANOVA revealed a statistically significant overall effect (F = 185.7, df = 2,33, p < 0.001; η² = 0.92). All pairwise differences were statistically significant on Tukey post hoc analysis (p < 0.05). EdgeOne Onyx 9/.09 demonstrated 42.2% greater NCF than EdgeTaper Platinum SX and 90.8% greater NCF than ProTaper Gold SX.

**Figure 2.** Cyclic fatigue resistance: mean number of cycles to failure (NCF) for the three orifice openers. Higher values indicate greater fatigue resistance. Error bars = SD. * Significant difference between all groups (p < 0.05, Tukey post hoc).

Test 3: Cutting Efficiency (Operative Torque)

The mean operative torque values recorded during 5 mm apical progression were: EdgeOne Onyx 9/.09, 0.85 ± 0.19 Ncm; EdgeTaper Platinum SX, 0.96 ± 0.28 Ncm; ProTaper Gold SX, 1.11 ± 0.34 Ncm. One-way ANOVA revealed a statistically significant overall effect (F = 8.62, df = 2,33, p = 0.001; η² = 0.34). Tukey post hoc analysis confirmed significant pairwise differences between EdgeOne Onyx 9/.09 and ProTaper Gold SX (p < 0.05) and between EdgeTaper Platinum SX and ProTaper Gold SX (p < 0.05). The difference between EdgeOne Onyx 9/.09 and EdgeTaper Platinum SX reached statistical significance (p = 0.041). The effect size for the cutting efficiency comparison was moderate (η² = 0.34), in contrast to the large effect sizes observed for flexibility (η² = 0.95) and cyclic fatigue (η² = 0.92).

**Figure 3.** Cutting efficiency (operative torque): mean torque (Ncm) recorded during 5 mm apical progression for the three orifice openers. Lower values indicate greater cutting efficiency and lower intracanal stress. Error bars = SD. * Significant difference between all groups (p < 0.05, Tukey post hoc).

Discussion

The present study rejected the null hypothesis: statistically significant differences were observed among all three orifice openers in each of the three mechanical parameters evaluated. EdgeOne Onyx 9/.09 consistently outperformed both EdgeTaper Platinum SX and ProTaper Gold SX in flexibility, cyclic fatigue resistance, and cutting efficiency, with large effect sizes for flexibility and cyclic fatigue and a moderate effect size for operative torque. These findings are consistent with the hypothesis that progressive refinement of proprietary heat treatment technologies in NiTi alloy manufacturing yields instruments with meaningfully superior mechanical properties.

The significantly greater flexibility of EdgeOne Onyx 9/.09 is the most mechanistically fundamental finding of this study. Instrument flexibility is the primary determinant of canal-following ability: flexible instruments adapt to canal curvatures with minimal elastic energy storage, reducing the deflecting forces applied to the canal walls and minimizing the risk of transportation, ledging, or perforation [4, 13]. Flexibility is directly related to the crystalline phase composition of the NiTi alloy: instruments in the martensitic phase at functional temperature are substantially more ductile and deformable than instruments in the austenitic phase, because martensitic NiTi can undergo stress-induced phase reorientation (detwinning) that accommodates large strains without exceeding the elastic limit [12]. The 41.4% reduction in deflection force observed for EdgeOne Onyx 9/.09 compared with ProTaper Gold SX, and the 24.1% reduction compared with EdgeTaper Platinum SX, suggest that the proprietary manufacturing process applied to the former instrument yields a substantially higher martensitic content at 37°C than either comparator system.

These observations are consistent with the metallurgical characterization data published for similar heat-treated alloys. Shen et al. [12] demonstrated using differential scanning calorimetry that controlled memory (CM) NiTi wire exhibits finish transformation temperatures (A_e) above body temperature, meaning that the instrument remains predominantly in the martensitic phase during intracanal function. This property underlies the superior flexibility and pre-bending characteristics of CM-based instruments. While the specific phase-transformation temperatures of the EdgeOne Onyx alloy have not been independently reported in the peer-reviewed literature, the mechanical data from the present study are consistent with a similarly elevated A_e profile. Future studies employing differential scanning calorimetry and X-ray diffraction analysis of the EdgeOne Onyx alloy would be valuable for confirming this interpretation.

The superiority of EdgeOne Onyx 9/.09 in cyclic fatigue resistance (90.8% more cycles to failure than ProTaper Gold SX; 42.2% more than EdgeTaper Platinum SX) is a clinically critical finding. Cyclic fatigue fracture is the most common cause of instrument separation in clinical endodontics, accounting for approximately 50%–55% of all NiTi fracture events, and is particularly insidious because it occurs without visible warning signs such as deformation or unwinding [23]. The mechanism of cyclic fatigue involves the nucleation and propagation of micro-cracks at surface defects on the instrument’s outer surface under repeated tension-compression cycling during rotation in a curved canal; failure occurs when the crack reaches a critical length and propagates rapidly through the cross-section [22]. Plotino et al. [15] comprehensively reviewed the factors influencing NiTi cyclic fatigue. They identified alloy phase composition, surface finish quality, and the absence of stress risers (defects, scratches, manufacturing irregularities) as the primary determinants of fatigue life. The substantially higher NCF values for EdgeOne Onyx 9/.09 observed in the present study are consistent with a combination of superior alloy phase composition and optimized surface finishing. However, the relative contributions of these factors cannot be delineated from mechanical testing data alone.

Grande et al. [24] evaluated the cross-sectional geometry and surface characteristics of multiple NiTi rotary systems. They demonstrated that instruments with more rounded cross-sectional edges and smoother surface finishes exhibit greater fatigue resistance than instruments with sharp-angled cross-sections or prominent surface irregularities. ProTaper Gold SX’s progressive taper design, while functionally advantageous for coronal flaring efficiency, involves a relatively large cross-sectional mass that may concentrate cyclic stress at the point of maximum curvature engagement, contributing to its lower NCF values [13]. EdgeTaper Platinum SX’s intermediate fatigue performance suggests a partial, but incomplete, resolution of this design limitation through its heat treatment process.

The operative torque data add a clinically meaningful dimension to the mechanical comparison. While the effect size for this parameter was moderate rather than large, the absolute differences in torque generation among the three instruments have direct implications for intracanal safety. Gambarini et al. [19], in an in vivo study of operative torques generated during NiTi instrumentation, demonstrated that torque values approaching or exceeding 1.0 Ncm in curved canals are associated with measurable stress transfer to the root dentinal walls and increased risk of microfracture propagation. All three instruments in the present study generated mean operative torques below 1.2 Ncm, suggesting that none pose an unacceptable risk of torsional overloading under normal clinical conditions. However, the statistically significant lower torque of EdgeOne Onyx 9/.09 (0.85 Ncm vs. 1.11 Ncm for ProTaper Gold SX) implies a safety margin that may become clinically relevant in challenging anatomical situations — severely curved canals, calcified orifices, or cases requiring multiple canal passes. The lower operative torque of EdgeOne Onyx 9/.09 is consistent with its greater flexibility, as a more flexible instrument exerts lower lateral forces on the canal wall during rotation, reducing both the normal force and the frictional torque component [17].

The findings of the present study are consistent with previously published data on heat-treated NiTi instruments in other instrument categories. Feghali et al. [14], evaluating reciprocating NiTi instruments including heat-treated and conventional variants, reported that heat-treated instruments demonstrated significantly greater flexibility and fatigue resistance, and attributed this advantage to the greater martensitic phase content of the heat-treated alloys — a conclusion directly applicable to the orifice openers evaluated in the present investigation. Similar patterns of heat-treatment-dependent mechanical superiority have been reported for single-file systems [25] and for continuous-rotation shaping instruments in multiple tip sizes and tapers [15].

Several limitations of this study merit acknowledgment. First, all testing was conducted under laboratory conditions using artificial canals and standardized artificial tooth models; the clinical translation of these results is inherently constrained by factors such as operator skill, variability in canal anatomy, pre-flaring protocols, and irrigation dynamics that cannot be replicated in vitro. Second, torsional resistance was not assessed in the present study;. At the same time, cyclic fatigue accounts for the majority of clinical NiTi fractures, torsional failure remains a relevant failure mode — particularly in narrow, calcified, or tortuous canals where the file tip may bind against the canal wall — and future studies should include this parameter for a complete mechanical characterization. Third, the cutting efficiency was evaluated indirectly through operative torque rather than through direct measurement of dentin removal rate;. In contrast, operative torque provides clinically interpretable information about instrument-tissue interaction, it does not capture all dimensions of cutting behavior. Fourth, the study evaluated instruments at a single point in their service life (new, unused instruments); the mechanical properties of heat-treated NiTi instruments may evolve differently from those of conventional NiTi instruments with clinical use and sterilization cycles, and this temporal dimension should be addressed in future studies.

Conclusions

Within the limitations of this ex vivo study, the following conclusions are supported by the data:

EdgeOne Onyx 9/.09 demonstrated significantly greater flexibility, cyclic fatigue resistance, and cutting efficiency (lower operative torque) compared to both EdgeTaper Platinum SX and ProTaper Gold SX under standardized laboratory conditions (p < 0.05 for all pairwise comparisons).
EdgeTaper Platinum SX showed intermediate mechanical performance, statistically superior to ProTaper Gold SX and inferior to EdgeOne Onyx 9/.09 in all three parameters.
ProTaper Gold SX exhibited the lowest flexibility, cyclic fatigue resistance, and cutting efficiency among the three instruments tested.
The progressive mechanical advantages observed from ProTaper Gold SX to EdgeTaper Platinum SX to EdgeOne Onyx 9/.09 are consistent with the hypothesis that successive generations of proprietary heat treatment technology confer incrementally superior mechanical properties to NiTi orifice openers.
Further studies evaluating torsional resistance, behavior after repeated use and sterilization, and clinical performance in prospective cohort designs are warranted to confirm and extend these laboratory findings.

References

1. Siqueira JF Jr, Rôças IN. Clinical implications and microbiology of bacterial persistence after treatment procedures. J Endod. 2008;34(11):1291–1301. doi:10.1016/j.joen.2008.07.028
2. Haapasalo M, Shen Y, Wang Z, Gao Y. Irrigation in endodontics. Br Dent J. 2014;216(6):299–303. doi:10.1038/sj.bdj.2014.204
3. Peters OA. Current challenges and concepts in the preparation of root canal systems. J Endod. 2004;30(8):559–567. doi:10.1097/01.DON.0000129039.59003.9D
4. Schafer E, Vlassis M. Comparative investigation of two rotary nickel-titanium instruments: ProTaper versus RaCe. Part 1. Shaping ability in simulated curved canals. Int Endod J. 2004;37(4):229–238. doi:10.1111/j.0143-2885.2004.00786.x
5. Gu LS, Kim JR, Ling J, Choi KK, Pashley DH, Tay FR. Review of contemporary irrigant agitation techniques and devices. J Endod. 2009;35(6):791–804. doi:10.1016/j.joen.2009.03.010
6. Versluis M, Boutsioukis C, van der Sluis LW. Mechanisms of irrigant mixing and transport during ultrasonic activation. Int Endod J. 2019;52(10):1422–1434. doi:10.1111/iej.13141
7. Kirchhoff AL, Fariniuk LF, Mello I. Apical extrusion of debris in flat-oval root canals after using different instrumentation systems. J Endod. 2015;41(2):237–241. doi:10.1016/j.joen.2014.10.009
8. Plotino G, Grande NM, Isufi A, et al. Fracture strength of endodontically treated teeth with different access cavity designs. J Endod. 2017;43(6):995–1000. doi:10.1016/j.joen.2017.01.022
9. Walia HM, Brantley WA, Gerstein H. An initial investigation of the bending and torsional properties of Nitinol root canal files. J Endod. 1988;14(7):346–351. doi:10.1016/S0099-2399(88)80196-1
10. Gambarini G, Plotino G, Grande NM, Al-Sudani D, De Luca M, Testarelli L. Mechanical properties of nickel-titanium rotary instruments produced with a new manufacturing technique. Int Endod J. 2011;44(4):337–341. doi:10.1111/j.1365-2591.2010.01835.x
11. Thompson SA. An overview of nickel-titanium alloys used in dentistry. Int Endod J. 2000;33(4):297–310. doi:10.1046/j.1365-2591.2000.00339.x
12. Shen Y, Zhou HM, Zheng YF, Campbell L, Peng B, Haapasalo M. Metallurgical characterization of controlled memory wire nickel-titanium rotary instruments. J Endod. 2013;39(2):156–159. doi:10.1016/j.joen.2012.10.026
13. Peters OA, Gluskin AK, Weiss RA, Han JT. An in vitro assessment of the physical properties of novel Hyflex nickel-titanium rotary instruments. Int Endod J. 2012;45(11):1027–1034. doi:10.1111/j.1365-2591.2012.02071.x
14. Feghali M, Daeen Al Atta AA, Galli M. A comparative analysis of mechanical properties of different reciprocating NiTi endodontic instruments. Ann Stomatol (Roma). 2023;14(4):9–13. doi:10.59987/ads/2023.4.9-13
15. Plotino G, Grande NM, Testarelli L, Gambarini G. Cyclic fatigue of NiTi rotary instruments: a review. Int Endod J. 2017;50(3):247–263. doi:10.1111/iej.12604
16. Capar ID, Ertas H, Ok E, Arslan H, Ertas ET. Comparative study of different novel nickel-titanium rotary systems for root canal preparation in severely curved root canals. J Endod. 2014;40(6):852–856. doi:10.1016/j.joen.2013.10.010
17. Sattapan B, Nervo GJ, Palamara JE, Messer HH. Defects in rotary nickel-titanium files after clinical use. J Endod. 2000;26(3):161–165. doi:10.1097/00004770-200003000-00009
18. Pruett JP, Clement DJ, Carnes DL. Cyclic fatigue testing of nickel-titanium endodontic instruments. J Endod. 1997;23(2):77–85. doi:10.1016/S0099-2399(97)80250-4
19. Gambarini G, Seracchiani M, Piasecki L, et al. Measurement of torque generated during intracanal instrumentation in vivo. Int Endod J. 2019;52(5):737–745. doi:10.1111/iej.13042
20. de Hemptinne F, Slaus G, Vandendael M, Jacquet W, De Moor RJ. In vivo intracanal temperature evolution during endodontic treatment after the injection of room temperature or preheated sodium hypochlorite. J Endod. 2015;41(7):1112–1115. doi:10.1016/j.joen.2015.02.019
21. Bahia MGA, Buono VTL. Decrease in the fatigue resistance of nickel-titanium rotary instruments after clinical use in a dentin curved root canal. Oral Surg Oral Med Oral Pathol Oral Radiol Endod. 2005;100(2):249–255. doi:10.1016/j.tripleo.2004.11.022
22. Pruett JP, Clement DJ, Carnes DL Jr. Cyclic fatigue testing of nickel-titanium endodontic instruments. J Endod. 1997;23(2):77–85. doi:10.1016/S0099-2399(97)80250-4
23. Parashos P, Messer HH. Rotary NiTi instrument fracture and its consequences. J Endod. 2006;32(11):1031–1043. doi:10.1016/j. joen.2006.06.008
24. Grande NM, Plotino G, Butti A, Messina F, Testarelli L, Gambarini G. Cross-sectional analysis of root canals prepared with NiTi rotary instruments and stainless steel reciprocating files. Oral Surg Oral Med Oral Pathol Oral Radiol Endod. 2007;103(1):120–126. doi:10.1016/j.tripleo.2006.06.001
25. Gambarini G, Galli M, Di Nardo D, Miccoli G, Seracchiani M, Testarelli L. Differences in cyclic fatigue lifespan between two different heat treated NiTi endodontic rotary instruments: WaveOne Gold vs EdgeOne Fire. J Clin Exp Dent. 2019;11(7):e616–e621. doi:10.4317/jced.55839