Dental Hypotheses

: 2022  |  Volume : 13  |  Issue : 2  |  Page : 49--52

A Comparative Examination of Cyclic Fatigue and Fragment Length of Three Different Types of Endodontic Rotary Files: An In Vitro Study

Hanaa Abduljabbar Saleh, Othman Husham Abdulhameed 
 Department of Conservative Dentistry, College of Dentistry, University of Anbar, Ramadi, Iraq

Correspondence Address:
Hanaa Abduljabbar Saleh
Department of Conservative Dentistry, College of Dentistry, University of Anbar, Ramadi


Introduction: Although of great scientific advancement in the properties and form, fracture of nickel-titanium (NiTi) files could occur during their use. The goal of this study was to compare resistance to cyclic fatigue of various rotary systems used in endodontics. Materials and Methods: Three types of NiTi rotary systems were tested group A: One Curve, group B: Edge File, and group C: lusterdent NiTi files. In these files, taper is 0.06, and their diameter is 25 mm. Stainless steel block was used. This block contains artificial canals with a 60o curvature, 5 mm radius of curvature, 21 mm length, and 1.5 mm width. A number of cycles before fracture were obtained and measurement of fragment length was achieved. Statistical evaluation of readings was accomplished with ANOVA and Tukey post hoc test. Results: There were statistically significant differences between the three types of NiTi rotary systems considering the number of cycles before file fracture (P < 0.001). The differences between fracture lengths were not statistically significant (P = 0.15). Conclusion: The Edge File revealed the highest cyclic fatigue resistance.

How to cite this article:
Abduljabbar Saleh H, Husham Abdulhameed O. A Comparative Examination of Cyclic Fatigue and Fragment Length of Three Different Types of Endodontic Rotary Files: An In Vitro Study.Dent Hypotheses 2022;13:49-52

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Abduljabbar Saleh H, Husham Abdulhameed O. A Comparative Examination of Cyclic Fatigue and Fragment Length of Three Different Types of Endodontic Rotary Files: An In Vitro Study. Dent Hypotheses [serial online] 2022 [cited 2022 Aug 10 ];13:49-52
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During endodontic, nickel-titanium (Ni-Ti) files are progressively employed because of their superior mechanical properties. In spite of their high flexibility, failure during endodontic treatment presents a vital problem. Fracture of these files can occur within their maximum elasticity without any detectable signal of earlier permanent distortion.[1],[2] There are two causes for rotary Ni-Ti instrument breakage, which include torsional overload and flexural fatigue.[3],[4] In the clinical conditions, torsional load and cyclic fatigue affect endodontic rotary instruments.[5] Fracture due to torsional load happens when the file is fixed inside the canal, but the other part of the instrument is still switched. Predictable fracture of the tip occurs when the torque applied by the handpiece exceeds the maximum elasticity of the metal.[6] Fracture of the instruments due to the cyclic fatigue is produced by the fatigue of alloy. The rotation of files in a curved canal creates a series of tensions/compressions at the extreme flexure point till instrument breakage happens.[2],[5],[7] There is no sign of plastic deformation noticed when the instruments reach the point of cyclic fatigue, but various deformation can be seen when files break as a result of torsional overload, such as unwinding, straightening, reverse winding, and twisting.[3],[8] The improper clinical procedure[9] and numerous additional reasons produce a fracture of files.[10] The goal of this study was to assess resistance to cyclic fatigue of different rotary systems used in endodontics.

 Materials and Methods

The study protocol was approved by the local ethical committee of the University of Anbar. Three types of NiTi rotary systems were tested in the current study, 75 files were separated into three groups, each group consisted of 25 files that included the following: group A: One Curve (Micro-Mega SA, Besançon, France), group B: Edge File (Edge Endo, EDGEFILE®, Canada), and group C: lusterdent (lusterdent, Zhengzhou, Henan, China) NiTi files. All these files have a 0.06 taper and are 25 mm in diameter. In the beginning, and to exclude any distortion, the tested files were examined under a microscope (Langenfeld, Germany) at ×20 magnification and no distortion was identified. A stainless steel block that contains an artificial canal with a 60o curvature, 5 mm radius of curvature, 21 mm length, and 1.5 mm width was used in this study.[11],[12] Lubrication of the canal with glycerin (Guangzhou Sanan Chemical Co., Ltd. China) was done after every file. NiTi rotary files were rotated according to the information of the companies with endodontic motor X-smart (Dentsply, Maillefer, Switzerland) till breakage took place. Rotation of One Curve was done at 300 rpm and 2.5 Ncm torque; Edge File at 300 rpm and 2.5 Ncm; and lusterdent at 300 rpm and 2 Ncm. For the purpose of standardization, the dental handpiece was fixed on a device that acts as a surveyor that is often employed in the dental laboratory. This device is called “drill stand base” (Henan Yogong Machinery Co., Ltd. Henan, China) and is used to simplify the procedure of files engagement into the artificial canal and for higher accuracy during each measurement and it also confirms a standardized three-dimensional orientation and places the tested files at a similar distance.[13] A stopwatch was used in determining the time in seconds until fracture, and the number of cycles to failure was obtained by multiplying the time by the rpm for each file/60. Measurement of the fragment lengths of the files by Digital Caliper (Mitech Metrology Co., Ltd. Guangdong, China) was performed so as to ensure that the files were placed properly in the synthetic canals and the same forces exerted on the tested instruments.

 Statistical methods

Data were analyzed using one-way ANOVA and Tukey post hoc test using R software (R Foundation for Statistical Computing, Vienna, Austria).


There were statistically significant differences between the three types of NiTi rotary systems considering the number of cycles before file fracture (P < 0.001). The differences between fracture lengths were not statistically significant (P = 0.15) [Figure 1].{Figure 1}


Clinically, NiTi rotary instruments have a great possibility of fracture.[14] Increasing the diameter of the file is directly proportional to the smaller resistance to cyclic fatigue[15]; therefore the diameter of the tested files was uniform in the present study. There are many aspects that can influence the fracture resistance of NiTi instruments, which include the structure of alloy, techniques of construction, and the shape of the cross section.[16],[17] Thermal technique for NiTi rotary instruments manufacturing is usually used in order to develop an instrument with enhanced microstructure and behaviors of conversion, so this will produce better activity of files during the endodontic instrumentation phase comprising the resistance to cyclic fatigue.[18],[19] When NiTi alloys are treated with heat, the percentage of the martensitic phase will increase more than the austenitic phase and this will give more flexibility and resistance to cyclic fatigue. The most common types of thermally treated NiTi alloys are M-Wire, Gold Technology, controlled memory wire or CM-Wire, and R-phase wire.[20] In the present study, various rotary files that are used for canal instrumentation were tested. These files are developed by various manufacturing procedures to study their resistance to cyclic fatigue. The present study compared lusterdent files that are thermally treated by M wire alloy and One Curve made by CM thermal treatment. Edge File is developed by thermal process (FireWire). The Edge File showed greater resistance to cyclic fatigue compared to One Curve and lusterdent instruments. As stated by the fabricator, Edge files demonstrated high flexibility and great strength, so they can resist torsional forces. Firewire alloy consists of an unusual three-dimensional phase of the crystalline matrix that provides a great cyclic fatigue resistance and high flexibility of the instruments.[21]. This result is in accordance with Gambarini et al.,[22] who evaluated the cyclic fatigue of the Gold treated WaveOne Gold and the Firewire treated Edge One Fire instruments. These files rotated in a reciprocating motion (counterclockwise) in an artificial canal with a 90° angle of curvature and a 2 mm radius of curvature. They concluded that Firewire endodontic instruments showed higher cyclic fatigue resistance compared with WaveOne Gold instruments. Another study showed that Edge File had a comparable cyclic fatigue resistance to the MTwo system and less cyclic fatigue resistance to Pro Design Logic.[23]

In the present study, lusterdent instruments showed greater cyclic fatigue resistance than One Curve endodontic files. lusterdent produced from M-Wire alloy has predictable higher flexibility, greater strength, and more wear resistance compared to the same rotary files that are made up of conventional superelastic NiTi rotary instruments due to the unique nanocrystalline martensitic microstructure.[24] One Curve showed the least resistance to cyclic fatigue than the other tested files. Thermally treated NiTi alloy (CM. Wire) is used for the production of this file. One Curve is one of the controlled memory NiTi. This file has the property of bending before insertion inside the root canals to simplify instrumentation and exclusion of any troubles during endodontic treatment.[25] Lack of superelastic properties at both room and body temperature is responsible for the lower cyclic fatigue resistance of the One Curve file.[26] Deformation of CM Wire files can occur due to the changed phase configuration, which produces reorientation of the martensite variants.[27]

According to the study findings, the Edge File gives a high resistance to cyclic load, but in our study the curvature of the artificial canal, the degree of taper, and diameter for all tested files were uniform. Therefore, further studies are required to compare cyclic fatigue resistance of the rotary files using various curvatures, degrees of taper, and diameters.

Financial support and sponsorship


Conflicts of interest

There are no conflicts of interest.


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