|Year : 2021 | Volume
| Issue : 1 | Page : 1-5
A comparative evaluation of cyclic fatigue resistance of Reciproc Blue, WaveOne Gold and 2Shape nickel–titanium rotary files in different artificial canals
Ankita Grace Lall1, Suparna Ganguly Saha1, Vijay Alageshan2, Parmeet Banga2
1 Department of Conservative Dentistry and Endodontics, College of Dental Science and Hospital, Indore, Madhya Pradesh, India
2 Department of Prosthodontics and Implantology, Yerla Dental College, Navi Mumbai, Maharashtra, India
|Date of Submission||13-Dec-2019|
|Date of Decision||20-Jan-2020|
|Date of Acceptance||13-Mar-2020|
|Date of Web Publication||23-Mar-2021|
Dr. Ankita Grace Lall
F-12, A. B. Road, College of Dental Science and Hospital, Rau, Indore, Madhya Pradesh
Source of Support: None, Conflict of Interest: None
Aim: The aim of this in vitro study was to compare the cyclic fatigue resistance (CFR) of continuous rotation file systems (2Shape) and two reciprocating file systems (Reciproc Blue [RB] and WaveOne Gold [WOG]) in canals with different angulations.
Materials and Method: Thirty files each of 2Shape (25, 0.06), RB R25 (25/0.08) and WOG Primary (25/0.07) were included in this study. All the instruments were used according to the manufacturers instructions in an endodontic fatigue testing block with three artificial grooves simulating root canals having angulations of 45°, 60°, and 90°. The files were allowed to rotate in the grooves, until fracture occurred and the time to fracture was recorded in seconds using digital chronometer. The data were analyzed statistically using one-way ANOVA followed by post hoc Tukey test.
Results: The reciprocating file systems RB showed significantly higher CFR at all angles of curvature, i.e., 45°, 60°, and 90° (P < 0.05).
Conclusions: Within the limitations of the present in vitro study, it may be concluded that RB tends to be more resistant to fracture in canals with a gentle curvature as well as may be more suited in canals with sharp and acute curvatures.
Keywords: Angle of curvature, cyclic fatigue resistance, nickel–titanium
|How to cite this article:|
Lall AG, Saha SG, Alageshan V, Banga P. A comparative evaluation of cyclic fatigue resistance of Reciproc Blue, WaveOne Gold and 2Shape nickel–titanium rotary files in different artificial canals. Endodontology 2021;33:1-5
|How to cite this URL:|
Lall AG, Saha SG, Alageshan V, Banga P. A comparative evaluation of cyclic fatigue resistance of Reciproc Blue, WaveOne Gold and 2Shape nickel–titanium rotary files in different artificial canals. Endodontology [serial online] 2021 [cited 2022 Aug 12];33:1-5. Available from: https://www.endodontologyonweb.org/text.asp?2021/33/1/1/311752
| Introduction|| |
Recent advancements in the metallurgy of rotary nickel-titanium (NiTi) instruments have led to their increased popularity due to superior flexibility, ability to maintain canal curvature, superior cutting efficiency, faster canal preparation, and overall higher success rate because of reduction in procedural mishaps.,,
Despite these advantages, rotary NiTi files demonstrate an increased risk of fracture, especially in curved root canals. The fracture of these NiTi files during clinical use occurs by two different mechanisms, i.e., torsional fatigue and cyclic fatigue.
Torsional fatigue fracture occurs when the torsional stress exceeds the elastic limit of the file whereas, cyclic fatigue fracture occurs due to alternating tension – compression cycles, at the apical third of severely curved root canals. To prevent this, the manufacturers modify the metallurgy by incorporating different combination of alloys, by altering the design properties and also by incorporating various heat treatments and kinematics.,,,
2Shape files (TS; Micro-Mega, Besancon, France) were used in the present study in continuous rotation motion. TS files are manufactured by a proprietary heat treatment (T-Wire), which, according to the manufacturer, aims to improve both flexibility and cyclic fatigue resistance (CFR).,, TS has the latest generation of triple helix cross-section with two main cutting edges for cutting efficiency and one secondary edge for improved removal of debris.
Reciproc Blue (RB; VDW, Munich, Germany) and WaveOne Gold (WOG; Dentsply Maillefer, Ballaigues, Switzerland) are new-generation single-file systems which use reciprocating motion. RB is manufactured by altering the molecular structure through a novel blue heat treatment in order to increase the CFR, which gives the file its blue color. RB file has an S-shaped cross-section, two cutting edges, and a noncutting tip. The WOG files are manufactured using gold heat treatment which involves heating and then slowly cooling the file after production, thus increasing the flexibility of file. The cross-section of the file is modified to a parallelogram, having two cutting edges. Moreover, the off-center design used in ProTaper Next (Dentsply Maillefer) files is also used in WOG files.
In a comprehensive literature review, there has been no previous study examining the CFR of WOG, 2Shape, and RB at 45°, 60°, and 90° canal curvatures. Therefore, the aim of the present study was to compare the CFR of continuous rotation file TS and two reciprocating files RB and WOG in simulated canals with different angulations (45°, 60°, and 90°). The null hypothesis was that there would be no significant difference in the CFR among the continuous rotation and reciprocating motion NiTi files when rotated in simulated canals at different canal angulations.
| Materials and Methods|| |
Thirty files each of 2Shape (25, 0.06), RB R25 (25/0.08), and WOG Primary (25/0.07) of length 25 mm were included in the present study. For the standardization and reliability of the experiment, the instruments tested were examined for defects under a stereomicroscope (Zoom Stereo Binocular Microscope (ZSM-111), Hicksville, NY, USA) with × 20 for any visible signs of defects. The files were stabilized inside simulating root canals having angulations of 45°, 60°, and 90°, respectively, for a locking system and thereby standardizing their positions in an endodontic fatigue testing block.
Using glycerine (Glycerine Pure; AB Enterprises Mumbai, India) as a lubricant the files were rotated in grooves, having an inner diameter of 1.5 mm, length of 20 mm, angles of curvature 45°, 60°, 90° and a radius of curvature of 5 mm until fracture occurred. To observe the fracture of files, top of the endodontic fatigue testing block was covered with glass.
During mechanical testing, 90 NiTi rotary files were divided into two experimental groups based on their movement kinematics into Group-I i.e., Continuous rotation motion files (n = 30) and Group-II, i.e., Reciprocating motion files (n = 60). Group-I was represented by TS files respectively while Group-II was further subdivided into IIA (n = 30) and IIB (n = 30) represented by RB and WOG files, respectively. Each file was stabilized inside the simulated root canals having angulations of 45°, 60°, and 90° respectively, by locking the handpiece of endomotor in a reproducible position within custom-made cyclic fatigue testing block.
The files, with their working lengths standardized at 18 mm, were activated using a 6:1 reduction handpiece powered by a torque-controlled motor (X-Smart Plus; Dentsply Maillefer, Switzerland). TS files were operated in continuous rotation at 300 rpm and 2.5 N cm, RB R25 in “Reciproc All” program (300 rpm and 2 N cm) and WOG Primary in “WaveOne All” program (350 rpm and 2 N cm), according to the manufacturers recommendations. The endodontic motor was recalibrated after the use of each instrument in order to avoid measurement errors due to motor mechanics.
The handpiece of the endomotor was locked in a reproducible position, and files of each group were used freely in the simulated canals created in an endodontic fatigue testing block, until fracture occurred. This testing procedure was performed by a single operator to avoid interoperator variability.
The instrument fracture was detected visually using a videocamera Canon EOS 700D (Canon Inc; Tokyo, Kanto; JP) on a tripod stand and time to fracture for each instrument was recorded by a digital chronometer. Using the time data, the number of cycles to failure (NCF) was determined to evaluate the CFR of different NiTi files using the formula: NCF = Revolution per minute (rpm) × Time to fracture in seconds (s)/60.
The NCF data were first analyzed using the Shapiro–Wilk test to verify the assumption of normality. One-way ANOVA followed by post-hoc Tukey test were performed to statistically analyze the data using SPSS 21.0 software (IBM-SPSS Inc., Chicago, IL, USA) with the significance level established at 5% (P < 0.05).
| Results|| |
The mean and standard deviations of the NCF of the groups tested are presented in [Table 1].
|Table 1: The mean and standard deviations of the number of cycles to failure of nickel-titanium instruments tested at three different canal curvatures (45°, 60°, and 90°)|
Click here to view
On comparing the NCF value, the reciprocating files RB showed significantly higher CFR in comparison to TS and WOG, respectively, at all the angles of curvature (P < 0.05). At 45°, 60°, and 90°angles of curvature, RB showed the highest CFR, followed by WOG and TS (P < 0.05), with the differences being statistically significant. CFR at 60° and 90° curvatures were significantly lower as compared to 45° canal curvature (P < 0.05).
| Discussion|| |
Cyclic fatigue has been reported to be one of the major factors resulting in file separation in curved canals, thus justifying the need for studies comparing the CFR of NiTi rotary files at different canal angulations.
The use of natural teeth was avoided because it is difficult to standardize root canal length, degree, and radius of curvature as well as dentin hardness. Although the simulated canal created in a nontooth device is unable to replicate clinical conditions, it minimizes the impact of other variables that may influence file fracture, thus facilitating standardization.,, CFR using nontooth device has been previously tested in both static and dynamic models. Although a dynamic model could closely replicate a clinical pecking motion, its drawback is that instruments being tested are not limited in a precise trajectory. In a dynamic model study, the amplitude, as well as speed of axial movement, is standardized. However, in clinical practice, both the amplitude and speed of axial motion are variable and subjective, as the pecking motion is manually controlled. The results of such studies must, however, be extrapolated to clinical conditions keeping in mind the contrast between the properties of a stainless steel block and dentin.
Based on the findings, the null hypothesis was rejected, as a significant difference in CFR was obtained among the different file systems at different canal curvatures.
Among the reciprocating files, RB showed higher CFR at all curvatures, i.e., the Novel Blue heat treatment that alters the molecular structure of RB showed superior results when compared to the gold heat treatment used in the production of WOG files. While some studies have reported that, cross-section design of files has no effect on CFR, others have confirmed their influence on fracture resistance of the files.,,, The S-shaped cross-section design of RB was found to show better CFR than the parallelogram cross-section design of WOG. Based on the findings of the present study, it could be said that the metal alloy, as well as the cross-section design, might influence the CFR of files.
At 45°, 60°, and 90° angles of curvature, RB presented with the highest CFR. This may be attributed to the superior fatigue properties imparted by Novel Blue heat treatment. This proprietary thermomechanical manufacturing process produces a specific oxide surface layer thereby altering the molecular structure and imparting blue color to the instrument.
In the present study, a statistically significant difference in terms of CFR was found between WOG files used in reciprocating motion and that of TS files used in continuous rotation motion at all angles of curvature. With very few studies examining the CFR of TS files, it may be postulated that gold heat treatment in WOG might have an influence on CFR. Moreover, further studies are needed to evaluate the properties of the T-Wire alloy used in the TS file.
However, in the present study, reciprocating motion file systems showed significantly higher CFR as compared to continuous rotation motion file systems at all the canal curvatures. The probable reason for higher CFR of reciprocating file systems may be attributed to the shorter circumferential distance traversed by the reciprocating files in comparison to continuous rotation motion files, which subjects the file to lower stress values. The results obtained in the present study are in accordance with a study conducted by Pedullà et al., who also concluded higher CFR of reciprocating motion file systems compared with a continuous rotation motion file system.
Even though all the instruments tested in the present study had the same tip size (#25), the taper, cross-sectional design, core diameter, and thermal treatment of NiTi instruments differ among them. TS, WOG, and RB presented tapers of 0.06, 0.07, and 0.08 mm/mm, respectively, over the first three millimeters from the tip. Usually, the instruments with lesser taper ensure higher CFR. However, the results of the present study showed that RB 25, 0.08 had significantly higher CFR than WOG 25, 0.07 and TS 25, 0.06. Thus, it may be said that other variables such as cross-sectional design, core diameter, and thermal treatment also have a significant role in determining the CFR of NiTi instruments. The results of the present study are in accordance with previous studies stating that lower CFR of NiTi instruments is associated with larger metal mass volume at their maximal stress point.
According to the results of the present study, all the experimental groups revealed a greater CFR at 45° angle of curvature as compared to 60° and 90° angles of curvature which is in accordance with the previous study by Peng et al. which postulated that at 45° angle of curvature, the CFR of NiTi files was found to be significantly higher than their resistance in canals with 60° and 90° angles of curvature. The results of the present study confirmed the findings of previous studies that the CFR of NiTi files is strongly influenced by the angle of curvature of the artificial canal used.,
| Conclusions|| |
Within the limitations of the present in vitro study, it may be concluded that
- At 45°, 60°, and 90° angles of curvature the novel NiTi rotary instrument, RB showed higher CFR when compared to WOG and TS instruments, which makes RB more appropriate to be used in canals with sharp and acute curvatures. It may also be concluded that the increase in the angle of curvature of artificial canals negatively affects the CFR of NiTi instruments.
Financial support and sponsorship
Conflicts of interest
There are no conflicts of interest.
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