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Research Article

The effect of canal curvature on cyclic fatigue resistance of rotary instruments using different irrigation materials (in vitro study)

[version 1; peer review: 3 approved with reservations]
PUBLISHED 27 Apr 2023
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Abstract

Background: The mechanical qualities of Ni-Ti is crucial because they give the files their flexibility and enable us to prepare curved and double-curved canals with more ease. It happens frequently for instruments to separate during canal preparation, and cyclic fatigue (metal fatigue) is a frequent cause.
This study aimed to assess how irrigation affected the two rotary endodontic instruments' cyclic fatigue resistance.
Methods: The Edge File and Fanta File rotary endodontic instrument groups were chosen. Each group (n = 42) was split into 3 subgroups (n = 14 each), one receiving NaOH, one Glycine, and one EDTA treatment. The number of cycles to failure (NCF) was determined after each subgroup underwent testing for cyclic fatigue resistance.
Results: The result appeared different significant between the two group and sub-group with the different materials that used with it with the length of fractures and time that recorded in each group.
Conclusion: NaOCl, glycine, and EDTA as chemical materials appeared to have considerably varied cycle fatigue resistance for various lengths of fractures and durations, according to the comparison between the two evaluated instruments.

Keywords

cyclic fatigue, rotation, fracture, M wire, autoclave, irrigation, curve canal

Introduction

The success of endodontic therapy is associated with the cleansing and shape of the root system, which is impacted by mechanical elements such the preparation system and preparation process. The effectiveness of chemical agents with irrigation solutions in tissue solution, germination, and residue removal is covered next (Estrela et al., 2003).

The amount of flexing a rotary endodontic tool experiences when placed inside of an angulated root canal determines how long it will last before becoming fatigued. A torsional fracture occurs when the instrument shaft is still rotating when the endodontic file's tip or a piece of it is lodged inside a canal. In this case, the metal's elastic limits are exceeded, causing plastic deformation and finally fracture (Berutti et al., 2012a).

In contemporary endodontic, NiTi rotary devices are utilized without exception to shape root canals (Torabinejad and Walton, 2009). Compared to standard stainless steel files, they are more flexible and have better cutting efficiency (Schafer et al., 2004). Because of their extreme flexibility, producing the desired tapering root canal form is simple and has a lower tendency to cause canal transportation (Chen and Messer, 2002). Despite these benefits, NiTi instruments are prone to separation (Arens et al., 2003), which is primarily caused by wear and torsional shear forces (Varela-Patino et al., 2010; Berutti et al., 2012b). As would happen during rotating instrumentation in a curved canal, cyclic fatigue happens when an instrument is repeatedly subjected to cycles of compression and tension (Chen and Messer, 2002).

Operational speed, metal surface treatment, and metallurgical characterization of the NiTi alloys are only a few of the variables that have been studied as potential influences on the fatigue resistance of NiTi rotary files (Gambarini et al., 2008).

Due to flexural loads and cyclic fatigue, canal curvature is thought to be the main cause of instrument failure (Hulsmann et al., 2005). Corrosion that could happen in the presence of an irrigating solution is another issue that could reduce resistance to fatigue fracture (Sonntag and Heithecker, 2006). The current gold standard for tissue disintegration and disinfection is the irrigation of root canals with NaOCl and EDTA (Torabinejad and Walton, 2009). When NiTi instruments are used to instrument a root canal, they come into contact with irrigating solutions.

As a result, corrosion patterns that involve the selective removal of nickel from the surface can result in micro pitting, which compromises the instrument's structural integrity. Very little can be done by the clinician to stop or lessen such stresses (Berutti et al., 2012a). This study aims to assess the impact of irrigation on the two rotary endodontic devices' cyclic fatigue resistance.

Methods

The Edge File (0.25/0.6) and Fanta file (0.25/0.6) groups of rotary endodontic instruments, respectively, were chosen. There were three subgroups total (n = 14) for each group (n = 42).

Subgroup1 = treated with glycerin

Subgroup2 = treated with EDTA

Subgroup3 = treated with sodium hypochlorite.

Due to the vast diversity of canal shapes present in real teeth, the cyclic fatigue test cannot be performed with natural teeth consistently.

This study was conducted in artificial canals made of tapered stainless steel that was created especially for the purpose. These synthetic canals have regular (60°) curvature angles and 5 mm radius of curvature and 1.5 mm width of coronal portion of canal gradually decrease to 1 mm at its end (Plotino and others, 2009).

The block was created in accordance with the files' specifications, and testing was done at the rotary system's manufacturer-recommended, according to fanta and edge system speed of 500 Rpm with a 2.5 N torque manipulating setting. The file tip, which has been set to its full working length, is now (Bhagabati et al., 2012) 7 mm from the center of the simulated curvature (19 mm). The working area is 25 mm long and the entire set of files is brand-new. The file was rotated freely during cyclic fatigue tests inside the artificial canal's tapered section, which produced a reproducible simulation of the file restrained in the canal's curved section (Schneider, 1971).

To make manipulating the hand-piece movement and the simple insertion of each file into the artificial canal possible, the dental hand-piece was mounted on a wooden block. This enabled uniform file depth placement and three-dimensional alignment. A transparent plastic sheet was placed over the artificial canal to stop the files from slipping out and to allow the researcher to observe the files as they were utilized and when a fracture developed. As a result, the fracture could be seen because the files could be seen through the transparent plastic sheet window (Plotino et al., 2010).

In the past, the wooden block was fastened to the stainless steel block in order to stop the wooden block from moving and to keep the relationship between the steel block and the hand-piece nearly constant (Yılmaz et al., 2017).

To reduce heat generation and friction, glycerin has been completely packed inside the artificial canal before each file was cut to the proper size (19 mm). Using the (ENDOMAX PLUS) cordless endodontic hand-piece, the files were triggered inside the canals. In order to improve productivity and reduce human mistake, video recording has been done concurrently (Bhagabati et al., 2012). Every file's (NCF) is described by this equation.

“Number of cycles to failure NCF = Speed RPM X Time (T) to fracture in minute” The armamentarium used in this study are show in Figure 1.

51ea9313-6f57-4aee-9f08-7a0fdc4c1a77_figure1.gif

Figure 1. The armamentarium used in this study.

After being removed from the solutions, each file was rinsed with bi-distilled water to counteract the effects of NaOCl, dried, given an ID number, and stored in glass vials.

Then, using a mechanical device created expressly for the job and capable of simulating the conditions of an instrument encased in a curved canal, instruments from all three groups and each brand were put through cyclic fatigue testing. (Grande et al. 2006; Plotino et al. 2009).

The apparatus was connected to the same dynamic immersion programs and motor set. This made it possible for the endodontic instruments to freely reciprocate and maintain constant pressure inside a stainless steel artificial channel. To make the artificial canal, the instrument's dimensions and taper were reproduced. When the file made contact with the canal walls in the simulated canal, a special high-flow synthetic lubricant (Super Oil; Singer Co Ltd, Elizabethport, NJ, USA) was sprayed into the canal to lessen friction. The time to fracture (TtF) for each instrument, measured in seconds from the start of the test until the point of breakage, was recorded and registered using a chronometer to the nearest whole number. The TtF was the dependent variable, whereas the type of files used and the immersion conditions were independent factors.

Statistical analysis

The Statistical Analysis System - SAS (2018) application was used to determine the effects of various factors on the research parameters. The least significant difference (LSD) test was used in this investigation to compare the means in a significant manner (ANOVA).

Results

Descriptive statistics of TtF for each file is summarized in Tables 1 and 2.

Table 1. Effect of type of File and chemical materials in length of fracture.

Chemical materialsMean ± SE of length of fractureLSDP-value
Edge fileFanta file
Glycerin3.02 ± 0.17 C b3.65 ± 0.16 A a0.490*0.0136
EDTA4.74 ± 0.11 A a3.45 ± 0.09 A b0.304**0.0001
Sodium hypo-chloride3.73 ± 0.12 B a3.28 ± 0.16 A b0.421*0.0371
LSD0.397**0.413 NS---
P-value0.00010.199

* P ≤ 0.05.

** P ≤ 0.01.

Table 2. Effect of type of file and chemical materials in time.

Chemical materialsMean ± SE of time (sec.)LSDP-value
Edge fileFanta file
Glycerin8.85 ± 0.32 A a4.48 ± 0.14 A b0.725**0.0001
EDTA5.61 ± 0.29 B a3.70 ± 0.22 B b0.764**0.0001
Sodium hypo-chloride5.45 ± 0.09 B a3.63 ± 0.24 B b0.543**0.0001
LSD0.741**0.598**---
P-value0.00010.010

** P ≤ 0.01.

In Table 1, we notice different significant differences in the effect of three materials on the edge file, which appeared a high significant differences for the material EDTA, then NaOH, then Glycerin in respectively, while there are no significant differences of the chemical materials on the Fanta file. While in Table 2 we notice very high significant differences between the effect of glycerin and the other two types of chemical materials, while appeared no significant differences between the two chemical materials when compared with each other on the two types of files.

Averages that carry different letters in Tables 1 and 2 are significantly different, and averages that carry similar letters do not differ significantly. The highest average takes the letter A and so on downwards. If you find an average that takes two letters like ab, this is no different neither from the average that carries a nor from the average that carries b. as appeared in Figures 2 and 3.

51ea9313-6f57-4aee-9f08-7a0fdc4c1a77_figure2.gif

Figure 2. The effect of types of file and chemical material on length of fractures.

51ea9313-6f57-4aee-9f08-7a0fdc4c1a77_figure3.gif

Figure 3. The effect of types of file and chemical material on time.

Discussion

Despite great improvements in NiTi instrument design and technology, the failure of NiTi instruments during root canal therapy continues to be a significant problem since these instruments are prone to fracture without visible symptoms of prior permanent distortion. Even with the creation of new endodontic instrument generations based on various manufacturing processes, instrument fracture is still a possibility.

Every file system must be disinfected for infection control before being used again, and while performing their functions, instruments are exposed to commonly used irrigants like NaOCl because the canals were filled with the irrigant during instrumentation. Even though various research has been conducted to assess the cyclic fatigue resistance of different file systems, autoclaving and exposure of file systems during operation may have varied effects on the properties of various file systems. As a result, in the current work, multiple file systems based on diverse manufacturing technologies have been contrasted for cyclic fatigue resistance after exposure to NaOCl, glycine, and EDTA.

The purpose of this study is to assess how irrigation affects the two rotary endodontic instruments' resistance to cyclic fatigue. A chemically active irrigation solution is used when clinically shaping curved root canals. Surface interactions between the file and canal walls during this process could lead to corrosion or surface roughness, which could then result in fissures and finally cyclic fatigue of the file (Hasegawa et al., 2014).

Some researchers used the pre-immersion of NiTi files in an irrigation solution while others tested the files for cyclic fatigue in synthetic oil as a method of evaluating the fatigue failure process (Pedullà et al., 2014). The interaction between the file and the irrigation solutions while the file is rotating in the irrigation solution is not considered by this design. In additional studies, the files were evaluated in an irrigation solution bath (Elnaghy and Elsaka, 2017). However, the relationship between the file and the canal walls was not considered.

The files were tested while rotating in a curved glass tube filled with the irrigation fluid as part of the current study's specially created apparatus, which duplicates the clinical settings. To prevent galvanic corrosion from happening during testing in metal to or in contact with metal pins, as was stated in the previous research, a heat-resistant curved glass tube was employed (Shen et al., 2012). Glass tubes, which are not found in natural teeth, may have several drawbacks that come from chemical reactions with various irrigation solutions and should not be extrapolated clinically.

Theoretically, employing aqueous media will allow the heat generated by friction to evaporate and gradually lengthen the fatigue lifetime of NiTi files. However, the current study's findings, which are in agreement with some reports (Shen et al., 2012; Hasegawa et al., 2014; Pedullà et al., 2011) and disagreement with others, show that the NCF of instruments tested in dry conditions without lubricant or coolant was significantly different from those tested in EDTA, Glycine, and NaOCl groups (Berutti et al., 2006; Elnaghy and Elsaka, 2017; Peters et al., 2007). These contradictory results could be the consequence of one of two factors.

The first is that these aqueous solutions may hurtan an adverse effect on cyclic fatigue due to their propensity to produce corrosion and the roughness of the NiTi alloy surface. As a result, the fatigue life did not improve. The second factor is that fatigue testing occurred in a location with minimal cyclic fatigue. Regarding the first factor, prior studies indicated that immersion in NaOCl and EDTA could result in file corrosion (Berutti et al., 2006; Peters et al., 2007).

However, in these studies, the file and shank were fully submerged for a long period of time, which led to galvanic corrosion, which is clinically inapplicable. Recent studies, which concur with the present findings, have shown that immersion does not, on the other hand, promote corrosion (Shen et al., 2012; Pedullà et al., 2011) or exhibit any adverse impact on cyclic fatigue even with an increased surface roughness of the files.

The second theory appears more believable. The NCF in the existing configuration was in the low-cyclic fatigue range (Cheung et al., 2007; Tobushi et al., 1997). This amount of time is insufficient to demonstrate how the various circumstances interact. When the number of cycles fell within the low-cyclic fatigue life, Shen et al. (2012) showed no difference in NCF between the NCF of various files in dry conditions and a bath of irrigation solutions including Glycine, EDTA, and NaOCl. In contrast to dry conditions, liquid media has shown improvement in cycle fatigue in long fatigue life. In the landmark study by Tobushi et al. (1997), the researchers discovered that in areas of mild tiredness, there was no difference between wet and dry environments.

Similarly, to this, Pedullà et al. (2014) demonstrated that submerging NiTi files in EDTA and NaOCl had no detrimental effects on the NCF. On the other hand, testing WaveOne Gold in the air revealed better fatigue resistanceto fatigue compared to aqueous media, according to Elnaghy and Elsaka (2017). The methodology, instrument design, and type of motion employed may all be to fault for the inconsistent outcomes.

The degree of curvature is another element that could obscure the effect of irrigation solutions on cycle fatigue. It is understood that a file moving through a steep curve experiences a significant strain amplitude, hastening the failure process (Cheung et al., 2007). A 60° curvature was used in the existing configuration. As a result, there wasn't enough time to demonstrate how a different environment (a low-fatigue region) affected things.

Hasegawa et al. (2014) revealed that when evaluated in a 60° curved environment, three separate files examined in various conditions had similar NCF results. When the files were examined under a 30° arc of curvature, water increased the NFC of the files, but a different NFC was recorded. So, it stands to reason that aqueous solution performance would be greater with longer testing periods.

It's interesting to note that two fracture sites in the NaOCl group spread toward the file's center after being launched from opposing cutting edges. This might be connected to surface roughness, which could serve as a site for crack propagation. Thus, many cracks might account for the group's lower cycle count. The short testing period is the study's main drawback. The impact of irrigation solutions in areas with high cyclic fatigue should be evaluated. Additionally, analyzing the frictional forces that each solution generates and how they might affect the NCF may be helpful.

Conclusion

The comparison between the two instruments that were tested revealed that NaOCl, glycine, and EDTA as chemical materials appeared to have noticeably different cycle fatigue resistance for various lengths of fractures and timeframes. The cyclic fatigue of NiTi files may be impacted by the irrigation environment. Chemical materials enhanced file NCF. However, due to the brief testing period (low-cyclic fatigue region), all other settings did not demonstrate any differences. Since cyclic fatigue takes far longer to develop than it does to shape actual teeth, the results of this in vitro study should not be directly applied to clinical situations. So, it's important to proceed carefully when drawing clinical conclusions. However, further research is required to fully understand the various variables that can impact an instrument's cyclic fatigue resistance, fracture modes, and novel apparatus designs that share more properties with root dentine. Further research is therefore required to support the results of the current study.

Contributor role

Conceptualization: Mohammed Hamoudi Alsunboli

Data Curation: Sally Saad Ali Ihsan

Formal Analysis: Sally Saad Ali Ihsan

Funding Acquisition: Mohammed Hamoudi Alsunboli

Investigation: Duha Qais Sabah

Methodology: Duha Qais Sabah

Project Administration: Sally Saad Ali Ihsan

Resources: Mohammed Hamoudi Alsunboli

Software: Duha Qais Sabah

Supervision: Duha Qais Sabah

Validation: Mohammed Hamoudi Alsunboli

Visualization: all authors

Writing – Original Draft Preparation: all authors

Writing – Review & Editing: all authors

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Alsunboli MH, Ihsan SSA and Sabah DQ. The effect of canal curvature on cyclic fatigue resistance of rotary instruments using different irrigation materials (in vitro study) [version 1; peer review: 3 approved with reservations]. F1000Research 2023, 12:449 (https://doi.org/10.12688/f1000research.130249.1)
NOTE: If applicable, it is important to ensure the information in square brackets after the title is included in all citations of this article.
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Key to Reviewer Statuses VIEW
ApprovedThe paper is scientifically sound in its current form and only minor, if any, improvements are suggested
Approved with reservations A number of small changes, sometimes more significant revisions are required to address specific details and improve the papers academic merit.
Not approvedFundamental flaws in the paper seriously undermine the findings and conclusions
Version 1
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PUBLISHED 27 Apr 2023
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Reviewer Report 28 Dec 2023
Mohamed Jamal, Hamdan Bin Mohammed College of Dental Medicine, Mohammed Bin Rashid University of Medicine and Health Sciences, Dubai, United Arab Emirates 
Rashid ElAbed, Hamdan Bin Mohammed College of Dental Medicine, Mohammed Bin Rashid University of Medicine and Health Sciences, Dubai, Dubai, United Arab Emirates 
Approved with Reservations
VIEWS 28
Major revision needed
 
Introduction
Add short paragraphs describing the tested files: EdgeEndo and Fanta files.
Methods:
Needs major revisions as it not very clear how the experiments were conducted. Here are few ... Continue reading
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HOW TO CITE THIS REPORT
Jamal M and ElAbed R. Reviewer Report For: The effect of canal curvature on cyclic fatigue resistance of rotary instruments using different irrigation materials (in vitro study) [version 1; peer review: 3 approved with reservations]. F1000Research 2023, 12:449 (https://doi.org/10.5256/f1000research.142991.r223743)
NOTE: it is important to ensure the information in square brackets after the title is included in all citations of this article.
  • Author Response 13 Apr 2024
    Susan F. K. Alsudani, Al-Bayan University , College of Dentistry, Iraq
    13 Apr 2024
    Author Response
    thank you Dr. Rashid ElAbed for these valuable comments
    I make grammar revisions for all articles and add your notes with highlighting
    thank you




    The effect ... Continue reading
COMMENTS ON THIS REPORT
  • Author Response 13 Apr 2024
    Susan F. K. Alsudani, Al-Bayan University , College of Dentistry, Iraq
    13 Apr 2024
    Author Response
    thank you Dr. Rashid ElAbed for these valuable comments
    I make grammar revisions for all articles and add your notes with highlighting
    thank you




    The effect ... Continue reading
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Reviewer Report 23 Dec 2023
Shehabeldin Saber, The British University in Egypt, El Shorouk City, Cairo Governorate, Egypt 
Approved with Reservations
VIEWS 22
- The manuscript need major language /grammar revision.
- It is not clear if this was a static or a dynamic test.
- limitations of the study should be added to the discussion section and should mention that ... Continue reading
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Saber S. Reviewer Report For: The effect of canal curvature on cyclic fatigue resistance of rotary instruments using different irrigation materials (in vitro study) [version 1; peer review: 3 approved with reservations]. F1000Research 2023, 12:449 (https://doi.org/10.5256/f1000research.142991.r223746)
NOTE: it is important to ensure the information in square brackets after the title is included in all citations of this article.
  • Author Response 08 May 2024
    Susan F. K. Alsudani, Al-Bayan University , College of Dentistry, Iraq
    08 May 2024
    Author Response
    thank you Dr. Shehabeldin Saber for these valuable comments
    its static test and I do it in a bath of 37 Cº
    I make grammar revisions for all articles and ... Continue reading
COMMENTS ON THIS REPORT
  • Author Response 08 May 2024
    Susan F. K. Alsudani, Al-Bayan University , College of Dentistry, Iraq
    08 May 2024
    Author Response
    thank you Dr. Shehabeldin Saber for these valuable comments
    its static test and I do it in a bath of 37 Cº
    I make grammar revisions for all articles and ... Continue reading
Views
33
Cite
Reviewer Report 13 Oct 2023
Ahmed Sleibi Mustafa, Mustansiriyah University, Baghdad, Baghdad Governorate, Iraq 
Approved with Reservations
VIEWS 33
The effect of canal curvature on cyclic fatigue resistance of rotary instruments using different irrigation materials (in vitro study)

The subject of study is of clinical value in the field of endodontics since the strategy of root canal ... Continue reading
CITE
CITE
HOW TO CITE THIS REPORT
Mustafa AS. Reviewer Report For: The effect of canal curvature on cyclic fatigue resistance of rotary instruments using different irrigation materials (in vitro study) [version 1; peer review: 3 approved with reservations]. F1000Research 2023, 12:449 (https://doi.org/10.5256/f1000research.142991.r208798)
NOTE: it is important to ensure the information in square brackets after the title is included in all citations of this article.
  • Author Response 13 Apr 2024
    Susan F. K. Alsudani, Al-Bayan University , College of Dentistry, Iraq
    13 Apr 2024
    Author Response
    Thank you Dr.Ahmed Sleibi for yout time to  this valuable notes i corrected as shown in highlighted.


    the effect of canal curvature on cyclic fatigue resistance of rotary ... Continue reading
COMMENTS ON THIS REPORT
  • Author Response 13 Apr 2024
    Susan F. K. Alsudani, Al-Bayan University , College of Dentistry, Iraq
    13 Apr 2024
    Author Response
    Thank you Dr.Ahmed Sleibi for yout time to  this valuable notes i corrected as shown in highlighted.


    the effect of canal curvature on cyclic fatigue resistance of rotary ... Continue reading

Comments on this article Comments (0)

Version 2
VERSION 2 PUBLISHED 27 Apr 2023
Comment
Alongside their report, reviewers assign a status to the article:
Approved - the paper is scientifically sound in its current form and only minor, if any, improvements are suggested
Approved with reservations - A number of small changes, sometimes more significant revisions are required to address specific details and improve the papers academic merit.
Not approved - fundamental flaws in the paper seriously undermine the findings and conclusions
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