|Year : 2020 | Volume
| Issue : 2 | Page : 158-162
Comparison of cyclic fatigue resistance of three NiTi glide path files with different cross-sectional geometric characteristics: An in vitro experimental study
Department of Restorative and Prosthetic Dental Sciences, College of Dentistry, King Saud bin Abdulaziz University for Health Sciences, King Abdullah International Medical Research Center, Ministry of National Guard Health Affairs, Riyadh, Kingdom of Saudi Arabia
|Date of Submission||23-Jul-2019|
|Date of Acceptance||04-Nov-2019|
|Date of Web Publication||28-Mar-2020|
Dr. Abdulmohsen Alfadley
Department of Restorative and Prosthetic Dental Sciences, College of Dentistry, King Saud bin Abdulaziz University for Health Sciences, Ministry of National Guard Health Affairs, P.O. Box: 22490, Riyadh 11426.
Kingdom of Saudi Arabia
Source of Support: None, Conflict of Interest: None
Aim: New nickel-titanium file systems with improved fatigue resistance are being introduced to the market. This study aimed to compare the cyclic fatigue resistance (CFR) of G1 (#12) file of G file system (Micro Mega, Besançon, France), ProGlider (Dentsply Maillefer, Ballaigues, Switzerland) single-file rotary pathfinding system, and the #13 file of the Flex Glide system (Neoendo, Gurugram, India). Materials and Methods: Each group had a sample size of 10 files. The cyclic fatigue test was conducted in an artificial stainless steel canal in a customized device. The artificial canal contained an inner diameter of 1.5 mm with 60° angle of curvature and 5 mm radius of curvature. The file tip was positioned at 18 mm with a stopper and then rotation began, synchronized with timing by a digital stopwatch (Timex, Middlebury, CT) to the thousandth of a second. The center of the curvature was located at 7 mm from the tip of the device. For each instrument, time to fracture and the number cycles to fracture (NCF) were recorded. The data were analyzed statistically. Results: ProGlider files had a significantly higher resistance to cyclic fatigue than G1 files, which in turn had significantly higher CFR than Flex Glide instruments (P < 0.05). The lengths of the fractured segment of ProGlider files and G1 files were significantly higher than the Flex Glide files. Conclusion: Thus, it can be inferred that the ProGlider files had the highest resistance to cyclic fatigue and can be advocated for glide path preparations in severely curved canals.
Keywords: Cyclic Fatigue Resistance, Flex Glide System, G File System, ProGlider
|How to cite this article:|
Alfadley A. Comparison of cyclic fatigue resistance of three NiTi glide path files with different cross-sectional geometric characteristics: An in vitro experimental study. J Int Oral Health 2020;12:158-62
|How to cite this URL:|
Alfadley A. Comparison of cyclic fatigue resistance of three NiTi glide path files with different cross-sectional geometric characteristics: An in vitro experimental study. J Int Oral Health [serial online] 2020 [cited 2020 May 28];12:158-62. Available from: http://www.jioh.org/text.asp?2020/12/2/158/281485
| Introduction|| |
Nickel-titanium rotary (NTR) files have brought about a paradigm shift in the biomechanical preparation process. The superelastic property of NTR has allowed greater flexibility and in turn greater ease of negotiating severely curved canals. However, one of the main drawbacks with NTR files is instrument fracture. Torsional fatigue and cyclic fatigue are the two modes of instrument separation., Among the two modes, cyclic/flexural fatigue has been implicated in the majority of the fractured instruments.
The establishment of a glide path during endodontic treatment is imperative for an error-free shaping of the canal. Smooth, reproducible glide path minimizes the torsional fatigue of the rotary shaping files and subsequently reduces its fracture tendency. Several NTR instruments for glide path preparation have been introduced in recent times in order to facilitate canal shaping procedures. Newer manufacturing processes with proprietary technological advancements are incorporated in the production of glide path files which improve their ability to negotiate constricted canals.
Elnaghy and Elsaka compared the cyclic fatigue resistance (CFR) of One Shape (OS; Micro-Méga, Besançon, France) size 25, .06 taper instrument used in continuous rotation with WaveOne (WO; Dentsply Sirona, Ballaigues, Switzerland) size 25, .08 taper operated in reciprocating motion in simulated canals. The results showed that WO instrument used in reciprocating motion had a greater resistance to cyclic fatigue. However, Karatas et al. found that instruments working in rotary motion (OS) had a greater CFR than instruments working in reciprocating motion (WO Primary).
G1 (#12) file of G file system (Micro Mega, France) is a glide path file that is made of a conventional NiTi alloy. It has an asymmetric cross-section, with three cutting blades. It has an electropolished surface with a constant taper of 3% throughout the shaft. ProGlider (Dentsply Sirona, Switzerland) is a single-file rotary pathfinding system manufactured from heat-treated M-wire alloy with a progressive taper from 2% to 8% over its length and a square cross-section. The #13 file of the Flex Glide system (Neoendo, Gurugram, India) undergoes a proprietary heat treatment, and has a triangular cross-section with 2% taper and 0.13 mm tip size.
To the best of our knowledge, the cyclic fatigue behavior of this system was not adequately examined before. Thus, the aim of this study was to compare the CFR of Flex Glide files in relation to the ProGlider and G1 file systems. The null hypothesis states that there are no significant differences between the three systems in the mean NCF.
| Materials and Methods|| |
This study is an in vitro analysis of the CFR of different rotary file systems. A sample size calculation for an effect size of 1.3 based on preliminary data comparing G1 and ProGlider files indicated at least 10 samples per group would be needed to achieve 95% power.
Samples were randomly selected from new packs for all three test groups; G1 (#12) file of the G file system, ProGlider, and the #13 file of Flex Glide system. Every file was examined to confirm absence of defects prior to its involvement in the study. The cyclic fatigue test was conducted in an artificial stainless steel canal in a customized device. The artificial canal has an inner diameter of 1.5 mm with 60° angle of curvature and 5 mm radius of curvature. The center of the curvature was located at 7 mm from the tip of the device. The files were operated using a torque controlled endodontic motor (VDW Gold; VDW, Munich, Germany) according to the manufacturer instructions. High-flow synthetic oil designed for lubrication of mechanical parts (SuperOil, Singer, Elizabethport, NJ) was applied to minimize the friction of the file during its rotation inside the artificial canal walls. The file tip was positioned at 18 mm with a stopper and then rotation began, synchronized with timing by a digital stopwatch (Timex, Middlebury, CT) to the thousandth of a second.
CFR was the parameter assessed in the study. For each instrument, time to fracture in seconds from the start of the test until the moment of breakage was recorded and the number cycles to fracture (NCF) was noted. The NCF for each file was calculated as follows:
NCF = rpm × Time to fracture (seconds) / 60.
The length of the fractured fragment was measured with a digital microcaliper. No other failures occurred during the study.
Mean values and standard deviation (SD) were calculated. The data were analyzed statistically using a two-way analysis of variance and Bonferroni’s post hoc tests for multiple comparisons at 0.05 level of significance. Data analysis was performed using the Statistical Package for the Social Sciences software, version 16.0 (SPSS, Chicago, IL).
| Results|| |
The mean and SD of the NCF and the length of the fractured fragment for each brand are presented in [Table 1]. ProGlider files had a significantly higher resistance to cyclic fatigue than G1 files which in turn had significantly higher CFR than Flex Glide instruments (P < 0.05). The lengths of the fractured segment of ProGlider files and G1 files were significantly higher than the Flex Glide files. No significant difference was found in the mean length of the fractured fragments between G1 and ProGlider files [Table 2][Table 3][Table 4][Table 5]., ,
|Table 3: Post hoc test multiple comparisons for number of cycles to fracture|
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|Table 5: Post hoc tests––multiple comparisons: dependent variable: fragment length|
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| Discussion|| |
The device used in this study was used in other studies.,,, Instrument separation in rotary endodontics poses a significant challenge and is one of the reasons of treatment failure. The numerous properties that influence the flexibility of NTR instruments are metal alloy, instrument geometry, composition, and thermomechanical treatment of the metal alloy.,, Of the various mechanical attributes of glide path preparation instruments, CFR is very critical. Fracture in files owing to cyclic fatigue occurs because of tension–compression cycles occurring in succession during instrumentation. The more complex the root canal, the more adverse are the effects on the CFR of the instruments. Literature search reveals that there are several tests for evaluating the CFR. The rotational bending test using artificial canals is the commonest method of fatigue testing of NiTi rotary instruments.
In agreement with other studies, ProGlider files exhibited higher resistance to cyclic fatigue than the other systems. ProGlider files are manufactured using M-Wire NiTi, whereas Flex Glide and G1 files are made from conventional NiTi alloy. The M-Wire technology has been proven to impart greater flexibility and resistance to cyclic fatigue than those made of regular superelastic wire. Gao et al. postulated that the multiphase microstructure of martensite, austenite, and R phase of M-wire increased the bending resistance as compared to conventional NiTi alloy comprising only austenite component. The rationale for this could be the superior reorientation and accommodation of deformation ability of the martensitic variants because of the lower symmetry of the monoclinic crystal structure of martensite than the cubic crystal structure of austenite. Another reason for the superior performance of ProGlider files may be attributed to its square cross-section which makes its core thinner, decreasing the strain on the files as compared to the triangular cross-section files with thicker core. Similar results were also reported by Uslu et al. who also found that ProGlider files performed better than G1 files. Zhang et al. showed that NiTi files with a triangular cross-section had lower resistance to fracture than files with square cross-section, which were similar to our findings where ProGlider files with square cross-section had highest CFR compared to asymmetrical and triangular cross-sectional files. Furthermore, the heat treatment of the files might have also increased its CFR. Heat treatment of files was shown to influence the flexibility and increase the life span of instruments.,,,
The results also revealed that G1 files performed better than Flex Glide files, which could be explained by the fact that these files have an asymmetrical triangular cross-section as opposed to the triangular cross-section of Neoendo Flex Glide files. Our results were in accordance with the previous study conducted by Sung et al., which reported that 3% G1 files had higher CFR as compared to 2% pathfiles. Also asymmetrical cross-sectional geometry of G1 files provides a variable pitch which minimize the screwing effect and file separation, whereas Flex Glide file’s triangular cross-section with sharp cutting edges and no radial lands may accelerate the screwing potential leading to early separation of files.
This study showed that files fractured at different points of their working length contrary to many studies which fractured almost at the same level. This results are in accordance with a study conducted by Capar et al., which showed that different file systems subjected to same cyclic fatigue testing methods fractured at different location on the files. The reasons attributed to this behavior of files are as follows: difference in bending moments of the files, different types of alloys from which they are manufactured, and presence of different degrees of tapers between the file systems. Also another reason that can be attributed to the varied fracture points is that as the files fit loosely within the testing apparatus they follow different type of curvature depending upon their stiffness. G1 files were compared with Edge glide path files by Lee et al., who found that G1 heat-treated wire showed higher cyclic fatigue resistance than conventional wire and M-Wire.
The difference between the measured lengths of the fractured segment of ProGlider and G1 files was not statistically significant; however, the ProGlider file and G1 had statistically significant longer length of the fractured apical segment as compared to the Flex Glide group. This could be because of the cross-section of the core of the various files. The metal volume in the point of maximum stress during a cyclic fatigue test affects the fatigue life of NiTi rotary instruments. The larger the metal volume, the lower the fatigue resistance., Thus, Flex Glide files with its triangular cross-section having larger core mass lead to its fracture at more lower/apical levels than the other two systems.
Although triangular cross-sectional geometry increases the flexibility allowing the files to pass along the root canal curvature in an effective way, this characteristic also increases the vulnerability for undesirable deformation at high rotational speeds. Various stress analysis studies showed bending moment caused stress to be more concentrated on the tip leading to separation of files closer to the tip at more apical level. This attribute can account for the more apical fracture level of Flex Glide files than the other two file systems. The clinicians must be aware of the different mechanical proprieties of the instruments in order to select the most appropriate instrument according to particular canal configurations. The limitation of this study is that it was performed under in vitro conditions. A further clinical study is planned to overcome this issue.
Within the limitations of this study, it can be inferred that the ProGlider files had the highest resistance to cyclic fatigue and can be advocated for glide path preparations in severely curved canals. Also G1 files performed better than Flex Glide files. It becomes imperative on the dentist part to select files based on their material type, taper, and cross-sectional geometry considering the various subjective clinical conditions which includes canal constriction, curvature, and taper.
Data availability statement
The data set used in this study is available on request from Dr. Abdulmohsen Alfadley (Fadleya@Ksau-hs.edu.sa).
Financial support and sponsorship
Conflicts of interest
There are no conflicts of interest.
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[Table 1], [Table 2], [Table 3], [Table 4], [Table 5]