|Year : 2019 | Volume
| Issue : 3 | Page : 161-168
Shaping ability of ProTaper Next and Navigator EVO rotary nickel–titanium file systems in simulated L-shaped and S-shaped root canals
Mashael Obaid Alshahrani1, Mohammad Al-Omari2
1 Department of Endodontics, Northern Riyadh Dental Complex, Ministry of Health, Riyadh, Kingdom of Saudi Arabia
2 Department of Endodontics, Restorative Dentistry, Riyadh Elm University, Riyadh, Kingdom of Saudi Arabia
|Date of Web Publication||16-Aug-2019|
Dr. Mashael Obaid Alshahrani
Department of Endodontics, Northern Riyadh Dental Complex, Ministry of Health, P.O. Box 3982 AlFirdaws, Unit 1, Riyadh 13316-6685
Kingdom of Saudi Arabia
Source of Support: None, Conflict of Interest: None
Objective: The objective of this study is to evaluate and compare the shaping ability of ProTaper Next (PTN) and Navigator EVO (N-Evo) rotary file systems in L- and S-shaped simulated resin root canals.
Materials and Methods: A total of forty L-shaped (n = 20) and S-shaped (n = 20) resin block root canals were randomly assigned into four groups (n = 10) based on the PTN and N-Evo rotary file systems. Before the instrumentation, simulated root canals were filled with the India blue ink and preinstrumentation images were taken using a digital camera. Each canal was prepared to the standard working length 16 mm, 0.15 mm apical foramen diameter, and 0.2 initial tapers. After the canal preparation, red India ink was filled in each canal and postoperative images were obtained. The two images were superimposed, five points were selected, and canal widths were measured with image analysis software. Canal preparation time, file failure, and presence of aberrations were recorded and compared between the two systems. Descriptive statistics of mean and standard deviation and inferential statistics of Independent samples t-test and analysis of variance tests were applied to the data.
Results: PTN file system showed significantly lesser preparation time (L-shape, 2.55 ± 0.38 min, and S-shape, 2.57 ± 0.44 min) in comparison to N-Evo file system (L-shape, 5.01 ± 0.37 min, and S-shape, 5.21 ± 0.30 min) (P < 0.001). N-Evo file removed significantly less resin in many positions and exhibited lesser canal straightening in both S- and L-types of canals compared to the PTN file system (P < 0.05). Both file systems created danger zone and outer widening of the canal. Three N-Evo files fractured in L-shaped canals.
Conclusions: N-Evo file system demonstrated better shaping ability compared to PTN in L- and S-shaped simulated canals. PTN file system prepared the canal in less time and maintained the original curvature. An almost similar number of canal aberrations found between tested file systems. However, three N-Evo files broke in L-shaped canals indicating possible limitation in this area.
Keywords: Canal aberration, L-shaped root canal, Navigator EVO, preparation time, ProTaper Next, S-shaped root canal
|How to cite this article:|
Alshahrani MO, Al-Omari M. Shaping ability of ProTaper Next and Navigator EVO rotary nickel–titanium file systems in simulated L-shaped and S-shaped root canals. Saudi Endod J 2019;9:161-8
|How to cite this URL:|
Alshahrani MO, Al-Omari M. Shaping ability of ProTaper Next and Navigator EVO rotary nickel–titanium file systems in simulated L-shaped and S-shaped root canals. Saudi Endod J [serial online] 2019 [cited 2020 Jun 5];9:161-8. Available from: http://www.saudiendodj.com/text.asp?2019/9/3/161/264640
| Introduction|| |
The principal objective of endodontic treatment is cleaning and shaping of the root canal space. The success of root canal treatment (RCT) depends on the removal of intracanal microorganisms. However, these microorganisms cannot be effectively removed unless the canal space is adequately prepared and disinfected with the use of the irrigant solution. The preparation of canal space is aimed at the removal of microorganisms, remaining pulp tissue, and dentin debris from the root canal system.
Originally, stainless steel endodontic hand files were used to achieve the goal of canal preparation. However, due to the stiff nature of stainless steel, these files did not serve the purpose, especially in the curved canals, and led to procedural errors such as canal transportation, apical zipping, canal ledges, and strip perforations. Recent advancement in endodontic file design, concepts, and root canal preparation techniques to receive filling material has completely modified the perspective of RCT.
A major breakthrough in the root canal preparation technique was achieved with the introduction of nickel–titanium (NiTi) alloy files in endodontics. It is considered a significant milestone in the development of endodontic treatment. Walia et al. first presented the NiTi canal preparation files in 1988 to overcome the rigidity of stainless steel files that do not possess shape memory and were not resistant to torsion. NiTi files prepared the canal easier and faster, thereby reducing the patient and operator fatigue. In addition, the original canal shape was maintained with significantly less iatrogenic errors. The scientific literature is abundant with studies on the numerous features of NiTi file's performance in canal preparation. This is attributed to the elastic nature of the NiTi files that have led to the reduced procedural errors during root canal preparation.
ProTaper Next (PTN) (Dentsply Maillefer, Ballaigues, Switzerland) files show a rectangular cross-sectional design for higher strength and special asymmetric rotary motion that improves canal-shaping effectiveness as supposed by the manufacturer. PTN files are manufactured using M-wire NiTi to improve flexibility and cyclic fatigue resistance. On the other hand, the Navigator EVO (N-Evo) file system (Medin, Nove Mesto na Morave, Czech Republic) consists of the new generation of the Wizard Navigator system (Medin). This system presents a triangular cross section and an inactive tip to assist the file trajectory along the root canal. The N-Evo files exhibit great flexibility and fatigue resistance because of thermal treatment of NiTi, as assumed by the manufacturer. Moreover, continuous rotation is the recommended kinematics for this file system. N-Evo files can be reused and resterilized easily.
To the best of our understanding, the shaping abilities of newly introduced PTN and N-Evo files systems have not been thoroughly investigated under standard root canal conditions. Further, the knowledge of the shaping ability of these endodontic file systems and their effect on file performance is important for the practitioner to select the files giving a perfect canal preparation outcome.
Hence, thisin vitro study aimed to evaluate and compare the shaping ability of PTN and N-Evo rotary file systems in L- and S-shaped simulated root canals in resin blocks.
| Materials and Methods|| |
The study design was approved by the Research Center of College of Dentistry, Riyadh Elm University, Riyadh, Saudi Arabia (RC/IRB/2018/1619), and its ethics committee.
A total of 40 simulated, S-shaped (n = 20), and L-shaped (n = 20) root canals in resin blocks (Endo Training Bloc, Dentsply, Maillefer, Tulsa, OK, USA) were selected in this study. These clear polyester resin blocks were then randomly assigned into four equal experimental groups (Group 1: PTN S-shaped canal [n = 10], Group 2: PTN L-shaped canal [n = 10], Group 3: N-Evo S-shaped canal [n = 10], and Group 4: N-Evo L-shaped canal [n = 10]) based on the NiTi rotary file system used for the preparation canal type.
Standardization of the simulated root canals
The standardization of each resin block was strictly ensured by considering canal length 16 mm, diameter of apical foramen 0.15 mm, initial taper 0.2, coronal radius 5 mm, coronal angle of curvature 35°, apical radius 4.5 mm, and apical angle of curvature 30°.
Evaluation of canal preparation
A metal pin was used to code each resin block by carving the assigned number on the outer surface of the canal, and four vertical orientation grooves were also marked away from the canal onto serve as an identification point for subsequent image analysis. Before experimental instrumentation of the resin blocks, all simulated canals were stained with India blue ink (Faber-Castell, Stein, Germany) using a 30-gauge insulin syringe. K-file no. 8 (Dentsply, Maillefer, Tulsa, OK) was inserted into the canal to allow uniform penetration of the ink within the simulated canal system and to prevent air bubble formation.
A stable platform for mounting camera was prepared at a fixed distance and at an angle of 90o to the resin block. All the images were captured using a digital camera (D 3300, Nikon, Tokyo, Japan). In this way, pre- and postcanal preparation images could be superimposed. Fixed distance of the camera also eliminated the doubt of distortion and magnification of the subsequent images and guaranteed image standardization.
All the resin blocks were stored for 48 h to air dry the India blue ink. A special holder was prepared to hold and cover each resin block using vinyl polysiloxane impression material to facilitate blind preparation of the canals to mimic the clinical setup during canal instrumentation. PTN and N-Evo files were attached to an endodontic torque-limited electric motor (ENDO-Mate DT, NSK, Tokyo, Japan).
Before using the PTN system, as per the manufacturer's instruction, a glide path was shaped with ProGlider file (Dentsply, Maillefer, Ballaigues, Switzerland) to the full working length of 16 mm. Then, the canals were prepared with X1 (17/04) and X2 (25/06) files for a working length of 16 mm. The endomotor was set according to the recommended torque of 2.0 N cm and rotation speed of 300 rpm. For the N-Evo file system, W-1 (10/04), W-2 (15/05), W-3 (20/06) and W-4 (25/06) rotary files were used in sequence to prepare the simulated canals (WL = 16 mm). The endomotor was set according to the recommended torque of 1.2 N cm for (W-1 and W-2) and 2.1 N cm for (W-3 and W-4) and a rotational speed of 300 rpm for all files in a continuous motion. The canal debris was flushed out using copious amount of distilled water with a 27-gauge needle. Flutes of the files were cleaned with gauze wetted with Glyde agent after every three cycles. Every rotary file was replaced with a new file after three canal preparations. Glyde File Prep™ (Dentsply, Maillefer, Tulsa, OK, USA) was used in all canals as a lubricating agent. After completion of the preparation, red India ink was filled in every canal, and postoperative photographs were taken similar to preoperative photographs. Pre- and postcanal instrumentation images were superimposed to create a single-composite image using Photoshop Elements ver. 7.0 software (Adobe System Inc., San Jose, CA, USA), as shown in [Figure 1]a and [Figure 2]a. Further measurement of the variables was performed using image analysis software (image J). All the images were desaturated and saved as JPEG format at a resolution of 4080 × 3072 at 300 dpi. The grid image of the platform ensured precise matching of pre- and postinstrumented simulated canal blocks. The following observations were recorded for each composite image.
|Figure 1: Superimposition image of L-shaped canal (a) and a composite image of L-shaped canal after defining the measurement positions in image (Image J) analysis software (b).|
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|Figure 2: Superimposition image of S-shaped canal (a) and the composite image of S-shaped canal after defining the measurement positions in image (Image J) analysis software (b)|
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Root canal preparation time
Time taken for preparation of each canal was recorded to the nearest second. It includes time taken by instrumentation and instrument changes during sequential filing, cleaning of the flutes, and irrigation of the canal and stopped when the sequence of the file is finished.
Failure of instruments
The number and size of fractured or deformed of instruments, for example, rollup or unwinding were recorded with the help of magnifying loops ×4.
Using the superimposed image with the image magnification × 4, the following root canal aberrations were used:
- Apical zipping
- Elbow formation
- Canal ledge
- Danger zone
- Outer widening.
The aberrations were made by an endodontist and postgraduate endodontic resident, and they were selected after careful review of the literature.
The amount of resin removed during preparation with two different filing systems was recorded at five points along the canal length of each simulated resin blocks. The measurement lines were placed on the image according to the method suggested by Alodeh and Dummer. The total, inner, and outer measurement of widths was carried out using the image analysis software program (Image J) along the following positions of L-shaped canals:
- Canal orifice (O)
- Halfway from the orifice to the beginning of the curve (HO)
- The beginning of the curve (BC)
- An apex of the curve (AC)
- 0.5-mm short of root apex (EP).
On each composite image of L-shaped canal, measurement positions were defined, and image analysis was performed using a software program (Image J) [Figure 1]b.
For the S-shaped canals, the following five positions were evaluated:
- Halfway of the straight part of the canal (A)
- The beginning of the curve (B)
- An apex of the first curve (C)
- An apex of the second curve (D)
- Apical end (E).
On each composite image of the S-shaped canal, measurement positions were defined, and image analysis was performed using a software program (Image J) [Figure 2]b.
All the collected data were entered analyzed using the Statistical Package for the Social Sciences (IBM-SPSS, version 23, Shanghai, China). Descriptive statistics of frequency distribution, mean, and standard deviation were calculated for the variables measured for all the groups. Assuming normal distribution of the data, parametric tests were applied to compare the variables. Analysis of variance test was applied to compare the mean canal preparation time across four groups (S- and L-shaped canals prepared by PTN file system and S- and L-shaped canals prepared by N-Evo file system). Further, Scheffe's post hoc tests were performed to find the significant differences in canal preparation time between the groups. Independent samples t-test was used to compare the total mean canal width at different positions of S- and L-shaped canals after preparation with PTN and N-Evo file systems. For all statistical purposes, a level of significance was set at P < 0.05.
| Results|| |
Canal preparation time
PTN file system showed significantly lesser preparation time (L-shape, 2.55 ± 0.38 min, and S-shape, 2.57 ± 0.44 min) in comparison to N-Evo file system (L-shape, 5.01 ± 0.37 min, and S-shape, 5.21 ± 0.30 min) (P < 0.001). Further, analysis by Scheffe's pair-wise multiple comparisons between the different groups showed a significant difference (P < 0.001) in mean canal preparation times (in minutes) between PTN in L-shaped canals and N-Evo in L-shaped canals and also PTN in L-shaped canals and N-Evo in S-shaped canals. A significant difference in mean canal preparation times between PTN in S-shaped canals and N-Evo in L-shaped canals and also PTN in S-shaped canals and N-Evo in S-shaped canals (P < 0.001) was observed [Figure 3].
|Figure 3: Mean values of canal preparation time in tested groups (*indicates P < 0.05)|
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Canal aberration and file fracture
Overall PTN and N-Evo file systems did not produce any apical zipping, elbow, ledging, and perforations in L- and S-shaped root canals. However, a single case of outer widening was observed with both the file systems (PTN with S-shaped canal and N-Evo with L-shaped canal). Excess removal of the resin material from the inner canal curve was observed in both the file systems. PTN file system showed the excess removal of the resin material in 2 cases (20%) of L-shaped canals and 1 case (10%) of S-shaped canals. Similarly, N-Evo file system produced 2 (20%) such cases in S-shaped canals. However, there was no over instrumentation with N-Evo file system which was reported in the danger zone of L-shaped canals. Three N-Evo files fractured in the apical part during the preparation of L-shaped canals. On the contrary, none of the other systems exhibited file fracture during the canal preparation process. Both the PTN and N-Evo systems did not show any unwinding or rollup, as shown in [Table 1].
|Table 1: Incidence of canal aberrations and file fracture among the tested groups|
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Total canal width in L-shaped canals
The total width of the L-shaped canals differed at various positions of the canal after preparation with PTN and N-Evo file systems. The canal position at HO, PTN (0.7477 ± 0.045 mm) exhibited significantly higher total canal width compared to the N-Evo (0.7056 ± 0.031 mm) file system (t = 2.401, P = 0.027). Similarly, at BC, PTN (0.6017 ± 0.065 mm) demonstrated significantly higher total canal width compared to the N-Evo (0.5344 ± 0.033 mm) file system (t = 2.895, P = 0.010). At the apex of the curve, PTN (0.4975 ± 0.050 mm) showed significantly higher total canal width compared to the N-Evo (0.4516 ± 0.031 mm) file systems (t = 2.443, P = 0.025). On the contrary, at O, PTN (0.863 ± 0.047 mm) showed marginally increased total canal width compared to the N-Evo file (0.8363 ± 0.048 mm) systems without any statistically significant difference (t = 1.269, P = 0.221). Similarly, at the position 0.5 mm (EP), PTN (0.3073 ± 0.048 mm) exhibited somewhat higher total canal width compared to the N-Evo file (0.2672 ± 0.086 mm) systems without any statistically significant difference (t = 1.274, P = 0.219), as shown in [Table 2].
|Table 2: Total canal width measurement (mm) of tested groups at different canal positions in L-shaped resin canal|
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Total canal width in S-shaped canals
A total width of S-shaped canals differed at various positions along the canal. At the apical end of the canal, PTN (0.222 ± 0.085 mm) exhibited significantly higher total canal width compared to the N-Evo (0.159 ± 0.023 mm) file system (t = 2.245, P = 0.038). On the contrary, total width of S-shaped canals at halfway of the straight part of canal (A, P = 0.951), beginning of the curve (B, P = 0.700), apex of the first curve (C, P = 0.743), and apex of the second curve (D, P = 0.671) did not differ significantly between PTN and N-Evo file systems as shown in [Table 3].
|Table 3: Total canal width measurement (mm) of tested groups at different positions for S-shaped canals|
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| Discussion|| |
The purpose of thisin vitro study was to assess the mechanical shaping ability of PTN and N-Evo file systems. The key elements in good root canal shaping of an endodontic file rely mostly on its centering ability within the canal space. Hence, L- and S-shaped curve canals were selected and prepared with PTN and N-Evo systems and evaluated for canal preparation time, number of aberrations, and the total width of the canal at various positions.
For the standardization of the experimental groups, simulated resin canals preferred over the natural teeth since the simulated resin canals allow a high degree of reproducibility as well as fixed curvature, angle, and diameter. Therefore, use of simulated canals avoided the variability observed in the canal dimension and morphology of extracted natural teeth.
Several approaches have been used to assess the final shape of the root canal after mechanical preparation. These include analysis with a stereomicroscope, serial sectioning technique, microcomputed tomography, and radiographic imaging. However, each of these techniques has their own advantages and disadvantages. Sectioning of the teeth is complicated, invasive, and may result in loss of material. Microcomputed tomography is not cost-effective. Alternatively, imaging technique using Adobe Photoshop program accurately details the outline of the original preoperative canal and the postoperative canal. Hence, by measuring the variation in width between the pre- and postoperative images, it was possible to compute the amount of resin material removed. However, resin canals lack inherent variations in hardness, water content, and smear layer formation during instrumentation. Although resin does not seem to be an ideal dentin replacement, the material can perform consistently in terms of hardness and dimensional stability. Using the different colored inks for pre- and postoperative imaging may allow increased precision in canal width measurement without destruction of the sample. In addition, a torque-limited electric motor was used to prevent the fracture of the endodontic file as it rotates the file in an inverted direction after the file locked in the canal.
Newly manufactured thermomechanically treated alloy rotary system provided distinctive characteristics of flexibility and fatigue resistance to the files. However, limited studies have been undertaken to assess the influence of these properties on shaping ability of the new rotary files mainly due to the disparity in assessment criteria. To the best of our knowledge, this is the first study that evaluated and compared the shaping abilities of N-Evo files system with the PTN files system. Moreover, L- and S-shaped canals were concurrently investigated in this study. Variation in the amount of resin removed from the canals at five different positions was also measured in this study., File system that produced less straightening the canal curvature in these defined positions was considered to have superior shaping ability because of less canal transportation and better perseveration of the original canal anatomy.
In this study, PTN and N-Evo systems prepared the canals with no apical aberrations (perforation, ledges, zip, and elbow formation) due to the noncutting tips that facilitate the guidance of the file inside the curved portion of the canal.
Analyzing the total canal width for PTN and N-Evo file systems, our study results suggested that the apical transportation of the root apex was within the safe range of 0.15–0.30 mm. In contrast, previous studies have reported >0.30 mm root apex transportation that may have numerous adverse effects on the apical seal., However, a statistically significant difference between PTN and N-Evo file systems with regard to total canal width was suggestive of the fact that the PTN has a tendency of thinning the wall at the beginning of the canal curve and may lead of strip perforation in vivo. In severely curved canals, the creation of zips and excessive widening might be seen along the inner aspect of curves with these files.
Our study finding suggests that PTN file has the potential to induce canal transportation at the beginning curve and apex of the curve with minimal removal of the resin material. This justifies the absence of detectable zipping and perforation in the L-shaped canal. The other possible explanation of the finding could be the cross-sectional design of the file and the fabrication technique of files using M-wire technology. The use of ProGlider file before the instrumentation with PTN file system could have helped in avoiding zips and strip perforation. The usefulness of the glide path with ProGlider in circumvention of canal aberrations when using the PTN file system was already reported in the literature.
The findings of the current study are in line with the previous studies,,,, in which the PTN system showed less tendency of canal transportation, better centering ability at all the five measured positions, and preserving the original curvature of the canal. The file systems used in this study are made up of similar metal alloys, but their manufacturing process is different. PTN is based on M-wire technology whereas N-Evo system is based on thermally treated NiTi technology. N-Evo rotary file system has been introduced recently with no enough previous data to compare the findings of this study.
In the present study, canal aberrations produced by PTN and N-Evo were analyzed to know the critical degree of curvature; these file systems can be used safely. N-Evo files fractured in 30% of the samples during the preparation of L-shaped canals. This indicated that the great care should be taken while preparing the canals with severe curvature due to the increased probabilities of file deformation and file fractures. The manufacturer claimed that N-Evo file system has 32% more flexibility and 47% more lifespan than its predecessor Wizard Navigator. Hence, N-Evo file system should be avoided in more curved canals. On the contrary, manufacturer's claim of elimination of zip-elbow, ledge, and stripping found to be convincing as not a single zip and elbow formation, ledging, and strip perforation was observed in with the N-Evo file system.
On the other hand, PTN was found to be reliable and efficient file system in shaping the S-shaped and L-shaped canals. This suggests that PTN files are more durable than the N-Evo file system. Moreover, the role of ProGlider is commendable in this study as the previous reports have already concluded that the glide path using ProGlider demonstrated better performance and fewer canal aberrations compared to PTN file system alone. However, 20% of the samples showed the excess removal of resin along the inner curvature of the canal leading to stripping perforation at the danger zone. The excessive widening of the canal along the inner curvature might be caused by the indiscriminate and uncontrolled action of these files within curved canals.
Evaluation of the canal preparation time provides useful information about the performance of endodontic files. In our study, the time required to prepare S- and L-shaped root canals by PTN and N-Evo file system was recorded. It was obvious that the PTN was more efficient in preparation L- and S-shaped canals. This could be due to the design of the file system that contacts the canal wall at two points in given cross section, thereby minimizing the contact area between file and canal wall in unique asymmetrical rotary motion.
On the contrary, the considerable time taken by the N-Evo files was due to the fact that it consists of four files (W-1, W-2, W-3, and W-4) and a greater number of file changes made during the canal preparation. While PTN system consisted of only two-files (X1 and X2) and required lesser number of file changes during the canal preparation. This could be the reason for the speedy canal preparation observed in PTN file system.
This was anin vitro study conducted using simulated resin canal blocks. Therefore, the study finding might not be correlated with the clinical performance of the PTN and N-Evo file system. The simulated resin canals may not match the different anatomical configurations and dentine hardness of real tooth structure. In this study, endodontic files prepared the simulated canal in three dimensions, and the shaping ability was assessed based on two-dimensional findings. Hence, this method did not resemble the real three-dimensional analysis of the canal.
| Conclusions|| |
Within the limitations of the study, it can be concluded that N-Evo file system demonstrated better shaping ability compared to the PTN file system in L- and S-shaped resin-simulated canals. PTN file system prepared the canal in short time and maintained the original curvature of the canal. The almost similar number of canal aberrations was produced by PTN and N-Evo file systems. PTN file system is safe to use in severely curved canals as none of the files fractured during the canal preparation. PTN file system is recommended to use in severely curved root canals and to reduce patient and operator fatigue during the canal preparation. However, three N-Evo files broke in L-shaped canals indicating possible limitation in L-shaped canals. Future studies with three-dimensional analysis of simulated canals are needed to confirm the findings of the current study.
Financial support and sponsorship
Conflicts of interest
There are no conflicts of interest.
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[Figure 1], [Figure 2], [Figure 3]
[Table 1], [Table 2], [Table 3]