|Year : 2021 | Volume
| Issue : 1 | Page : 25-29
A comparative evaluation of the shaping ability of four different single-file systems in severely curved mesiobuccal root canals of mandibular first molars: An in vitro study
Vivek Kumar Pathak, Rajnish K Singhal, Anurag Jain, Saurabh Mankeliya, Kaushal Singh, Ashish Sharma
Department of Conservative Dentistry and Endodontics, Maharana Pratap College of Dentistry and Research Centre, Gwalior, Madhya Pradesh, India
|Date of Submission||24-Apr-2020|
|Date of Decision||07-Jun-2020|
|Date of Acceptance||27-Jun-2020|
|Date of Web Publication||23-Mar-2021|
Dr. Vivek Kumar Pathak
B-4, Suri Nagar, Morar, Gwalior, Madhya Pradesh
Source of Support: None, Conflict of Interest: None
Aim: The aim of this study was to compare the shaping ability of four different single-file systems in severely curved mesiobuccal root canals in extracted human mandibular first molars.
Materials and Methods: Sixty extracted intact human mandibular first molars with at least one curved mesial root were collected and used for the study. The study samples (n = 60) were divided into four experimental groups (n = 15 each): WaveOne (WO) (Group I), WaveOne Gold (WOG) (Group II), OneShape (Group III), and F360 (Group IV). The working length was established. All the study samples were prepared with respective file systems according to manufacturer's instructions. Pre- and postinstrumentation radiographs were taken and images were transferred to AutoCAD 2016 to determine the radius of curvature of each root canal. The canal curvature was assessed as a difference between before and after instrumentation to determine canal straightening. The data obtained were subjected to statistical analysis using SPSS version 20.0.
Results: The pre- and postinstrumentation readings were compared using one-sample t-test, and difference was found to be statistically significant (P < 0.05). The mean difference in root curvature was estimated by pre- and postinstrumentation readings. According to mean change in the root curvature, the order determined was Group IV < III < II < I. Intergroup comparison was conducted using ANOVA statistical analysis, and it was found to be statistically significant.
Conclusion: WOG and WO reciprocating files showed a marked tendency to straighten the severely curved canals, whereas F360 and OneShape continuous files maintained the original canal curvatures well.
Keywords: Curved canals, F360, mesiobuccal root, OneShape, single file, WaveOne Gold, WaveOne
|How to cite this article:|
Pathak VK, Singhal RK, Jain A, Mankeliya S, Singh K, Sharma A. A comparative evaluation of the shaping ability of four different single-file systems in severely curved mesiobuccal root canals of mandibular first molars: An in vitro study. Endodontology 2021;33:25-9
|How to cite this URL:|
Pathak VK, Singhal RK, Jain A, Mankeliya S, Singh K, Sharma A. A comparative evaluation of the shaping ability of four different single-file systems in severely curved mesiobuccal root canals of mandibular first molars: An in vitro study. Endodontology [serial online] 2021 [cited 2021 Apr 10];33:25-9. Available from: https://www.endodontologyonweb.org/text.asp?2021/33/1/25/311748
| Introduction|| |
The biomechanical canal preparation is based on the objectives of shaping the root canals, three-dimensional cleaning, chemical disinfection, and preparing canals for final obturation., It aims to achieve the complete removal of vital or necrotic tissue while preserving the integrity, location, and apical anatomy of the canal. However, these goals are adversely influenced by the highly variable root canal anatomy.
Root canal instrumentation should preserve the existing apical foramen with a flared shape from the apical to the coronal end with no change in the original canal curvature. However, during preparation, especially in curved canals, iatrogenic errors such as a zipping, ledge, perforation, and root canal transportation can occur., Technological advancements in rotary nickel–titanium (NiTi) instruments have led to new design concepts with easier and faster techniques that preserve the original canal shape with a considerably less iatrogenic error. Numerous root canal shaping techniques with NiTi systems and different kinematics have been advanced to maintain the original canal shape, even in a severely curved canal., Single-file root canal preparation system is one of them that uses reciprocating working motion: counterclockwise (cutting direction) as well as clockwise motion (releasing of the instrument).,, OneShape and F360 are the popular single-file systems that work in a continuous clockwise rotational motion.
The other most commonly used file for curved canals is WaveOne (WO) system that consists of three files. An upgraded version of WO is WaveOne Gold (WOG) (four file systems) that provides greater flexibility than NiTi and M-wire files by changing the metallurgy of the files from M-wire to a gold alloy. It features the off-center design and parallelogram with two cutting edges, which improves the elasticity of the file.,
Till date, a limited number of studies have been carried out on WO, WOG, OneShape, and F360 single-file systems.,,, Therefore, the purpose of this in vitro study was to evaluate the shaping ability of four different single-file systems in the severely curved mesiobuccal root canal in an extracted human mandibular first molar.
| Materials and Methods|| |
Sixty extracted intact human mandibular first molars with at least one curved mesial root were collected and used for the study.
Teeth with intact mature root apices, with curvature ranging between four and nine millimeters and angle of curvature between 25° and 39°, were included in the study. Teeth that did not allow the insertion of size 15 K-file to within one millimeter of the foramen and canals wider than 20 K-file size were discarded. Teeth with developmental anomalies and vertical/horizontal root fracture were excluded from the study. Coronal access was achieved using endo access diamond burs. Standardized digital radiographs were taken using no. 15 K-file into the curved canal to assess the degree of curvature before determining the working length (WL). Each tooth was placed in radiographic mount made up of silicon-based impression material to fix film–object–source distance. The mount comprised a radiographic sensor holding paralleling device. The exposure parameters (0.08 s, 70 kv, and 8 mA) were maintained for all radiographs, and radiographic images were then transferred to AutoCAD 2016. The radius of curvature of each root canal was determined.
The study samples (n = 60) were divided into four experimental groups (n = 15 each): WO (Group I), WOG (Group II), OneShape (Group III), and F360 (Group IV). The WL was established with a size 10 K-file, using 3% sodium hypochlorite (NaOCl) as a lubricant, until the file tip become visible at the major foramen. The WL was established one millimeter short of the obtained length. Biomechanical preparation of all the study samples in all the four groups was performed by a single operator in accordance with the manufacturers instructions.
Primary WO and WOG files were operated in a reciprocating motion powered by endomotor using preset adjustments, whereas OneShape and F360 files were operated in continuous rotation motion using an electric motor with torque control. All the instruments were used in slow in-out pecking motion, with an amplitude of about 3 mm. The flutes of files were cleaned after three in-out packs. Canals were flushed with two milliliters of 3% NaOCl solution using a 30G needle that was inserted as deeply as possible into the canal without binding.
Once the rotary instrument had negotiated to the end of the canal, it was removed. Each instrument was used to prepare only one mesiobuccal canal. At the end of canal preparation, radiograph was again taken using the standardized radiographic technique. The radiographic images thus obtained were transferred to AutoCAD 2016, and the postinstrumentation radius of curvature of each root canal was determined.
To determine the straightening of canal, the change in canal curvature was assessed as a difference between before and after instrumentation. The data obtained were subjected to statistical analysis using Statistical package of Social Sciences (SPSS), Software Version 20, SPSS Inc., Chicago, IL, USA.
| Results|| |
The preinstrumentation root canal curvatures were observed for all the study samples in respective study groups, with maximum mean curvature found in Group IV, followed by Groups II, III, and I. The ANOVA statistical analysis, followed by post hoc Tukey's test, was done to analyze statistical difference in preinstrumentation readings between the four study groups, which was found to be statistically significant [Table 1]. All the study samples of respective groups were subjected to canal preparation. During the preparation of mesiobuccal curved root canals, no instrument fracture or deformation was observed. All instruments maintain the WL with no overextension.
|Table 1: Evaluation of root canal curvature of respective samples distributed in four respective groups before instrumentation|
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In all the four study groups, the postinstrumentation curvature readings were observed in triplicate. Mann–Whitney test was done to analyze the intraobserver bias that was found to be insignificant for all the four study groups, showing negligible intraobserver bias in all the four groups [Table 2]. Null hypothesis was rejected at significance level at 0.05.
|Table 2: Mann-Whitney U-test to find intraobserver bias in all four groups|
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Then, the intragroup comparison was done by comparing the pre- and postinstrumentation readings using one-sample t-test. Statistically difference was found to be significant in all the four groups (P < 0.05) [Table 3].
The mean difference in root curvature after instrumentation was calculated for all the four study groups. The minimum change in root curvature was noticed in Group IV and maximum change was observed in Group I after instrumentation. The order of mean change in the root curvature, from minimum to maximum change, was observed to be: Group IV < III < II < I. The intergroup comparison was determined to find the level of significance between mean changes between all the four groups using ANOVA statistical analysis, and it was found to be statistically significant [Table 4].
|Table 4: Intergroup comparison between mean differences in root curvature for all the study groups|
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| Discussion|| |
Mechanical instrumentation of the root canal system is an important phase of root canal preparation as it creates the space that allows irrigants and antibacterial medicaments to effectively eradicate bacteria and eliminate bacterial byproducts. Fauchard described the instruments and instrumentation technique used for canal preparation, whereas in 1892, Oltramare introduced the rotary instruments for root canal preparation. Since then, many techniques and instruments came into advent. The challenge lies in canal preparation due to the complex morphology of the root canal system. Severe canal curvatures of different degrees within the roots can lead to a variety of problems including ledge formation, separation of instruments, canal blockage, and teardrop transportation at the apex or perforation. It is essential to have such an instrument system that can maintain the original root canal morphology, even after biomechanical preparation., Various studies have been conducted from time to time that concluded that the shaping efficacy of rotary NiTi systems is good in maintaining the curvature in severely curved root canals.,, Thus in our study, we used various NiTi systems to determine change in canal curvature after instrumentation.
Various methods have been used to determine root canal curvature such as Schneider's, Weine's, Lutein and Cunningham's, and Senia's methods., However, in our study, we used canal access angle method, and we found it as effective as the Schneider angle method in evaluating root canal curvature with respect to its influence on the operation of root canal instruments. In addition, it is found to be a better method to measure the effectiveness of new root canal instruments.,
The present study compared the shaping ability of four single-file systems having different design features that were used in different working motions. The parameters assessed were the maintenance of the root canal curvature, which is a primary requisite during the preparation of curved root canals. Efforts were made to obtain anatomically comparable groups using teeth that were balanced with respect to the apical diameter and canal length.
The result of this present study revealed that Group IV (F360) and Group III (OneShape) resulted in significantly less root canal straightening than Group II (WOG) and Group I (WO). This could be because of the design of instruments like F360, having S-shaped cross-sectional design with sharp cutting edges over the entire WL, and is characterized by a relatively good shaping ability when used in full clockwise rotation., When canals were prepared with F360 and OneShape systems, less variation in canal curvature was observed. This could be because these file systems have better centering ability as compared to WO systems, as stated by a study conducted by Rashid and Saleh. It was found in many studies that reciprocating files showed a marked tendency to straighten the S-shaped canals, whereas F360 and OneShape files maintained the original canal curvatures well. Thus, single files that are less tapered should be preferred when preparing S-shaped canals because they maintain the original canal curvatures better than files having greater tapers.,
The use of NiTi files in continuous rotation, driven by an endodontic motor, is capable of speed and torque control that maintains the original pathway of the canal while limiting the amount of apically extruded debris. There are many advantages of using continuously rotating NiTi files that are being influenced by cyclic fatigue and torque, especially in longer, narrower, and more curved canals.
Among Group I (WO) and Group II (WOG) reciprocating NiTi files, Group II (WOG) files proved to create less canal straightening. This could be because WOG instruments are manufactured utilizing a new thermal process, producing superelastic NiTi file. The gold process is a postmanufacturing procedure in which the ground NiTi files are heat-treated and slowly cooled. From a technical perspective, the heat treatment modifies the transformation temperatures (austenitic start and austenitic finish), and this has a positive effect on the instrument properties. While this process gives gold finish, it considerably improves its strength and flexibility far in excess of its predecessor. It was observed in a study conducted by Webber J that the flexibility of WOG Primary was found to be 80% greater than that of WO Primary. Similar results were found in a study conducted by Takeshi et al. who also observed similar findings that the shaping ability of WOG was better than WO.
According to some studies, instruments made of M-wire alloy have an increased torsional resistance of up to 400% compared with conventional NiTi. Thus, the fact that reciprocating instruments showed no fractures under the conditions of this laboratory study can be explained by the properties of the M-wire alloy. However, it is remarkable that no fractures were observed with F360 and OneShape instruments. This could be because both are made of a conventional 55-NiTi alloy and are used in a full clockwise rotational movement. Currently, no detailed information had been given by the manufacturers on whether surface treatments were carried out to improve the mechanical properties of the instruments. This aspect warrants further investigations.
The results of this study are in agreement with several previous studies conducted by Capar et al., Bürklein et al., Takeshi et al., and Marzouk and Ghoneim. Various studies revealed that F360, OneShape, and WO maintained the original curvature of severely curved canals., Studies conducted using cone-beam computed tomographic imaging found that WO and OneShape maintained root canal curvature equally well during the preparation of mesial canals of mandibular molars.,,
Although significant differences were observed statistically regarding canal straightening, from a clinical point of view, these differences might be of no importance. Taking into account that severely curved canals were instrumented, the clinical relevance of a maximum difference in canal straightening of mere 2°–4° caused by the different instruments remains questionable. All the four instruments tested in the present study maintained the original canal curvature well, if considered clinically.
| Conclusion|| |
The present study concluded that all single-file instruments were safe to use and maintained the original canal curvature well. Within the parameters of this study, WOG and WO reciprocating files showed a marked tendency to straighten the severely curved canals, whereas F360 and OneShape continuous files maintained the original canal curvatures well. Single files that are less tapered should be preferred when preparing severely curved canals because they maintain the original canal curvatures better than files having greater tapers. Further investigations are required to assess and compare the shaping ability of new WOG single-file systems with other continuous rotary NiTi systems.
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Conflicts of interest
There are no conflicts of interest.
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[Table 1], [Table 2], [Table 3], [Table 4]