|Year : 2020 | Volume
| Issue : 4 | Page : 198-203
Evaluation of canal transportation and centering ability in mesiobuccal canals of maxillary molars using two Ni-Ti file systems: An ex-vivo micro-computed tomographic study
Anuradha Vijay Sawardeker, Aseem Prakash Tikku, Ramesh Bharti, Rhythm Bains
Department of Conservative Dentistry and Endodontics, Faculty of Dental Sciences, King George's Medical University, Lucknow, Uttar Pradesh, India
|Date of Submission||09-Apr-2020|
|Date of Decision||14-Jun-2020|
|Date of Acceptance||03-Nov-2020|
|Date of Web Publication||18-Jan-2021|
Dr. Anuradha Vijay Sawardeker
Department of Conservative Dentistry and Endodontics, Faculty of Dental Sciences, King George's Medical University, Lucknow - 226 003, Uttar Pradesh
Source of Support: None, Conflict of Interest: None
Aim: This study aims to evaluate and compare the canal transportation and centering ability of two nickel–titanium file systems, ProTaper Next and WaveOne Gold, in comparison with ProTaper Universal in mesiobuccal canals of maxillary molars using micro-computed tomography.
Materials and Methods: Seventy-five permanent maxillary first and second molars having mesiobuccal canals with curvatures between 20° and 30° were selected and subjected to pre-operative micro-computed tomographic scans. They were then divided into three groups (n = 25) based on the file system to be tested: Group 1-ProTaper universal (control), Group 2: ProTaper Next, and Group 3-WaveOne Gold. Access cavities were prepared, following which each specimen was instrumented using the specific file system. Post-instrumentation micro-computed tomographic scans were then carried out for each specimen. Pre- and post-instrumentation measurements of mesiobuccal canals were performed using the ImageJ 1.8.0 software. Canal transportation and centering ratio were calculated at three cross-section levels that corresponded to 3-mm, 6-mm, and 9-mm distance from the apical end of the root. The data obtained were then subjected to statistical analysis using ANOVA and Tukey's post-hoc tests.
Results: It was seen that WaveOne Gold caused the least overall canal transportation and exhibited the highest centering ability, followed by ProTaper Next and ProTaper Universal, though the difference was not significant. Furthermore, there was no significant difference between the canal transportation and centering ability of ProTaper Universal, ProTaper Next, and WaveOne Gold at all three levels.
Conclusion: None of the systems evaluated exhibited perfect centering ability and zero canal transportation. All file systems caused root canal transportation and minor changes in the root canal anatomy.
Keywords: Canal transportation, centering ability, micro-computed tomography, nickel-titanium, protaper next, waveone gold
|How to cite this article:|
Sawardeker AV, Tikku AP, Bharti R, Bains R. Evaluation of canal transportation and centering ability in mesiobuccal canals of maxillary molars using two Ni-Ti file systems: An ex-vivo micro-computed tomographic study. Endodontology 2020;32:198-203
|How to cite this URL:|
Sawardeker AV, Tikku AP, Bharti R, Bains R. Evaluation of canal transportation and centering ability in mesiobuccal canals of maxillary molars using two Ni-Ti file systems: An ex-vivo micro-computed tomographic study. Endodontology [serial online] 2020 [cited 2021 Mar 2];32:198-203. Available from: https://www.endodontologyonweb.org/text.asp?2020/32/4/198/307312
| Introduction|| |
Successful endodontic therapy is dependent on three factors, namely diagnosis, debridement, and three-dimensional obturation. Meticulous debridement and disinfection of the root canal eliminate infected pulpal remnants as well as bacteria and their by-products, leading to a good prognosis and enhanced longevity of the tooth following endodontic therapy. Preservation of the root canal configuration is of paramount importance during root canal shaping, as stated by Schilder. However, the intricacies of the root canal system present a serious challenge for achieving the above-mentioned goals.
Negotiation and instrumentation of curved canals followed by their meticulous shaping and thorough debridement go a long way in ensuring the success of endodontic therapy. However, this poses a serious challenge to novice and experienced endodontists alike. Faulty instrumentation of such canals may lead to many procedural errors that may further compromise the prognosis of endodontic therapy. According to the Glossary of Endodontic Terms of the American Association of Endodontists, canal transportation is defined as“the removal of canal wall structure on the outside curve in the apical half of the canal due to the tendency of files to restore themselves to their original linear shape during canal preparation, which may lead to ledge formation and possible perforation”.
The centering ability of an instrument is its ability to remain centered in the root canal. It is an indication of whether or not the dentine removal over the prepared area is spread evenly by the instrument and hence ensures symmetric preparation, i.e., equal removal of dentin from the root canal.
The discovery of nickel–titanium alloy by Buehler was a stepping stone in the field of endodontic material science. In 1988, the first hand-held nickel-titanium endodontic instruments made by machining orthodontic wire were introduced by Walia et al. Two characteristic properties of this alloy that make it suitable for the fabrication of endodontic instruments are its superelasticity and shape memory following controlled thermal treatment, which afford nickel–titanium its superior flexibility.
Another advancement in the field of endodontic instrumentation was the introduction of reciprocating instruments that machined canals by repetitive back-and-forth motion, based on the balanced-force technique by Roane. This technique allows a file to progress more readily, cut efficiently, and effectively remove intracanal debris, in addition to making it possible to shape canals using a single instrument, thereby saving time.
The invention of computed tomography has made it easier to accurately visualize three-dimensional structures without superimposition or distortion, thereby overcoming the shortcomings associated with conventional two-dimensional imaging. Microcomputed tomography is a relatively recent innovation in imaging technology that enables one to obtain high-resolution three-dimensional images of two-dimensional entities.
Considering the fact that too many file systems exist in the market and with new instruments being launched very often, it is imperative to know the shaping ability of an instrument before choosing it for instrumentation of canals exhibiting curvatures. Therefore, this study was conducted to evaluate and compare the canal transportation and centering ability of two nickel-titanium instruments, namely ProTaper Next (Dentsply Maillefer, Ballaigues, Switzerland) and WaveOne Gold (Dentsply Maillefer, Ballaigues, Switzerland), with ProTaper Universal (Dentsply Maillefer, Ballaigues, Switzerland) in mesiobuccal canals of maxillary molars, using micro-computed tomography as the imaging modality. The null hypothesis tested was that there was no difference in the three instruments with regard to canal transportation and centering ability in curved canals.
| Materials and Methods|| |
The study was approved by the institutional Ethical Committee (90th ECM II B-Thesis/P34) prior to its initiation. A total of two hundred and fifty extracted permanent maxillary first and second molars having closed apices and extracted for reasons not related to this study were collected.
Teeth with previous endodontic treatment, calcified root canals, an open apex and those that underwent surgical extractions were excluded from the study.
Intraoral periapical radiographs were taken in the buccolingual direction to determine the curvature angle of the mesiobuccal root. The angle of curvature was calculated using Schneider's method [Figure 1]. The criteria for determining the severity of canal curvature was as follows: if the angle is less than 5°, the canal is straight; if the angle is 5–20°, the canal is moderately curved; and if the angle is >20°, the canal is classified as a severely curved canal (Schneider 1971). Seventy-five specimens with canal curvatures between 20° and 30° were selected as this indicated a severe curvature according to Schneider's classification. The specimens were then stored in 0.1% thymol solution at 5°C for the study.
|Figure 1: Schematic diagram demonstrating the measurement of canal curvature using three reference points, namely point A denoting the midpoint of the canal orifice, point B denoting the point at which the flare deviates and point C denoting the apical foramen. The angle formed by the intersection of the lines connecting points A and B and points B and C is the angle of curvature of the canal|
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The specimens were then individually subjected to scans using Quantum FX micro-computed tomography imaging system (Perkin Elmer Inc., Massachusetts, United States) to visualize the root canal morphology. A series of 512 images were obtained per specimen in the form of DICOM files, which were then viewed using ImageJ v1.8.0 (64-bit) software.
The specimens were then randomly divided into three groups based on the file system to be used:
- Group 1: ProTaper Universal (Dentsply Maillefer, Ballaigues, Switzerland) (Control)
- Group 2: ProTaper Next (Dentsply Maillefer, Ballaigues, Switzerland)
- Group 3: WaveOne Gold (Dentsply Maillefer, Ballaigues, Switzerland).
Access cavities were prepared on all teeth, and the mesiobuccal canals were explored and their apical patency was established using a No. 10 K-file. The working length was established at 1 mm short of this measurement. A glide path was created up to the working length using No. 15 K-files and Dentsply ProGlider (Dentsply-Sirona, Ballaigues, Switzerland). The specimens were then instrumented using the three file systems as per manufacturers' instructions, powered by Dentsply X-Smart Plus endomotor (Dentsply Maillefer, Ballaigues, Switzerland) using a 6:1 contra-angle handpiece.
After the glide path and between each file, the root canals were irrigated with 2 mL 5.25% sodium hypochlorite for 1 min using a 30 G side-vented needle at 2 ml/min, along with a chelator, Glyde (ethylene diamine tetraacetic acid and carbamide peroxide) (Dentsply Maillefer, Ballaigues, Switzerland). A total volume of 30 mL 5.25% sodium hypochlorite was used per root canal during biomechanical preparation. A final rinse with 5 mL 17% EDTA followed by a 5-min 5 mL rinse with distilled water was performed for all groups. Then, all canals were dried with absorbent paper points.
The specimens were then considered ready for post-instrumentation micro-computed tomographic evaluation as each group had been prepared to a similar apical diameter, i.e., F2 (size 25, 0.08 taper), X2 (size 25, 0.06 taper), and Primary file size (25, 0.07% taper) for ProTaper Universal, ProTaper Next, and WaveOne Gold, respectively, to keep a similar apical diameter in all three groups to minimize bias. The instruments were discarded after the preparation of every five specimens to prevent instrument separation. The WaveOne Gold instruments were discarded after one use.
Following root canal preparation, a postoperative micro-computed tomography scan of each specimen was individually performed and visualized using ImageJ v1.8.0 (64-bit) software. Canal transportation and centering ability were then evaluated at three cross-sectional levels: 3 mm, 6 mm, and 9 mm from the apical end of the root using Gambill's formula. The three levels were determined from the three-dimensional reconstructed images of the specimens using the ImageJ v1.8.0 software.
Degree of canal transportation = (m1–m2) – (d1–d2)
Canal centering ratio = (m1–m2)/(d1–d2) or (d1–d2)/(m1–m2)
here m1 is the shortest distance from the mesial margin of the root to the mesial margin of the non-instrumented canal, m2 is the shortest distance from the mesial margin of the root to the mesial margin of the instrumented canal, d1 is the shortest distance from the distal margin of the root to the distal margin of the non-instrumented canal, and d2 is the shortest distance from the distal margin of the root to the distal margin of the instrumented canal. All measurements were done using the ImageJ v1.8.0 (64-bit) software [Figure 2].
|Figure 2: (a): Visualization and measurement on a micro-computed tomographic image of the uninstrumented canal using ImageJ software. (b) Visualization and measurement on a micro-computed tomographic image of the instrumented canal, using ImageJ software|
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Canal transportation equal to zero meant that no transportation occurred, a negative value meant that transportation occurred in the distal direction, and a positive value indicated transportation in the mesial direction.
The formula adopted for the centering ability calculation depends on the value obtained by the enumerator, which should always be lower than the values obtained by the differences. Therefore, values equal to one indicated perfect centering ability of the instrument, while values closer to zero indicated a reduced ability of the instrument to maintain in the central axis of the root canal.
The data obtained were then subjected to statistical analysis using one-way ANOVA and Tukey's post hoc tests, using SPSS Version 25. The level of significance was P < 0.05.
| Observation and Results|| |
WaveOne Gold caused the least canal transportation at 3 mm (P = 0.982), 6 mm (P = 0.766) and 9 mm (P = 0.915) although the differences were not statistically significant. At the 3 and 6 mm levels, ProTaper Next caused lesser transportation than ProTaper Universal, while it caused more transportation at the 9 mm level. Overall, WaveOne Gold caused the least canal transportation (P = 0.952). However, these results were not statistically significant [Table 1].
|Table 1: Comparison of canal transportation by Protaper Universal, Protaper Next, and WaveOne Gold|
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Furthermore, WaveOne Gold exhibited the highest centering ability at 3 mm (P = 0.160), 6 mm (P = 0.660) and 9 mm (P = 0.068), followed by ProTaper Next and ProTaper Universal, though the differences were not statistically significant. Overall, WaveOne Gold significantly exhibited the highest centering ability (P = 0.022) [Table 2].
|Table 2: Comparison of centering ability of Protaper Universal, Protaper Next, and WaveOne Gold|
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| Discussion|| |
Meticulous cleaning and shaping of the root canal ensures thorough debridement of necrotic pulp tissue remnants, bacteria and their by-products as well as creates sufficient space for the placement of irrigants and intracanal medicaments, which are adjuncts root canal disinfection. It is imperative to respect the canal's original anatomy and ensure that the same proportion of the material is removed from the inner as well as the outer aspects of the root canal, in addition to minimizing displacement of the apical foramen, so as to minimize the incidence of potential procedural errors such as canal transportation, ledge formation, zip formation, and perforation. According to Peters OA, the occurrence of up to 0.15 mm of root canal transportation has been considered to be acceptable, whereas the canal transportation above 0.30 mm may have a negative impact on the apical seal after obturation of the canal.
In the current study, canal transportation and centering ability of the three instruments was assessed at three levels, i.e., 3, 6, and 9 mm from the apex, corresponding to the apical, middle, and coronal portions of the root, respectively, as these zones are commonly prone to procedural errors. ProTaper Next and WaveOne Gold were chosen for this study as the two instrument systems have different cross-sectional designs and metallurgical compositions. ProTaper Next is a rotary file system that has an off-centered rectangular cross-section and is made from M wire, while WaveOne Gold is a reciprocating file system that has alternating off-centered parallelogram-shaped cross-section design with two 85 degree cutting edges and is made from Gold wire. ProTaper Universal files were used as the positive control because they have a convex triangular cross-section and are made from the traditional nickel-titanium alloy. Instruments exhibiting rotary motion were compared with those exhibiting reciprocation to determine the influence of instrument motion on the canal anatomy during instrumentation.
Extracted human maxillary molars were used since they effectively simulated the clinical situation owing to their intricate canal anatomy. Mesiobuccal roots of maxillary molars were chosen for this study as these canals exhibit an accentuated curvature, which pose a serious challenge when performing cleaning and shaping procedures. The crowns were maintained to simulate the clinical situation as accurately as possible as the interference of cervical dentine projections tends to cause stresses on the files during canal shaping.
Teeth having mesiobuccal canals with curvatures ranging 20–30° were selected as this indicated a severe curvature according to Schneider's classification and a moderate curvature according to the American Association of Endodontists Endodontic Case Difficulty Assessment (2019) guidelines. Micro-computed tomography was used as the imaging modality as it is a non-invasive technology that enables one to obtain accurate high-resolution three-dimensional images of two-dimensional entities. The diameter of the apical preparation was limited to size 25, as an increase in file size predisposes curved canals to an increased risk of transportation.
At all three levels, WaveOne Gold caused the least canal transportation; however, the differences were not significant. Overall, WaveOne Gold also caused the least canal transportation, though not statistically significant. These findings are concurrent with those from a study by van der Vyver et al. who compared the shaping effect of instruments manufactured from nickel–titanium, M-Wire, and Gold wire with different glide path preparation techniques and concluded that ProTaper Next (M-Wire) exhibited more canal transportation compared to WaveOne Gold (Gold Wire); therefore, WaveOne Gold respected the original anatomy of the canal. This can be attributed to the differences in working motion, cross-sectional design, and metallurgy: WaveOne Gold instruments have an alternating off-centered parallelogram-shaped cross-sectional design with two 85° cutting edges and shapes canals using a reverse balanced force action, in a repetitive alternating back and forth reciprocal motion. Moreover, WaveOne Gold is fabricated from Gold wire which is obtained after repeated heating and cooling of the nickel-titanium alloy that affords it more flexibility and resistance to cyclic fatigue. Increased transportation caused by ProTaper Next in comparison with WaveOne Gold may be also attributed to its offset mass of rotation, as it has been proposed by Çapar and Arslan that instruments with an offset rotational mass may describe a larger envelope of motion than similarly sized files with symmetrical mass and axis of rotation.
ProTaper Universal exhibited more canal transportation than ProTaper Next at 3 mm and 6 mm but the differences were not statistically significant; similar findings were reported by El-Gendy and Negy, and Gagliardi et al. This can be attributed to the differences in metallurgy; ProTaper Next is made from M-wire that makes it more flexible, whereas ProTaper Universal is made from conventional nickel-titanium alloy. Alrahabi also concluded that ProTaper Universal caused more transportation toward the inside of the canal curvature compared with ProTaper Next at the 5 mm and 7 mm levels.
Franco et al. demonstrated that instruments used in a continuous rotary motion produced the largest enlargement of the canal in the most apical third of the canal, as compared to when used in a reciprocating motion, in addition to significantly greater enlargement of the canal at the external side, as aggressive continuous rotating motion tends to remove the dentine toward the external wall of the canal, especially in the apical third. Similar findings were reported by Yoo and Cho, who concluded that the WaveOne reciprocating system maintains original canal contour better than files with continuous rotation, which tend to transport the outer canal wall of the curve in the apical part of the canal. Studies by Tambe et al., Saber et al., Dhingra et al. and Haimed et al. proved that reciprocating instruments caused less canal transportation and better respected the canal anatomy. These findings can be attributed to the instrument kinematics and metallurgical properties, as proved by Franco et al. and Plotino et al.
At all three levels, WaveOne Gold exhibited the highest centering ability, followed by ProTaper Next and ProTaper Universal, though the differences were not statistically significant. Comparative evaluation of the overall centering ability revealed that WaveOne Gold significantly exhibited the highest centering ability, followed by ProTaper Next and ProTaper Universal (P = 0.022).
The centering ability of an instrument is dependent upon the kinematics and design characteristics such as cross-section, metallurgy and taper, as well as upon the root canal morphology. Franco et al. suggested that instruments when used in reciprocating motion facilitate more centered instrumentation than in continuous rotating motion, as aggressive continuous rotating motion tends to remove the dentine toward the external wall of the canal, especially in the apical third. The Gold wire composition of WaveOne Gold instruments increases the flexibility and cyclic resistance of the file. Moreover, its design includes a reverse helix, a semi-active and modified guiding tip and offset parallelogram-shaped cross-section, in addition to a decreasing taper.
WaveOne exhibits better centering ability owing to its reciprocating motion. Vallabhaneni compared the shaping ability of WaveOne Gold and Neoniti file systems and concluded that WaveOne Gold tended to respect the original anatomy of the canal. This was supported by Berutti who reported that reciprocating movement allows a more centralized chemomechanical preparation when compared to continuous rotary motion, especially in the apical third. Furthermore, Yang et al. stated that instruments having a constant taper produced lesser transportation and better centering as compared to instruments with a progressive taper.
Furthermore, ProTaper Next exhibited better centering ability than ProTaper Universal at all levels. This may be attributed to the increased flexibility of ProTaper Next owing to its M-wire composition, as stated by El-Gendy.
| Conclusion|| |
It can be said that both file systems, i.e., ProTaper Next and WaveOne Gold can be used for instrumenting curved canals without causing significant changes in the root canal anatomy. However, WaveOne Gold, which is a reciprocating system, tends to stay more centered in the canal while causing minimal aberrations in the canal anatomy, thereby ensuring equal dentin removal and preserving the canal configuration.
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Conflicts of interest
There are no conflicts of interest.
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[Figure 1], [Figure 2]
[Table 1], [Table 2]