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ORIGINAL RESEARCH ARTICLE  
Year : 2018  |  Volume : 21  |  Issue : 6  |  Page : 637-641
Comparative analysis of canal-centering ratio, apical transportation, and remaining dentin thickness between single-file systems, i.e., OneShape and WaveOne reciprocation: An in vitro study


1 Sr. Lecturer, Maitri College of Dentistry and Research Center, Durg, Chhattisgarh, India
2 Reader, Rungta College of Dental Sciences and Research Center, Bhilai, Chhattisgarh, India
3 Reader, Maitri College of Dentistry and Research Center, Durg, Chhattisgarh, India

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Date of Submission12-Mar-2018
Date of Decision11-Apr-2018
Date of Acceptance06-Jul-2018
Date of Web Publication13-Nov-2018
 

   Abstract 

Aim: This study aimed to compare the canal-centering ability, apical transportation, and remaining dentin thickness (RDT) of OneShape and WaveOne (WO) systems using cone-beam computed tomography.
Objective: The objective of this study was to evaluate the efficiency of two rotary systems in maintaining original root canal anatomy.
Materials and Methods: Forty extracted human single-rooted mandibular premolars were used in the present study. Preinstrumentation scans of all teeth were taken, canal curvatures were calculated, and the samples were randomly divided into two groups with twenty samples in each group: Group 1 – OneShape (OS) rotary system and Group 2 – WO reciprocation system. Postinstrumentation scans were performed using DICOM software and the two scans were compared to determine the canal-centering ability, canal transportation, and RDT at 1, 3, and 5 mm from the root apex.
Results: Using Student's unpaired t-test, results were as follows: for canal-centering ability and RDT, Group 1 showed nonstatistically significant difference at 1 and 5 mm, while statistically significant difference (P < 0.05) at 3 mm was obtained. For canal transportation, Group 1 showed statistically significant difference (P < 0.05) at 1 and 3 mm and nonsignificant difference was obtained at 5 mm, but for Group 2, nonstatistically significant difference (P > 0.05) was obtained at 1, 3, and 5 mm. When comparing the RDT between both the groups, the difference was not statistically significant (P > 0.05).
Conclusion: WO single reciprocation file has better canal-centering ability, maintains original canal curvature, causes lesser canal transportation, and preserves more dentine as compared to OS.

Keywords: Canal curvature; cone-beam computed tomography; M-wire; root canal anatomy

How to cite this article:
Jain A, Gupta AS, Agrawal R. Comparative analysis of canal-centering ratio, apical transportation, and remaining dentin thickness between single-file systems, i.e., OneShape and WaveOne reciprocation: An in vitro study. J Conserv Dent 2018;21:637-41

How to cite this URL:
Jain A, Gupta AS, Agrawal R. Comparative analysis of canal-centering ratio, apical transportation, and remaining dentin thickness between single-file systems, i.e., OneShape and WaveOne reciprocation: An in vitro study. J Conserv Dent [serial online] 2018 [cited 2018 Dec 16];21:637-41. Available from: http://www.jcd.org.in/text.asp?2018/21/6/637/245237

   Introduction Top


Successful root canal therapy depends on effective debridement of the root canal by eliminating debris and microorganisms and shaping of the root canal system without deviating from the original anatomy. Ideally, during root canal preparation, the instruments should always conform to and retain the original shape of the canal. The ability to keep the instruments centered in curved canals and to deliver an accurate enlargement to the root canal without any unnecessary weakening to the root structure is crucial. A prepared root canal should have a continuously tapered funnel shape while maintaining the original outline form of the canal.[1] When curvatures are present, preparation becomes more difficult and there is a tendency for all preparation techniques to divert the prepared canal away from the original axis. Endodontic mishaps are unfortunate occurrences that can occur during root canal treatment which include ledging, zipping, blockage, strip perforations, and canal transportations. Factors that affect canal-centering ability are design of the instrument which includes cross section, taper, tip size, and flexibility.

Canal transportation is one of the most common mishaps during the instrumentation of curved root canals. When transportation occurs, it has two components – direction and deviation. Direction is an excessive dentine removal in a single direction off the main tooth axis of the canal. Deviation is any undesirable departure from the original canal path, which is the distance in millimeters from the pre- to post-instrumented canal as a function of file action.[2]

Transportation in the apical third of the root canal promotes the harboring of debris and residual microorganisms as a result of insufficient cleaning of the root canals and overreduction of the sound dentin and destruction of the integrity of the root. The etiology associated with an increased risk of canal transportation includes insufficiently designed access cavities, use of inflexible instruments, instrumentation technique, tip design, insufficient irrigation during mechanical enlargement, unseen canal curvatures in two-dimensional radiography, skill of operator, and the degree and radius of a root canal curvature both induce a stress on the instruments.[3] Radial lands support the edge of the cutting angle and help to distribute the pressure of the blades more uniformly around the circumference of a curved canal and thus reduce apical transportation.[4]

The more severely curved and the shorter the radius of curvature, the greater the risk of transportation. An ideal instrumentation should have equal dentin removal from the canal walls so that it could avoid excessive thinning of root structure.

Recently, WaveOne (WO) and OneShape (OS) represent single NiTi file systems which are made up of a special NiTi alloy called M-Wire that is created by an innovative thermal treatment process. OS (Micro Mega, Besancon, France) is to be used in full continuous rotation, whereas WO NiTi single-file system is to be used in reciprocation.[5] The benefits of this M-Wire NiTi alloy are increased flexibility and improved resistance to cyclic fatigue.[6] Thus, it is important to assess the canal-centering ability of single-file systems before they can be considered a viable replacement of full-sequence rotary file systems.[7]

In the past, methods for assessment of canal transportation, remaining dentin thickness (RDT), and canal-centering ability included radiographic analysis, serial sectioning technique, diafanization, stereomicroscopic assessment, clinical and scanning electronic microscopy, and computer manipulation technique.[8] The above-mentioned methods were invasive in nature and accurate repositioning of pre- and post-instrumented specimens is difficult, and there is a disadvantage of loss of specimen, whereas radiographs provide two-dimensional image of three-dimensional objects.[9]

Cone-beam computed tomography (CBCT) utilizes a cone-shaped X-ray beam and an area detector that captures a cylindrical volume of data in one acquisition, which is also used in the analysis of the root canal area, and parameters such as canal transportation, centering ratio, and the amount of root dentin removed by endodontic instruments.[10]

Thus, the purpose of this study was to evaluate and compare the canal transportation, canal-centering ability, and RDT after instrumentation with OS and WO reciprocation systems using CBCT.


   Materials and Methods Top


After approval by Ethical Institutional Board, forty freshly extracted human single-rooted mandibular premolar teeth for an orthodontic treatment purpose or for periodontal reasons were collected for this study. Teeth without any previous endodontic treatment, fractures, resorptive defects, calcifications, or open apices were selected for the study. They were cleaned of any residual tissue tags, rinsed under running water, and stored in 10% formalin solution. The presence of a single root and root canal in each tooth was confirmed on radiographs. To get the flat reference, the crowns were decoronated with a diamond disk (DFS, Germany) and a final dimension of 9-mm length was achieved for each tooth. The root canal length was established by measuring the penetration of a size 10 K-file (Dentsply/Maillefer, Switzerland) until it reached the apical foramen and then subtracting 0.5 mm. Angle of curvature was assessed according to the criteria described by Schneider.[11] Teeth were radiographed using radiovisiography in buccolingual direction. A line was drawn parallel to the long axis of the canal. A second line was drawn from the apical foramen to intersect with the first at the point where the canal began to leave the long axis of the tooth. The acute angle thus formed was measured and the angle of curvature was thus determined. Further, only teeth with a degree of curvature ranging between 10° and 24° were included in the study.[11] A template of Self cure acrylic resin (DPI RR cold cure) was made, in which the roots were embedded till the cervical region so that a constant position could be obtained.[11] The teeth were coded with a permanent marker. The template mounting was horizontally fitted to a chin support with its occlusal plane parallel to the plate.

All teeth were scanned by CBCT before instrumentation. The exposure time was 3.0 s, operating at 75 kV and 2.0 mA. The images were stored in the computer's hard disk for further comparison between pre- and post-instrumentation data using DICOM software.

The teeth were then randomly divided into two groups of twenty each which received the following treatment.

Group 1

Canals were shaped using OS rotary files (Micro Mega, France) having a size of 25 and a taper of 0.06 till the working length with the X-Smart Plus motor set to 350 rpm and a 5-Ncm torque with a 16:1 contra-angle. Each file was used once and then discarded.

Group 2

Canals were shaped using a primary WaveOne rotary files (Dentsply / Maillefer, Switzerland) having a size 25 and a taper of 0.08 in a reciprocating, slow in-and-out pecking motion according to the manufacturer's instructions. X-Smart Plus endomotor (Dentsply Maillefer, Switzerland) was used. After each instrumentation, the canals were irrigated copiously with 3% sodium hypochlorite (Vishal Dentocare, Pvt. Ltd., India) and the flutes of the instrument were cleaned. The final apical preparation size was 25 for both the groups. Again, all the specimens were scanned by CBCT after instrumentation. Pre- and post-instrumentation images were compared using DICOM software.

Canal-centering ratio calculation[12]

The canal-centering ratio was calculated according to the following ratio:

(a1 − a2)/(b1 − b2) or (b1 − b2)/(a1 − a2)

The canal-centering ratio is the difference between the instrumented and noninstrumented canals, which measures the ability of an instrument to stay centered. If the numbers are not equal, the lower figure is considered as the numerator and a result of “1” indicates perfect canal-centering capacity and, the closer the result to 0, the worse the ability of the instrument to keep itself in the canal's central axis [Figure 1] and [Figure 2].
Figure 1: Pre- and post-operative cone-beam computed tomography image at 1, 3, and 5 mm by using OneShape

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Figure 2: Pre- and post-operative cone-beam computed tomography image at 1, 3, and 5 mm by using WaveOne

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Apical transportation calculation

The following formula introduced by Gambill et al. to measure the degree of canal transportation was used:[12]

([a1 − a2] − [b1 − b2])

where

a1 is the shortest distance from the mesial edge of the root to the mesial edge of the uninstrumented canal, b1 is the shortest distance from the distal edge of the root to the distal edge of the uninstrumented canal, a2 is the shortest distance from the mesial edge of the root to the mesial edge of the instrumented canal, and b2 is the shortest distance from the distal edge of the root to the distal edge of the instrumented canal. Result of “0” indicates no canal transportation and other than “0” means that transportation has occurred in the canal.

Remaining dentin thickness calculation[12]

The RDT was determined by subtracting the uninstrumented canal from the instrumented canal, that is, the shortest distance from the outer wall to the inside canal wall was calculated at 1, 3, and 5 mm levels pre- and post-instrumentation.


   Results Top


Student's unpaired t-test was used for statistical analysis with 0.05 level of significance. The mean and standard deviation values for canal-centering ratio at the levels of 1, 3, and 5 mm between both the groups are presented in [Table 1]. When OS was used at 1 and 5 mm, nonstatistically significant difference was obtained, whereas at 3 mm, there was statistically significant difference. However, for WO, nonstatistically significant difference was obtained at all the three levels.
Table 1: Mean and standard deviation of canal-centering ability with P values of t-test for comparison of groups

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Evaluation of canal transportation was done at three levels between the two groups [Table 2]; there was significant difference at 1 and 3 mm and, at 5 mm, no statistically significant difference was found when using OS system, but for WO, nonstatistically significant difference was obtained at all the three levels. There was no statistically significant difference between the two groups with respect to the remaining root dentin at 1, 3, and 5 mm [Table 3].
Table 2: Mean and standard deviation of canal transportation with P values of t-test for comparison of groups

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Table 3: Mean and standard deviation of remaining dentin thickness with P values of t-test for comparison of groups

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   Discussion Top


None of the two systems evaluated had perfect canal-centering ability and zero canal transportation. In the present study, we have utilized OS and WO reciprocation NiTi file systems and the final apical preparation size was 25 for both the groups. WO NiTi single-file reciprocating system has different cross-sectional designs over the entire length of the working part. In the tip region, the cross section presents radial lands, while in the middle part of the working length and near the shaft, the cross-sectional design changes from a modified triangular convex cross section with radial lands to a neutral rake angle with a triangular convex cross section.[13],[14],[15] Only one single-shaping file is required to provide the canal with an adequate size and taper.

This design helps to eliminate threading and binding of the instrument in continuous rotation. Although there is literature on the reduction of fatigue and extended life span of the instrument, there is requirement of investigations regarding canal-shaping ability of single-file systems.[16] These are necessary because fast approaches toward the apex with fewer instruments and sharp cutting edges produce aberrations.[17]

OS is a single file intended for single use to avoid risk of contamination and has better cutting efficiency on continuous rotation, pertinent to its cross-sectional design. It has a variable cross section at three different levels, which progressively changes from three to two cutting edges.[18] An additional advantage of antibreakage control is a safety bonus,[12] which would help the instrument to unwind to avoid separation.[16] CBCT analysis has been found to be the gold standard method for the analysis of canal geometry following instrumentation and for the analysis of variables such as volume, surface area, cross-sectional shape, and taper of the root canal system.[19] Moreover, the results of this study show that the quality of the three-dimensional images obtained by CBCT scanning is an accurate and efficient method of assessment of root canal instrumentation.

The lack of difference in RDT between instruments at 1, 3, and 5 mm from the apical foramen, in the present investigation, may be attributed to the noncutting tip and the standardization of the apical diameter size of the tested instruments.

Canals prepared with OS showed the maximum canal transportation at 1 and 3 mm levels. The reason may be attributed to the reduction in instrument flexibility, strength, and indicating a tendency to straighten curved canals. WO primary file preserves canal shape, respects the anatomical J shape, and produces continuously tapered funnel shape of the canal.[7] Earlier studies have revealed no statistically significant difference in canal transportation and canal-centering ratio between ProTaper Universal (PU), WO, and ProTaper Next, and Reciproc files exhibited greater volumetric changes compared with OS, Twisted File Adaptive, and PU.[18]

The absence of root canal transportation toward the so-called danger area results in more dentin preservation toward the furcation. It seems reasonable to consider that fracture is more frequent when dentin thickness is reduced. Based on the results of the present investigation, it can be reported that root canal preparation with WO and OS resulted in less dentin loss, thereby favoring tooth preservation.

Technological advancement has contributed to the improvement of technical procedures, but still, there is a faint line between research findings published and its clinical significance. Further studies should be conducted in severely curved canals with bigger sample size.


   Conclusion Top


Within the limitations of the present study, it was found that WO single reciprocation file produced significantly less transportation and remained centered and respected the original canal anatomy better than OS with an apical instrumentation diameter of #25. Further studies are needed to extrapolate these results to clinical conditions.

Financial support and sponsorship

Nil.

Conflicts of interest

There are no conflicts of interest.

 
   References Top

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2.
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McCann JT. The effect of maintaining apical patency on canal transportation. Int Endod J 2008;41:431-5.  Back to cited text no. 3
    
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Schneider SW. A comparison of canal preparations in straight and curved root canals. Oral Surg Oral Med Oral Pathol 1971;32:271-5.  Back to cited text no. 11
    
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Shah DY, Wadekar SI, Dadpe AM, Jadhav GR, Choudhary LJ, Kalra DD, et al. Canal transportation and centering ability of ProTaper and self-adjusting file system in long oval canals: An ex vivo cone-beam computed tomography analysis. J Conserv Dent 2017;20:105-9.  Back to cited text no. 19
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Correspondence Address:
Dr. Aditi Jain
D 13, Kailash Nagar, Rajnandgaon - 491 441, Chhattisgarh
India
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Source of Support: None, Conflict of Interest: None


DOI: 10.4103/JCD.JCD_101_18

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