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Year : 2023  |  Volume : 13  |  Issue : 1  |  Page : 73-79

Comparison of root canal transportation and centering after instrumentation through conservative and traditional access cavities using different file systems: An in vitro study

Department of Restorative and Aesthetic Dentistry, College of Dentistry, University of Baghdad, Baghdad, Iraq

Date of Submission09-Jun-2022
Date of Decision19-Jul-2022
Date of Acceptance22-Jul-2022
Date of Web Publication11-Jan-2023

Correspondence Address:
Dr. Samer Abbas Kadhim
Department of Restorative and Aesthetic Dentistry, College of Dentistry, University of Baghdad, Baghdad
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Source of Support: None, Conflict of Interest: None

DOI: 10.4103/sej.sej_112_22

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Introduction: While conservative access preparations could increase fracture resistance of endodontically treated teeth, it may influence the shape of the prepared root canal. The aim of this study was to compare the prepared canal transportation and centering ability after continuous rotation or reciprocation instrumentation in teeth accessed through traditional or conservative endodontic cavities by using cone-beam computed tomography (CBCT).
Materials and Methods: Forty extracted intact, matured, and 2-rooted human maxillary first premolars were selected for this study. Teeth were equally divided into two groups according to the access cavity design (traditional or conservative). Each group (n = 20) was further subdivided according to instrumentation technique (n = 10) into rotary 2 shape and reciprocation R-motion file subgroups. The teeth were scanned pre and post instrumentation using Planmeca ProMax to obtain two CBCT images for each sample. Images were analyzed and root canal transportation and centering ability were calculated for both buccal and palatal roots at three levels from their apices (3, 5 to 7 mm).
Results: Although conservative access cavities showed more canal transportation and less centering ability than the traditional one, there was no statistically significant difference (P > 0.05) between them at all levels. Furthermore, no statistically significant difference has been identified in the same parameter between the two instrumentation techniques (continuous rotation and reciprocation) (P > 0.05). However, longer instrumentation time was measured in the conservative group compared to traditional.
Conclusion: The size of endodontic access cavity has no effect on root canal transportation and centering ability when instrumentation was performed using 2 shape and R-motion file systems.

Keywords: Centering ability, conservative endodontic access cavity, R-motion file, transportation, two shape file

How to cite this article:
Kadhim SA, Mahdee AF, Ali AH. Comparison of root canal transportation and centering after instrumentation through conservative and traditional access cavities using different file systems: An in vitro study. Saudi Endod J 2023;13:73-9

How to cite this URL:
Kadhim SA, Mahdee AF, Ali AH. Comparison of root canal transportation and centering after instrumentation through conservative and traditional access cavities using different file systems: An in vitro study. Saudi Endod J [serial online] 2023 [cited 2023 Feb 3];13:73-9. Available from: https://www.saudiendodj.com/text.asp?2023/13/1/73/367509

  Introduction Top

Tooth fracture is considered the most common cause of tooth loss following caries and periodontal disease.[1] Endodontically treated teeth are more susceptible to fracture due to many reasons but are commonly due to the loss of a substantial amount of tooth structure during the various steps of endodontic treatment.[1],[2],[3],[4] One of the most influential steps during endodontic treatment is access cavity preparation.[5],[6] Correct access preparation facilitates the detection of root canal orifices and removal of pulp tissue remnants which might act as microorganism substrates.[7],[8],[9] It also affects the quality and efficiency of irrigation during root canal instrumentation and the ability to shape the canals.[7],[10],[11]

For many years, the only method for preparing the access cavity was the traditional one, which includes the removal of entire roof of the pulp chamber and getting a straight line access into the coronal part of the root canals.[12] However, in the past few years, new methods for access cavity preparations were developed with different names such as; conservative access cavity, contracted endodontic access, modified endodontic cavity, ninja endodontic cavity, truss access cavity, and other 22 different names for such techniques summarized by.[13]

The main purpose of these new preparations was to maintain dentine structure by preserving the roof of the pulp chamber and pericervical dentine to improve the fracture resistance of the endodontically treated teeth by applying the concept of minimal invasive endodontics.[14] At the same time, such type of access cavity might affect other steps of endodontic treatment including locating the canal orifices, cleaning, shaping, and filling procedures.[6],[11],[15],[16] It might also increase the possibilities of iatrogenic complications such as fractured instruments.[6],[15],[17],[18] However, the development in rotary file manufacturing technology, such as heat treatment, considerably improved their ability to resist multiple tensional stresses during work.[19] Removal of remnants of pulp tissue and other debris in the pulp chamber might become more complicated by preserving the roof of pulp chamber. These stagnated debris might cause tooth discoloration, facilitate microbial growth and negatively affected on sealers and composites.[7],[11],[20],[21]

Regarding this new technique of endodontic access cavity preparation, still there is a controversy on the effectiveness, practicality, and benefits of using such access instead of the traditional access cavity preparation.

Therefore, this study aimed to compare the prepared root canal transportation and centering ability of continuous rotation and reciprocation instrumentation in teeth accessed by two endodontic access cavity designs (traditional versus conservative) using cone-beam computed tomography (CBCT).

  Materials and Methods Top

The work of this study was approved by the Research Ethics Committee in the College of Dentistry at the University of Baghdad (NO 345523).

Forty extracted human maxillary first premolars were selected from a pool of more than 200 teeth, extracted for orthodontic purposes, according to the certain criteria. These criteria included; intact, mature 2-rooted maxillary first premolars, with moderate canal curvature (5°–20°) according to Schneider.[22] The position of the apical foramen was also considered to be within 1 mm from the root apex. The external dimensions of the crowns (mesio-distal and bucco-palatal) were measured and those with comparable sizes were only included. The selected teeth were carefully inspected for any signs of caries or cracks before cleaning and storing them in a humid atmosphere at 25°C.

Teeth were equally divided into two groups according to the access cavity design (traditional or conservative). These groups were further subdivided according to instrumentation technique (n = 10) whether rotary 2 shape file (Micro Méga, Besançon, France) or reciprocation R-motion file (FKG Dentaire SA).

A single operator did all steps. Magnification using eye loupes (3.5 × china) was used during the entire course of work. A mannequin for the upper arch was modified and used for sample fixation during work for standardization purposes. A modified dental surveyor was used during access cavity preparations to hold the high-speed handpiece (NSK, Japan) in a way that the preparation bur was perpendicular to the occlusal surface of the tooth.

The conservative access cavities [Figure 1] were prepared using diamond round burs NO1014 (Microdont, Brazil). The teeth were accessed at the central fossa in a single downward movement until the roof of the pulp chamber was reached by the bur. Only part of the roof which did not exceed the diameter of the bur was removed to keep the access cavities standardized.[23]
Figure 1: Image showing the conservative endodontic access cavity

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The traditional access cavity preparation was also started by using diamond round burs NO1014 (Microdont, Brazil) until the roof of the pulp chamber was reached. Then, endo Z bur (Dentsply Maillefer, Switzerland) was used to extend the cavity buccoligually to ensure the removal of the entire pulp chamber roof and maintain straight-line access to the endodontic file without any occlusal interference. After finishing the access cavity for each sample, a k-file size 10 was used to create a glide path and determine the initial size of the canals. Teeth with canals wider than the initial file size 10 at the apex were excluded. Furthermore, working length of each root was calculated by measuring the length of the file after emerging from the apical foramen subtracted by 1 mm.

During instrumentation, each tooth was placed in the mannequin inside a phantom head to simulate the clinical condition. The instrumentation process was done with the aid of magnification and according to manufacturer instructions of each file system by using Rooter Universal endodontic motor (FKG Dentaire Switzerland). In the teeth group prepared with R-motion file system, R-motion glide file (15/03) was used before shaping the canal with R-motion 25 (25/06) to the full working length in a reciprocation motion (by selecting the preset program for R-motion in the endodontic motor). For the two shape samples, a glide path was created using manual K file size 15, before rotary files 2 shape TS1 (25/04) then TS2 (25/06) used sequentially to the full working length with a speed of (350 rpm) and a torque of (2 Ncm). Copious irrigation with 0.9 normal saline was used throughout the procedure of instrumentation. The time of instrumentation was also calculated for each sample.

The CBCT scanning procedures were performed pre and post instrumentation [Figure 2] through a standardized method using Planmeca ProMax (ProMax 3D classic, Finland) to get two CBCT images for each sample. The following parameters were adjusted within CBCT machine: (90 kV, 10 mA and 75 μm voxel size) in a field of view (FOV) of 5 cm × 5 cm. The mannequin was used to hold the teeth during imaging in a standardized position. The adjustable adapter and 3D max guide holder units of the Planmeca CBCT device were used to hold the mannequin in a standardized position guided by the device's laser guiding lines [Figure 3].
Figure 2: CBCT image showing an axial view of the tooth sample pre (a) and post (b) instrumentation. CBCT: Cone-beam computed tomography

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Figure 3: Mannequin placement above 3D max guide holder and aligned with the aid of laser guiding lines before CBCT scanning. 3D: Three dimensional, CBCT: Cone-beam computed tomography

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These settings were kept for all exposures. The pre- and post-instrumentation CBCT images were collected and processed by using the Planmeca Romexis Viewer software (Planmeca, Helsinki, Finland) [Figure 4]. From each CBCT, three axial images were acquired at three levels from the root apex (3, 5, and 7 mm). The measurements of canal transportation and centering ability were performed using the following equations: [24],[25]
Figure 4: Axial view of CBCT image during processing with Planmeca Romexis Viewer software. CBCT: Cone-beam computed tomography

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Canal transportation:

Mesio-distal = (m1 − m2) − (d1 − d2)

Bucco-palatal = (b1 − b2) − (p1 − p2)

Canal centering ability:

Mesio-distal = (m1 − m2)/(d1 − d2) or (d1 − d2)/(m1 − m2)

Bucco-palatal = (b1 − b2)/(p1 − p2) or (p1 − p2)/(b1 − b2)

m1, d1, b1, and p1 represent the shorter distance from the root margin to the canal margin before preparation at the mesial, distal, buccal, and palatal sides, respectively. While m2, d2, b2, and p2 refer to the shorter distance from the root margin to the canal margin after preparation at the mesial, distal, buccal, and palatal sides, respectively.

According to the equations that had been used for calculating canal transportation any result that does not equal zero means that transportation has occurred. Therefore, positive values mean that the transportation occurs toward mesial or buccal sides, while negative values mean that transportation occurs toward distal or palatal sides according to the transportation equations.

The statistical analysis in this study was done by using SPSS program (version 23, IBM, Armonk, New York, USA). Initially, the normality of data distribution was tested using the Shapiro–Wilk test. The results for this test showed that all the study groups are normally distributed and considered as parametrical results. Followed by testing the statistically significant difference between groups, unpaired t-test was used for this purpose.

  Results Top

Canal transportation measurements for the traditional and conservative access cavities within the buccal and palatal roots using both instrumentation techniques (continuous rotation and reciprocation) are shown in [Table 1].
Table 1: Means and standard deviations (μm) of the prepared root canal transportation in the buccal and palatal roots of maxillary first premolars accessed with traditional and conservative access cavities for both instrumentation techniques (rotary and reciprocation)

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In the traditional access cavity, it is apparent that means of bucco-palatal canal transportation for the buccal roots have positive values at all the levels of measurements (3, 5, and 7 mm) from the apex. While the palatal roots showed negative values. This is not true for canal transportation in mesio-distal direction which shows positive results only. The measurements in the conservative access cavity groups appeared with similar changes but slightly higher in values, especially in the buccal and palatal roots in comparison to the traditional cavity group.

Root canal centering ability measurements within traditional and conservative access cavities within buccal and palatal roots of the prepared teeth using two instrumentation techniques (continuous rotation and reciprocation) are displayed in [Table 2]. According to centering ability equations, the value which is closer to one, the better the canal centering ability. This means that in this study the conservative access cavity groups show less centering ability when compared to the traditional access.
Table 2: Means and standard deviations for prepared canal centering ability in traditional and conservative access cavities within buccal and palatal roots of maxillary first premolars instrumented with rotary and reciprocation techniques

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To compare between the data, the unpaired t-test was employed. This test showed no statistically significant difference (P > 0.05) for the access cavity design on the prepared canal transportation and centering ability within all samples including buccal and palatal roots. Furthermore, no statistically significant difference has been identified between the two instrumentation techniques (rotation and reciprocation) regarding the prepared root canals transportation and centering ability.

The average time for the instrumentation process within each access cavity (traditional and conservative) was also calculated. There was a longer instrumentation time for teeth accessed with the conservative access cavities (17.8 min for R-motion and 20.6 min for 2 shape) when compared to the traditional (10.9 min for R-motion and 12.9 min for 2 shape) for both rotary and reciprocal instrumentation techniques.

  Discussion Top

With the advancement in magnification and imaging technologies, the concept of minimal invasive endodontics has been developed[26] The main aim behind that is to preserve tooth structure and enhance fracture resistance postendodontic treatment.[14] However, limited access cavity design may influence the final shape of the prepared canal. Therefore, this study aimed to compare transportation and centering ability of conservative versus traditional access cavity designs using two instrumentation techniques. These techniques include continuous rotation using (2shape TS2) and reciprocation (R motion 25) that were chosen with similar file size and tapering (0.25 taper 6%) for standardization purposes. Furthermore, both systems have been processed by heat treatment during manufacturing for better flexibility and resistance to fracture.[27],[28],[29] The tooth model used in this study was human maxillary premolars for the availability of sound teeth which have been extracted for orthodontic purposes.

For standardization of the methodology, the whole work was done by a single operator. Instrumentation was performed within the phantom head to simulate the clinical procedure. Although micro-CT is a more validated method for assessing the shape of a root canal before and after instrumentation. However, it has a long scanning time, with quit high radiation dose and highly expensive equipment. CBCT, in comparison is more clinically relevant if proper voxel size obtained via exposures in the limited FOV (75 μm voxel size within this study) with shorter scanning time and lower radiation dose.[30],[31]

The results of the current study showed no statistically significant differences in root canal transportation and centering ability between the traditional and conservative access cavities groups. These results go in line with previous studies such as.[32],[33],[34] Although these studies used a micro-CT for the determination of transportation and centering ability, their values appeared comparable to the values obtained in the current study.

On the other hand, the current results disagree with other studies[6],[10] and.[23] This could be explained by the differences in the methodology, study samples, root curvature, and the file systems used. The tooth sample used by Alovisi et al.[10] was the mesio-buccal root of the mandibular first molars with canal curvature reached up to 30°. The measurements were done only at two levels from the apical foramen, 1 mm and 3 mm. Furthermore, the used file system was Wave One gold primary file (0.25 taper 7%) with different design and taper to the two files used in the current study. In the study by Rover et al.,[6] the tooth sample was maxillary first molar and the instrumentation was performed using Reciproc file system R25 (0.25 taper 8%) in buccal canals and R40 (0.40 taper 6%) in palatal canal. These differences in tooth sample and file system size and tapering could be behind the discrepancy with the results of the current study. While in the last study by Pereira et al.,[23] tooth samples were also maxillary premolars with two roots, but the instumentation files were different including protaper universal, reciproc, reciproc blue, and hyflex EDM.

Although there was no statistical difference in transportation and centering ability with different types of access, the values appear slightly higher in the conservative access samples. An explanation for such difference could be due to the coronal interference for the shaping files occurring more within the conservative access cavity. This may lead to an increase in the bending forces while the file engages more within the canal deviating the files toward the outer walls.[10],[14],[23],[35] The angulated insertion of the file into the canal in the conservative access associated with the tendency of the file to regain its shape could be the reason behind this. However, both file systems used in this study had super elasticity to overcome this problem as they both manufactured by the heat treatment technology. This process can improve the flexibility of NiTi files and created files with controlled shaped memory to reduce the chances of transportation,[23],[36] and these have been confirmed through the results of this study.

Furthermore, there was no statistically significant difference between R-motion and 2-Shape regarding transportation and centering ability. These results are in agreement with other studies which also identified no differences between rotary and reciprocation systems used in shaping of root canals.[37],[38] While other studies disagree with the results of the current study.[39],[40] This could be attributed to many reasons including differences in methodology, model of the study (resin blocks instead of natural teeth) or using canals with high degree of curvature or S-shaped canals.[40] Also using file systems that differ from each other by many factors such as the metallurgy, design, tip, taper, and diameter.[41]

Regarding the time of instrumentation, it was longer in the conservative access groups compared to the traditional ones in both file systems. This agrees with previous studies.[11],[33] This could be attributed to the extra difficulty of canal instrumentation caused by the limited coronal cavity which lacks the straight-line access of the file toward the apical region within the conservative access cavity groups.[33]

Even with the attempts to simulate the clinical conditions in this study by using a phantom head and using magnification during instrumentation, it is still an in vitro study and the results of this study cannot be generalized. Another limitation of this study is the use of CBCT for examination. Although it is a valid and accurate method for determining transportation and centering ability, it still has less accuracy in comparison to micro-CT imaging; therefore, further investigation can be suggested using such technology. In addition, using similar measurements on different teeth with complex root anatomy such as molars or teeth with greater root curvature can be suggested for future work.

  Conclusion Top

Within the limitations of this study, both conservative and traditional endodontic access cavities were associated with slight canal transportation and eccentricity when instrumentation was performed with 2 shape or R-motion file systems. However, there was no statistically significant difference between these two parameters neither with different access cavity designs nor with different file systems. The use of two file systems with controlled shape memory and proper elasticity could be the main reason behind these results. Therefore, the conservative endodontic access cavity could be recommended over traditional for the better preservation of the tooth structure.

Financial support and sponsorship

This research was funded by University of Baghdad College of Dentistry.

Conflicts of interest

There are no conflicts of interest.

  References Top

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  [Figure 1], [Figure 2], [Figure 3], [Figure 4]

  [Table 1], [Table 2]


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