|
 
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| ORIGINAL RESEARCH |
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| Year : 2020 | Volume
: 12
| Issue : 7 | Page : 30-40 |
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Effect of different kinematic cutting motion in multiple versus single-file concept on dentinal crack formation: An in vitro study
Weaam H Anous1, Salma Al-Ashry2, Magdy M Ali3, Mohamed M Kataia4
1 Department of Endodontics, Faculty of Dentistry, Assiut University, Assiut, Egypt
2 Department of Endodontics, Faculty of Dentistry, Ain Shams University, Cairo, Egypt
3 Department of Endodontics, Faculty of Dentistry, Beni Suef University, Beni Suef, Egypt
4 Department of Endodontics, Faculty of Dentistry, The British University in Egypt, Cairo, Egypt
| Date of Web Publication | 17-Jan-2020 |
Correspondence Address:
Weaam H Anous
Assistant Lecturer of endodontics, Faculty of dentistry, Assiut univeristy, Assiut.
Egypt
 Source of Support: None, Conflict of Interest: None  | Check |
DOI: 10.4103/jioh.jioh_141_19
Aims and Objectives: The aim of this study was to assess crack formation using two different cutting motions (rotation and reciprocation) in nickel–titanium rotary instrument. Materials and Methods: One hundred extracted human mandibular incisors were selected for this study. Before root canal instrumentation, low-speed saw (under water cooling) was used to section the tooth horizontally at 3, 6, and 9 mm from the apex of 0.1 mm. A digital stereomicroscope at ×25 magnification with a cold light source was used to observe the slices. Then all teeth were placed again inside the mold. Samples were classified according to the system used into the following groups: Group 1: negative control, Group 2: the ProTaper Next files, Group 3: a primary reciprocating WaveOne Gold file, Group 4: a small reciprocating WaveOne Gold followed by primary reciprocating WaveOne Gold file, and Group 5: OneShape rotary file. Samples were scanned by using a digital stereomicroscope to detect crack formation. Results: Apical level: WaveOne Gold (primary) group showed the highest prevalence of cracks. Middle level: OneShape group showed the highest prevalence of cracks followed by WaveOne Gold (small and primary) group. Coronal level: The five groups showed no statistically substantial difference in the presence of cracks. Conclusion: All rotary systems can lead to the crack formation. Keywords: Crack, OneShape, ProTaper Next, Reciprocating Instrument, Rotary Instrument, WaveOne Gold
How to cite this article:
Anous WH, Al-Ashry S, Ali MM, Kataia MM. Effect of different kinematic cutting motion in multiple versus single-file concept on dentinal crack formation: An in vitro study. J Int Oral Health 2020;12, Suppl S1:30-40 |
How to cite this URL:
Anous WH, Al-Ashry S, Ali MM, Kataia MM. Effect of different kinematic cutting motion in multiple versus single-file concept on dentinal crack formation: An in vitro study. J Int Oral Health [serial online] 2020 [cited 2022 Dec 6];12, Suppl S1:30-40. Available from: https://www.jioh.org/text.asp?2020/12/7/30/276082 |
| Introduction | |  |
In endodontic treatment, canal shaping is performed to provide sufficient space for efficient dentine disinfection.[1] However, this step generates stresses that can also weaken the root[2] and consequently lead to crack formation (especially in the apical portion of the root[3],[4]). It has been reported that these dentinal cracks and minute fractures can propagate into vertical root fracture (VRF) if the tooth is subjected to repeated stresses from endodontic or restorative procedures.[5]
There was a study that reported a potential association between the design of nickel–titanium (NiTi) instruments and the incidence of VRFs and confirmed that file design affects the apical stress and accumulation of tensile stress during root canal preparation.[6]
Recently, advent of NiTi files and rotary systems revolutionized endodontic treatment. These instruments reduce the clinician’s fatigue and allow faster endodontic treatment.
Most of these instruments have tapers in the range of 4%–12%, which are greater than the The International Organization for Standardization (ISO), ISO standard no. 3630-1 standard of 2%, and cause high stress to root dentin, as root canal preparation with rotary instruments compared to that with hand files requires higher rotations of instruments inside the canal. Due to the variability in types of rotary systems available and limited information on the quality of new systems, assessment of the efficacy of these systems for root canal treatment is a priority.[7]
More recent data suggested a relationship between the presence of dentinal defects and different shaping motions for the rotary NiTi systems.[8],[9] In the past few years, there has been a growing interest among scientists to correlate different preparation cutting motions and techniques and file designs and their responsibility for different degrees of dentinal damage and the induction of micro cracks.
It is of prime importance in this study to shed light on the variable effects of different rotary motions and instrument number on developing of dentinal cracks.
| Materials and Methods | | |
One hundred extracted human mandibular incisors were selected for this study. Teeth included in this study have mature apex, straight root, and single canal. To ensure standardization, the teeth were sectioned horizontally (decoronated) under water-cooling with a low-speed saw by a standardized length of 16 mm from the apex.[7],[10] All teeth were placed in a cylinder mold and surrounded by acrylic resin.[11] The internal diameter of the mold was 15 mm and the height was 20 mm. Before root canal instrumentation, low-speed saw (under water-cooling) was used to section the tooth horizontally at 3, 6, and 9 mm from a 0.1-mm long apex. A digital stereomicroscope at ×25 magnification with a cold light source was used to observe the slices. Then all teeth were placed again inside the mold. A metal bar was placed on the side of each block to insure reassembly in the same site.
To ensure the placement of sectioned discs back to their proper order to start preparation, a metal bar was placed in the inner wall of the mold along with numbering of each disc in the descending order, so that disc number one disc (apical slice) will be placed in the bottom of the mold back to its original place. This was to ensure the proper placement of the discs back to their original place.
A #10 k-file was used to obtain canal patency. The root canal-shaping procedures were performed according to the manufacturers’ instructions for each instrument system. Samples were classified according to the system used into the following groups: Group 1: negative control, where teeth were left unprepared. Group 2: the ProTaper Next files were used in the sequence X1 with a tip size of 17 and a taper of 0.04, X2 with a tip size of 25 and a taper of 0.06, with a rotational speed of 300rpm and 200g/cm torque. Each file was used with a brushing motion away from the root concavities. Group 3: a primary reciprocating WaveOne Gold file with a tip size of 25 and a taper of 0.08 was used in a reciprocating, slow in-and-out pecking motion until reaching the full working length according to the manufacturer’s instructions. The X-smart plus endomotor was used with the manufacturer’s configuration setup. Group 4: a small reciprocating WaveOne Gold with a tip size of 21 and a taper of 0.06 was used in reciprocating motion followed by primary reciprocating WaveOne Gold file. Group 5: OneShape rotary file #25 with a taper of 0.06 using a low-torque motor at a constant speed of 400rpm and 400g/cm torque was used in pecking motions according to the manufacturer’s instructions. After each instrument change, irrigation was performed with 5.25% sodium hypochlorite solution. After preparation, the specimens from the prepared groups were rinsed with 5-mL distilled water. After root canal preparation, a digital stereomicroscope at ×25 magnification with a cold light source was used to observe the slices and the pictures were captured.
Statistical analysis of qualitative data was presented as frequencies and percentages. Qualitative data were compared using Fisher’s exact test with a significance level of P ≤ 0.05. Statistical analysis was performed with the Statistical Package for the Social Sciences (SPSS) software, version 20, for Windows (IBM, Armonk, New York).
| Results | | |
Presence of crack:
Apical level: Preoperatively, the five groups showed a statistically substantial difference in the presence of cracks (P = 0.010, effect size = 0.345). OneShape group showed the highest prevalence of crack (6 [30%]). WaveOne Gold (small and primary) and ProTaper Next groups showed lower and same prevalence of cracks (3 [15%]). WaveOne Gold (primary) and control groups showed no cracks (0 [0%]).
Postoperatively, the five groups showed a statistically substantial difference in the presence of cracks (P = 0.012, effect size = 0.323). WaveOne Gold (primary) group showed the highest prevalence of cracks (6 [30%]). WaveOne Gold (small and primary), ProTaper Next, and OneShape groups showed lower and same prevalence of cracks (3 [15%]). Control group showed no cracks (0 [0%]). ProTaper Next and OneShape groups only showed the increased cracks (3 [15%] and 3 [15%], respectively) [Figure 1][Figure 2][Figure 3][Figure 4][Figure 5]. | Figure 1: Bar chart representing presence of cracks at the apical levels in the five groups
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,  | Figure 2: Representative apical cross-section image for pre- and post-instrumentation for OneShape (The arrows point to the crack)
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,  | Figure 3: Representative apical cross-section image for pre- and post-instrumentation for ProTaper Next (The arrows point to the crack)
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,  | Figure 4: Representative apical cross-section image for pre- and post-instrumentation for WaveOne Gold (small, primary)
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,  | Figure 5: Representative apical cross-section image for pre- and post-instrumentation for WaveOne Gold primary (The arrows point to the crack)
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Middle level: Preoperatively, the five groups showed a statistically substantial difference in the presence of cracks (P = 0.048, effect size = 0.317). OneShape group showed the highest prevalence of cracks (6 [30%]) followed by WaveOne Gold (primary) group (3 [15%]). ProTaper Next group showed lower prevalence of cracks (1 [5%]) followed by WaveOne Gold (small and primary) group (2 [10%]). Control group showed no cracks (0 [0%]).
Postoperatively, the five groups showed a statistically substantial difference in the presence of cracks (P < 0.001, effect size = 0.405). OneShape group showed the highest prevalence of cracks (6 [30%]) followed by WaveOne Gold (small and primary) group (1 [5%]). WaveOne Gold (primary), ProTaper Next, and control groups showed no cracks (0 [0%]). WaveOne Gold (primary) group showed the highest prevalence of increased cracks (3 [15%]). WaveOne Gold (small and primary) and ProTaper Next groups showed lower and same prevalence of increased cracks (1 [5%]). OneShape and control groups showed no prevalence of increased cracks (0 [0%]) [Figure 6][Figure 7][Figure 8][Figure 9][Figure 10]. | Figure 6: Bar chart representing presence of cracks at the middle levels in the five groups
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,  | Figure 7: Representative middle cross-section image for pre- and post-instrumentation for OneShape (The arrows point to the crack)
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,  | Figure 8: Representative middle cross-section image for pre- and post-instrumentation for ProTaper Next
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,  | Figure 9: Representative middle cross-section image for pre- and post-instrumentation for WaveOne Gold (small, primary) (The arrows point to the crack)
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,  | Figure 10: Representative middle cross-section image for pre- and post-instrumentation for WaveOne Gold primary
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Coronal level: Preoperatively, the five groups showed no statistically substantial difference in the presence of cracks (P = 0.143, effect size = 0.250). The prevalence of cracks in WaveOne Gold (small and primary), WaveOne Gold (primary), ProTaper Next, OneShape, and control groups were 2 (10%), 3 (15%), 0 (0%), 3 (15%), and 0 (0%), respectively.
Postoperatively, the five groups showed no statistically substantial difference in the presence of cracks (P = 0.435, effect size = 0.186). The prevalence of cracks in WaveOne Gold (small and primary), WaveOne Gold (primary), ProTaper Next, OneShape, and control groups were 2 (10%), 3 (15%), 3 (15%), 3 (15%), 0 (0%), respectively [Figure 11][Figure 12][Figure 13][Figure 14][Figure 15]. | Figure 11: Bar chart representing presence of cracks at the coronal levels in the five groups
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,  | Figure 12: Representative coronal cross-section image for pre- and post-instrumentation for OneShape (The arrows point to the crack)
Click here to view |
,  | Figure 13: Representative coronal cross-section image for pre- and post-instrumentation for ProTaper Next (The arrows point to the crack)
Click here to view |
,  | Figure 14: Representative coronal cross-section image for pre- and post-instrumentation for WaveOne Gold (small, primary) (The arrows point to the crack)
Click here to view |
,  | Figure 15: Representative coronal cross-section image for pre- and post-instrumentation for WaveOne Gold primary
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Changes in the presence of crack postoperatively: Data for changes in the presence of crack postoperatively are presented in [Table 1] and [Figure 16][Figure 17][Figure 18]. | Table 1: Descriptive statistics and results of Wilcoxon signed-rank test for comparison between presence of crack pre- and postoperatively within each group
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,  | Figure 16: Presence of crack pre- and post-instrumentation in different groups at apical level
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,  | Figure 17: Presence of crack pre- and post-instrumentation in different groups at middle level
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,  | Figure 18: Presence of crack pre- and post-instrumentation in different groups at coronal level
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In WaveOne Gold (small and primary) group, there was no statistically significant difference in the presence of cracks postoperatively at the apical, middle, and coronal levels (P = 1.000, effect size = 0.000), (P = 0.317, effect size = 0.224), and (P = 1.000, effect size = 0.000), respectively.
In WaveOne Gold (primary) group, there was a statistically significant increase in the presence of cracks postoperatively at the apical level (P = 0.014, effect size = 0.548). There was no statistically significant difference in the presence of cracks postoperatively at the middle and coronal levels (P = 0.083, effect size = 0.387) and (P = 0.083, effect size = 0.387), respectively.
In ProTaper Next group, there was no statistically significant difference in the presence of cracks postoperatively at the apical, middle, and coronal levels (P = 0.083, effect size = 0.387), (P = 0.317, effect size = 0.224), and (P = 0.083, effect size = 0.387), respectively.
In OneShape group, there was no statistically significant difference in the presence of cracks postoperatively at the apical, middle, and coronal levels (P = 0.083, effect size = 0.387), (P = 1.000, effect size = 0.000), and (P = 1.000, effect size = 0.000), respectively.
In control group, there was no statistically significant difference in the presence of cracks postoperatively at the apical, middle, and coronal levels (P = 1.000, effect size = 0.000), (P = 1.000, effect size = 0.000), and (P = 1.000, effect size = 0.000), respectively.
| Discussion | | |
The chemo-mechanical root canal preparation aims to remove microorganisms, debris, and tissues completely through the enlargement of the root canal diameter.[12] During the preparation, stress concentrations that originate from the contact of the endodontic instrument with the dentin may cause dentinal defects as, for example, microcracks.[13] Through the application of repeated tension via occlusal forces, these dentinal microcracks could potentially create VRF.[8] Evidence shows that VRFs are probably caused by the propagation of smaller and less-pronounced dentinal defects rather than the force used during the preparation or the obturation of the root canal.[14],[15]
Generations of NiTi engine-driven instruments were introduced with various designs, alloy treatments, and kinematics. Among them, OneShape was a rotary NiTi single-file system with variable cross-section along the entire length of instrument. The OneShape instrument has been claimed to have three different cross-sections along the blade. The apical zone has a triangular design with three cutting edges. The second zone, termed as the transition zone, has a cross-section that changes from three cutting edges to two, whereas the coronal zone has an S-shaped cross-section with two cutting edges.
The ProTaper Next system is built via heat treatment of the surface. The ProTaper Next system is composed of three instruments manufactured using a special NiTi alloy and M-wire fabricated through a thermal treatment process. This process includes a variable taper design and a special offset mass of rotation. Consequently, the strength and flexibility along its active part is improved. The design of ProTaper Next produces an asymmetric rotary motion that decreases the screw effect by reducing the contact area between the file and the dentinal wall.[16] As a result, the apical control of extruded debris improves.[9],[17]
Recently, the WaveOne Gold file was released, which performs root canal preparation using a single instrument with a reciprocating movement. Moreover, it has a new heat treatment, the Gold Wire. WaveOne Gold is a recently introduced single-file system that adopts reciprocating motion. These instruments are manufactured using a new proprietary thermal process to produce a superelastic NiTi file.[18] Post-manufacturing, the ground NiTi files are heat treated and slowly cooled (which is called Gold process). In addition to the distinctive gold finish of the file, this process enhances the file’s strength and flexibility far in the excess of its predecessor.[18] The files are available in the four sizes as follows: small (20.07, yellow), primary (25.07, red), medium (35.06, green), and large (45.05, white). WaveOne Gold has a parallelogram cross-section with two 85° cutting edges and an alternate one- and two-point contact.[19]
Mandibular incisors with a single canal were selected as results from the literature report a deep flattening in the mesiodistal direction of long transversal sections and a greater diameter in the buccolingual direction. Thus, standardizing the preparation with all canals instrumented on the buccal and lingual extensions. Furthermore, the canals of these teeth had small anatomical diameters in the apex,[20] making them compatible with the preparation size of 25.
All experimental groups had dentinal defects, corroborating the findings of several studies.[21],[22],[23],[24]
In this study, in the apical level, there is a significant difference in crack formation. The WaveOne Gold group (primary) shows the highest prevalence of crack that may be due the design of the instrument’s cross-section, which can affect the number of times that it touches the root dentin. Consequently, this creates the possibility of provoking different degrees of tension. More contact of the instrument with the walls of the canal can induce the formation of dentinal defects.[13] The Waveone gold (WOG) single file has a cross-section that alternates touches on the dentin with two and one edges during a 360° rotation. In this way, the contact of this instrument with the dentinal walls might increase, promoting the formation of dentinal defects. Also, it may be due the flexibility of the instrument, which is produced through the heat treatment and its parallelogram-shaped cross-section,[25] and this finding is in full agreement with that of Kim et al.[26] This finding is in disagreement with that of Pedullà et al.,[27] who stated that WaveOne Gold file showed less cracks.
In the middle level, OneShape shows the highest prevalence in crack. As the design of file may affect shaping forces on root dentin, these forces may cause root fracture. OneShape has asymmetrical cross-section over the entire length. This is in agreement with other studies.[6],[28] This is in disagreement with Garg et al.[5] who stated that OneShape showed less crack than ProTaper Next file.
The WaveOne Gold (small and primary) follows the OneShape in prevalence of crack as during canal preparation, there is a high concentration of tension on the buccolingual extensions in addition to the medium and cervical thirds as the WOG instrument had the highest percentage of touches on the dentin in 6- and 9-mm sections. This finding is in agreement with that of Versluis et al.[29]
In the coronal level, there is no significant difference in the crack formation. This may be due to the influence from rotary file systems with different cross-sections used as variable taper, which can reveal a decreased number of microcracks in coronal teeth section. This is in agreement with the previous study,[27] which stated decreased number of cracks in the coronal third. This is in disagreement with Monga et al.[30] who stated increased number of cracks in coronal third than apical and middle third.
These results show that the microcrack formation due to the shaping motion is negligible and unpredictable. Moreover, the synergistic effect of kinematic and other factors, such as NiTi alloy and geometric features, influence microcracks. Less dentinal damage is reported in some studies for reciprocating motion than continuous rotation[21] and vice versa.[4] Kinematics has no effect on microcracks.[31] The differences in results could be due to the different methodologies (i.e., Gates-Glidden instruments,[21] sectioning levels,[21] and instrument’s type and size).[4],[21]
All rotary instruments can cause dentinal crack. WaveOne Gold primary file showed the highest prevalence of crack in the apical third. OneShape file showed the highest prevalence of crack in the middle third.
Data availability
The data set used in this study is available on request from (Weaam Anous/[email protected]).
Acknowledgement
We would like to thank Dr. Khaled Mohamed Keraa, Biostatistician, Quality Management Specialist, Faculty of Oral and Dental Medicine, Misr International University (MIU), Egypt for his help in the statistical analysis of the results.
Financial support and sponsorship
Nil.
Conflicts of interest
There are no conflicts of interest.
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[Figure 1], [Figure 2], [Figure 3], [Figure 4], [Figure 5], [Figure 6], [Figure 7], [Figure 8], [Figure 9], [Figure 10], [Figure 11], [Figure 12], [Figure 13], [Figure 14], [Figure 15], [Figure 16], [Figure 17], [Figure 18]
[Table 1]
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