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 Table of Contents  
Year : 2020  |  Volume : 32  |  Issue : 4  |  Page : 220-224

Effect of three different rotary file systems on dentinal crack formation – A stereomicroscopic analysis

Department of Conservative Dentistry and Endodontics, Army College of Dental Sciences, Secunderabad, Telangana, India

Date of Submission26-Jul-2020
Date of Decision18-Aug-2020
Date of Acceptance03-Nov-2020
Date of Web Publication18-Jan-2021

Correspondence Address:
Dr. Neha Verma
Department of Conservative Dentistry and Endodontics, Army College of Dental Sciences, Secunderabad, Telangana
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Source of Support: None, Conflict of Interest: None

DOI: 10.4103/endo.endo_96_20

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Background: This study is aimed to analyze and compare the formation of dentinal cracks after root canal preparation with three different rotary file systems using a stereomicroscope.
Materials and Methods: Forty extracted human mandibular premolars were selected and divided into three experimental groups and a control group of 10 each. The root canals were prepared in the experimental groups. Group I: ProTaper Gold files (PTG), Group II: Neo Endo flex files, and Group III: Waldent Wal flex files. No preparation was done in the control group (Group IV). The roots were sectioned at 3, 6, and 9 mm from the apex, and the surfaces were examined under a stereomicroscope. The data were analyzed using the Chi-square test.
Results: There were no cracks in the control group. Neo Endo flex showed maximum cracks at 3 mm level, which was statistically significant compared to other groups (P < 0.05). There was no statistically significant difference among experimental groups at 6 mm and 9 mm levels (P > 0.05).
Conclusion: All the rotary files that were tested produced dentinal cracks. Neo Endo flex files group was associated with more number of cracks than PTG and Waldent Wal flex files group. The apical section of samples showed significantly higher defects compared to the middle and coronal sections.

Keywords: Dentinal crack, Neo Endo flex, ProTaper Gold, stereomicroscope, Waldent Wal flex file

How to cite this article:
Soujanya E, Verma N, Kaushik M, Nagamaheshwari X, Mehra N, Prasad LK. Effect of three different rotary file systems on dentinal crack formation – A stereomicroscopic analysis. Endodontology 2020;32:220-4

How to cite this URL:
Soujanya E, Verma N, Kaushik M, Nagamaheshwari X, Mehra N, Prasad LK. Effect of three different rotary file systems on dentinal crack formation – A stereomicroscopic analysis. Endodontology [serial online] 2020 [cited 2021 Mar 5];32:220-4. Available from: https://www.endodontologyonweb.org/text.asp?2020/32/4/220/307320

  Introduction Top

The main goal of chemo-mechanical root canal preparation is to eradicate microorganisms, debris, and organic tissue by enlarging the root canal and to create the canal space for adequate obturation.[1],[2] However, various procedural errors occur during root canal preparation such as perforations, canal transportation, ledge formation, zip formation, fracture of instruments, and dentinal cracks formation.[3]

Stress concentration that originates from the contact of the endodontic instrument with the dentin may induce the formation of dentinal cracks, which under repetitive occlusal forces propagate to turn complete fracture. A vertical root fracture is a catastrophic complication of endodontic treatment caused by the propagation of smaller and less pronounced dentinal defects. Therefore, a crucial goal in endodontic research is to overcome the potential problem of dentinal crack formation during instrumentation with rotary instruments.[1],[4]

One of the significant inventions in endodontic instruments has been the replacement of stainless steel (SS) with a nickel-titanium (Ni-Ti) alloy.[5] Ni-Ti instruments have increased flexibility and short working time as an advantage when compared to SS.[6] Various generations of Ni-Ti engine-driven instruments introduced differ in parameters such as cutting blades, taper and tip configuration, and alloy treatment.[7]

ProTaper Gold (PTG), Neo Endo flex files, and Waldent Wal flex files are the 3rd generation rotary files.

PTG rotary files (PTG, Dentsply Maillefer, Ballaigues, Switzerland) feature the identical geometries as ProTaper Universal (PTU, Dentsply Tulsa Dental Specialties, Tulsa, OK) but offer increased flexibility and advanced metallurgy.[8] Neo Endo flex files (Orikam Healthcare, India) are controlled memory files with a triangular cross-section, sharp cutting edges and are extremely flexible.[9] Waldent Wal flex files (Waldent, India) are rotary files with super flexibility, more resistant to cyclic fatigue, enhanced cutting efficiency, triangular cross-section, and sharp cutting edges.[10] Ni-Ti file systems with different designs, alloys, and kinematics, can cause micro-cracks during root canal preparation procedures. On literature search, no studies have evaluated the incidence of dentinal cracks resulting from the use of Neo Endo flex files and Waldent Wal flex file.

Thus, the aim of this study was to analyze and compare the incidence of dentinal cracks after root canal preparation with PTG, Neo Endo flex files, and Waldent Wal flex files using a stereomicroscope. The null hypothesis is that there would be no difference in crack formation among the groups.

  Materials and Methods Top

Extracted human mandibular premolar teeth with closed apices were selected. The teeth were cleaned with a periodontal scaler to remove soft-tissue debris and were disinfected with 0.1% thymol solution, subsequently stored in phosphate buffered saline (PBS) until use. Radiographs were taken from mesiodistal and buccolingual aspects of the teeth. Teeth with root fractures, cracks, open apices, curved canals, multiple roots, caries or restorations, severe anatomic variations, calcified canal, and resorption were excluded.

The teeth were decoronated with a diamond disc (Addler, Golden Nimbus, Mumbai, India) underwater cooling at 16 mm from the apex. All the samples were inspected under a stereomicroscope (Leica M60; Leica Microsystems GmbH, Wetzlar, Germany) with ×2.5to exclude external defects or cracks. A total of forty teeth with a single root, single patent canal with closed apex were selected for this study.

Root canal preparation

The patencies of the root canals were established with a size #10 K-file (Mani Co, Tokyo, Japan) and the working lengths determined as 1 mm short of the apex. A glide path was prepared by size #15 K-file (Mani Co, Tokyo, Japan).

Periodontal ligament (PDL) simulation was done using polyvinylsiloxane impression material (Dentsply Aquasil, Germany). Teeth were immersed into molten wax to achieve a 0.2–0.3 mm thick wax layer all around the root and mounted in self-curing acrylic resin. Once the resin set, the teeth were retrieved and the wax scraped off from the root surfaces. The space created by the molten wax was filled with impression material to simulate PDL.

The forty teeth were randomly assigned into three experimental groups and one control group (n = 10) based on different Ni-Ti files used for preparation. Group I – PTG, Group II – Neo Endo flex files, Group III – Walden Wal flex files and Group IV – Control group.

The canals were prepared using an X-Smart endodontic motor (Dentsply Maillefer, Ballaigeus, Switzerland) with the torque and speed (1.5–3 Ncm, 300 rpm for PTG; 1.5 Ncm, 350 rpm for Neo Endo flex files; and 1.8–3 Ncm, 300 rpm for Waldent Wal flex files) as recommended by the manufacturer.

A single experienced operator performed all the procedures to overcome bias. In the instrumentation sequence of Group I (PTG), Sx (19/0.04), S1 (18/0.02), S2 (20/0.04), F1 (20/0.07) and F2 (25/0.08) instruments were used. Size 15/0.06 followed by size 20/0.04, 25/0.06 instruments were used in the sequence for Group II (Neo endo flex files). In Group III (Waldent Wal flex files), W1 (17/0.08), W2 (19/0.02), W3 (20/0.04), W4 (20/0.06), W6 (25/0.06) were used sequentially. Each file was used only once for the instrumentation of one canal. A complete rotation with light pecking in and out motion was done for instrumentation. No preparation was done in the control group. The canals were irrigated with 2 mL of 3% sodium hypochlorite (Vishal Dentocare Pvt. Ltd, India), 5 mL of saline (Eurolife, Pirmeera Healthcare Pvt. Ltd, Pune, India) and 5 mL of 17% ethylene diamine tetraacetic acid (Dentwash, Prime Dental, Bhiwandi, India) between each instrument change, followed by a final rinse with 2 mL of distilled water.

Dentinal crack evaluation

The samples were stained with methylene blue (0.5%) for 24 h and washed in running water and after that washed with distilled water. All the samples were sectioned perpendicularly to the long axis of the teeth at 3 mm (apical), 6 mm (middle), and 9 mm (coronal) slices from the root apex with a diamond disc.

The slices were viewed under a stereomicroscope, and digital images of each section at ×2.5 were shot using a digital camera (Canon EOS 1500D).

A crack is defined as the defect originating from the inner root canal space and propagating to the periphery.[11] All other defects that did not originate from the canal wall, as craze lines were not considered as cracks [Figure 1].
Figure 1: Dentinal cracks

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Statistical analysis

The data was tabulated on excel sheet (MS Office 2010) and analyzed with Chi-square test using the Statistical Package for the Social Sciences (20.0) software package (IBM, Chicago, IL, USA). The result showing P < 0.05 is considered statistically significant.

  Results Top

The control group showed no defects at any level. There was a significant difference found amongst the experimental groups (P < 0.05) when compared to the control. At 3 mm Neo Endo flex files were associated with significantly higher cracks when compared with the other groups (P = 0.033). No significant difference was observed among the experimental groups at the 6 and 9 mm levels (P > 0.05). The PTG files produced the lesser cracks compared to Waldent Wal flex and Neo Endo flex files; however, this difference was ally significant [Table 1]. Intragroup comparison did not show any significant difference among the groups at 3 mm, 6 mm, and 9 mm [Table 2].
Table 1: Defects in the dentinal cross sections at 3, 6, and 9 (mm) (n=10)

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Table 2: Comparison of dentinal cracks in experimental groups

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  Discussion Top

In the present study, the effect of PTG files, Neo Endo flex files and Waldent Wal flex files on dentinal crack formation was compared. All the systems evaluated in the study produced dentinal cracks, and these findings are in agreement with previous studies.[7],[12],[13] According to this study, the experimental groups exhibited dentinal cracks, and the control group showed no cracks. Hence, the null hypothesis was rejected.

Freshly extracted teeth were used in the study to minimize its interference with crack formation outcome. Teeth were disinfected with 0.1% thymol solution and subsequently stored in PBS to prevent dehydration of samples, as dehydration can have impact on crack formation. Acrylic blocks and silicone impression material were used to simulate bone and PDL, respectively. PDL simulation acts as a stress absorber during preparation, thereby better mimicking the clinical situation.[14],[15]

Three percent NaOCl was preferred over 5.25% NaOCl for irrigation as higher concentrations solution of NaOCl significantly decreases the elastic modulus and flexural strength of human dentin. Methylene dye solution (0.5%) was used to differentiate the cracks, as it has a smaller molecular size (120 nm) than the bacterium, which penetrates more deeply than other dyes.[16]

In this study, the teeth were sectioned at different levels for the evaluation of cracks. Sectioning of specimens can lead to crack formation; however, there were no cracks in the control group. Thus, indicating that the dentinal cracks seen are due to preparation and not sectioning. More cracks were found in the apical section of all the experimental groups than at middle and coronal sections, which is in agreement with previous studies conducted by Karataş et al.,[3] Nishad and Shivamurthy,[16] and Chole et al.[17]

The occurrence of stress due to successive instrumentation, and low capability to the thin and fragile dentin in the apical area to the mechanical stress produced by direct contact with the instrument tip, may cause the formation of cracks.[6],[18] The tip design, cross-sectional geometry, pitch, taper, and flute of rotary instruments could affect the crack formation.[18] Greater tapered files reportedly cause increased stress on canal walls (constant or variable).[19] However, in the present study, there were no significant differences between the PTG, Neo Endo flex, and Waldent Wal flex in crack formation, although taper of PTG (F2-25/08) is more than Neo Endo flex (N3-25/06), and Waldent Wal flex (W6-25/06) files.

In this study, the least number of cracks were found in PTG. These results are similar to the study conducted by Nishad and Shivamurthy,[16] and Chole et al.,[17] who compared PTG, ProTaper Next, and PTU; where PTG had shown least number of cracks. This could be due to greater flexibility, two-stage-specific transformation behavior, a reverse transformation of the alloy which passes via the intermediate R-phase aiding as an advantage at some point in the manufacturing process, and high transition temperature (Af), explaining the superelasticity of PTG.[20] The varying taper and the convex triangular section of PTG also aid in decreasing the friction, thereby contributing to lesser crack formation.

Neoendo files[9] and Waldent Wal flex files[10] both have the same tip design, triangular cross-sectional geometry, high flexibility, and enhanced cutting efficiency due to gold treatment. Waldent Wal flex files showed lesser crack formation compared to Neo endo, which can be due to differences in the manufacturing process (opening of the flutes when the stress level is reached control memory wire) in Waldent Wal flex files.[10] In contrast, Neo Endo flex having greater speed (350 rpm) and increased cutting efficiency showed more number of cracks in the present study.

Different speeds and torques have been used for three-file systems according to manufacturer's instructions. According to Peter et al.[21] and Capar et al.,[22] the increased rotational speed is related to increased cutting efficiency and lesser crack formation. However, Neo Endo flex files, which were operated at a higher speed (350 rpm) when compared to the remaining groups, produced more cracks. As no studies have evaluated the dentinal crack formation with neoendo files before, there are no data to compare this unexpected finding. It could be attributed to instrument design and toughness, though the factors responsible cannot be ascertained.

The limitations of the current study are the usage of stereomicroscope over Micro-computed tomography (CT) whose resolution is higher than stereomicroscope; however, Micro-CT produces hundreds of slices, which are not easy to assess and also some microcracks may be overlooked.[23]

This study signifies the importance of varying taper, convex triangular cross-section of PTG to be superior to the rest of groups in producing fewer cracks as these features decrease the friction between the file and canal system. The rest of the design features of the three groups do not vary much. Neo Endo flex files produced more cracks, which could be due to the tough nature[9] of the instrument, implying that flutes of the file are stable at high-stress levels. However, more studies and evidence are required to have more conclusive results and assess the effect of these rotary files on crack formation.

  Conclusion Top

All the rotary files that were tested produced dentinal cracks. Neo Endo flex files group was associated with more number of cracks than PTG files and Waldent Wal flex files group. The apical section of samples showed significantly higher defects compared to the middle and coronal sections.

Financial support and sponsorship


Conflicts of interest

There are no conflicts of interest.

  References Top

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Karataş E, Gündüz HA, Kırıcı DÖ, Arslan H. Incidence of dentinal cracks after root canal preparation with ProTaper Gold, Profile Vortex, F360, Reciproc and ProTaper Universal instruments. Int Endod J 2016;49:905-10.  Back to cited text no. 3
Khasnis SA, Kidiyoor KH, Patil AB, Kenganal SB. Vertical root fractures and their management. J Conserv Dent 2014;17:103-10.  Back to cited text no. 4
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Langaliya AK, Kothari AK, Surti NR, Patel AR, Doshi PR, Pandya DJ. In vitro comparative evaluation of dentinal microcracks formation during root canal preparation by different nickel-titanium file systems. Saudi Endod J 2018;8:183-8.  Back to cited text no. 6
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  [Figure 1]

  [Table 1], [Table 2]


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