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 Table of Contents  
Year : 2022  |  Volume : 13  |  Issue : 2  |  Page : 53-56

Dentinal Defects Induced by Offset and Alternating Contact Endodontic Rotary Files: An In Vitro Study

Department of conservative dentistry, College of Dentistry, Mustansiriyah University, Baghdad, Iraq

Date of Submission04-Oct-2021
Date of Decision25-Feb-2022
Date of Acceptance20-Apr-2022
Date of Web Publication12-Jul-2022

Correspondence Address:
Firas S. O Albaaj
Department of conservative dentistry, College of Dentistry, Zayona 712, Baghdad
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Source of Support: None, Conflict of Interest: None

DOI: 10.4103/denthyp.denthyp_138_21

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Objective: Dentinal defects during root canal preparation could lead to treatment failure and tooth extraction. Many rotary files are manufactured with asymmetric cross sections or alternating cutting edges to minimize contact with the canal wall. Decreasing contacts may generate low stresses and, hence, fewer dental defects during root canal instrumentation. This study aimed to evaluate the incidence of dentinal defects induced by ProTaper Next, Wave One Gold (Dentsply Maillefer, Ballaigues, Switzerland), and iRace (FKG Dentaire SA, La Chaux-de-Fonds, Switzerland) in comparison to the symmetric file HyFlex CM (Coltene-Whaledent, Allstetten, Switzerland). Materials and Methods: Sixty extracted single-rooted premolars with round canals were selected for this study. All teeth were decoronated and divided into four experimental groups according to the tested file systems. In each group, 15 canals were prepared with the crown down technique using a speed and torque recommended by manufacturers. The root samples were then sectioned horizontally at 3, 6, and 9 mm from the apex and examined under a stereomicroscope to evaluate the presence or absence of dentinal defects. Data were statistically analyzed with SPSS software using a chi-square test. Results: Dentinal defects were observed at all canal levels following all methods of instrumentation. ProTaper Next showed the lowest values of dentinal defects, whereas Hyflex CM displayed the highest values. Conclusion: Files with few contacts with the canal wall decreased the number of dentinal defects compared to the HyFlex CM file, with a nonsignificant difference being observed.

Keywords: Alternating contact files, dentinal defects, offset files, root canal instrumentation

How to cite this article:
Abass AA, Fadhil HT, Albaaj FO. Dentinal Defects Induced by Offset and Alternating Contact Endodontic Rotary Files: An In Vitro Study. Dent Hypotheses 2022;13:53-6

How to cite this URL:
Abass AA, Fadhil HT, Albaaj FO. Dentinal Defects Induced by Offset and Alternating Contact Endodontic Rotary Files: An In Vitro Study. Dent Hypotheses [serial online] 2022 [cited 2022 Aug 10];13:53-6. Available from:

  Introduction Top

The aim of root canal instrumentation is to remove infected tissues and shape the root canal into a smooth conical lumen while maintaining the original canal path and anatomy.[1] The instrumentation process is a critical phase that can affect endodontic treatment prognosis. Incorrect instrumentation can induce errors, such as canal stripping and preformation, or complications such as dentinal crack and root fracture.[2] Apart from iatrogenic factors, criteria such as file design and the type of alloy used to fabricate these files have been reported to directly impact the incidence and severity of such errors and complications.

Dentinal defects occur when stresses applied to a dentinal wall exceed the tensile stress limit of dentine.[3] Manufacturer attempts to reduce these stresses have been seen in developing files with asymmetrical cross sections, files with variable tapers, and files with alternating contact edges. These designs could reduce the screw-in effect of the file in the canal and, hence, reduce the tensile forces on the dentinal wall. Rotary ProTaper Next files are produced with asymmetrical rectangular cross sections with two-point contacts with the canal wall and progressive/regressive tapers.[4] Reciprocating Wave One Gold files are produced with an offset parallelogram-shaped cross section design and gold-wire technology characteristics to control the unfavorable effect of high stresses observed during canal preparation with the first-generation files.[5]

iRace is a rotary file with an asymmetrical triangular cross-section design and sharp cutting edges. The file is electromechanically polished to improve cyclic and torsional fatigue resistance. The file works with full rotation and an alternating cutting action to minimize stresses on dentine and wedging in the canal.[6] Furthermore, the file is designed with a thin core that can provide increased flexibility and more space to remove debris coronally, as claimed by the manufacturer.[6],[7]

HyFlex CM files have a symmetrical convex-triangular cross section making contact with the canal wall with three points at any given cross section.[8] The files are manufactured from a heat-treated NiTi alloy to ensure high flexibility during navigation of a curved canal.[9]

This study aimed to evaluate the incidence of dentinal defects induced by ProTaper Next, Wave One Gold, and iRace compared with HyFlex CM using a stereomicroscope.

  Materials and Methods Top

Sixty extracted single-rooted premolars were collected for this study following the approval of the Research Ethics Committee of the College of Dentistry, Mustansiriyah University. Remnants of periodontal ligaments were cleaned with a periodontal scaler (Acteon, Aquitaine, France). Teeth with severely curved roots, calcified root canals, or an additional canal were excluded. The crowns were sectioned with a diamond disc under water cooling, leaving roots of 15 mm in length. Root surfaces were examined with a stereomicroscope under 24× magnification to discard roots with preexisting cracks or craze lines. Roots were stored in distilled water at 4°C until use. The root samples were randomly divided into four groups of 15 samples each. The working length was estimated at 0.5 mm short of the apical foramen. Apical patency was established utilizing a #15 K-file (Dentsply Maillefer, Ballaigues, Switzerland). To facilitate the removal of roots during the testing procedure, they were wrapped with aluminum foil and inserted into a cylindrical metal mold containing silicon impression material (President dental, Allershausen, Germany). Canal instrumentation was made in a crown-down brushing motion with the speed and torque set according to manufacturer recommendations [Table 1].
Table 1 Specifications of each file system used in this study

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File flutes were cleaned of dentinal debris with an endodontic sponge following every three in-out strokes. Each file was used to prepare five canals. To irrigate the canal during preparation with each instrument, 1 mL of 2% sodium hypochlorite solution (Cerkamed, Stalowa Wola, Poland) was used. Canal patency was regularly maintained with the #15 K-file.

After preparation, the samples were removed from the set silicon impressions, and the foils were discarded. Using a dental surveyor, the roots were placed centrally in clear acrylic resin in a cylindrical plastic mold to control root sectioning. Sample sectioning was performed at 3, 6, and 9 mm from the apex using a diamond disc under water cooling. Sections were then coded by the authors and visualized by two blind examiners using the stereomicroscope at 24× magnification. Dentinal defects, including cracks and craze lines, were recorded as “0 = no defect” and “1 = defect” according to the classification used by Milani et al. with modification.[10] Data were statistically analyzed with SPSS (V. 24) (SPSS Inc., Chicago, IL, USA) using a chi-square test at a significance level of P < 0.05 (α = 0.049) and a 95% confidence interval.

  Results Top

The distribution and frequency of dentinal defects for each group are presented in [Table 2]. The distribution of dentinal defects at each root level is provided in [Table 3].
Table 2 Distribution and frequency of dentinal defects induced by each file system

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Table 3 Distribution of dentinal defects induced by file systems at each root level

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All tested file systems induced defects on dentine at all canal levels. The difference was nonsignificant among groups (P > 0.05). ProTaper Next induced the lowest number of dentinal defects, whereas HyFlex CM showed the highest number. A significant difference (P < 0.05) was found between apical and middle levels of the HyFlex CM group, and a nonsignificant difference was noted among the different levels of the other groups (P > 0.05).

  Discussion Top

Recently, several NiTi rotary file systems have been developed with various cross-sectional and longitudinal designs. Variations in file geometry have demonstrated different levels of tensile stress on the canal wall during the instrumentation process.[11],[12] The goal of the present study was to assess to what extent offset and alternating contact NiTi rotary file systems including ProTaper next, Wave One Gold, and iRace induce dentinal defects compared with the symmetrical HyFlex file system.

The current study revealed that all file systems induced dentinal defects at the three root levels. This finding agrees with the results of other studies that relied on the same stereomicroscope methodology.[13],[14] However, the results contradict those of other studies that relied on noncontact assessments of root dentine using microCT. For instance, Katanec et al. and De-Deus et al. found that rotary files did not generate new dentinal cracks; rather, cracks were observed in the pretreatment phase.[15],[16] Tooth extraction, storage conditions, and tooth sectioning are factors that could generate dentinal defects apart from root canal instrumentation in vitro. Hence, it may be that the preoperative evaluation of external root surfaces with a stereomicroscope cannot detect preexisting cracks or craze lines located deep in the root structure. Such a methodology shortcoming could cause false-positive results of dentinal defects following root canal instrumentation.

In the current study, ProTaper Next, Wave One Gold, and iRace files produced similar percentages of dentinal defects. These results agree with the findings of Saberi et al., where both ProTaper Next and iRace files caused similar dentinal defect percentages.[17] A previous finding showed that files with a larger taper or driven with high torque and a reciprocating motion can generate high tensile stress on the canal wall.[13] In this study, the large taper and high torque used with the reciprocating Wave One Gold file were not recognized as factors that aggravate dentinal defects, potentially because these aggravating factors are compensated by the offset design, which offers one or two contact points with the canal wall at any given cross section.[5] This notion is further supported by Pedullà et al., who found that the Wave One Gold file induced significantly fewer dentinal defects than the conventional Wave One file with the symmetrical cross section.[18]

In our study, files with an asymmetrical cross section or with alternating cutting edges produced fewer defects than the symmetrical HyFlex CM files did. This result is consistent with the work of Shori et al., where files with more contact points showed more defects in the canal wall.[19] HyFlex CM has three contact points, which could add more foci of stresses on root canal dentine when compared with the fewer contact points of the other files. Furthermore, less contact with the canal wall could leave more spaces, as claimed by manufacturers. These spaces can facilitate debris removal and reduce debris packed in canal recesses, permitting more unrestricted file movement. Additionally, HyFlex CM files have a fixed taper, which increases the possibility of file wedging and, hence, stresses in the canal.[20]

  Conclusion Top

Within the limitations of this in vitro study, the offset and alternating contact file systems induced fewer dentinal defects than did the symmetric file system, but these differences were not significant.

Financial support and sponsorship


Conflicts of interest

There are no conflicts of interest.

  References Top

European Society of Endodontology. Quality guidelines for endodontic treatment: consensus report of the European Society of Endodontology. Int Endod J 2006;39: 921–30.  Back to cited text no. 1
Hendi SS, Karkehabadi H, Eskandarloo A. Iatrogenic errors during root canal instrumentation performed by dental students. Iran Endod J 2018;13:126.  Back to cited text no. 2
Dane A, Capar ID, Arslan H, Akçay M, Uysal B. Effect of different torque settings on crack formation in root dentin. J Endod 2016;42:304–6.  Back to cited text no. 3
Dentsply. ProTaper Next brochure: Dentsply 2012. Accessed June 5, 2020. Available from:  Back to cited text no. 4
Ruddle CJ. Single-file shaping technique: achieving a gold meal result. Dent Today 2016;35: 1–7.  Back to cited text no. 5
FKG-Dentair. iRace: quick, effective and safe 2013. Accessed June 5, 2020. Available from:  Back to cited text no. 6
Versiani MA, Carvalho KK, Mazzi-Chaves JF, Sousa-Neto MD. Micro–computed tomographic evaluation of the shaping ability of XP-endo Shaper, iRaCe, and EdgeFile systems in long oval-shaped canals. J Endod 2018;44: 489–95  Back to cited text no. 7
Coltene. The new NITi file generation: Hyflex CM & EDM 2018. Accessed July 8, 2020. Available from:  Back to cited text no. 8
Razcha C, Zacharopoulos A, Anestis D, Mikrogeorgis G, Zacharakis G, Lyroudia K. Micro-computed tomographic evaluation of canal transportation and centering ability of 4 heat-treated nickel-titanium systems. J Endod 2020;46:675–81.  Back to cited text no. 9
Milani AS, Froughreyhani M, Rahimi S, Jafarabadi MA, Paksefat S. The effect of root canal preparation on the development of dentin cracks. Iran Endod J 2012;7:177.  Back to cited text no. 10
Kim H-C, Lee M-H, Yum J, Versluis A, Lee C-J, Kim B-M. Potential relationship between design of nickel-titanium rotary instruments and vertical root fracture. J Endod 2010;36:1195–9.  Back to cited text no. 11
Shantiaee Y, Dianat O, Mosayebi G, Namdari M, Tordik P. Effect of root canal preparation techniques on crack formation in root dentin. J Endod 2019;45:447–52.  Back to cited text no. 12
Kesim B, Sagsen B, Aslan T. Evaluation of dentinal defects during root canal preparation using thermomechanically processed nickel-titanium files. Eur J Dent 2017;11:157–61.  Back to cited text no. 13
[PUBMED]  [Full text]  
Wei X, Hu B, Peng H, Tang M, Song J. The incidence of dentinal cracks during root canal preparations with reciprocating single-file and rotary-file systems: A meta-analysis. Dent Mater J 2017;36:243–52.  Back to cited text no. 14
Katanec T, Miletić I, Baršić G, Kqiku-Bliblikaj L, Žižak M, Krmek SJ. Incidence of Dentinal Micro Cracks during Root Canal Preparation with Self Adjusting File, Reciproc Blue, and ProTaper Next. Iran Endod J 2020;15:6–11.  Back to cited text no. 15
De-Deus G, Belladonna FG, Souza EM et al.Micro–computed tomographic assessment on the effect of ProTaper Next and Twisted File Adaptive systems on dentinal cracks. J Endod 2015;41:1116–9.  Back to cited text no. 16
Saberi E, Mohammadi A, Ebrahimipour S, Baniasadi S, Techniques. In-vitro comparison of NiTi Tee, RaCe and Protaper instruments in dentinal crack formation. J Dent Mate 2017;6:152–8.  Back to cited text no. 17
Pedullà E, Genovesi F, Rapisarda S et al.Effects of 6 single-file systems on dentinal crack formation. J Endod 2017;43:456–461.  Back to cited text no. 18
Shori DD, Shenoi PR, Baig AR, Kubde R, Makade C, Pandey S. Stereomicroscopic evaluation of dentinal defects induced by new rotary system:“ProTaper NEXT”. J Conserv Dent 2015;18: 210–3.  Back to cited text no. 19
[PUBMED]  [Full text]  
Ha J, Cheung G, Versluis A, Lee C, Kwak S, Kim H. ‘Screw-in’ tendency of rotary nickel–titanium files due to design geometry. Int Endod J 2015;48: 666–72.  Back to cited text no. 20


  [Table 1], [Table 2], [Table 3]


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