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Year : 2020  |  Volume : 23  |  Issue : 4  |  Page : 510-514

The effect of cervical preflaring on the apical debris extrusion of single or multiple rotary Ni-Ti files

Department of Endodontics, Faculty of Dentistry, Eskisehir Osmangazi University, Eskişehir, Turkey

Date of Submission01-Nov-2019
Date of Acceptance07-Dec-2019
Date of Web Publication4-Apr-2020

Correspondence Address:
Dr. B Gunes
Department of Endodontics, Faculty of Dentistry, Eskisehir Osmangazi University, Eskisehir
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Source of Support: None, Conflict of Interest: None

DOI: 10.4103/njcp.njcp_599_19

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Background: There were no comparing data about the effect of recently developed file system OneCurve on apical debris extrusion. Aim: The aim of this in vitro study was to compare the influence of the rotary nickel—titanium (Ni-Ti) files on apical debris extrusion after cervical preflaring. Materials and Methods: Sixty-six lower incisor teeth with a single root canal were used in this study. After the determination of working length, the specimens were divided into six experimental groups according to root canal preparation. G1: ProTaper-Next, G2: EndoFlare + ProTaper-Next, G3: 2Shape, G4: EndoFlare + 2Shape, G5: OneCurve, and G6: EndoFlare + OneCurve. Each specimen was inserted into separate preweighed Eppendorf tubes to collect apically extruded debris. A total of 8 mL of distilled water was used for each specimen for irrigation. After the completion of root canal preparation, the Eppendorf tubes were weighed again after evaporation to calculate the amount of extruded debris. The data were statistically analyzed with one-way analysis of variance (P > 0.05). Results: There was no statistically significant difference between the experimental groups. The amount of apically extruded debris was similar after preparing root canals with ProTaper-Next, 2Shape, and OneCurve with and without cervical preflaring. Conclusion: Under the conditions of this in vitro study, ProTaper-Next, 2Shape, and OneCurve files had similar apical debris extrusion values. Cervical preflaring of root canals did not affect the amount of apically extruded debris.

Keywords: Cervical preflaring, C-wire heat treatment, debris extrusion, rotary Ni-Ti files

How to cite this article:
Gunes B, Yeter K Y. The effect of cervical preflaring on the apical debris extrusion of single or multiple rotary Ni-Ti files. Niger J Clin Pract 2020;23:510-4

How to cite this URL:
Gunes B, Yeter K Y. The effect of cervical preflaring on the apical debris extrusion of single or multiple rotary Ni-Ti files. Niger J Clin Pract [serial online] 2020 [cited 2022 Oct 3];23:510-4. Available from:

   Introduction Top

The main target of endodontic treatment is the removal of irritating factors from the root canal system to maintain healthy periapical tissues.[1] During the chemomechanical preparation of root canals, microorganisms and their byproducts, pulp tissue remnants, dentin chips, and irrigation solutions may be transported through the apical foramen and extruded into the periapical tissues.[2],[3] The apical extrusion of infected debris into the periapical tissues may cause postoperative pain and flare-ups and provoke an acute inflammatory response.[4],[5],[6] Although several instruments, instrumentation, and irrigation techniques have been introduced, there is no method associated with no extrusion of debris.[2],[4],[7],[8]

By introducing rotary nickel–titanium (Ni-Ti) rotary systems for the mechanical preparation of the root canal system, endodontic treatment may be completed with less treatment time, operator fatigue, and procedural errors.[9] Although Ni-Ti rotary files have several advantages, the risk of instrument fracture is increased mainly because of the high flexural and torsional stresses.[10]

The mechanical preparation of root canals might be achieved safely and more successfully by creating a coronal flare and glide path before the root canal instrumentation.[11] Straight line access to the middle and apical thirds of the root canal causes a decrease in the risk of instrument fracture caused by torsional and cyclic fatigue.[12] Progressive and continuous dentin formation on the pulp space floor narrows the canal diameter and causes dentin projections mainly in the cervical and middle thirds.[13],[14] Coronal preflaring of the root canal improves the determination of the apical patency[13] and minimizes the change in the working length (WL) determination.[15] Less debris extrusion beyond the apical foramen was observed when the cervical preflaring was performed prior to the mechanical preparation of the root canal with engine-driven Ni-Ti files.[14],[16] The mechanical preparation of root canals with Ni-Ti rotary files is associated with less debris extrusion than manual preparation techniques.[17],[18]

EndoFlare (Micro-Mega, Besançon, France) can be used to flare the coronal part of the root canal before chemomechanical preparation.[19] The file has a 0.12 taper, a 10-mm blade length, and a tip size of #25.

Single-file Ni-Ti systems simplify the preparation of root canals and require less time than multiple rotary Ni-Ti file systems.[20],[21] The OneCurve continuous rotating single-file system has recently been launched by Micro-Mega Company. This file is manufactured with patented C-wire heat treatment technology. This technology provides a pre-bending opportunity and a controlled shape memory effect.[22] The tip size of OneCurve file is #25, and the file has a 0.06 taper. The OneCurve instrument has a variable cross section which ensures better cutting and centering ability.[23] The 2Shape (Micro-Mega) continuous Ni-Ti system includes two files, a TS1 with a 0.04 taper and a #25 tip size and a TS2 with a0.06 taper and a #25 tip size. Files were produced with T-wire heat treatment technology and have a triple helix cross section with two main cutting edges (Micro-Mega, Besançon, France). ProTaper Next (Dentsply Maillefer, Ballaigues, Switzerland) was manufactured with M-wire Ni-Ti technology for better cyclic fatigue resistance and greater flexibility. The file system includes five instruments for shaping the root canals: X1 (0.17/0.04), X2 (0.25/0.06), X3 (0.30/0.07), X4 (0.40/0.06), and X5 (0.50/0.06) (Dentsply Maillefer, Ballaigues, Switzerland). The files have an off-centered rectangular cross section and use full rotary motion.[24],[25]

The aim of thisin vitro study was to compare the effect of new single rotary file OneCurve and multiple rotary files on apically extruded debris after cervical preflaring. The null hypothesis of this study was that there would be no significant difference in the amount of apically extruded debris after preparing the root canals with different file systems with and without cervical preflaring.

   Materials and Methods Top

Thisin vitro study was approved by the Ethics Committee of Eskisehir Osmangazi University (25403353-050.99-E.122330) and was conducted according to the principles of the Declaration of Helsinki. A total of 104 extracted human mandibular incisor teeth with a single and straight root canal and completely formed apices were selected for this study. Buccal and proximal radiographs were taken to verify whether each sample had a single root canal. Teeth with external or internal root resorption, calcified root canals, root fracture or cracks, prosthetic crowns, endodontic treatments, and abnormal root canal morphology were discarded from the study. The specimens with a root canal curvature >5° were excluded from the study.[26] The crowns of the remaining 70 teeth were separated using a diamond disk using water cooling to obtain a 15-mm root length. The apical patency of the root canals was established using a #08 K-file (VDW, Germany), and specimens which had a root apex width greater than #15 were rejected. A size 10 K-file was introduced into the remaining 66 root canals until the tip of the instrument was visible at the apical foramen under a stereomicroscope. One millimeter was subtracted from this length to establish the WL. The roots were randomly split into six experimental groups with respect to the root canal instrumentation procedure (n = 11).

  • Group 1 – ProTaper Next (PN): The root canals were prepared with ProTaper Next X1 and X2 files at the full WL. The Ni-Ti file system was used following the manufacturer's recommendations
  • Group 2 – EndoFlare + ProTaper Next (EPN): The root canals were prepared with ProTaper Next X1 and X2 files after performing cervical preflaring with EndoFlare file (Micro-Mega). The EndoFlare file (#25, 0.12) was used to enlarge the cervical 3 mm of the canal with an in-and-out motion
  • Group 3 – 2Shape (TS): The root canals were prepared using 2Shape files (TS1 and TS2) following the manufacturer's instructions
  • Group 4 – EndoFlare + 2Shape (ETS): Root canal enlargement was performed with TS1 and TS2 files after coronal preflaring with EndoFlare
  • Group 5 – OneCurve (OC): The OneCurve file was used according to the manufacturer's recommendations to prepare the root canals
  • Group 6 – EndoFlare + OneCurve (EOC): The cervical preflaring of the root canals was carried out using EndoFlare file and the root canals were prepared with a OneCurve file.

All the instruments were used with X-Smart Plus (Dentsply Maillefer) at the regulated torque and speed levels following the manufacturers' instructions. Rotary Ni-Ti instruments were used with slow motion and an in-and-out movement. After three pecks or each instrument change, the root canals were irrigated with distilled water and the flutes of the files were cleaned. A total volume of 8 mL of distilled water was used for irrigation during the preparation of the root canals. An irrigation needle (NaviTip 31-G; Ultradent Products Inc., South Jordan, UT, USA) was inserted 2 mm short of the WL. The apical patency was controlled after changing each file and the final irrigation. After finishing the root canal instrumentation, for the purpose of collecting the debris that had attached the outer surface of the apical part of the root it was washed with 1 mL of distilled water. Root canal preparation was accomplished when the file reached the WL. All the root canal preparation procedures were finished by a single operator who was a specialist in endodontics with more than 10 years of experience.

Debris collection

Separate Eppendorf tubes were selected for each specimen and numbered. The weight of each tube was measured using an electronic analytical balance (Shimadzu AP225WD, Kyoto, Japan) with an accuracy of 10−5. Each tube was weighed three times and the average of the measurements was calculated.

The method described by Myers and Montgomery[27] was chosen to collect the debris that apically extruded during the root canal instrumentation procedures. The preweighed Eppendorf tubes were placed into the separate glass flasks. The silicone cover of the flask was perforated to form a round hole. The roots were placed into the silicone cover up to the cementoenamel junction and were bonded with cyanoacrylate glue (Pattex, Henkel) to prevent the potential leakage of debris and distilled water through the outer surface. The internal and external air pressures were equalized by placing a 27-gauge needle through the rubber cover. Each tooth with the silicone cover was inserted in a separate Eppendorf tube. A rubber dam sheet was used to avoid the operator from viewing the extrusion of debris during the instrumentation procedures. The experimental setup is shown in [Figure 1].
Figure 1: A schematic illustration of the experimental setup

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After the completion of the root canal instrumentation, the Eppendorf tubes with the extruded debris and irrigation solution were removed from the experimental setup and stored in an incubator at 68°C for 5 days. After evaporation of the distilled water, the tubes were reweighed to calculate the amount of extruded debris. Three serial measurements were obtained, and the average weight was calculated for each Eppendorf tube. The weight of the extruded debris was calculated by subtracting the initial weight from the final weight.

The data were statistically analyzed using a one-way analysis of variance test after logarithmic transformation. SAS 9,3 GLM (SAS Institute Inc., Cary, NC, USA) statistical program was used for statistical analyses. The level for accepting statistical significance was set at P < 0.05.

   Results Top

There was no statistically significant difference between the experimental groups (P > 0.05). Using preflaring files had no effect on the apically extruded debris during root canal preparation with the OneCurve, 2Shape, and ProTaper Next systems. The mean and standard deviation values of each experimental group are shown in [Table 1].
Table 1: Minimum, maximum, standard deviation, and mean±SE values (values with the same superscript letter are not statistically different)

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   Discussion Top

The extrusion of endodontic obturation materials, irrigation solutions, or medicaments into the periradicular tissues may cause delayed healing or an unsuccessful treatment outcome because of a foreign body reaction.[28],[29] The extrusion of microorganisms or infected debris during chemomechanical preparation of root canals can disrupt the balance, and a periradicular acute reaction will begin. The intensity of this reaction will depend on the virulence and volume of the extruded microorganisms.[4],[7] Although minimal debris extrusion is aimed by practitioners while preparing root canals to reduce the postoperative pain and to increase the healing potential, there is no method which causes no debris extrusion.[7] Only X1 and X2 files were used in the ProTaper groups to ensure that the root canal preparation of all the samples finished with #25/0.06 files in this study. Tınaz et al.[30] reported that the increase in the apical patency of the root canal causes more irrigation solution and debris extrusion beyond the apex. Thus, specimens with apical patency larger than a #15 K file were excluded to standardize the specimens in our study. In addition, rotary Ni-Ti files with a similar tip size (#25) and taper (0.06) were used to maintain equivalent apical enlargement and similar root canal preparation.

To the best of our knowledge, there is no study comparing the effect of new C-wire rotary file OneCurve on apical debris extrusion. All tested instrumentation procedures caused a statistically similar amount of extruded debris in thisin vitro study. Cervical preflaring had no effect on the debris extrusion while preparing root canals with the rotating OneCurve, 2Shape, and ProTaper Next Ni-Ti file systems. The null hypothesis of this study was accepted. Similar to our study, Topcuoglu et al.[16] found that coronal preflaring prior to the root canal preparation with a rotating single Ni-Ti file did not affect the amount of extruded debris. Borges et al.[14] used several Ni-Ti reciprocating and rotating systems and compared the amount of apically extruded debris with or without cervical flaring. Conversely, they reported that cervical preflaring reduced the amount of apically extruded debris. Different instrument design and size, experimental methods, root canal anatomy, and the apical diameter of specimens might be effective on different test results.

The continuous rotational movement of endodontic instruments could improve the coronal transportation of dentin debris and chips by acting like a screw conveyor.[21] Bürklein et al.[2] found no difference between the amount of apically extruded debris after preparing root canals with single and multiple rotary file systems. Similarly, Uslu et al.[31] reported that HyFlex EDM and XP-endo Shaper continuous rotating single files caused similar debris extrusion values. In accordance with their results, there was no difference between the effects of TS, PN, and OC rotary Ni-Ti file systems on the amount of apically extruded debris in our study.

Distilled water was used for the irrigation procedure to avoid any possible crystallization of sodium hypochlorite.[32] Crystals of irrigation solution such as sodium hypochlorite might be effective on the test results because the debris and sodium crystals cannot be separated from each other.[7]

No attempt has been made to simulate natural pulp tissue and the resistance of periapical tissues in this ex vivo experimental model. Therefore, the results of this study should be transferred to a clinical situation with caution. Floral foam could be used for the simulation of periapical back pressure, but it might cause the absorption of extruded debris and irrigation solution.[2]

According to the results of our study, the recently produced C-wire OneCurve file caused similar debris extrusion with 2Shape and ProTaper file systems. Although cervical preflaring did not change the amount of extruded debris in this study, we cannot ignore that cervical preflaring improves the determination of the apical patency and WL.

   Conclusion Top

Within the limitation of this ex vivo study, all tested systems caused apical debris extrusion. The amount of apically extruded debris was statistically similar after preparing root canals with 2Shape, ProTaper Next, and OneCurve rotary files. Coronal preflaring had no effect on the amount of the extruded debris while using the tested rotary file systems.


This study was presented at the “20th Scientific Congress of the Asian Pacific Endodontic Confederation and The 14th International Congress of Turkish Endodontic Society” in Istanbul as an oral presentation.

Financial support and sponsorship


Conflicts of interest

There are no conflicts of interest.

   References Top

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  [Figure 1]

  [Table 1]


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