Tanta Dental Journal

: 2019  |  Volume : 16  |  Issue : 2  |  Page : 73--79

The efficacy of different single file systems in cleaning oval shaped root canal

Neveen A Shaheen 
 Department of Endodontics, Faculty of Dentistry, Tanta University, Tanta, Egypt

Correspondence Address:
Neveen A Shaheen
Department of Endodontics, Faculty of Dentistry, Tanta University, Tanta


Aim The aim of this in-vitro study was to compare the effectiveness in cleaning oval shaped canal using different single file systems (WaveOne, OneShape, and XP-endo shaper). Materials and methods Thirty freshly extracted single rooted premolars with single, oval shaped root canals were selected. The crowns of all teeth were cut at the cementum–enamel junction to obtain root segment of ~14 ± 1 mm length. After working length determination, samples were randomly divided into three groups (n = 10) according to the file system used for root canal preparation as follow: group 1: Primary WaveOne; group 2: OneShape file; group 3: XP-endo Shaper. Sodium hypochlorite irrigant was used throughout instrumentation followed by 17% EDTA then normal saline as final rinse. The roots were splitted longitudinally into two halves and then prepared for scanning electron microscopy evaluation. The presence of smear layer and debris was recorded at apical, middle, and coronal sections of the canal. The scanning electron microscopy photomicrographs were scored based on four-scale numerical scoring system, and the scores were tabulated accordingly and statistically analyzed using Kruskal–Wallis test at a significance level of P value less than 0.05 then Mann–Whitney test was done for multiple pairwise comparisons. Results XP-endo Shaper instrument was efficient for root canal cleaning when compared with the other two single file systems. There was statistical significant difference between cleaning efficiency of all instrumentation systems at the cervical or middle as compared with the apical thirds of root canal. Conclusion Complete canal cleanliness cannot be achieved with any of the investigated single file systems.

How to cite this article:
Shaheen NA. The efficacy of different single file systems in cleaning oval shaped root canal.Tanta Dent J 2019;16:73-79

How to cite this URL:
Shaheen NA. The efficacy of different single file systems in cleaning oval shaped root canal. Tanta Dent J [serial online] 2019 [cited 2020 Mar 28 ];16:73-79
Available from: http://www.tmj.eg.net/text.asp?2019/16/2/73/267567

Full Text


Total elimination of infected pulp tissue from the root canal and proper cleansing of the canal space are the main objectives of chemomechanical instrumentation and considered essential for success in endodontics. To achieve these objectives, pulpal remnants and debris must be removed from the root canal walls [1].

The internal anatomy of the root canal system and the pulpal space are highly complex, there are fins, isthmuses, lateral and accessory canals in addition to oval shaped canal that lead to more difficult root canal treatment [2],[3]. Most of the currently available instrumentation systems have failed to improve debridement of oval shaped canals [3].

Different instrumentation techniques have been described to prepare oval shaped canals. These include the use of sonic and ultrasonic instruments [4], manual instrumentation [5] or full rotary nickel–titanium (Ni–Ti) instrumentation techniques [6],[7] and finally reciprocating instrumentation techniques [8],[9]. Most rotary Ni–Ti instrumentation techniques as well as manual instrumentation will lead to deviation from the original oval shape showing key-hole, dumbbell-shaped, or central bulge effects in these oval shaped canals [10]. Some areas of root canal walls remain untouched after instrumentation [11],[12],[13],[14]. These areas may contain bacteria and compromise the outcome of endodontic treatment [15]. In addition to, root canal instrumentation leads to formation of smear layer [16], which is 1–2 μm thick amorphous layer at the surface [17]. However, this layer is not present on uninstrumented canal walls. The cutting debris is forced into dentin tubules at variable depths creating the smear plugs [18]. This layer often contains bacteria and blocks dentinal tubules, which significantly decrease the effect of irrigant, affecting the quality of obturation and finally the outcome of endodontic treatment [19],[20].

The cleaning ability of root canal instruments are dependent on their particular design as well as the dynamics used during instrumentation. Various single file systems with different metallurgy and design characteristics have been promoted to prepare the root canals with one instrument using either continuous rotation or reciprocation motion.

WaveOne file system works in a reciprocating motion and is manufactured from a special Ni–Ti alloy called M-Wire that is produced by a novel thermal treatment process. This M-Wire has been claimed to improve the instrument flexibility and increase resistance to cyclic fatigue [21]. Primary WaveOne file with a tip size of 25 has a fixed 8% taper from D1 to D3 and a gradually decreasing percentage tapered design from D4 to D16 to preserve dentin [22].

On the other hand, OneShape rotary system is made of a conventional austenite Ni–Ti alloy with a tip size of 25 and a constant 6% taper. Its cutting blade incorporates several cross sectional designs (variable three cutting edges at the tip and S-shaped two cutting edges near the shaft) and variable pitch along its entire length [23].

XP-endo Shaper (XPS) is a novel introduced snake shaped instrument with adaptive core and innovative thermomechanically treated Ni-Ti alloy termed as Max-Wire (Martensit-Austenite-electropolish-fileX). This instrument is relatively straight in their martensitic phase (M-phase) at room temperature and changes to a curved shape when exposed to intracanal temperature due to a phase transformation to austenitic phase (A-phase). Thus, this instrument exhibits a shape memory effect when inserted into the root canal (M-phase to A-phase) and possess superelasticity during preparation. The file has an initial taper of 0.01 in its M-phase when it is cooled, but, upon exposure to body temperature (35°C), the taper changes to 0.04 [24].

None of the currently available instrument systems and techniques can lead to completely clean root canal surface. Therefore the aim of this study was to evaluate the efficacy of recently introduced rotary XPS in comparison to other single file systems in different motion kinematics: WaveOne reciprocating and OneShape rotary systems in cleaning oval shaped canals using scanning electron microscopy (SEM).

 Materials and Methods

This study was conducted on 30 freshly extracted human premolars; teeth were extracted for orthodontic or periodontal reasons. The inclusion criteria were: morphological similarity, straight roots with no decay, absence of previous endodontic treatment and single oval shaped canals whose buccolingual dimensions were more than twice their mesiodistal dimensions as confirmed by digital radiograph taken in both directions. The purpose of the study was explained to the patients and informed consents were obtained to use their extracted teeth in the research according to the guidelines adopted by the Research Ethics Committee at Faculty of Dentistry, Tanta University. Teeth were cleaned by removing the hard deposits using hand curettes and the soft tissues were dissolved by soaking them in 5.25% sodium hypochlorite (Clorox Co., Ramadan, Egypt) for 10 min and then stored in daily changed normal saline solution until use.

The crown of each tooth was removed at the level of cementum–enamel junction using water cooled diamond disc (Komet; Brasseler, Lemgo, Germany) to obtain similar root segments of ~14 ± 1 mm in length. The working length of each sample was determined by inserting hand stainless-steel K-file (Mani Inc., Tochigi, Japan) size 15 and 0.02 taper until its tip just appeared through the apical foramen. An individual working length for each one was calculated by subtracting 1 mm from the measured length. Teeth with apical diameters larger than size 15 were excluded from this study.

All roots were randomly assigned into three equal groups of 10 samples each according to the preparation system used as follows:

Group 1: Root canals were prepared using Primary WaveOne (Dentsply, Maillefer, Switzerland) size 25 and 8% taper operated by X-smart plus endodontic motor (Dentsply, Tulsa Dental, Tulsa, Oklahoma, USA) using the preset reciprocation mode.

Group 2: The canals were prepared with using OneShape (Micro Mega, Besancon, France) size 25 and 0.06 taper operated in continuous rotation motion with a rotational speed set at 350 rpm and a 5-Ncm torque by adjusting a program on X-smart plus motor.

Group 3: Root canal preparation was performed with XPS (FKG Dentaire SA, La Chaux-de-Fonds, Switzerland) (#30/04) at speed of 800 rpm and 1-Ncm torque in gentle 3–5 strokes until the canal was prepared to the full working length.

In all groups, 3 ml of freshly prepared 2.5% NaOCl irrigating solution was delivered using 30 G NaviTip closed end needle tips (Ultradent, South Jordan, Utah, USA) attached to a disposable plastic syringe throughout the preparation procedure. The needle was inserted as deep as possible inside the canal without binding. The instrument was placed into the canal filled with irrigant and with gentle movements of pulling in and out following the manufacturer's instructions. After instrumentation, root canals were flushed with 3 ml of 17% EDTA for 1 min followed by 3 ml of normal saline as final rinse and then dried with paper points (Diadent, Chongju City, Korea).

Two parallel longitudinal grooves were prepared on the buccal and lingual aspect of each root using carbide fissure bur (Dentsply Maillefer, Tulsa, Oklahoma, USA) to facilitate vertical splitting, the grooves were not deep enough to penetrate the canal space. A stainless steel chisel and mallet were then used to separate the root into two halves. The root half with the most visible part of root apex was prepared for SEM evaluation.

SEM images were obtained at standard magnification of ×1000 (for debris evaluation) and ×5000 (for smear layer evaluation). Cleanliness of each root canal was evaluated at 3, 6, and 9 mm. from the apex representing apical, middle, and coronal thirds and then scored for the presence or absence of debris and smear layer on the root canal surface at the predetermined portions. A four-category scale system [25] was used for debris and smear layer as follows:

Score 1, presence of debris/smear layer that covers 0–25% of the surface examined.

Score 2, presence of debris/smear layer that covers 25–50% of the surface examined.

Score 3, presence of debris/smear layer that covers 50–75% of the surface examined.

Score 4, presence of debris/smear layer that covers 75–100% of the surface examined.

Higher presence of smear layer and remaining debris is indicated by higher score values (scores 3, 4) while scores 1, 2 indicated cleaner canal surface.

Scores of remaining debris and smear layer were recorded at the three canal regions and compared statistically within the same group and among different groups. Due to the ordinal nature of the recorded scores, statistical analysis was performed using nonparametric Kruskal–Wallis tests at a significance level of P value up to 0.05 to find if there is any difference in the cleaning effectiveness of the instrument systems. Then if there was a significant difference, Mann–Whitney test was done for multiple pairwise comparisons. SPSS software version 20 (SPSS Inc., Chicago, Illinois, USA) was used in all statistical analysis.


Varying amounts of remaining debris and smear layer were exhibited along the entire length of the instrumented canal walls in all instrumentation groups [Figure 1], [Figure 2], [Figure 3]. Summary of smear layer and remaining debris scores recorded at coronal, middle and apical thirds were shown in [Table 1]. However, completely clean root canals were not observed in any of the tested instrumentation systems.{Figure 1}{Figure 2}{Figure 3}{Table 1}

When comparing between the instrumentation systems regardless root canal section [Table 2], score 4 represented the highest smear layer and remaining debris, it was represented by 50% of samples of WaveOne group, 40% of samples of OneShape group while 10% of samples of XPS group. Score 3 was represented by 26.7% of samples of WaveOne group, 36.7% of samples of OneShape group while 23.3% of samples of XPS group. Score 2 was represented by 23.3% of samples of WaveOne and OneShape groups while 50% of samples of XPS group. On the other hand, score 1 represented the lowest smear layer and remaining debris, it was represented by 0% of samples of WaveOne and OneShape groups while represented by 16.7% of samples of XPS group.{Table 2}

Scores of remaining debris and smear layer recorded median values of 3.5, 3, and 2 for WaveOne, OneShape, and XPS, respectively. Root canal preparation with XPS resulted in significantly less smear layer and remaining debris compared to the other two instrument systems regardless root canal section (P = 0.001), while no significant difference was obtained between WaveOne and OneShape instruments (P > 0.05).

There were statistically significant higher amounts of smear layer and remaining debris in the apical region compared to the coronal and middle portions when comparing the root canal thirds regardless the instrumentation systems (P = 0.004) [Table 3].{Table 3}


Oval shaped canals were selected in this study as their internal anatomy represented a challenge to any instrumentation technique as a result of leaving debris and unprepared root canal surfaces [11],[12],[13],[14].

The latest advances in canal preparation techniques have moved toward single file concept to simplify instrumentation protocol [26]. So WaveOne, OneShape, and XPS single file systems representing different motion kinematics were used in this study.

The smear layer which is formed after root canal instrumentation with either hand or rotary instruments, might block the dentinal tubules openings. Therefore it prevents penetration or diffusion of irrigants or intracanal medicaments into the dentinal tubules and finally compromising the sealing ability of the obturating material [19],[20],[27].

Debris have been used as another evaluation criteria in this study to assess the cleaning efficiency of different instruments, because debris comprises dentine chips, residual vital or necrotic pulp tissue that loosely attached to the root canal walls and mostly considered infected [28]. Additionally, SEM is considered a valuable method for the assessment of remaining debris and smear layer.

NaOCl was used as the irrigating solution throughout instrumentations in this study as it has both antibacterial and organic tissue dissolving potential, but it is not capable of completely removing smear layer so it was followed by 17% EDTA to maximize the cleansing effect of instrumented canal wall. Also, final rinse with normal saline was done to remove any residues of irrigant solutions that were used. Equal volumes of irrigants were used in all specimens to eliminate variables.

Scanning electron microscope has been used to evaluate the cleanliness of canal walls after instrumentation as it allows high resolution, magnification and measurements at coronal, middle and apical levels. In this study, magnification of ×1000 was employed for scoring debris as it offered a wider view allowing detection of large fragments of remaining debris at low magnification. Whereas, ×5000 magnification was used for scoring the smear layer as high magnification covers too small surface giving more accurate information, allowing the evaluation of the smear layer and the identification of the patency of the dentinal tubule openings [29].

The results indicated significantly more efficient canal cleaning when XPS was used in root canal preparation. This may be explained by its adaptive core technology, extreme flexibility and snake like design that enables this instrument to change its shape as it expands and contracts during rotation within the canal, reaching inaccessible areas of the canal leading finally to more cleaning canal surface [30]. Moreover the initial taper is 0.01; XPS expands once inside the canal, achieving a taper of at least 0.04 and allowing to reach a final canal preparation of minimum 30/0.04 with only one instrument [24].

The inferior cleaning efficiency of WaveOne reciprocating instrument may be explained by various reasons related to its design and motion kinematics. The continuous motion of the rotary files favors upward elimination of debris along the flutes of the file, while each backward motion of the reciprocating file leading the debris to be compacted along the dentinal walls and pushing them into lateral canals [31]. In addition to, WaveOne is characterized by three cutting edges with radial lands to support the blades and a relatively small chip space. The smaller the chip space of an instrument, the less its debris removal capacity [32]. Moreover, presence of radial lands tend to burnish the cut dentine onto the root canal wall and that the instruments with active cutting edges are superior to instruments with radial lands with respect to debris removal capacity [33],[34].

OneShape had better cleaning efficiency than WaveOne with no significant difference, this may be attributed to the greater taper of WaveOne (size 25, taper 0.08) compared with OneShape (size 25, taper 0.06) and this might be another reason for the increased amounts of residual debris especially in the apical portion of the canals. In addition to, the characteristic design features of OneShape as variable pitch along its working blade improve removal of debris. In addition to, the increased chip space allowing more debris to transport in a coronal direction [35].

The results of this study were in agreement with Bandekar et al.[36] and Dagna et al.[37] that found better cleaning efficiency of OneShape in comparison to WaveOne system and this was supported by the results of Bürklein et al. [32].

Coronal part recorded better cleanliness than the apical one in all instrumentation systems, this may be attributed to that cleaning the apical third of the root canal is a challenge due to anatomical specificities (constrictions, ramifications, additional canals) [38], the small diameter of the apical preparation that additionally complicates canal debridement [39] and the difficulties in achieving proper irrigation in the apical portion of the root canal. This result was in agreement with the previous studies in which cleanliness increased from the apical to the coronal part of the root canal [25],[40],[41],[42],[43],[44].


Complete canal cleanliness cannot be achieved by any of the studied instrumentation systems either full rotary or reciprocating, with remaining debris and smear layer on the dentinal walls therefore sufficient disinfection and copious irrigation are essential to improve canal cleanliness.

The presence of remaining debris and smear layer on the canal wall during instrumentation is inevitable due to the complex morphology of oval shaped canal.

Financial support and sponsorship


Conflicts of interest

There are no conflicts of interest.


1Castelo-Baz P, Martin-Biedma B, Cantatore G, Ruiz-Pinon M, Bahillo J, Rivas Mundina B et al. In vitro comparison of passive and continuous ultrasonic irrigation in simulated lateral canals of extracted teeth. J Endod 2012; 38:688–691.
2Wu MK, Wesselink PR. A primary observation on the preparation and obturation of oval canals. Int Endod J 2001; 34:137–141.
3Versiani MA, Leoni GB, Steier L, De-Dues G, Tassani S, Pécora JD, de-Sousa-Neto MD. Micro-computed tomography study of oval-shaped canals prepared with the self-adjusting file, Reciproc, WaveOne, and ProTaper universal systems. J Endod 2013; 39:1060–1066.
4Lumley PJ, Walmsley AD, Walton RE, Rippin JW. Cleaning of oval canals using ultrasonic or sonic instrumentation. J Endod 1993; 19:453–457.
5Wu MK, van der Sluis LW, Wesselink PR. The capability of two hand instrumentation techniques to remove the inner layer of dentine in oval canals. Int Endod J 2003; 36:218–224.
6ElAyouti A, Chu AL, Kimionis I, Klein C, Weiger R, Lost C. Efficacy of rotary instruments with greater taper in preparing oval root canals. Int Endod J 2008; 41:1088–1092.
7Barbizam JV, Fariniuk LF, Marchesan MA, Pecora JD, Sousa-Neto MD. Effectiveness of manual and rotary instrumentation techniques for cleaning flattened root canals. J Endod 2002; 28:365–366.
8Zmener O, Pameijer CH, Banegas G. Effectiveness in cleaning oval-shaped canals using Anatomic Endodontic Technology, ProFile, and manual instrumentation: a scanning electron microscopic study. Int Endod J 2005; 38:356–363.
9Grande NM, Plotino G, Butti A, Messina F, Pameijer CH, Somma F. Cross-sectional analysis of root canals prepared with Ni-Ti rotary instruments and stainless steel reciprocating files. Oral Surg Oral Med Oral Pathol Oral Radiol Endod 2007; 103:120–126.
10Jou YT, Karabucak B, Levin J, Liu D. Endodontic working width: current concepts and techniques. Dent Clin North Am 2004; 48:323–335.
11Li KZ, Gao Y, Zhang R, Hu T, Guo B. The effect of a manual instrumentation technique on five types of premolar root canal geometry assessed by microcomputed tomography and three-dimensional reconstruction. BMC Med Imaging 2011; 15:11–14.
12Markvart M, Darvann TA, Larsen P, Dalstra M, Kreiborg S, Bjorndal L. Micro-CT analyses of apical enlargement and molar root canal complexity. Int Endod J 2012; 45:273–281.
13Elsherief SM, Zavet MK, Hamounda IM. Cone-beam computed tomography analysis of curved root canals after mechanical preparation with three nickel-titanium rotary instruments. J Biomed Res 2013; 27:326–335.
14Zhao D, Shen Y, Peng B, Haapasalo M. Root canal preparation of mandibular molars with 3 nickel-titanium rotary instruments: a micro-computed tomographic study. J Endod 2014; 40:1860–1864.
15Haapasalo M, Shen Y, Qian W, Gao Y. Irrigation in endodontics. Dental Clin North Am 2010; 54:291–312.
16McComb D, Smith C. A preliminary scanning electron microscopy study of root after endodontic procedures. J Endod 1975; 7:238–242.
17Goldman L, Goldman M, Kronman J. The efficacy of several irrigating solutions for endodontics: a scanning electron microscopic study. Oral Surg Oral Med Oral Pathol 1981; 2:197–204.
18Mader C, Baumgartner J, Peters D. Scanning electron microscopic investigation of the smeared layer on root canal walls. J Endod 1984; 10:477–483.
19Torabinejad M, Handysides R, Khademi AA, Bakland LK. Clinical implications of the smear layer in endodontics: a review. Oral Surg Oral Med Oral Pathol Oral Radiol Endod 2002; 94:658–666.
20Silva PV, Guedes DF, Nakadi FV, Pecora JD, Cruz-Filho AM. Chitosan: a new solution for removal of smear layer after root canal instrumentation. Int Endod J 2013; 46:332–338.
21Shen Y, Cheung GS, Bian Z, Peng B. Comparison of defects in ProFile and ProTaper systems after clinical use. J Endod 2006; 32:61–65.
22Webber J, Machtou P, Pertot W, Kuttler S, Ruddle C, West J. The WaveOne single-file reciprocating system. Roots 2011; 7:28–33.
23Bürklein S, Benten S, Schafer E. Shaping ability of different single file systems in severely curved root canals of extracted teeth. Int Endod J 2013; 46:590–597.
24Azim AA, Piasecki L, da Silva Neto UX, Cruz ATG, Azim KA. XP Shaper, a novel adaptive core rotary instrument: micro-computed tomographic analysis of its shaping abilities. J Endod 2017; 43:1532–1538.
25Arvaniti IS, Khabbaz MG. Influence of root canal taper on its cleanliness: a scanning electron microscopic study. J Endod 2011; 37:871–874.
26De-Deus G, Barino B, Marins J, Magalhaes K, Thuanne E, Kfir A. Self adjusting file cleaning-shaping-irrigation system optimizes the filling of oval-shaped canals with thermoplasticized gutta-percha. J Endod 2012; 38:846–849.
27Tyagi A, Prasad BSK, Shashikala K. Evaluation of effectiveness of cleaning of root canals using Protaper and K3 rotary systems: a SEM study. World J Dent 2015; 6:20–25.
28Hülsmann M, Rümmelin C, Schäfers F. Root canal cleanliness after preparation with different endodontic handpieces and hand instruments: a comparative SEM investigation. J Endod 1997; 23:301–306.
29Bertrand MF, Pizzardini P, Muller M, Medioni E, Rocca JP. The removal of smear layer using the Quantec system. A study using the scanning electron microscope. Int Endod J 1999; 32:217–224.
30Neves MA, Provenzano JC, Rocas IN, Siqueira JFJr. Clinical antibacterial effectiveness of root canal preparation with reciprocating single-instrument or continuously rotating multi-instrument systems. J Endod 2016; 42:25–29.
31Robinson JP, Lumley PJ, Cooper PR, Grover LM, Walmsley AD. Reciprocating root canal technique induces greater debris accumulation than a continuous rotary technique as assessed by 3-dimensional-computed tomography. J Endod 2013; 39:1067–1070.
32Bürklein S, Hinschitza K, Dammaschke T, Schafer E. Shaping ability and cleaning effectiveness of two single-file systems in severely curved root canals of extracted teeth: Reciproc and WaveOne versus Mtwo and ProTaper. Int Endod J 2012; 45:449–461.
33Hülsmann M, Peters OA, Dummer PMH. Mechanical preparation of root canals: shaping goals, techniques and means. Endod Topics 2005; 10:30–76.
34Jeon IS, Spångberg LSW, Yoon TC, Kazemi RB, Kum KY. Smear layer production by 3 rotary reamers with different cutting blade designs in straight root canals: a scanning electron microscopic study. Oral Surg Oral Med Oral Pathol Oral Radiol Endod 2003; 96:601–607.
35Yoo YS, Cho YB. A comparison of the shaping ability of reciprocating NiTi instruments in simulated curved canals. Restor Dent Endod 2012; 37:220–227.
36Bandekar S, Medha A, Patil S, Sathawane N, Aurangabdkar A. In vitro comparison of cleaning ability of OneShape and WaveOne rotary systems. Int J Cur Res 2016; 8:39833–39836.
37Dagna A, Gastaldo G, Beltrami R, Poggio C. Debris evaluation after root canal shaping with rotating and reciprocating single-file systems. J Funct Biomater 2016; 7:28–35.
38Gulabivala K, Patel B, Evans G, Ng YL. Effects of mechanical and chemical procedures on root canal surfaces. Endod Topics 2005; 10:103–122.
39Trope M, Debelian G. XP Endo Finisher file – The next step in restorative endodontics. Endod Pract US 2015; 8: 22–24.
40Hülsmann M, Gressmann G, Schafers F. A comparative study of root canal preparation using Flex Master and HERO 642 rotary Ni-Ti instruments. Int Endod J 2003; 36:358–366.
41Haapasalo M, Endal U, Zandi H, Coil JM. Eradication of endodontic infection by instrumentation and irrigation solutions. Endod Topics 2005; 10:77–102.
42Paque'F, Musch U, Hülsmann M. Comparison of root canal preparation using RaCe and ProTaper rotary Ni-Ti instruments. Int Endod J 2005; 38:8–16.
43Schäfer E, Vlassis M. Comparative investigation of two rotary nickel-titanium instruments: ProTaper versus RaCe. Part 2. Cleaning effectiveness and instrumentation results in severely curved root canals of extracted teeth. Int Endod J 2004; 37:239–248.
44Fornari VJ, Silva-Sousa YT, Vanni JR, Pécora JD, Versiani MA, Sousa-Neto MD. Histological evaluation of the effectiveness of increased apical enlargement for cleaning the apical third of curved canals. Int Endod J 2010; 43:988–994.