|Year : 2014 | Volume
| Issue : 2 | Page : 70-76
A comparison of canal preparations by Mtwo and RaCe rotary files using full sequence versus one rotary file techniques; a cone-beam computed tomography analysis
Mohsen Aminsobhani1, Abdollah Ghorbanzadeh2, Somayyeh Dehghan3, Allahyar Nezadi Niasar4, Mohammad Javad Kharazifard5
1 Department of Endodontics, AJA University of Medical Sciences; Dental Research Center, Dentistry Research Institute; Department of Endodontics, Tehran University of Medical Sciences, Tehran, Iran
2 Dental Research Center, Dentistry Research Institute; Department of Endodontics, Tehran University of Medical Sciences, Tehran, Iran
3 Dental Research Center, Dentistry Research Institute, Tehran University of Medical Sciences, Tehran; Qom University of Medical Sciences, Qom, Iran
4 Department of Radiology, Dental School, AJA University of Medical Sciences; Department of Radiology, Tehran, Iran
5 Epidemiologic Department, Dental Research Center, Dental School, Tehran University of Medical Sciences, Tehran, Iran
|Date of Web Publication||19-May-2014|
Department of Endodontic, Faculty of Dentistry, Qom University of Medical Sciences, Shahid Lavasani St, Qom
Source of Support: This research was supported by a grant from
Dental Research Center, Dentistry Research Institute, Tehran
University of Medical Sciences, Tehran, Iran,, Conflict of Interest: The
authors deny any confl icts of interest related to this study.
Objectives: Using one rotary file can result in a faster canal preparation. This can be done with several file systems and endodontic motors. In the present study, a newly single file technique (one rotary file technique) with available rotary file systems is introduced. The aim of the present study was to evaluate centering ability and remaining dentin thickness of 2 rotary nickel-titanium systems (Mtwo versus RaCe) and instrumentation techniques (conventional versus one rotary file) by cone-beam computed tomography. Materials and Methods: A total of 76 mandibular molar teeth were selected and divided to 4 groups (n = 19 teeth with 57 canals). The teeth were mounted in resin and pre-instrumentation scans were prepared by Cone Beam Computed Tomography (CBCT). The canals instrumented with Mtwo and RaCe rotary files either in conventional or one rotary file technique (ORF). After cleaning and shaping of distal and mesial canals, post instrumentation scans were performed by CBCT in the same position as pre instrumentation scans. Centering ability and remaining dentin thickness were evaluated by Planmeca Romexis viewer. The data were analyzed with analysis of variance and post hoc t test (P < 0.05). Results: Mean centering ratios for Mtwo/conventional, Mtwo/ORF, RaCe/conventional and RaCe/ORF groups were assessed. At overall, there were no significant differences between instrument types and instrumentation techniques (P > 0.05). However, in a few cross-sections, conventional technique and/or RaCe showed higher centering ability. One rotary file technique with either RaCe or Mtwo was significantly faster than conventional technique (P = 0.02). There was no significant difference among groups regarding file fracture. Mesiolingual canals showed more transportation compared with mesiobuccal and distal canals. Conclusions: Both of the instrumentation systems and techniques produced canal preparations with adequate centering ratio. One rotary file technique prepared canal significantly faster than conventional technique.
Keywords: Centering ability, Cone beam computed tomography, Mtwo, one file technique, RaCe, root canal preparation
|How to cite this article:|
Aminsobhani M, Ghorbanzadeh A, Dehghan S, Niasar AN, Kharazifard MJ. A comparison of canal preparations by Mtwo and RaCe rotary files using full sequence versus one rotary file techniques; a cone-beam computed tomography analysis. Saudi Endod J 2014;4:70-6
|How to cite this URL:|
Aminsobhani M, Ghorbanzadeh A, Dehghan S, Niasar AN, Kharazifard MJ. A comparison of canal preparations by Mtwo and RaCe rotary files using full sequence versus one rotary file techniques; a cone-beam computed tomography analysis. Saudi Endod J [serial online] 2014 [cited 2018 Dec 10];4:70-6. Available from: http://www.saudiendodj.com/text.asp?2014/4/2/70/132722
| Introduction|| |
Cleaning and shaping are essential steps in root canal treatment procedures for removing debris and microorganisms that are responsible for endodontic pathosis. , Since the introduction of nickel-titanium (NiTi) rotary instruments, it has been shown that several NiTi file systems can maintain original canal shape, reduce procedural errors and prepare the canal faster. ,
RaCe (FKG, La Chaux-de-Fonds, Switzerland) rotary endodontic instruments have triangular cross sections except for #15/.02 and #20/.02 instruments.  The file has alternating cutting edges; this design reduces file threading into the canal wall.  The instrument surface has been electro polished. 
Mtwo (VDW, Antaeus, Munich, Germany) instruments have an S-shaped cross-sectional design and a positive rake angle with 2 cutting edges.  Moreover, Mtwo instruments have an increasing pitch length from the tip to the shaft. This design has two advantages: 1- eliminates threading into canal walls 2- reduces debris extrusion beyond apex.  Mtwo preparations were well-centered in curved canals, even without a manual glide path before rotary instrumentation. 
According to the manufacturers, crown-down and standard preparation techniques are suggested for RaCe and Mtwo systems, respectively. The recently introduced NiTi files such as Reciproc and WaveOne are claimed to be able to completely prepare and clean root canals with only one instrument. These files are used in a reciprocal motion and need special devices and motors. , One Shape ® is another new NiTi file with three different cross-sections along the file length. It works in continuous rotation motion with no need to special motors.  In the present study, one rotary file technique of instrumentation was suggested. Using a single file of available rotary file systems is proposed in this technique. Reduced working time, less cost, no need to new special motors and a previously experienced sense during canal preparation are some advantages of this technique.
Different methods such as serial sectioning, simulated canals and radiographic analysis have been used for evaluating centering ability of different systems. Since cone-beam computed tomography (CBCT) is more accessible and precise for three dimensional evaluation without destructing the teeth, we used CBCT for evaluating centering ability.  The aim of the present study was to evaluate centering ability and remaining dentin thickness in root canals prepared by two rotary nickel-titanium systems (Mtwo versus RaCe) and two canal preparation methods (conventional versus only one rotary file) by cone-beam computed tomography.
| Materials and methods|| |
Seventy six extracted human first and second mandibular molars that were extracted because of periodontal problems were selected. Teeth were disinfected in sodium hypochlorite 5.25% for 30 min and then maintained in normal saline solution until use.  Straight radiographs in mesiodistal and buccolingual directions were taken to determine the root canal anatomy. The teeth with mature apices, no resorption, without restoration, no cracks and distinct mesial and distal roots with curvature within 15 to 45◦ limit were selected. Canal curvature was determined by using Schneider method.  Teeth with multiple, rapid apical curvature, or calcified canals were excluded from the study. Specimens were coded and randomly divided into 4 groups (n = 19). The apical foramina were sealed with dental wax and all teeth were then mounted in acrylic resin blocks of 10 cm diameter (19 teeth in each resin block and collectively 76 teeth in four resin blocks). Pre instrumentation images were taken by CBCT machine Alphard VEGA, Asahi Roentgen Ind., Kyoto, Japan) with following settings: 80 kV, 4 mA, 51 × 51 mm field of view and 0.1/voxel (mm) size. Access cavities were prepared by using diamond burs and apical patency was checked with stainless steel #10 K-file (Dentsply Maillefer, Ballaigues, Switzerland). Each resin block was divided to 4 rows by a dental saw so that we could determine working length by radiography. The working length was established with #15 K-file that was 1mm shorter than radiographic apex. The experimental groups were as following:
Group 1 (Mtwo, conventional): The canals were prepared by single-length technique as recommended by the manufacturer using Mtwo Ni-Ti rotary files in torque-limited electric motors (Dentaport ZX, Morita corp., USA) at 2 N/cm torque and 300 rpm. Four files were used in the following sequence: 10/.04, 15/.05, 20/.06 and 25/.06. Each file was removed when rotated freely at the end of the canal.
Group 2 (Mtwo, ORF): The canals were prepared with only one Mtwo #25/0.06 file. The values of torque and rpm were the same as in group 1. After preparation by #10 and #15 stainless steel K-files, the coronal and middle thirds of the canal were prepared by a #25/.06 Mtwo file with active lateral force in an anticurvature in-and-out motion until the file reached the working length. If the file did not reach the working length, the preparation was continued using #15 and #20 K-files in a watch winding movement and then #25/.06 Mtwo file was used until rotated freely at the apex.
Group 3 (RaCe, conventional): Distal and mesial canals were prepared by using RaCe NiTi rotary files. Instrumentation was carried out with a crown-down technique starting with the 40/.10 instrument at 600 rpm and 2 N/cm torque as suggested by the manufacturers, followed by 35/.08, 25/.06, 25/.04 and 25/.02 if necessary. Then canals were instrumented to working length with 25/.04 and 25/.06.
Group 4 (RaCe, ORF): For each tooth, instrumentation was carried out with only #25/.06 RaCe file at 600 rpm and 2 N/cm torque. Instrumentation technique was the same as in group 2.
In all experimental groups, as each instrument was changed, the canal was irrigated with 1 mL of 2.5% NaOCl by using a 30-gauge needle (Max-i-Probe; Dentsply, Rinn, Elgin, IL) and then recapitulated with a #15 K-file. After canal preparation, smear layer was removed by 3 ml of 17% EDTA. 1.3% NaOCl was used for final irrigation accompanying with Passive ultrasonic agitation. Preparation time was measured separately for distal and mesial canals to compare different systems and techniques. The preparation time included active instrumentation as well as the time required for changing instruments, cleaning the flutes of the instruments and irrigation. The number of fractured and permanently deformed instruments during preparation was also recorded. If there was any file fracture, another tooth was replaced for preparation. After canal shaping, post instrumentation CBCT scans were performed with similar values and position as pre instrumentation scans.
Evaluation of centering ability and remaining dentin thickness
CBCT images were analyzed by Planmeca Romexis viewer software (Version 2.3.1.R, Finland). Dentin thickness and centering ability was measured in 4 planes as shown in [Figure 1]: At furca, 3 mm apical to furca (coronal), 6 mm apical to furca (middle) and 3 mm coronal to the apex (apical). In each plane, dentin thickness of buccal, lingual, mesial and distal walls were measured in pre and post instrumentation CBCT scans [Figure 2]. The measurements were recorded for each canal (mesiobuccal, mesiolingual and distal) separately. The following formula was used for the centering ability calculation in mesiodistal dimension: [(E 1 -E 2 )-(I 1 -I 2 )]/Y MD . E 1 and E 2 represented the shortest distance from the external surface of each root to the periphery of the uninstrumented and instrumented canals, respectively. I 1 and I 2 represented the shortest distance from the internal surface of each root to the periphery of the uninstrumented and instrumented canals, respectively. Y MD was the diameter of final canal preparation in mesiodistal direction. A result of zero indicated no canal transportation. A negative result indicated transportation toward the furcation region and a positive result indicated transportation away from the furcation region. The following formula was used for the centering ability calculation in buccolingual dimension: [(B 1 -B 2 )-(L 1 -L 2 )]/Y BL . B 1 and B 2 represented the shortest distance from the buccal surface of each root to the periphery of the uninstrumented and instrumented canals, respectively. L 1 and L 2 represented the shortest distance from the lingual surface of each root to the periphery of the uninstrumented and instrumented canals, respectively. Y BL was the diameter of final canal preparation in buccolingual direction. A result of zero indicated no canal transportation. A negative result indicated transportation toward lingual and a positive result indicated transportation toward buccal.
|Figure 1: CBCT images were analyzed by Planmeca Romexis viewer software before and after instrumentation in 3 mm-thick sections: a- furcal, b- coronal, c- middle, d- apical|
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|Figure 2: In each canal, dentin thickness of buccal, lingual, mesial and distal walls was measured in pre and post instrumentation CBCT scans|
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The data for centering ability were statistically analyzed by using analysis of variance with a post hoc t test and the level of significance was P < 0.05.
| Results|| |
Centering ratio values of different sections in mesiodistal (MD) and buccolingual (BL) directions are listed in [Table 1] and [Table 2]. At overall, all instruments and techniques had low centering ratio with no significant difference except in few sections.
|Table 1: Mean centering ratio values of different sections of canals and SD in mesiodistal direction|
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|Table 2: Mean centering ratio values of different sections of canals and SD in buccolingual direction|
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In distal canal (only in MD direction), centering ratio values in RaCe system were significantly lower than Mtwo in the apical thirds ( P = 0.03). Also, centering ratio values in the conventional technique were significantly lower than one rotary file technique (P < 0.001).
In mesiobuccal canal (only in MD direction), conventional technique showed significantly lower centering ratio values than one rotary file technique at the coronal third (P = 0.01).
In mesiolingual canal, conventional technique presented a significantly lower centering ratio values than one rotary file technique in the furcal (only in MD direction) (P = 0.046) and coronal (only in MD direction) ( P < 0.001) thirds of the canal. Centering ratio values of RaCe system were significantly lower than Mtwo only at the apical third of the canal (in MD direction) ( P = 0.01). Also, conventional technique had a significantly lower centering ratio values than one rotary file technique at the apical third of the canal (in BL direction) ( P = 0.01).
In distal canal (in MD direction), there was a significant difference between 4 sections regarding centering ratio except coronal with the middle section. In BL direction, there was no significant difference between 4 sections.
In mesiobuccal and mesiolingual canal (in MD direction), there was a significant difference between 4 sections regarding centering ratio. In BL direction, there was no significant difference between 4 sections except furcal section with the other sections.
The highest centering ratio values were seen in furcal section. Despite higher values at furcal section, it was toward external surface of the root. At 3 and 6 mm apical to furca level (coronal and middle sections), there was lower centering ratio values but it often was toward inner surface of the root. There were more tendencies toward internal surface in Mtwo system with one rotary file technique although it was not significantly different.
The mean time taken to prepare the canals with the different instruments is shown in [Table 3]. Instrumentation in one rotary file technique with either RaCe or Mtwo was significantly faster than conventional technique in mesial ( P = 0.01) and distal canals (P = 0.02). There was no significant difference between Mtwo with RaCe and mesial with distal canals.
|Table 3: Mean preparation time and SD (in seconds) with different instruments and techniques|
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Three RaCe instruments (one file in the conventional technique and two files in one rotary file technique) were fractured during preparation. Only one Mtwo file was deformed permanently in one rotary file technique. The number of fractured instruments was not significantly different between the file systems and or techniques.
| Discussion|| |
The main purpose of instrumentation is to clean the canal while maintaining the anatomy and morphology of the canal.  Recently, different single file systems have been introduced. A recent study by Bόrklein et al.  demonstrated that Reciproc and WaveOne with Mtwo and ProTaper rotary instruments could maintain the original canal curvature well with no significant differences. Also, they found no significant differences between Mtwo, Reciproc and WaveOne in coronal and middle thirds regarding debris removal. However, these files are used in a reciprocal motion and require specific automated devices.
Another new single NiTi file system, One Shape® that is introduced by Micro Mega Company  is an instrument that works in continuous rotation. It has three different cross-section zones along the blade.
In the present study, one rotary file technique using a Mtwo/RaCe #25/.06 file for each tooth was offered. The most notable benefits of this technique are no excess cost, no need to buy new instruments or specific motors. Reduced preparation time and a previously experienced sense during canal preparation are the other benefits.
Several methods have been used to evaluate the quality of root canal preparations, such as serial sectioning and microscopic evaluation, simulated canals, radiographic evaluation and cone beam computed tomography. ,,,, Serial sectioning  can result in loss of tooth structure. Another method is by using simulated root canals. It is reproducible and standard, but it cannot simulate complex anatomy of canals.  More complex simulated canals, True Tooth™ training replicas have been introduced recently.  These models have five difficulty scales that many factors (i.e. pulp chamber size, canal curvature, apical branching, etc.) determine their difficulty, but these models also have drawbacks such as different hardness with dentin. Radiographic evaluation is another method that is not destructive, but only allows two dimensional evaluations.  Cone beam volumetric tomography and micro computed tomography have been introduced to dentistry with good precision and resolution as well as no destruction of the specimen. , In the present study, cone beam computed tomography was used to compare centering ability of one rotary file technique with the established rotary Mtwo and RaCe instruments in curved root canals (round or oval shape) of extracted human mandibular molar teeth.
Preparation time is dependent on the technique and the numbers of instruments used.  In the present study, the preparation time included active instrumentation as well as the time required for changing instruments, cleaning the flutes of the instruments and irrigation. Therefore, preparation time significantly decreased in one rotary file technique because of no need to changing the files and more focus on canal preparation.
There were 3 RaCe fractured files versus 1 Mtwo deformed file in this study. Because of the S-shaped cross section, Mtwo instruments showed the higher torsional strength and higher resistance to torsional breakage compared with the triangular cross-sectional instruments. ,
Mandibular molars, like most teeth, usually have significant curvature in both mesiodistal and buccolingual planes. Furthermore, they often have concavities on mesial and distal surfaces of the root.  These factors make the tooth susceptible to transportation and preparation errors such as perforations. There is limited information regarding transportation in buccolingual direction but in this study centering ability was evaluated in both directions.
As mentioned in [Table 2], canal transportation at furcal level (In buccolingual direction) for mesiobuccal and mesiolingual canals was toward buccal and lingual sides respectively that is more valuable because they are safe zones with thicker dentin.
In mesiodistal direction, the highest centering ratio was seen at furcal section. Since transportation was toward external side of the root (safety zone) with more dentin thickness, so it was favorable too. Higher incidence of canal transportation in mesiolingual canals may be due to more curvature in these canals.
According to the results of this study, centering ability in RaCe system was better than Mtwo system in a few sections. Although Alsudani et al.  reported significantly more canal transportation with RaCe files, other authors concluded that RaCe system create well-centered preparations. ,
Mtwo instruments have good cutting efficiency, low cross-sectional area and relatively low number of spirals in each length unit. Therefore, it can resist deformation, but it is more rigid too. , This might explain the slightly higher incidence of canal aberrations observed in Mtwo system. Although the results of the present study were inconsistent with Bonaccorso et al.  and Celik et al.  researches, previous studies concluded the lowest transported canals in Mtwo groups. 
According to the results of the present study, only one rotary file technique showed relatively good centering ability and can be regarded suitable for cleaning and shaping of curved canals. Since preparation time was decreased significantly by using one rotary file technique; therefore, chemical debridement of the canal system was reduced. Larger volumes of irrigant and additionally activation of the irrigant should be used to improve disinfection. Further research is needed to evaluate this aspect.
| Conclusions|| |
Within the limitations of this study, both of the instrumentation systems and techniques produced canal preparations with adequate centering ratio. One rotary file technique prepared canal significantly faster than conventional techniques.
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[Figure 1], [Figure 2]
[Table 1], [Table 2], [Table 3]