Dental Hypotheses

: 2022  |  Volume : 13  |  Issue : 1  |  Page : 6--9

Comparison of Cutting Efficiency and Safety of 10/0.04 RaCe and Mtwo Rotary File Systems in Reaching the Full Root Canal Working Length: An In Vitro Study

Pouya Abedi1, Peiman Gilani1, Mahmood Sheikh Fathollahi2, Foad Iranmanesh3,  
1 Student Research Committee, Rafsanjan University of Medical Sciences, Rafsanjan, Iran
2 Department of Biostatistics, Rajaie Cardiovascular Medical and Research Center, Iran University of Medical Sciences, Tehran, Iran
3 Department of Endodontics, Dentistry Faculty, Rafsanjan University of Medical Sciences, Rafsanjan, Iran

Correspondence Address:
Foad Iranmanesh
Department of Endodontics, Dentistry Faculty, Rafsanjan University of Medical Sciences, Khalij Fars Blvd, Rafsanjan


Introduction: Both RaCe and Mtwo rotary systems introduced the 10/0.04 file as the first file used in the root canal (Glide path). This study aims to compare different factors of both the rotary systems, including cutting efficacy, file fracture, topography changes of files, and changes of the root canal. Materials and Methods: In this laboratory study, 12 RaCe and 12 Mtwo files were prepared and tested on 24 resin blocks with 30° curvature. The time to reach the working length was recorded. Topographical changes of the files have been observed with a stereomicroscope if needed. Changes in resin blocks were measured by photographing and using Photoshop software. Data were analyzed through an independent two-sample t test and likelihood-ratio chi-squared test. Results: Time to reach the working length was significantly lower in the RaCe group than in the Mtwo group (3.57 ± 0.56 s vs. 10.33 ± 2.25 s, P < 0.001). File fracture did not occur in any of the two rotary systems. Topographical changes of the files in RaCe group were also less than the Mtwo group (P = 0.032). Conclusion: The RaCe file is faster in reaching the working length. Both files are safe and do not cause drastic changes in the root canal.

How to cite this article:
Abedi P, Gilani P, Fathollahi MS, Iranmanesh F. Comparison of Cutting Efficiency and Safety of 10/0.04 RaCe and Mtwo Rotary File Systems in Reaching the Full Root Canal Working Length: An In Vitro Study.Dent Hypotheses 2022;13:6-9

How to cite this URL:
Abedi P, Gilani P, Fathollahi MS, Iranmanesh F. Comparison of Cutting Efficiency and Safety of 10/0.04 RaCe and Mtwo Rotary File Systems in Reaching the Full Root Canal Working Length: An In Vitro Study. Dent Hypotheses [serial online] 2022 [cited 2022 May 20 ];13:6-9
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Full Text


Cutting efficiency is a significant characteristic of nickel–titanium (NiTi) endodontic instruments that are manufactured in many designs to enhance performance, safety, and facilitate root canal preparation even in curved canals[1],[2],[3]; however, their major problems are excessive torsion and flexural stress, which cause their failure.[4] Effective dentinal removal is the complicated interrelationship of various parameters, such as helical and rake angle, tip design, number and depth of the flutes, raw material, and production processes.[5] Moreover, several factors such as rotational speed,[6] frequency of applications,[1] and shape of the canal[2] may influence the cutting efficacy and fracture rate of the rotary instrument.

Mtwo (VDW GmbH) and RaCe (FKG Dentaire) are commonly used systems for root canal cleaning and shaping. Mtwo instruments have a cross-section shape in the form of an italic “S” with two cutting edges and a noncutting tip, which reduces the tendency of the instrument to get stuck into the root canal.[7] Several studies have proved that all Mtwo files should be used for the full-length root canal.[8],[9] The manufacturers claim that a crown-down instrumentation sequence is no longer required because the Mtwo files can be applied to the full working length of the root canal as well as to shape its entire length. RaCe instruments have triangular or square-shaped cross sections and sharp alternating cutting edges,[10] reducing the screw-in effect. Furthermore, electrochemical polishing enhances its resistance to fatigue and corrosion.[11]

Both companies have recommended the use of file #10/0.04 in the early stages of root canal preparation. Although extensive studies have been conducted on the cutting ability of endodontic rotary instruments, to our knowledge, no scientific research has evaluated file #10/0.04, therefore this study evaluated the cutting efficacy, safety (resistance to fracture), and the deformation of these two files compared with each other in transparent resin blocks.

 Materials and Methods

Sample size calculation

This laboratory study was approved by the Institutional Review Board of the Rafsanjan University of Medical Sciences (Institutional Review Board no. 31/20/998). Due to the laboratory nature of the current study, according to the previous similar studies, [12],[13] 24 resin blocks and 24 rotary instruments (12 in each group) were considered for the present study.

Classification of the samples

The criterion for excluding the files from the research was the presence of any structural deformation compared to the standard type by visual examination using a magnifying glass, which was performed by a single experienced endodontist (F.I.). No files were excluded at this point. Accordingly, 24 resin blocks (Nissin, Kyoto, Japan) with a curvature of 30° were prepared and randomly allocated to one of the two rotary system groups by one of the authors (P.G.) with a coin toss (n = 12).

Evaluation of files

Twelve new Mtwo files (size 10 and 0.04 taper) (VDW GmbH, Munich, Germany) and 12 RaCe files (FKG Dentaire, La Chaux-de-Fonds, Switzerland) with similar characteristics were rotated by an Endo Mate electric motor (NSK, Tokyo, Japan) during the experiment. The speed was set to 300 rpm, and the rotational force was set to 1 Ncm. Each instrument was used only once. [14],[15] The filing was performed by an endodontist (F.I.) blinded to the instrument used to minimize errors during operation.

Before and after canal preparation, an image of the blocks was taken using a digital camera (Canon, Tokyo, Japan) to observe possible changes after the procedure. To match these two images, the camera was fixed on a flat surface with a determined distance of the lens from the block to provide the same conditions for both modes. The white light was projected perpendicular to the block to prevent shadows. To facilitate the naming of the images, the block was assumed to have a tooth with a distal curve, and thus three images were prepared from buccal, mesial, and distal views.

Cutting adequacy will be equal to the time to reach the working length using a stopwatch (Q&Q, Tokyo, Japan). Thus, when the active instrument started its operation from the orifice of the artificial canal, the operating time for each instrument was recorded until the tip of the instrument reached the end of the artificial canal. The four parameters of time, file fracture, changes in the artificial canal, and topographical changes of the file were measured and recorded in a pre-prepared checklist.[16]

All used files with no fracture were re-evaluated visually by a magnifying glass for plastic changes, and in the case of visible changes, they were examined using a stereomicroscope (F.I.). Adobe Photoshop CS6, Ver.13.0.1 (Adobe Systems Inc., San Jose, CA, USA) was used to change the background color of the image to better see the changes ([Figure 1]). Due to the same conditions, a change in the canal was visible and was recorded in the checklist[16] by one of the authors blinded to the instrument used (P.G.).{Figure 1}

Statistical Analysis

Results were reported as mean ± SD (standard deviation) for numeric variables and were summarized by absolute frequencies and percentages for categorical variables. Numeric variables were compared using an independent two-sample t test and categorical variables were compared using the likelihood-ratio chi-squared test across the two groups of RaCe and Mtwo. Nonparametric Kolmogorov–Smirnov test indicated that the presumption of normality was met for numeric variables (P > 0.05). Statistical analysis was performed with SPSS version 15.0 for Windows (SPSS Inc., Chicago, IL, USA). All P-values were two-tailed, with statistical significance defined by P ≤ 0.05.


The operating time parameter in the RaCe files was significantly superior to Mtwo files ([Table 1]). None of the RaCe and Mtwo files were fractured in the present study.{Table 1}

Two blocks in the RaCe group and five blocks in the Mtwo group underwent minor changes (P = 0.172). As for file deformation, RaCe files were not deformed. However, three of 12 Mtwo files underwent twisting and deformation at their cutting tip [Supplementary Figure][17] [Table 1].


None of the RaCe and Mtwo files were fractured in the present study. However, in a study by Pedulla et al.[18] on the cyclic fatigue resistance of four NiTi rotary instruments fracture in Mtwo files was significant. However, this difference can be attributed to the higher degree of deviation (60°) in Pedulla’s study. Further, the use of files with a taper of 6% and a size of 25, which were larger than those of the present study, could be another reason for the higher file fracture.

None of the RaCe files were deformed in the present study, while three of the 12 Mtwo files were deformed. This result was consistent with those of a study by Topçuoğlu et al.,[19] in which the Mtwo file was less resistant to cyclic fatigue. Moreover, in Aydin et al.[20] study on differences between new and used RaCe instruments in synthetic stainless-steel canals, the new RaCe files had fewer topographical changes, which is similar to the present study results where all the instruments were used for the first time.

In the current study, resin canals did not change significantly. These files are used to reach the working length as the first file or are used in narrow canals.[21] In a study conducted by Plotino et al.[18] on Mtwo files by two groups of novice and experienced operators, the changes in the artificial canals that were filled by the novice team were detectable and determinable, which can be attributed to the size of the files used.

In a study by Narayan et al.[22] on the cleaning and shaping ability of RaCe, Mtwo, and K3 files on natural teeth, the Mtwo file could transform the canal more aggressively. This result was also consistent with the results of the present study. On the other hand, Canga et al.[23] showed that Mtwo instruments are a better choice for the curved canals as their flexibility helps these instruments follow the angles better. This difference could be the result of using the full sequence of the Mtwo rotary system and different techniques (crown down) for the RaCe system.

Human teeth can simulate clinical conditions more accurately to evaluate the cutting efficacy and safety of rotary instruments but, as a limitation, a tooth can only be used once due to changes in the shape of the root canal during instrumentation, making it impossible to standardize the in vitro conditions.[24] Therefore, we used resin blocks to facilitate the observation of possible changes in the canal and create the same conditions for all instruments.[14]

Cutting adequacy has different interpretations in different studies. In a study by Cecchin et al.[25] on the cutting adequacy of four rotary systems with #25/0.04 sizes on resin blocks, the amount of material lost from each block (by weighing each block before and after filing) was equivalent to the cutting adequacy. This interpretation was not significant in the present study because the instruments of this study were smaller as mentioned above, so the amount of change they made in the canal was very small and could not be measured by the method used in Cecchin et al.’s[25] study. Therefore, in this study, by considering the time to reach the working length, the amount of topographical change the file made in the canal, the file resistance to deformation, and their comparison, the concept of cutting adequacy of the instruments used was achieved.

Gambarini et al.[12] examined the cutting adequacy of different types of NiTi rotary instruments. They examined them in plastic samples, of which RaCe and Mtwo had the highest cutting adequacy. This result was consistent with the results of the current study. It can be concluded from both studies that the RaCe file has the highest cutting adequacy among the files used.


RaCe files reached the working length faster, indicating that using this file can save the operator’s time. Both files are safe to reach the working length and do not cause drastic changes in the canal. In general, 10/0.04 RaCe files appear to be more efficient instruments than Mtwo.

Author Contributions

F.I. contributed to study design, P.G. helped with data collection, M.S.F. contributed to data analysis and result interpretation, and P.A. contributed to manuscript writing and preparation.

Financial support and sponsorship

The authors would like to thank Rafsanjan University of Medical Sciences for financial support.

Conflicts of interest

There are no conflicts of interest.


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