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 Table of Contents  
Year : 2021  |  Volume : 11  |  Issue : 2  |  Page : 173-180

Shaping ability of different single-file rotary systems in simulated S-shaped canals by a new investigation approach: An in vitro study

1 Department of Endodontic and Operative Dentistry, College of Dentistry, Damascus University, Damascus, Syria
2 Department of Restorative Dental Sciences, College of Dentistry, Taibah University, Madina, Saudi Arabia; Department of Endodontic and Operative Dentistry, College of Dentistry, Aleppo University, Aleppo, Syria

Date of Submission16-Mar-2020
Date of Decision16-Apr-2020
Date of Acceptance22-Apr-2020
Date of Web Publication8-May-2021

Correspondence Address:
Dr. Ahmad A Madarati
Department of Restorative Dental Sciences, College of Dentistry, Taibah University, Madina 43353

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Source of Support: None, Conflict of Interest: None

DOI: 10.4103/sej.sej_50_20

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Introduction: The aim of this study was to compare the shaping ability of single-file nickel–titanium systems in simulated S-shaped canals.
Materials and Methods: Sixty simulated S-shaped canals were photographed and 12 levels along their length were determined. They were divided into four groups: A and B where the WaveOne Gold and Reciproc Blue reciprocating systems were used and Groups C and D for the OneCurve and Fanta-AF F-one rotary systems. Blocks were re-photographed and the before- and after-preparation photos were superimposed. Canals' widths were measured at each canal's level before and after preparation to calculate canals' deviations. The preparation times were recorded, and the data were analyzed by one-way ANOVA and Chi-square tests (P = 0.050).
Results: The mean deviation in the middle third (0.14 mm) was greater than those in the coronal (0.08 mm) and apical thirds (0.09 mm) (P = 0.000). Furthermore, in this third, the OneCurve system caused the lowest greatest deviation (0.13 mm) but not different from the WaveOne Gold system (0.18 mm). At the apical third, the OneCurve showed the least mean deviation (0.07 mm) (P = 0.001) and the lowest mean of the greatest deviation (0.12 mm) (P = 0.000). Significantly, the highest percentage of the greatest deviations located within the canals' middle third (68.4%). The Fanta-AF-F-one and Reciproc Blue systems had higher percentages of the greatest deviation within the middle third (86.7% and 85.7%, respectively) than the OneCurve (42.9%) and WaveOne Gold systems (57.1%) (P = 0.013). The OneCurve and WaveOne Gold systems needed the least shaping times (57.15 and 63.07 s, respectively).
Conclusions: The OneCurve system followed by the WaveOne Gold system had better shaping ability than other systems. The OneCurve and WaveOne Gold systems required shorter shaping times. The “greatest-deviation” can be more appropriate analysis than the mean deviation when the shaping ability is investigated.

Keywords: Centering, shaping, simulated, single-file, S-shaped

How to cite this article:
Kaddoura R, Madarati AA, Al Tayyan M. Shaping ability of different single-file rotary systems in simulated S-shaped canals by a new investigation approach: An in vitro study. Saudi Endod J 2021;11:173-80

How to cite this URL:
Kaddoura R, Madarati AA, Al Tayyan M. Shaping ability of different single-file rotary systems in simulated S-shaped canals by a new investigation approach: An in vitro study. Saudi Endod J [serial online] 2021 [cited 2023 Mar 27];11:173-80. Available from: https://www.saudiendodj.com/text.asp?2021/11/2/173/315649

  Introduction Top

Cleaning and shaping of the root-canal system is an essential procedure for successful root-canal treatments[1] which can be challenging in some cases, especially in complex root-canal systems. Proper cleaning and shaping of the root-canals should neither interfere the tooth structure nor weaken it. Furthermore, it should maintain the original shape of the root canals as much as possible[2],[3] and as centered as possible.[4] Complex root-canal systems with severe curvatures may adversely affect preparations, leading to procedural errors, such as root-canal transportation[5] or instruments' fracture.[6] Root-canal transportation may occur due to the stiffness of endodontic instruments[7] because they tend to regain their original straight shapes, which may cause an excessive removal of the inner root-canal surface, changing its original position. This, in turn, may lead to ledge formations, zipping, or perforations, which may affect the treatment long-term outcome.[8]

Unlike stainless-steel instruments (SSIs), nickel–titanium (NiTi) instruments are more flexible, better maintain the original shape and position of root canals and cause less complications.[9],[10],[11] Nevertheless, one disadvantage of traditional NiTi rotary systems is that they consist of several instruments, with various tip sizes and tapers, causing longer preparation times.

In 2008, Yared re-introduced the reciprocating motion concept and proposed the concept of single-file rotary systems.[12] Many manufacturers introduced different NiTi single-file systems that can be rotated in reciprocating or continuous motions. Instrumentation using these systems can be faster when compared to that by traditional multiple-file systems.[13] Furthermore, the single use of these files can reduce instruments' fracture and improves cross-infection control.[14] Moreover, the special heat treatments of the metallic alloys resulted in single-file systems with greater resistance to fatigue failure, hence safer root-canal instrumentation, when compared to traditional systems.[15] Moreover, single-file systems have greater ability to maintain the original position of root canals, termed as the centering ability or shaping ability.[16]

The WaveOne Gold system (Dentsply Sirona, Ballaigues, Switzerland) is an updated version of the WaveOne system (M-wire alloy) by exposing the file to heat and then cooling it slowly to achieve greater flexibility as manufacturers claim. Furthermore, the modified convex triangular cross-section was changed to a parallelogram one.[17] The Reciproc Blue system's design (VDW, Munich, Germany) remained the same as that in the Reciproc system, but the metallic alloy underwent a different heat treatment that increased flexibility and fatigue resistance and reduced microhardness.[18] The OneCurve system (Micro Mega Colten, Besancon, France) is made of the C-wire alloy which undergoes a special heat treatment. The Fanta AF F-one system (Fanta Dental, Changzhou, China) is a new single-file system that is made of the AF-R Wire. It has a flat design that reduces the instrument's cutting surface area. The manufacturer claims that the vertical blades can sweep the debris from flutes to the relieved area.

The aims of this study were to compare the shaping ability and the performance (preparation time and associated complications) of OneCurve, Fanta AF F-one, Reciproc Blue, and WaveOne Gold single-file systems in simulated S-shaped canals.

  Materials and Methods Top

Sixty simulated S-shaped canals in resin blocks, with a 0.15 mm diameter, a 0.02 taper, and a 16 mm length (Endo Training Blocks S-shape Ø15; Dentsply Sirona) were used. Each simulated canal contained two curves: the coronal curvature angle was 30° with a 5 mm radius and the apical curvature angle was 20° with a 4.5 mm radius. Each sample was painted with a red ink before preparation and was photographed with a Sony α-6300-digital camera (Sony, Tokyo, Japan) fixed on the Zumax-OMS2350 dental microscope (Zumax Medical Co, Jiangsu, China) in a fixed position with constant settings (height, illumination, magnification, and focusing). The blocks were fixed and attached to a pliers' jaw-shaped-like device with a hinge to enable more controlled gripping. Canals' patency was confirmed by #10 K-files. Blocks were randomly divided into four equal groups (n = 15) according to the four single-file systems used. All systems were used according to the manufacturer's instructions, as follow:

  • Group-A: The WaveOne Gold Primary (25/0.07) system was used in a reciprocating rotation (170° counterclockwise then 50° clockwise) in an in-and-out pecking motion
  • Group-B: The Reciproc Blue R25 (25/0.08) system was used in a reciprocating rotation (150° counterclockwise then 30° clockwise) in an in-and-out pecking motion
  • Group-C: The OneCurve (25/0.06) system was used in a continuous rotation, at a 400 rpm and a 2.5 Ncm torque, in an in-and-out brushing motion
  • Group-D: The Fanta AF F-one (25/0.06) system was used in a continuous rotation, at a 500 rpm and a 2.6 Ncm torque, in an in- and-out brushing motion

All the simulated canals were prepared by an experienced operator to the #25 (0.25 mm) apical size preparation. A new file was used for shaping of each simulated canal. During preparation, canals were irrigated by distilled water and the flutes of the instruments were cleaned after three pecks. Blocks were re-photographed after preparation in the same before-preparation position under standardized conditions. The before- and after-preparation photos were exported to the Adobe Photoshop Elements 7.0 program (Adobe Systems Inc., San Jose, CA, USA). They were superimposed using the auto-align layers command which can automatically align layers based on a similar content in different layers [Figure 1]a. The AutoCAD-2017 image analysis' software (Autodesk Inc., CA, USA) was used to determine 12 points (levels) along the simulated S-shaped canals' length [Figure 1]b. While the point A was the most apical level, the L one was the most coronal level, with 1-mm intervals between levels (except the intervals between the A, B, and C points which were 0.5 mm). Canals' widths were measured at each selected level of the simulated canals before and after preparation. The amount of deviation was calculated as the absolute value of the difference between the two canals' widths (amount of resin removed from the inner and outer canals' walls) before and after preparation. Two parameters were considered: the mean deviation and the greatest deviation. The time required for each canals' preparation, ledges formation, and instruments' fracture, if any, were recorded.
Figure 1: (a) Superimposition of the before. and after-preparation photos. (b) The before. and after-preparation canalfs widths at the 12 levels

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Data were analyzed by the Shapiro–Wilk, one-way-ANOVA, and Chi-square tests (P = 0.05) using the SPSS software (IBM, SPSS Inc., Chicago, IL, USA). The Shapiro–Wilk test showed that the data (deviation mean's values and shaping times) were normally distributed (P > 0.05).

  Results Top

Comparisons of mean-deviation values at each level

There were no significant differences among the four rotary systems at A, B, J, and K levels (P = 0.174, 0.498, 0.793, and 0.057, respectively) [Graph 1]. Due to the discrepancies and the wide range of results among the study groups at different levels, statistical analysis were performed at different canals' thirds and the whole canals' length as shown in the following comaprisons.

Comparisons of the mean-deviation and the greatest-deviation values at each third of the canals

The mean deviation recorded in the middle third (0.14 mm) was significantly greater than those in the coronal and apical third (0.08 and 0.09 mm, respectively) (P = 0.000) [Table 1].
Table 1: Comparisons of mean deviation and the greatest deviation mean values at each third of the canals

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Coronal third

The mean-deviation values of the four groups were not statistically different (P = 0.139), with an overall mean deviation of 0.08 mm. The WaveOne Gold caused significantly the lowest value of the greatest deviation (0.09 mm) compared to those caused by other systems (P = 0.001) [Table 1].

Middle third

The OneCurve system caused the lowest value of the greatest deviation (0.13 mm) compared to those caused by other systems but not different from that caused by the WaveOne Gold system (0.18 mm) (P = 0.111) [Table 1].

Apical third

The OneCurve system caused the least mean deviation (0.07 mm) compared to those recorded in other systems (P = 0.001). Similarly, the OneCurve system showed the lowest mean of the greatest-deviation values (0.12 mm) compared to those recorded by other systems (P = 0.000) [Table 1].

Location of the greatest deviations at each canal's levels and thirds

Significantly, the highest percentage of the greatest deviations located within the canals' middle third (68.4%) followed by the coronal third (19.3%) (P = 0.000) [Table 2]. There were significant differences among the four systems. The Fanta-AF F-one and Reciproc Blue systems had higher percentages of the greatest deviation within the middle third (86.7 and 85.7%, respectively) than those of the OneCurve and WaveOne Gold systems (42.9 and 57.1%, respectively) (P = 0.013). Sixty percentage of the samples exhibited the greatest deviation at the G-level which was significantly greater than the second highest percentage (13.3%) which was recorded at the F-level (P = 0.000) [Table 2].
Table 2: Percentages of the greatest deviation at different canals levels and canals' thirds

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Time required for shaping and complications

The OneCurve system needed significantly the shortest shaping time (57.15 s) but not different from that recorded by the WaveOne Gold system (63.07 s) (P = 1.00). No complications (ledge formation or fractured instrument) were encountered [Graph 2].

  Discussion Top

This study investigated the centering ability of four single-file rotary systems when shaping double-curved simulated canals. The S-curve of root canals is one of the most difficult curves to be maintained after preparation. Previous studies reported different prevalence percentages of S-curve canals, while Zeng et al.[19] reported 6.84% and Schäfer et al.[20] reported a 17.5% prevalence. The middle and apical thirds of the root canals are more likely to be deviated from their original positions. The curvature angle and more importantly the curvature radius are very important aspects that should be considered when treating teeth with S-curved canals. Shorter radii increase both stress on instruments during canals' preparation[21] and instruments' fracture.[22] Moreover, when several factors were investigated, the curvature radius was the most influencing factor in rotary files failure.[23]

The conditions of ex vivo studies should be standardized to enable more reliable comparisons of different instruments' shaping ability. Hence, any significant differences among groups are attributed only to the differences among rotary systems used. Shaping of samples to the same apical size preparation enables more reliable comparisons of the of different files or systems.[24] Therefore, samples, in this study, were apically prepared to the 0.25 mm size. Simulated S-shaped canals were used in this study, as they are cheap, acceptable alternative to the extracted teeth,[25] and are suitable for research purposes as they can be easily photographed, which facilitates the before- and after-preparation measurements.[26] More importantly, standardization of the curvatures' angle and radius is paramount. However, these blocks are made of resin that has less hardness than that of the human teeth dentin, which may be considered as one limitation. Hence, results of studies performed on resin blocks should be extrapolated cautiously to clinical condition.[27]

Some studies used the terminology “shaping ability” and defined the canal deviation as the absolute value of the difference between the amount of removal resin from inner and outer aspect of canals before and after preparation at different levels (in the coronal–apical direction).[27],[28] The closer the values to zero, the better the shaping ability of the rotary systems. Other studies used the centering ability terminology to express the centering ratio, which was calculated using the amount of removal resin from two aspects of the canals by dividing the smaller value to the greater one. The closer the values to 1, the more centralized the root canal after preparation, hence the better centering ability of the rotary system (s) used. However, both methods are two sides of the same coin, as they reveal the ability of the rotary system to keep the original position of the root canal system after preparation. One previous study investigated the centering ability of the Reciproc Blue rotary system with or without glide path preparation, using both methods of calculation.[28] Both showed similar results and confirmed that glide path preparation enhances the centering ability of this system. The first method was adopted in the current study to compare the centering ability “shaping ability” among the four systems at the canals' 12 levels. As mentioned earlier in the results section, there were discrepancies and wide range of results among the study groups at different levels. There were no significant differences among the four rotary systems at A, B, J, and K levels [Graph 1]. However, at other levels, the OneCurve system showed overall better performance than other systems. To better illustrate these discrepancies, while the WaveOne Gold system showed significantly the least mean deviation at the L level, it showed the highest mean deviation at the D level. Consequently, how to decide whether this system is better, worse, or similar to other systems? Such discrepancies were noticed also in many previous studies.[17],[27],[28],[29] Therefore, the authors of the current study adopted a different approach, by performing statistical analysis at different canals' third (coronal, middle, and apical third) and at the entire canals' length (overall of the canal). Moreover, the authors introduced a new approach for investigating the centering ability by adopting the what-so-called “the greatest deviation” as alternative standard to the what-so-called “mean deviation.” While the mean deviation is the value that is calculated according to many values for different levels of each canal's third or the entire canal's length, the greatest deviation is a single deviation value, the highest, at specific level of the canal's third or the entire canal's length. Authors believed that such modifications could provide better understanding of the centering ability of the four systems being compared.

NiTi instruments have been superior to SSIs in reducing iatrogenic errors and canals' deviations from their original positions when both are used in curved canals.[30] Heat treatment procedures of NiTi instruments aimed at improving the flexibility and simulating the original anatomy of the root canals.[31] NiTi rotary systems with greater taper instruments were less flexible and more likely to change the original shape of root canals compared with those of less tapers but have the same tip size, especially when both were used in S-shaped canals.[21] Similarly, the current study's results revealed that the OneCurve system (06% taper) caused the least canals' deviation compared with the Reciproc Blue and the WaveOne Gold systems with tapers 8% and 7%, respectively. However, the Fanta-AF F-one system was an exception and caused the greatest canals' deviation, though it has taper 6% as well. Deviation of the root canal occurs when instruments remove dentin (or resin) from one wall more than from other walls. With greater tapers, instruments may remove greater dentin (or risen), but they still may not cause canals' deviation as they can remove almost the same amount of dentin/resin from all walls. Hence, increasing the canal diameter (width) after preparation does not mean greater canals' deviation, and it is better not to be correlated to deviations of the root canals, hence instruments' centering ability. Consequently, these conflicting results, related to instruments' tapers, suggest other influencing factors, such as: the type and angle of rotation, instruments' cross-section shapes, rake angles, depth of flutes, and the number of flutes per unit length.[21],[31] Studies reported the superiority of reciprocating motion in centering ability and less canal transportation.[32] By contrast, less apical transportations caused by the continuous motion were reported in other studies.[17] The OneCurve system, rotated continuously, was better than the Reciproc Blue and the WaveOne Gold reciprocating systems. The two latter caused significantly greater canals' deviations. However, the Fanta AF F-one, which rotated continuously, caused the highest-deviation values. Consequently, within the limitations of the present study, these conflicting results suggest that instruments motion' modes, continuous versus reciprocating, had no impact on maintaining the original position of simulated S-shaped canals.

One main objective of cleaning and shaping is to maintain the original shape and position of the root-canal apical constriction.[2] Any changes in this anatomical remark may be reflected negatively on the apical seal.[33] Therefore, most previous studies gave more attention to the performance of rotary systems in the root-canal apical third.[29] The OneCurve system, in this study, showed the least overall mean deviation (0.07 mm) in the canals' apical third compared to those caused by other systems. Furthermore, it showed similar superiority in the middle third and an overall for the whole canals' length. A previous study revealed that the gold wire used in the WaveOne Gold system resulted in better shaping ability and less canals' transportation than the OneShape and ProTaper Next systems.[34] The OneCurve is the newest generation of the OneShape system that is made of a heat-treated C-wire alloy, which better keeps the original canals' curvature during preparation and more flexible than the OneShape system, as the manufacturer claims. The S-shaped cross-section in the OneCurve system is similar to that in the Reciproc Blue and Fanta AF F-one systems in the middle and coronal two-third of the instruments. However, unlike the Reciproc Blue and the Fanta AF F-one, the cross-section shape of the OneCurve files at the apical portion is a triangle one. This may explain the better performance of the OneCurve system in reducing the canals' deviation in the current study. Another possible reason is the different heat treatment of the OneCurve system that uses the C-wire alloy. Nevertheless, there was no difference in the mean deviation between the four systems in the coronal third. The instruments most probably undergo similar stresses while shaping this straight part of canals.

About 69% of the greatest deviation was in the middle third of the canals. Moreover, 60% of the greatest deviation were in the G-level, which was located in the middle third of the canals. Interestingly, the canals' curvatures start at this level. The Reciproc Blue and Fanta AF F-one systems had the highest percentages of greatest-deviation values in these two anatomical remarks. By contrast, the OneCurve and WaveOne Gold systems had the lowest percentages. These findings again confirm the superiority of the OneCurve system. More importantly, the results related to the location of the greatest deviations at certain canals' one-third and at certain canals' levels showed the importance of the new analysis approach that was adopted in this study (the greatest deviation at each canals' third). It gave more insight and better understanding of maintaining the original shape of the canals among different rotary systems. This is especially true as the results of investigating canals' transportation at the 12 different canals' level were inconsistent and meaningless, as explained earlier. The results of the greatest-deviation values of each system at the G-level reflected the overall results, suggesting it as a reference point (level) in determining the best system that maintains the canals' original positions. Nevertheless, future investigations in this regard will be paramount.

The flat design of the Fanta AF F-one system may result in an inconsistent or unequal distribution of stresses on the instrument, causing decentralized cutting efficiency, hence canals' deviation. Furthermore, the complete flat design in one half of the cross-section, which may allow the accumulation of more resin debris between the instrument and canals' walls (occupying the spaces created by the flat design instrument). This may result in inconsistent cutting of the surrounding resin walls. These trapped debris also may reduce the instrument's cutting surface that caused a less amount of resin removal/sec, making it the most time-consuming system in this study. Many factors may affect preparation time, such as number of instruments in each system, operator experience, and the specific study conditions. The OneCurve system required the least shaping time when compared to Reciproc Blue and Fanta AF F-one systems. Single-file systems have been reported faster for canals shaping than traditional multiple-file systems.[13] Nevertheless, shaping times reported in ex vivo studies do not reflect those needed in shaping real clinical cases, which can be mainly due to different work conditions.

In the present study, no complications (ledges formations or instruments fracture) were encountered. These findings were consistent with those of previous studies, in which single-file systems were used in severely curved canals of the extracted teeth[35] or in simulated S-shaped canals.[27],[36] The number of uses is one of the factors that influence incidents of instruments fracture.[37] Each file was used, in this study, for shaping one canal to the 0.25 mm apical size preparation. Another possible reason for no incidents of instruments fracture is the use of new generation heat-treaded NiTi single-file systems. These systems have been reported to be superior in shaping S-shaped resin canals.[15]

It is important to indicate that the current study investigated the centering ability of the single-file rotary systems using the superimposed two-dimensional (2D) images of before and after preparation, which can be considered as one limitation. Therefore, a further research study to investigate the centering ability of the same rotary systems used in this study, in simulated canals and extracted teeth, is paramount. Microcomputed tomography analysis provides comparison of the shaping ability in the 3D.[34],[38]

  Conclusions Top

Within the limitations of this study, it can be concluded:

  • Instruments' tapers and motion modes (continuous vs. reciprocating) seem to have no impact on rotary systems' shaping ability
  • The OneCurve system had better shaping ability in simulated S-shaped canals than the WaveOne Gold, Reciproc Blue, and Fanta AF F-one systems
  • The OneCurve followed by the WaveOne Gold systems required the shortest preparation times
  • Considering the “greatest-deviation” at different canals thirds and levels rather than the mean deviation may be more appropriate approach when the shaping ability of rotary systems is investigated. However, future works are needed to validate such recommended investigation method.

Financial support and sponsorship


Conflicts of interest

There are no conflicts of interest.

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  [Figure 1]

  [Table 1], [Table 2]


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