Introduction
The main purpose of endodontic treatment is to remove and prevent infection of the root canal system through good endodontic preparation and three-dimensional obturation of the canals (1, 2). The root canal instrumentation needs to preserve the existing root anatomy, the position of the apical foramen and the original curvature (3, 4). One of the greatest advances of the 1980s in the field of root canal preparation was the development of the NiTi alloy for endodontic instruments (5). Rotary NiTi instruments were introduced to improve root canal preparation because they deliver simpler, faster shaping (6).
The recent F360® files (Komet Dental, Lemgo, Germany) have a 4% taper and are available in sizes 25, 35, 45 and 55. They have a modified S cross-section, are made of NiTi, and rotate continuously in a clockwise direction (7).
Mtwo® rotary files (VDW, Munich, Germany) also have an S-shaped cross-section. Their low radial contact and almost vertical cutting edges ensure good control of the instrument’s progress. Several studies assessed different characteristics of these files and confirmed their superiority compared to other systems (8).
The RaCe® system (FKG Dentaire, La Chaux-de-Fonds, Switzerland) provides electrochemical polishing, which improves their mechanical performance. The files have a triangular cross-section. Owing to their alternate helical angles and to cutting edges that are almost parallel to their longitudinal axis, there is less likelihood of blocking or screw-in effects (9).
The Hyflex® system (Coltene-Whaledent, Allstetten, Switzerland) has a similar cross-section to EndoSequence® (Brasseler, Savannah, USA). These NiTi files are manufactured by an innovative method that gives control over the material’s memory (10).
The aim of this study was to compare the cutting area, instrumentation time, root canal anatomy preservation and non-instrumented areas of F360®, Mtwo®, RaCe® and Hyflex® files of size 35.
Materials and Methods
A total of 120 extracted permanent teeth were divided randomly with no preference into 4 groups (n = 30). The criteria for teeth selection were: upper and lower central incisors with a single straight root and root canal. The exclusion criteria were: lateral incisors, canines, premolars and molars.
The endodontic opening was made with a round diamond bur with water cooling, followed by the use of an Endo-Z bur once the pulp chamber was reached. The working length was calculated with digital radiographs with a #15 K-file (Dentsply Maillefer, Ballaigues, Switzerland). A black line on each vestibular side and a red line on each palatine/lingual side were drawn with indelible markers (Paper Mate, Atlanta, USA). Using a series 532 Vernier caliper with fine adjustment (Mitutoyo America Corporation, Illinois, USA), the root lengths and the points at which they were to be sectioned were calculated according to their length.
The roots were sectioned into coronal, middle and apical thirds with a handpiece and a 0.17 mm thick diamond disk. Each third was observed and photographed through a Nikon SMZ-2T stereoscopic microscope (Nikon, Tokyo, Japan) fitted with a Nikon D70 camera (Nikon, Tokyo, Japan) and an Intralux 4000-1 light source (Volpi, Schlieren, Switzerland). The teeth were reconstructed with the aid of a #10 K-file inserted through the endodontic aperture made in the crown and through the canal in each third of the root. The lines previously marked on the teeth assisted in adjusting the tooth sections, which were mesially and distally joined with epoxy glue.
A preoperative analysis confirmed that all groups were adjusted, both by thirds and generally. The mesiodistal width of the coronal third of tooth #4 was measured with the caliper and this measurement (5 mm) was entered into the AutoCAD 2013 program in order to scale up and calculate the canal areas of the radicular thirds prior to biomechanical preparation. The statistical analysis of the preoperative areas was carried out with the SPSS 18 program at a 95% confidence level (P < 0.05), using Levene’s test to assess variances and ANOVA to compare means. If significant differences had been found, some samples would have been discarded and other added to balance the groups.
The glide path was made with a #15 K-file and used a #10 K-file for patency filing. The root canals were flushed with 5.25% sodium hypochlorite (NaClO) between files, using a side opening syringe. The instrumentation time was measured with a 1/100 second chronometer from the moment files entered the canals until they got out. The root canal instrumentation sequences were:
Group 1: F360® 25/04 and 35/04 files at 300 rpm and 1.8 Ncm.
Group 2: Mtwo® files in the following sequence: 10/04, 15/05, 20/06, 25/06, 30/05 and 35/04, with 10/04 and 15/05 at 1.3 Ncm, 20/06, 25/06 and 30/05 at 2.3 Ncm and 35/04 at 280 rpm and 1.2 Ncm.
Group 3: RaCe® 15/06, 25/04, 30/04 and 35/04 files at 600 rpm and 1.5 Ncm.
Group 4: Hyflex® files in the following sequence: 25/08 (similar to the ProTaper® SX file (Dentsply Maillefer, Ballaigues, Switzerland)), 20/04, 25/04, 20/06, 30/04 and 35/04, at 500 rpm and 2.5 Ncm.
The final irrigation protocol for all the groups was 2 mL of 0.9% saline solution, 17% ethylenediamenetetracetic acid (EDTA) for one minute, 2 mL of 0.9% saline solution, 2 mL of 5.25% NaClO and 2 mL of 0.9% saline solution.
Lastly, the root thirds were sectioned and observed under an SMZ-2T stereoscopic microscope, taking photographs at x15 magnification. The root canal areas of each third after biomechanical preparation were measured using the scale calculated previously. The cutting areas were quantified by calculating the difference between the preoperative and postoperative areas (Figure 1). Root canal anatomy preservation was studied by superimposing the preoperative and postoperative areas with AutoCAD 2013 system (Figure 2). Finally, non-instrumented areas were observed with Nikon SMZ-2T stereoscopic microscope at x15 magnification and confirmed with AutoCAD 2013 system.
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The SPSS 18 program at a 95% confidence level (P < 0.05) was used for statistical analysis with normality of distribution, using Levene’s Test to assess variances and ANOVA to compare means of the cutting area and instrumentation time. For the instrumentation time Levene´s Test, ANOVA and Bonferroni Test were used. For root canal anatomy preservation and non-instrumented areas, Pearson´s Chi-square Test was used.
Results
Table 1 shows the means of pre-instrumentation and cutting areas (mm2). Table 2 shows the statistical analysis of the areas. Table 3 shows the means of instrumentation time (s) and the statistical analysis. Table 4 shows the percentages of teeth and the statistical analysis of the root canal anatomy preservation and non-instrumented areas. No files were fractured during the study.
| Preinstrumentation | Cutting area | |||
|---|---|---|---|---|
| Third | Levene | ANOVA | Levene | ANOVA |
| Coronal Middle Apical Global | 0.128 0.100 0.166 0.736 | 0.718 0.318 0.199 0.948 | 0.381 0.126 0.509 0.782 | 0.953 0.201 0.159 0.839 |
| System | Time | Levene´s Test | ANOVA | Bonferroni |
|---|---|---|---|---|
| F360 (F) | 27.23 | 0.095 | 0.018 | F vs M 0.011* F vs R 0.035* F vs H 0.010* M vs R 0.033* M vs H 0.097 R vs H 0.028* |
| Mtwo (M) | 58.76 | |||
| RaCe (R) | 46.53 | |||
| Hyflex (H) | 60.45 |
*Significant differences – P < 0.05
With respect to the pre-instrumentation areas, there were no significant differences between the four groups, determining that the groups were stabilized (P > 0.05, Table 2). Regarding the cutting area, RaCe® made a higher cutting area (1.65±0.27mm2) than the other systems in the coronal third, Mtwo® and Hyflex® made the same cutting area in the middle third with a small difference in the margin of error (0.55±0.10mm2 and 0.55±0.09mm2), in the apical third it was Hyflex® (0.39±0.06mm2). On the whole, Mtwo® was better than the other systems (0.85±0.16mm2) (Table 1). Similarly to the pre-instrumentation areas, no significant differences were found between the systems (P > 0.05, Table 2).
Regarding the instrumentation time, F360® was the fastest system (27.23s) and Hyflex® was the slowest (60.45s), and there were significant differences between all systems (P < 0.05, Table 3) except Mtwo® with Hyflex® (P > 0.05, Table 3).
For root canal anatomy preservation, Mtwo® had a higher percentage than the other systems in the coronal third (100%), Mtwo® and Hyflex® in the middle third (96.67%) and F360®, Mtwo® and Hyflex® in the apical third (100%). However, there were no significant differences (P > 0.05, Table 4).
For non-instrumented areas, Mtwo® and RaCe® achieved the smallest percentage in the coronal third (3.33%), RaCe® in the middle third (3.33%) and F360®, RaCe® and Hyflex® in the apical third (0%). Nevertheless, no significant differences were found (P > 0.05, Table 4).
Discussion
Using an SMZ-2T stereoscopic microscope and the AutoCAD 2013 system, the effects of four present-day instrumentation systems that had the same taper, size and rotation motion but differed in their designs, numbers of files, speeds and torques were compared in the cutting area, preservation of the root canal anatomy and non-instrumented areas.
In recent years, several studies have examined the different results of instrumentation systems. In 2009, Semaan et al. (11) published a paper on the evolution of rotary instrumentation systems, explaining the individual characteristics of each, the shaping techniques, modes of action and advantages and disadvantages of each system, and the error correction methods. In the present study, the cutting area, root canal anatomy preservation and non-instrumented areas were investigated in 4 different rotary systems (F360®, Mtwo®, RaCe® and Hyflex®) with a common size and taper.
The instrumentation achieved with the different rotary systems can be assessed in resin blocks or extracted human teeth. However, resin blocks do not reflect the action of the rotary systems in the same way as extracted human teeth, as the heat generated by the instruments can soften the resin (12, 13). Therefore, extracted human teeth were used for this study.
Over the years, researchers have used different methods to assess the root canal instrumentation effected by rotary systems. These methods include AutoCAD, micro-computed tomography (μ-CT), X-rays and photographs taken with a stereoscopic light microscope or an electronic microscope (12, 14, 15). In the present study, a Nikon SMZ-2T stereoscopic microscope and the AutoCAD 2013 system were used because the pictures have high quality and the measurements are accurate and even architects use AutoCAD system to design buildings and structures.
A number of researchers have used AutoCAD to study different parameters. Günday et al. (16) used AutoCAD to assess torque and cyclic fatigue, Kim et al. (17) to calculate root curvature, and Durán-Sindreu et al. (18) to study apical transportation. Grande et al. (19) used AutoCAD 2000 to compare the EndoEZE AET® (Ultradent, South Jordan, USA) and ProTaper®, and they found significant differences in the coronal and middle thirds, but not in the apical third. Al-Manel et al. (20) examined Twisted Files® (SybronEndo, Orange, CA) and Profile GTX® (Dentsply Maillefer, Ballaigues, Switzerland) systems in curved canals and found no significant differences. In the present study, the AutoCAD 2013 system was used to assess the cutting area and root canal anatomy preservation of different systems, and unlike Grande et al., we determined the absence of significant differences similar to Al-Manel et al. and high root canal anatomy preservation percentages.
Regarding the results in the cutting area (Table 1), RaCe® obtained the highest mean, 1.65±0.27mm2, in coronal third but, Mtwo® got 1.62±0.33mm2, Hyflex® 1.58±0.22mm2 and F360® 1.54±0.32mm2. Mtwo® and Hyflex® obtained the same mean in middle third, 0.55±0.10mm2 and 0.55±0.09mm2 respectively, the only difference was the margin of error. In this third, F360® made 0.45±0.09mm2 and RaCe® 0.47±0.05mm2. In apical third, Hyflex® was the best with a mean of 0.39±0.06mm2. In this third, F360® realized 0.29±0.09mm2, Mtwo® 0.37±0.05mm2 and RaCe® 0.37±0.06mm2. In the last point, Mtwo® got the highest mean and F360® the lowest mean globally, 0.85±0.16mm2 and 0.76±0.16mm2 respectively, and RaCe® obtained 0.83±0.15mm2 and Hyflex® 0.84±0.13mm2.
In the same way as in our study, Talati et al. (21) used the AutoCAD system to compare instrumentation systems, in this case RaCe® and Mtwo® in curved canals, and they observed better cleaning of the canals by Mtwo® with significant differences. In another study, Sadeghi (22) compared Mtwo®, FlexMaster® and K-Flexofile by X-ray in resin blocks with curved canal at 1, 3, 5, 7 and 9mm of apex. In results, significant differences were found between the inner curve and the outer curve to all systems, except FlexMaster® at 9mm and K-Flexofile at 5mm of apex. Yang et al. (23) contrasted ProTaper® and Mtwo® with μ-CT in teeth with curved canals, and found no significant differences. In turn, Herrero Moraes et al. (24) published an investigation of ProTaper®, Mtwo® and K3® using an analytical balance (Bioprecisa, Săo Paulo, Brasil) which calculated the cutting area in grams. The results showed significant differences and concluded that ProTaper® was the best system. Bürklein et al. (25) compared the shaping ability and cleaning effectiveness of Wave One® (Dentsply Maillefer, Ballaigues, Switzerland) and Reciproc® (VDW Dental, München, Germany) in comparison to ProTaper® and Mtwo®, using different sizes with scanning electron microscopy, and they found significant differences in the apical third. In contrast, Mtwo® was not better than the other systems in this study, no significant differences were found in cutting area compared to Yang et al., using Nikon SMZ-2T stereoscopic microscope and AutoCAD system that calculated the cutting area in mm2 like Talati et al., instead of X-ray, analytical balance or μ-CT.
Moreover, Marceliano-Alves et al. (26) compared Hyflex® with Reciproc®, Wave One® and Twisted Files® using μ-CT, and they did not find significant differences for all systems. Zhao et al. (27) published a study in which Hyflex®, Twisted Files® and K3® (SybronEndo, Orange, CA) were compared with μ-CT, and they reached similar conclusions as Marceliano-Alves et al. and us, but Nikon SMZ-2T stereoscopic microscope and AutoCAD system (mm2) were used in this investigation to examine the cutting area instead of μ-CT (mm2).
In addition, on comparing the instruments with the same 0.04 taper (F360®, Mtwo®, RaCe® y Hyflex®), we achieved the same results as Fayyad et al. (28) who observed an absence of significant differences on comparing changes in volume using One Shape® (MicroMega, Besançon, France), ProTaper® and TF Adaptive® with the same 0.06 taper with computed tomography, although we used other systems.
On the other hand, the instrumentation time is important when the endodontic treatment is performed, because if this time is reduced, the dentist will have more time to disinfect with irrigants. In this section, F360® was the fastest system with 27.23s of mean, Hyflex® got 60.45s, the slowest system, and Mtwo and RaCe obtained 58.76s and 46.53s respectively (Table 3). Bürklein et al. (29) compared the instrumentation time of Hyflex®, Mtwo and Revo-S® (MicroMega, Besançon, France). The authors found significant differences with Hyflex® and Mtwo® versus Revo-S®, but they did not find significant differences between Hyflex® and Mtwo®. Saber et al. (30) examined the instrumentation time of Wave One®, Reciproc® and One Shape®. In turn, the authors found significant differences between Reciproc® and Wave One®, and One Shape® versus Reciproc® and Wave One®. In our results, we also observed significant differences between all systems except Mtwo® versus Hyflex®.
Root canal anatomy preservation is very important for three-dimensional obturation and for the success of the endodontic treatment. Regarding our results, Mtwo® was the most constant system obtaining a percentage of 98.89%. In contrast, F360®, RaCe® and Hyflex® obtained lower percentages: 94.44%, 95.56% and 97.78% respectively (Table 4). Yoo et al. (31) published a study in which they compared Reciproc®, Wave One®, ProTaper®, Profile® and K-files, by superimposing the preoperative and postoperative images with microscope, and they did not find any significant differences in root canal anatomy preservation on comparing. In the present study with other systems, high percentages of preservation and no significant differences were found for all the systems examined similarly to Yoo et al.
The success of the endodontic treatment can be jeopardized if the canal instrumentation leaves non-instrumented areas. In this investigation, RaCe® obtained 2.22% overall, the best percentage. However, F360® got the highest percentage on the whole, 8.89%, and Mtwo® and Hyflex® obtained 7.78% and 5.56% respectively (Table 4). Paqué et al. (32) compared ProTaper® with 3 different shapes and H-files using μ-CT. The authors found high percentages of non-instrumented areas, but in our results all the systems obtained very low percentages and there were no significant differences.
In conclusion, the four different rotary systems produced similar cutting area, root canal anatomy preservation and non-instrumented areas statistically. F360® was the fastest system statistically.
