Comparison of the Efficacy of NeoNiTi, ProTaper, and Reciproc Files in the Retreatment of Curved Root Canals: a CBCT Assessment

Abstract

Objective

Effective tools and methods are applied during root canal retreatment to eliminate root canal obturation materials and preserve the initial root canal anatomy. The present study compared the efficacy of Reciproc, Neoniti, ProTaper, and Hedstrom files in the retreatment of curved root canals.

Material and methods

In the present in vitro study, 100 root canals with 25‒45º curvatures were used. After the samples were initially prepared and examined by CBCT, the root canals were obturated with gutta-percha and randomly assigned to four groups (n=25). A retreatment was carried out in each group with NeoNiTi, ProTaper, Reciproc, and Hedstrom files. CBCT examinations were carried out again under the same conditions. The samples were evaluated at 3-, 6-, and 9-mm distances from the apex on the first and the second CBCT image for root canal transportation and remaining gutta-percha in the root canals. The time required for retreating each canal in each sample was recorded. One-way ANOVA and corresponding non-parametric tests were applied for data analysis.

Results

The root canal transportation in the NeoNiTi group was lower than that in the other groups and significantly different from the ProTaper group (P<0.05). There was a remaining gutta-percha after retreatments in all the four groups, which was not statistically significant (P>0.05).

Conclusion

Despite the fact that the NeoNiTi file produced less transportation than other file systems evaluated in the retreatment of curved root canals, all the files were very effective at the clinically acceptable levels.

Introduction

Despite an 86-96% success rate of root canal treatment, postoperative conditions might necessitate retreatment (1). One of the most critical steps in root canal retreatment is to eliminate the root canal filling materials from the root canal, which is carried out with different tools (2-4). Rotary systems are effectively used during root canal retreatment. These systems have been developed using NiTi alloys. However, conventional NiTi alloys exhibit some drawbacks, including pre-curvature inability, structural shortcomings, and inadequate cutting ability (5). Of all the different rotary systems, ProTaper universal files (Dentsply, Ballaigues, Switzerland) used for retreatment are effective in straight and curved root canals (6-8).

The NeoNiTi (Neolix, Chatres-La-Forte, France) was introduced in 2012 as a single file rotary system. A study showed that this file could provide easy and safe access to the root canal without a binding effect, even in curved root canals (9). However, there is currently not sufficient number of studies on the efficacy of this system and its comparison with other tools used for curved root canals treatment.

Reciproc files (VDW, Munich, Germany), too, are single-file systems but they have a reciprocal mechanism. Numerous NiTi rotary systems have been developed to overcome this shortcoming (10), with their efficacy being evaluated in the retreatment procedures of curved root canals in some studies (11-13).

However, hand files, such as Hedstrom (Dentsply, Ballaigues, Switzerland), are still used in the retreatment of root canals as a conventional method. Some studies have shown that these files can be more effective in removing gutta-percha than the ProTaper universal files designed for retreatment (2, 4). However, some other studies have reported similar efficacy for these files compared to ProTaper and Reciproc files designed for the retreatment of straight and curved root canals (4, 7, 11). However, it has been reported that irrespective of the file type, it is not possible to completely eliminate root canal filling materials from the root canals with the available methods (4, 14).

On the other hand, the root canal retreatment of curved root canals is challenging due to variations in the normal anatomy of the root canal and root canal transportation (15). To overcome this problem, we can use rotary systems due to their NiTi alloy, which has unique properties that lead to greater flexibility and reduced transportation (16).

Different techniques are available to evaluate root canal transportation, including scanning electron microscopy (17), radiographic evaluation (18), photographic evaluation (19), etc. The CBCT is a non-invasive and non-destructive technique introduced to evaluate the root canal anatomy and compare it before and after its preparation. According to previous studies, this technique can provide accurate cross-sectional 3D images of samples that can be verified and is more accurate than other techniques. Besides, this technique preserves the samples and can provide several images from one sample (20, 21).

Considering the discrepancies in the results of studies evaluating the efficacy of different rotary and manual systems in the retreatment of root canals, the present study aimed to compare the efficacy of NeoNiTi, ProTaper, and Reciproc rotary files in comparison to Hedstrom hand files in the retreatment of curved root canals. The hypothesis of this study was: A) The efficiency of Reciproc, NeoNiTi, ProTaper, and Hedstrom files in removing gutta-percha from the canal and maintaining the curvature of the root canal is not different. B) The time required to retreat curved canals with Hedstrom files is longer than the time required with NeoNiTi, ProTaper, and Reciproc files.

Material and methods

The steps of the study are presented in Figure 1.

Figure 1.

Flowchart of study’s methodology sequences

Selection and initial preparation of the samples

Firstly, the software PASS 11 AND the One-way ANOVA method was used to determine the sample size. For this purpose, with α= 0.05 and β= 0.2 (power=80%), and considering the mean values and the required standard deviation from similar studies, the number of samples in each group was calculated at n=25 (a total of 100 samples).

The present study evaluated one hundred freshly extracted human teeth, including maxillary and mandibular molars. The teeth had been extracted due to periodontal problems or caries and could not be preserved. The teeth were stored in 0.5% chloramine T solution until they were used in the study. The inclusion criteria consisted of a root canal length of 11‒13 mm (from the root canal orifice at CEJ to the radiographic apex), a curvature range of 25‒45º according to the method proposed by Schneider (22), no visible obstruction of the root canal, calcification, resorption, fracture, and root defects under visual evaluation of the radiographs, no double curvature of the root, and no previous root canal treatment.

First, an access cavity was prepared with a 0.12 fissure carbide bur (Tizkavan, Tehran, Iran) in a high-speed handpiece (Bien Air, Switzerland) under air and water spray to prepare the samples. Then the tooth crowns were removed using a diamond disk (Tizkavan, Tehran, Iran) in a slow-speed handpiece (Bien Air, Bienne, Switzerland) to leave one single root (the mesiobuccal root of maxillary molars and the mesial root of mandibular molars), measuring 18 mm in length. Then the patency of the root canals was evaluated with a # 10 K-file (Dentsply, Ballaigues, Switzerland), and when the file was slightly entangled in the working length, these root canals were confirmed for the study. The samples were separately mounted in fast-setting acrylic resin (Acroopars 200, Tehran, Iran) and numbered from 1 to 100.

In the first step, the samples were prepared with the RaCe rotary system (FKG Dentaire, La Chaux-de-Fonds, Switzerland) up to file #25, with 4% taper using an endodontic motor (NSK, Japan) at 500 rpm and 1 Ncm; 5.25% NaOCl was used for root canal irrigation between instruments.

The sampling method was non-randomized (sequentially judgmental). The samples were numbered from 1 to 100 and randomly distributed among the groups by Research randomizer program software (www.randomizer.org) and mounted in a hand-made arch-form wax cast for CBCT examinations; 5-10 samples were mounted in each cast. Then, the prepared casts underwent CBCT (Planmeca ProMax 3D, Helsinki, Finland) examinations under the following exposure conditions: mA=6, kVp=76, time=6 s, vocal size=0.15×0.15, FOV=8×8 mm.

Axially images were recorded for each sample at 3-, 6- and 9-mm distances from the apex using the Planmeca Romixs Viwewes 5.4.0.R software (Planmeca, Helsinki, Finland) separately and saved as the initial record (Figure 2).

Figure 2.

One sample of initial recorded image in CBCT The measurements made to calculate root canal transportation on axial cross-sections.

The lateral compaction technique was applied for root canal obturation with gutta-percha (Ariadent, Tehran, Iran) and AH26 sealer (Dentsply, Ballaigues, Switzerland) using a #B spreader (Dentsply, Ballaigues, Switzerland). After cutting and removing gutta-percha from the root canal orifice, the access cavity was sealed with Cavisol (Golchai, Karaj, Iran) temporary dressing. The samples were radiographically examined using a digital intraoral x-ray unit (Planmeca, Helsinki, Finland) to confirm the accuracy of all the steps at exposure conditions of mA=8, kVp=60, and 0.16 s with a PSP sensor and a phosphor plate Acteon scanner (Sopro, La Ciotat, France). Then, the obturation quality was confirmed by an endodontist. Finally, the samples were incubated for one week at 100% relative humidity at 37ºC for the complete setting of the sealer.

Root canal retreatment

The temporary dressing was removed, and the area was irrigated with normal solution. The gutta-percha was removed up to 1 mm from the canal orifices by a heat carrier, and 0.2 mL of chloroform solution (Sina Bartar, Tehran, Iran) was placed. A #15 C-Pilot file (VDW, Munich, Germany) was used to create a path along the root canal. Preparations were carried out in each group as follows:

ProTaper group (n=25): ProTaper universal files (Dentsply, Ballaigues, Switzerland) in an endodontic motor (NSK, Osaka, Japan) were used at 500 rpm and 1 Ncm^-1 torque in the root canals, respectively, as follows: D1 file for the coronal third with 11-mm length, D2 file for the middle third with 14-mm length, and D3 file for the apical third with 17-mm length, followed by ProTaper F2 file up to the working length for the final apical preparation (23).

NeoNiTi group (n=25): After preparation of the coronal third with #3 and #2 Gates-Glidden drills up to 11 mm with the crown-down technique, the middle and apical thirds were prepared with an A1 file (Neelix, Chatres-La-Forte, France) up to the working length in an endodontic motor at 500 rpm and 1.5 Ncm^-1 torque.

Reciproc group (n=25): After preparing the coronal third, similar to the NeoNiTi group, the R25 file (VDW, Munich, Germany) was used in a Silver Reciproc motor (VDW, Munich, Germany) for the middle and apical thirds up to the WL following the manufacturer’s instructions.

Hedstrom group (n=25): After preparing the coronal third, similar to the NeoNiTi group, the procedure continued with #20 to #35 Hedstrom files (Dentsply, Ballaigues, Switzerland) with the crown-down technique, and the final apical preparation was carried out up to #30 file.

Each file was replaced by a new one after four uses. After the final irrigation, the root canals were dried with paper points. One operator carried out all the preparation procedures (a senior postgraduate student in endodontics). In addition, the time required to complete the retreatment procedure was calculated in each group.

At the end of these procedures, the samples were put back to their places in the wax casts to undergo the CBCT examinations under the same conditions.

Determining root canal transportation and residual gutta-percha

To increase the accuracy of the CBCT measurements before evaluating axial cross-sections, first, the distance between the CEJ and the apex of the samples was determined on the coronal plane on the two preoperative and postoperative images superimposed to eliminate possible errors. Then axial sections were prepared at 3-, 6-, and 9-mm distances from the apex in each sample, similar to the initial CBCT, and saved.

To create a similar condition for correct measurement on initial and secondary CBCT images, first, the longest buccolingual diameter in each axial cross-section was drawn as a guide using the Paint 10.0 software (Coronal Corporation Inc., USA) (BL) (Figure 3A). Then, from a point on the BL line at the root canal center, a line was drawn perpendicular to B (MD) (Figure 3B). At this stage, the images were saved and transferred to the Image Tool 3.0 software (University of Texas Health Science Center, USA) to calculate root canal transportation extent. In the software, the BL line was measured first, based on which the initial and final CBCT cross-sections were matched. The a and b values, as the distances between the external border of the root cross-section and the border of the prepared root canal on the MD line on the mesial and distal aspects, respectively, were then calculated on the initial and final CBCT images (Figure 3C). Finally, root canal transportation was calculated using the formula below and recorded for statistical analysis for each axial cross-section (in which a1 and b1 represent the values before retreatment; in addition, a2 and b2 represent the values after retreatment.):

Figure 3.

The measurements made to calculate root canal transportation on axial cross-sections

Transportation = [(a1-a2)-(b1-b2)]To determine the amount of residual gutta-percha after retreatment, the surface area determining tool was first used to calculate the root canal surface area in mm² on each cross-section of the final CBCT. Then, the surface area occupied by gutta-percha was measured, and the percentage of the residual gutta-percha was calculated on each cross-section (Figure 4) (5). All the measurements in the present study were made by one operator (a radiologist). Three measurements were taken, and their mean value was used as the data.

Figure 4.

One sample of the image of the residual root fillings recorded by CBCT

Statistical analysis

Statistical analyses were performed using SPSS 20 (IBM Corp., Armonk, NY, USA). First, the distribution of data was analyzed using the Kolmogorov-Smirnov test. Normally distributed data were analyzed with one-way ANOVA to compare the groups. Tukey tests were used for two-by-two comparisons of the groups. Besides, repeated-measures ANOVA was used to compare the different sections; the Bonferroni test was used for two-by-two comparisons of the sections. In cases when the data were not distributed normally, non-parametric Kruskal-Wallis and Mann-Whitney tests were used to compare the groups. Friedman and Wilcoxon signed-rank tests were used to compare the sections. Statistical significance was set at P<0.05.

Ethical Statement

This study was approved by the Ethics Committee of Qazvin University of Medical Sciences with an ethics code of IR.QUMS.REC.1394.391. There was no conflict with ethical considerations.

Results

The results of one-way ANOVA confirmed the homogeneity of the samples between the four study groups.

Root canal transportation

The one-sample Kolmogorov-Smirnov test confirmed the normal distribution of data of this variable (P>0.05). Repeated-measures ANOVA revealed significant reciprocal effects between the groups and cross-sections (P<0.05).

One-way ANOVA showed significant differences in the extent of root canal transportation at 6- and 9-mm distances from the apex between the study groups (P=0.027 and P=0.002, respectively), with no significant difference at 3-mm distance from the apex between the groups (P=0.8) (Table 1).

Table 1. Comparison of the results of root canal transportation and residual gutta-percha variables at different sections between the four study groups.

Cross-section	Group	Root canal transportation (mm)			Residual gutta-percha (%)
		Mean	SD	pvalue	Percent	Pvalue
9-mm distance	ProTaper	0.17	0.02	0.002	42.48	0.08
	Neoniti	0.11	0.01		60.32
	Reciproc	0.01	0.01		47.68
	Hedstrom	0.13	0.01		46.10
6-mm distance	ProTaper	0.17	0.02	0.027	44.27	0.266
	Neoniti	0.08	0.01		52.70
	Reciproc	0.15	0.01		56.04
	Hedstrom	0.13	0.01		43.10
3-mm distance	ProTaper	0.13	0.02	0.8	42.48	0.311
	Neoniti	0.15	0.01		57.26
	Reciproc	0.20	0.02		50.10
	Hedstrom	0.18	0.02		46.56

Based on the results of post hoc Tukey tests concerning the two-by-two comparisons of the groups, there was a significant difference in root canal transportation at the 9-mm distance from the root apex only between the NeoNiTi and ProTaper groups (P=0.008); at the 6-mm distance, there were significant differences only between the NeoNiTi and ProTaper and Reciproc groups (P=0.002 and P=0.016, respectively).

Repeated-measures ANOVA showed that the root canal transportation extent at different sections was not significantly different in the ProTaper and Reciproc groups (P=0.067 and P=0.097, respectively). However, the differences were significant in the NeoNiTi and Hedstrom groups (P=0.001 and P=0.044).

Two-by-two comparisons of different sections with the Bonferroni test showed significant differences in the extent of root canal transportation at 3- and 6-mm sections in the NeoNiTi and Hedstrom groups (P=0.002 and P=0.044, respectively).

Residual gutta-percha

Since the data on this variable were not distributed normally, non-parametric tests were used to compare residual data in different study groups. The Kruskal-Wallis test showed no significant difference in the percentages of residual gutta-percha at 3-, 6-, and 9-mm sections from the apex between the study groups (P=0.311, P=0.266, and P=0.080, respectively). A comparison of different sections in each group with the non-parametric Friedman test showed significant differences in the amount of residual gutta-percha between different sections in all the groups (P<0.01) except for the NeoNiTi group (P=0.184). Concerning two-by-two comparisons of different sections, there were significant differences between the 6- and 9-mm sections and between the 3- and 9-mm sections from the apex in the ProTaper group according to Wilcoxon signed-rank test (P=0.033 and P=0.014, respectively), with no significant difference between the 3- and 6-mm sections from the apex (P=0.404). In the Reciproc groups, too, similar results were obtained (P=0.344, P=0.008, and P=0.002, respectively). In the Hedstrom group, 3- and 6-mm sections and 3- and 9-mm sections from the apex exhibited significant differences (P=0.023 and P=0.002, respectively); however, 6- and 9-mm sections from the apex were significantly different (P=0.106) (Table 1).

The time spent completing retreatment

One-way ANOVA showed significant differences in the time required to complete retreatment between the four study groups (P=0.001). Based on the results of two-by-two comparisons with post hoc Tukey tests, presented in Table 2, the differences in this variable were not significant between the ProTaper, NeoNiTi, and Reciproc groups (P=0.944). However, the differences between the Hedstrom group and the three other groups were significant (P<0.001) (Table 2).

Table 2. Comparison of the times required to complete retreatment between the different groups.

Group	Time (s)		Pvalue
	Mean	SD
ProTaper	270.50	11.68	0.001
Neoniti	262.35	8.90
Reciproc	266.40	8.84
Hedstrom	594.16	11.48

Discussion

Root canal retreatment is investible due to the possible failure of the initial treatment (1). One of the chief aims of root canal treatment is to preserve the original shape of the root canal during mechanical debridement and shaping of the root canal (2-4, 24). Therefore, it is necessary to gain access to tools and techniques that are effective in retreatment procedures.

We used the three rotary systems of NeoNiTi, ProTaper, and Reciproc files to compare the efficacy of different currently used systems in the retreatment of curved root canals. Reciproc (VDW, Munich, Germany), a single file system with an s-shaped cross-section, removes root canal dentin using the reciprocal back (150 degrees counterclockwise) and forward (30 degrees clockwise) movements. The ProTaper files are triangular in cross-section or exhibit a modified triangular cross-section with lower cutting efficiency and smaller space for debris accumulation compared to the Reciproc file system. NeoNiTi A1 (NEOLIX, Châtres-la-Forêt, France) constitutes a single-file system with full rotary and continuous rotating movements. It has been manufactured using a special alloy to achieve superior file flexibility. According to the manufacturer data, the wire-cut electric discharge machining mechanism has provided a sharper edge and superb flexibility. This file system is associated with a single-length preparation procedure for canal preparation at WL with a single disposable file. Such simplified single-file systems might prove effective due to their ease of application (25-27).

One of the iatrogenic problems during root canal instrumentation is root canal transportation. If root canal transportation exceeds 0.3 mm, the apical sealing ability of root canal obturation materials is severely compromised, worsening the treatment prognosis (28). None of the evaluated files exceeded this limit in the present study, thus pointing to the efficacy of these files.

Different techniques, including radiography and CBCT, have been used in various studies to evaluate the efficacy of the instruments used in root canal retreatment. Due to the difficulty of the exact superimposition of images and the two-dimensional nature of radiographic images (29), the CBCT technique has attracted attention because it provides three-dimensional images (30). In the present study, the CBCT technique was used to evaluate the extent of root canal transportation and the residual gutta-percha in the retreatment of curved root canals.

The results showed differences in root canal transportation between the study groups at 6- and 9-mm distances from the apex, with no significant differences at 3-mm distance from the apex. At the 9-mm distance from the apex, the highest transportation was related to the ProTaper group, with the lowest in the NeoNiTi group. This difference might be attributed to not using Gates-Glidden drills in the ProTaper group because they are used at high speeds. Therefore, they soften gutta-percha by the heat they produce, decreasing the need to apply lateral forces to the root canal walls. On the other hand, the special files of the ProTaper system for retreatment procedures have a cutting tip, and the D1 file has higher rigidity than D2 and D3 files, which are considered factors in increasing root canal transportation in this area. At the 6-mm distance from the apex, the greatest root canal transportation was detected in the ProTaper and Reciproc groups, with the lowest in the NeoNiTi group. Such a difference might be attributed to differences in file design. In addition, a lack of significant difference in the extent of root canal transportation at the 3-mm distance from the apex might be attributed to the similarity in diameter and instrument convergence in these sections.

An evaluation of root canal transportation by each instrument in different sections showed no significant differences between the different sections in the ProTaper and Reciproc groups. However, in the NeoNiTi and Hedstrom groups, such difference was significant, with a higher mean of transportation in the 3-mm section than the 6-mm section. Such differences might be attributed to greater root curvature in the apical area and the higher tendency of these files to straighten the root curvature.

However, Arruda et al. reported a similar root canal transportation rate by ProTaper and Reciproc instruments during root canal retreatment, which was clinically acceptable (31). Nabawizadeh et al. and Gergi et al. showed a greater extent of root canal transportation by Reciproc files during root canal preparation (29, 32). On the other hand, Mokhtari et al. reported that stainless steel hand files resulted in more root canal transportation than rotary files (33), which is different from the results of the present study. Such a difference might be attributed to two reasons. First, there are differences in the root canal anatomy during the initial root canal treatment. In addition, there is a difference between the root canal preparation during the initial treatment and retreatment. In the abovementioned study, the rotary files that were used differed from those used in the present study (33).

The amount of remaining gutta-percha at 3-, 6-, and 9-mm distances from the apex was not significantly different in different study groups, indicating similar efficacy of the files to eliminate gutta-percha from curved root canals.

Rodig et al. reported that Reciproc, ProTaper, and Hedstrom files were equally effective in eliminating gutta-percha from the curved root canal (11). Rios et al. compared the efficacy of Reciproc, ProTaper, and Wave-one files in root canal retreatment. They concluded that the reciprocal systems were as effective as rotary files in eliminating gutta-percha from the root canals (34), which was confirmed in a study by Caper et al. (12) and is consistent with the present study.

On the other hand, Unal et al. and Aguiar et al. showed that the efficacy of the ProTaper universal retreatment file was lower than Hedstrom files in eliminating gutta-percha in the retreatment of root canals (2, 35). However, in this respect, Grewal et al. and Ozyurek et al. reported higher efficacy for ProTaper files than Hedstrom files (36, 37). Such a discrepancy in the results might be attributed to differences in the root canal preparation techniques.

A comparison of residual gutta-percha between different sections in each group revealed significant differences in all the groups except for the NeoNiTi group. In all these three groups, the maximum residual gutta-percha was found in the 3-mm sections from the apex. Such a difference might be attributed to differences in the designs of different files, lower efficacy of these instruments in the apical area, the use of Gates-Glidden drills and other instruments with a higher diameter and convergence in the coronal area, and differences in the root canal anatomy in the apical area, including greater root canal curve, the root canal coalescence area, the presence of isthmuses, and accessory root canals.

In the present study, more time was required to complete the retreatment procedure with hand files than that with engine-driven instruments, with no significant difference between the three engine-driven groups, which is consistent with studies by Zuolo et al., Rodig et al., Betti et al. (4, 11, 38).

Conclusion

All four file types effectively eliminated gutta-percha from curved root canals. Although the NeoNiTi file system resulted in less root canal transportation in the retreatment of curved root canals than the other file systems, all these files were clinically acceptable. More time is required to complete the retreatment of curved root canals with hand files compared with the time required to complete the retreatment of curved root canals with engine-driven files.

Limitations

The rotary systems used in this study were different in removing gutta-percha from the coronal part of the canal. Finally, although Micro-CT is the gold standard to evaluate the aims of the study, it is not normally available.