The efficacy of the Self-Adjusting File versus WaveOne in removal of root filling residue that remains in oval canals after the use of ProTaper retreatment files: A cone-beam computed tomography study.

AIM: The current ex vivo study compared the efficacy of removing root fillings using ProTaper retreatment files followed by either WaveOne reciprocating file or the Self-Adjusting File (SAF).
MATERIALS AND METHODS: Forty maxillary canines with single oval root canal were selected and sectioned to obtain 18-mm root segments. The root canals were instrumented with WaveOne primary files, followed by obturation using warm lateral compaction, and the sealer was allowed to fully set. The teeth were then divided into two equal groups (N = 20). Initial removal of the bulk of root filling material was performed with ProTaper retreatment files, followed by either WaveOne files (Group 1) or SAF (Group 2). Endosolv R was used as a gutta-percha softener. Preoperative and postoperative high-resolution cone-beam computed tomography (CBCT) was used to measure the volume of the root filling residue that was left after the procedure. Statistical analysis was performed using t-test.
RESULTS: The mean volume of root filling residue in Group 1 was 9.4 (±0.5) mm(3), whereas in Group 2 the residue volume was 2.6 (±0.4) mm(3), (P < 0.001; t-test).
CONCLUSIONS: When SAF was used after ProTaper retreatment files, significantly less root filling residue was left in the canals compared to when WaveOne was used.

INTRODUCTION

The primary reason for an endodontic failure is the persistence or regrowth of bacteria within the root canal system (RCS); such cases require retreatment.[1] When retreatment is indicated, efficient and thorough removal of all the root canal filling material is required, allowing effective disinfection and a favorable outcome.[2] However, many studies have reported that complete removal of the root canal filling is difficult.[345]

Various instrumentation techniques are available for effective removal of root fillings. These include endodontic hand files, engine-driven rotary files, ultrasonic tips and files, and heat-carrying instruments. The use of rotary files successfully facilitates an effective removal of the bulk of gutta-percha–based fillings from the RCS.[678]

The use of gutta-percha solvents in conjunction with endodontic instrumentation results in easier removal of gutta-percha from the root canals.[910] Chloroform is the most commonly used gutta-percha solvent because it acts very rapidly, but was proposed to be a potential carcinogen.[1112] Other solvents include xylene, Endosolv R (Septodont, Paris, France), refined orange oil, eucalyptol, and tetrachloroethylene.[910]

Fruchi et al. reported that WaveOne (25/0.08, Dentsply Tulsa Dental Specialties, Tulsa, OK) reciprocating files, when used alone to remove the root fillings, leave some residue within the RCS.[13] It is a published fact that ProTaper retreatment files (Dentsply Maillefer) alone leave around 10-35% of the root fillings after their use.[1415] Hence, use of supplementary files is recommended. Recently, Abramovitz et al. reported that the use of Self-Adjusting File (SAF; ReDent, Ra’anana, Israel) as a supplementary tool after the use of D1-D3 ProTaper retreatment files resulted in much cleaner canals during retreatment.[15] Solomonov et al. also concluded that a combination of ProFile (Maillefer Instruments, Ballaigues, Switzerland) for removal of the bulk of root filling and SAF to remove the remaining root filling residue was more effective than ProTaper retreatment files followed by ProTaper F1 and F2. The ProFile + SAF group was also reported to consume less time than the ProTaper group.[16] Nevertheless, the design of this study did not allow isolation of the effect of the SAF per se on either the cleaning efficacy or the time required to accomplish the procedure.

As root filling residue is present after using retreatment files and the use of supplementary file is indicated,[141516] the present ex vivo study was designed to compare the efficacy of removing root fillings from oval canals using ProTaper retreatment files followed by either WaveOne reciprocating file or the SAF using high-resolution cone-beam computed tomography (CBCT).

MATERIALS AND METHODS

Selection of teeth

Forty maxillary canines with single root canal with no previous endodontic treatment and completely developed apices were selected from a collection of recently extracted teeth. The teeth were cleaned ultrasonically (UDS-P, Woodpecker, Guangxi, China) of any calculus and plaque accumulation. The teeth were sectioned at/below the cementoenamel junction (CEJ) to obtain a root length of 18 mm for all the samples. A #15 K-file was placed in the root canal to the apical foramen and the working length was established by reducing 1 mm. The teeth were instrumented with WaveOne primary files (25/0.08), using X Smart Plus endomotor (Dentsply Maillefer). The shaping procedure was continued till the file reached the working length. Irrigation was done with 3% sodium hypochlorite (NaOCl) and ethylenediaminetetraacetic acid (EDTA) Gel (RC Help, Prime Dental Products, Mumbai, India) as used as lubricant. After instrumentation, the canals were irrigated with 17% aqueous EDTA solution, followed by flushing the canal with distilled water and drying the canal with paper points.

Obturation was done using standard WaveOne master cones (Dentsply Tulsa Dental Specialties) and AH-Plus sealer (Dentsply DeTrey, Konstanz, Germany) followed by warm lateral compaction using accessory gutta-percha cones. The excess gutta-percha was removed using a heated hand plugger. The teeth were then kept for 30 days at 37°C and 100% humidity to allow complete setting of the sealer. The samples were mounted on wax-blocks, and preoperative CBCT scan was performed.

The teeth were then randomly divided into two groups (N = 20) for the retreatment procedure.

Retreatment procedures

Group 1: ProTaper retreatment files followed by WaveOne file

ProTaper retreatment files D1-D3 were used to remove the bulk of the root canal filling material, following manufacturer's instructions. These files were used till no gutta-percha was visible on the file when it was withdrawn from the root canal. Endosolv R was used as a gutta-percha softener. The canals were irrigated with 3% NaOCl between each file and a final rinse was performed with 2 mL of 3% NaOCl.

After the procedure detailed above, a WaveOne primary file was used with Endosolv R. A drop of the solvent was placed in the canal and the WaveOne file was used for removal of residual root filling material. Whenever the file met resistance the file was withdrawn, the canal was irrigated with NaOCl, the canal was dried, Endosolv R was placed again, and the procedure was continued. The instrumentation was continued till the file reached the working length and till no debris was visible on the file. After instrumentation the canal was irrigated with 2 mL of 3% NaOCl.

The teeth were then dried and a postoperative CBCT was performed.

Group 2: ProTaper retreatment files followed by SAF

The initial stage of the procedure for removing the bulk of root filling was carried out in a similar manner as in Group 1.

After removing the bulk of root filling material, a SAF file (2.0 mm diameter) was used to remove the remaining root filling residue. It was operated with an RDT3-NX handpiece-head (ReDent-Nova, Ra’anana, Israel) attached to an X-Smart Plus endomotor, at 5000 vibrations/min. Irrigation, as indicated below, was provided using a VATEA peristaltic pump (ReDent-Nova).

First, the SAF was operated in the canal for 1 min under continuous NaOCl irrigation to remove coarse root filling debris.[17] Next, the VATEA pump was turned off and the canal was dried. The canal was then filled with a drop of Endosolv R, following by SAF operation in the canal again for 1 min. Subsequently, the Endosolve R was removed by irrigating the root canal with 1 mL of 3% NaOCl, the canal was dried, the canal was filled again with Endosolv R, and the SAF was operated again for 1 min. Next, the VATEA pump was turned on, and the SAF operated with 3% NaOCl irrigation for an additional 30 s. The teeth were then dried and a postoperative CBCT performed.

CBCT scans

The CBCT scans were obtained using ProMax 3D Mid (Planmeca OY, Helsinki, Finland). The samples were exposed to 90 kV and 8 mA with a FOV of 4.5 × 4.5 cm2 and an isotropic resolution of 0.1 mm, with 12.28 s exposure time. The artifacts created by the radiopaque root fillings were decreased/eliminated using inbuilt software (Romexis v3.20, Planmeca OY, Helsinki, Finland).

Statistical analysis

Mean [±standard deviation (SD)] were calculated for each parameter for each group and the groups compared to each other using Student's t-test (SPSS Inc. software v20 Inc., Chicago, IL, USA).

RESULTS

Volume of the root fillings

The mean preoperative volume of the root canal fillings was 36.3 (±1.8) mm3 in Group 1 and 36.6 (±1.3) mm3 in Group 2. Statistical analysis revealed that the two groups did not differ from each other.

Volume of root filling residue

The mean postoperative volume of the root filling residue was 9.4 (±0.5) mm3 in Group 1 and 2.6 (±0.4) mm3 in Group 2. These residue volumes represented 26% and 7% of the original root filling volumes in Group 1 and Group 2, respectively. [Figure 1a–d] The amount of residue left in the canal after the ProTaper retreatment files + WaveOne procedure was 3.6× larger than that which was left after the ProTaper retreatment files + SAF procedure. The difference was statistically significant (Student's t-test, P < 0.001) [Figure 2]. The mean time required for the completion of the retreatment procedure was 8.6 (±0.56) min and 8.41 (±0.36) min for Group 1 and Group 2 respectively (P > 0.05; Student's t-test).

Figure 1

(a and b) Preoperative CBCT scans after 3D reconstruction showing root canal filling in (a) Group 1 and (b) Group 2 (c and d) Postoperative CBCT scans after 3D reconstruction showing the residual root canal filling material after the retreatment protocol in (c) Group 1 (ProTaper retreatment files + WaveOne) and (d) Group 2 (ProTaper retreatment files + SAF)

Figure 2

The mean preoperative and root filling residue remaining after two different retreatment protocols

DISCUSSION

Retreatment is considered a valid alternative for extraction in case of failure in endodontic treatment. The complete removal of root filling material is difficult, but it is one of the main goals of nonsurgical endodontic retreatment procedures.[345]

A warm lateral compaction obturation technique was chosen in the present study because it produces a better gutta-percha adaptation to the root canal walls than the lateral compaction technique.[18] This was especially important as the canals of the canines that were used in the present study had oval cross sections. Wilcox et al.[3] and Friedman et al.[19] have shown that epoxy-resin–based sealers adhere to the dentine and are more difficult to remove. Therefore, in order to test the retreatment protocols in challenging conditions, AH-Plus sealer, an epoxy-resin sealer was used in the present study.

Both of retreatment protocols that were compared in the present study consisted of a two-stage procedure. The first stage was standardized by the use of ProTaper retreatment files (D1-D3) to remove the bulk of root filling material. The second stage aimed to remove the remaining root filling residue.

Previous studies have reported that retreatment with ProTaper retreatment files (D1-D3) alone failed to render the canals completely free of root filling residue.[1520] Therefore, an additional file has been used in an attempt to effectively remove the root filling residue. The inability of the D1-D3 files to remove the root filling residue in the apical part of the canal is not surprising and could be expected, as the apical size of the D3 file is 20 and in many clinical cases the initial preparation of the apical part of the canal was greater than 20. In the present study, too, the initial preparation of the canal was done with WaveOne primary file (apical size of 25).

In the present study, an additional procedure was performed after the D3 file, using either WaveOne primary files in Group 1 or the SAF in group 2. The WaveOne file was tested here as it was the file used to initially prepare these canals and was likely to remove the root filling residue without excessive altering of the shape of the canal. The use of larger files, such as the WaveOne “large” file with an apical size of 40, was avoided as they might alter the shape of the canal, increasing the risk of canal transportation.[16]

The SAF was used in Group 2. This file adapts to the cross section of the canal and has a scrubbing effect on the walls.[212223] The ability of the SAF to adapt to an oval cross section of the canal may explain its better cleaning ability, which was found in the present study. While the WaveOne reciprocating file was likely to reach all the canal walls that were initially instrumented with the same size and type of file, it most probably could not reach root filling material that was present in the buccal and/or lingual recesses.

Solomonov et al. found that a retreatment procedure consisting of ProFile followed by the SAF was more effective than ProTaper retreatment files followed by ProTaper F2 file. They had used two different files for removal of the bulk of root filling material. In one group this was done using three files (D1-D3) and in the other just one ProFile (#25 with 0.6 taper) file, which could be the possible reason for the time required being less when ProFile and SAF were used.[16] In order to isolate the second part of the procedure as a single variable, the removal of bulk of root filing material in each group of the present study was standardized.

It was recently reported that the use of two-dimensional (2D) radiographs failed to represent the real cleanliness of the canal and thus the effectiveness of retreatment procedures.[24] In the present study, three-dimensional (3D) CBCT, which is readily available to more researchers than micro-CT, was used to compare the efficiency of two retreatment protocols.

CONCLUSIONS

This ex vivo study has shown that root filling material could not be removed completely from the root canals by either of the retreatment protocols tested. However, a retreatment procedure consisting of ProTaper retreatment files followed by SAF resulted in cleaner root canal space when compared to ProTaper retreatment files followed by WaveOne. CBCT with its built-in software may also be a valid tool for such ex vivo studies.

Financial support and sponsorship

Nil.

Conflicts of interest

There are no conflicts of interest.