A comparative study of the penetration time of different instruments and kinematics for reaching the apical limit during gutta-percha removal in endodontic retreatment

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Editor’s intro: This article evaluates three file systems and the time required to penetrate the gutta percha. 

Drs. Gonzalo García, Denise Alfie, Pablo Alejandro Rodríguez, and Fernando Goldberg evaluate the time required by three endodontic file systems with three different types of kinematics to penetrate the gutta percha in endodontic retreatment

Abstract

Introduction

Figure 1: Radiographic images in buccal-lingual and prox-imal-proximal directions showing the homogeneity of the endodontic obturation

This study aims to compare the time required by ProTaper Next™ (PTN; Dentsply Sirona, Ballaigues, Switzerland) in clockwise rotation and WaveOne® Gold (WOG; Dentsply Sirona) and RECIPROC® Blue (RcPB; VDW, Munich, Germany) in either reciprocating motion or counterclockwise rotation to penetrate the gutta percha until reaching the apical limit in endodontic retreatment.

Materials and methods

Fifty extracted human upper canines were instrumented manually up to a No. 40 K-file (Dentsply Sirona) and filled using the lateral compaction technique and AH Plus® (Dentsply DeTrey, Konstanz, Germany). The samples were divided into five groups of 10 teeth each (n = 10), according to the instrument and kinematics utilized: PTN X3 in continuous rotation; WOG medium with reciprocating motion; WOG medium with counterclockwise rotation; RcPB R40 with reciprocating motion; and RcPB R40 with counterclockwise rotation. The time to reach the working length (WL) was recorded and statistically analyzed. For statistical evaluation, an analysis of variance was performed by complementing it with orthogonal contrasts. The degrees of freedom were adjusted to calculate the contrasts because no homogeneity of variance was observed. SPSS 15.0 software was used for analysis.

Results

PTN instruments in clockwise rotation and WOG and RcPB in counterclockwise rotation required a significantly shorter time in seconds than WOG and RcPB in reciprocating motion to penetrate the gutta percha up to the WL (F4,45; P < 0,001). During the procedure, two WOG and one RcPB instruments in reciprocating motion fractured.

Conclusion

PTN instruments in clockwise rotation and WOG and RcPB in counterclockwise rotation are valid alternatives to penetrate the gutta percha in endodontic retreatment.

Significance

This study evaluated the time required by three endodontic file systems with three different types of kinematics to penetrate the gutta percha in endodontic retreatment. PTN in clockwise rotation and WOG and RcPB in counterclockwise rotation yielded the shortest penetration time.

Introduction

Endodontic treatment failure may result from the presence of bacterial remnants that are not completely eliminated with instrumentation and irrigation procedures — obturation that is insufficient or from bacteria, which may have penetrated through deficient restorations in well-treated teeth.1-3 In this situation, the efficient removal of the filling material is necessary to assist with reinstrumentation, disinfection, and refilling of the root canal system up to the apical foramen.4

Currently, a large number of referrals include the need for endodontic retreatment or conventional orthograde retreatment.5-6

In these circumstances, once the coronal-radicular restoration is eliminated, the gutta percha of the first endodontic treatment should be removed. The required procedures depend on the homogeneity of the filling material and length of the filled canal. Various procedures have been employed for this purpose — namely, heat, gutta-percha solvents, manual files, Gates-Glidden burs, ultrasound, and instruments specially designed for this purpose.7 When the filling is radiographically poor, Hedströem files are indicated to remove the gutta percha. In the case of retreatment due to persistent coronal leakage, the obturation material needs to be removed, which in most cases is well compacted and reaches the entire root canal from the cervical area to the apical foramen.

In this situation, mechanical preparation favors gutta-percha removal, rapidly reaching the apical limit of the obturation.7 For this purpose, different special instruments are marketed for gutta-percha removal, which include GPX™ (Brasseler, Savannah, Georgia); ProTaper® Universal Retreatment (Dentsply Sirona); R-Endo (Micro-Mega, Besançon, France); and XP-endo® Finisher R (FKG Dentaire SA, La Chaux-de-Fonds, Switzerland). Generally, these instruments act in a clockwise rotational direction and are used at a higher rotation speed than those used for endodontic preparation. The heat generated by the faster rotational speed aids in softening the gutta-percha component of the obturation material, making removal easier.

Currently, rotary and reciprocating instruments are used for root canal instrumentation. Within both systems, ProTaper Next (PTN) (Dentsply Sirona), used in continuous clockwise rotation, and WaveOne Gold (WOG) (Dentsply Sirona) and RECIPROC Blue (RcPB) (VDW, Munich, Germany), used in reciprocating motion, are found.

PTN is an M-Wire NiTi instrument with a rectangular cross section and semi-active tip operated in continuous clockwise rotation. It is supplied in five sizes and tapers: X1 (#17.04), X2 (#25.06), X3 (#30.07), X4 (#40.06), and X5 (#50.06).

WOG is a file with a parallelogram cross section with a semi-active tip. The files are marketed in four sizes — namely, small (#20.07), primary (#25.07), medium (#35.06), and large (#45.05) —  and are used as the instrumentation for the root canal walls in a reciprocating motion. RcPB is also a NiTi instrument with reciprocating motion and an S-shaped cross section. It is supplied in three sizes and tapers: R25 (#25.08), R40 (#40.06), and R50 (#50.05). Both NiTi instruments are subjected to thermal treatments, providing greater flexibility and resistance to cyclic fatigue.

This study offers a new alternative in the use of reciprocating instruments for the removal of gutta percha through a counterclockwise rotational movement.

The aim of the present study is to compare the time required by PTN, WOG, and RcPB, to penetrate the gutta percha and reach the apical limit in retreatment procedures with different instruments and kinematics.

Materials and methods

Fifty extracted upper human canines with a similar root length, completely formed apices, and no signs of root resorption were selected for this study. The tooth crowns were sectioned at 21 mm to obtain a standardized length. After access cavity preparation, apical patency was confirmed with a size 15 K-file (Dentsply Sirona). The cervical and middle thirds were enlarged with sizes 1, 2, and 3 Gates Glidden (Dentsply Sirona). The root canal was manually instrumented using a step-back technique up to a 40 K-file (Dentsply Sirona) master apical size. Copious irrigation with sodium hypochlorite 2,5% was used during the shaping. The root canal system was dried with paper points (Meta Dental Co. Ltd, Republic of Korea) and obturated to the working length (WL) using a lateral compaction technique and AH Plus (Dentsply DeTrey, Konstanz, Germany).

Next, radiographs of the specimens were obtained in the ortho-radial (buccal-lingual) and proximal-proximal directions to evaluate filling homogeneity (Figure 1). Accesses were sealed with Cavit™ (3M ESPE, Germany), and samples were stored in 100% humidity at 37º C for 10 days to allow the sealer to set.

The samples were randomly divided into five groups of 10 teeth.

  • Group 1: Obturation removal with a PTN X3 file at a speed of 700 rpm and a torque of 4 Ncm (Figure 2).
  • Group 2: Obturation removal with WOG medium in reciprocating motion according to the program established by the endodontic motor (Figure 3).
  • Group 3: Obturation removal with WOG medium in continuous counter-clockwise rotation at a speed of 700 rpm and a torque preset by the endodontic motor.
  • Group 4: Obturation removal with RcPB R40 in reciprocating motion according to the program established by the endodontic motor (Figure 4).
  • Group 5: Obturation removal with RcPB R40 in continuous counterclockwise rotation at a speed of 700 rpm and torque preset by the endodontic motor.

The Cavit coronal temporary restoration was removed, and for obturation removal, all instruments were used in a single crown-down movement until they reached the WL. Each instrument was discarded after being used in three root canals.

The motor used was the X Smart® Plus (Dentsply Sirona), and all the samples were treated by the same operator. The penetration time of the instrument up to the WL was recorded with a Tressa (LAT-CRON, China) digital timer, and the values obtained were entered into an Excel spreadsheet prepared for that purpose.

For the statistical evaluation, an analysis of variance was performed by complementing it with orthogonal contrasts to analyze the differences listed below.

  1. Reciprocating motion versus clockwise or counterclockwise motion.
  2. Clockwise motion versus counterclockwise motion.
  3. Counterclockwise motion with RcPB versus counterclockwise motion with WOG.
  4. Reciprocating motion with RcPB versus reciprocating motion with

The degrees of freedom were adjusted to calculate the contrasts because no homo-geneity of variance was observed. SPSS 15.0 software (SPSS Inc. 233 South Wacker Drive, Chicago, Illinois) was used for analysis.

Results

The average time recorded in seconds required by the different instruments to penetrate the gutta percha up to the WL is summarized in Table 1.

According to the analysis of variance complemented with orthogonal contrasts, the instruments used in continuous clockwise and counterclockwise rotation required a significantly shorter time in seconds to penetrate the gutta percha up to the WL (F4,45; P < 0.001).

During the procedure, two WOG and one RcPB instruments in reciprocating motion fractured. These teeth were discarded and replaced with new ones.

The analysis of variance showed a significant effect of the evaluated variable (reciprocating motion versus clockwise or counterclockwise motion) (P < 0.001).

Discussion

Many studies have reported that nickel-titanium instruments in either rotary or reciprocating motion are suitable for gutta-percha removal from the root canal in retreatment procedures.8-22,25-28 When the filling material is sufficiently compacted, access to the interior of the root canal is more complex. In this case, the procedure has mainly been performed with Gates Glidden burs and manual instruments, with or without solvents as adjuvants.7-9,11,13,20,21,24,26-28 Currently, the use of rotary or reciprocating mechanical instrumentation facilitates and speeds up this operative procedure.8-22,25-28 It is important to note that the published findings on the efficiency of the different engine-driven instruments are diverse and controversial.

In an ex vivo study, Ma, et al.,13 observed that the use of solvents allowed the rotary instruments to reach the WL faster; however, in turn, they prevented the complete removal of the first filling material, as the chloroform-softened gutta percha is distributed as a film on the surface of the root canal walls.22 This can hamper intimate contact with the subsequent re-obturation of the canal system, leading to increased coronal leakage potential. Therefore, the use of solvents was avoided in the present study by penetrating the gutta percha up to the WL by mechanical motion.

In the present study, the obturation to be removed was made using the lateral compaction technique because it is the most universally used technique.13,23 Ma, et al.,13 and Frajlich, et al.,24 emphasized that filling-material removal, using the techniques involving thermoplasticized gutta percha, is difficult because of the greater compaction and homogeneity of the gutta percha.

Multiple publications show that Wave-One, WOG, and/or RECIPROC instruments are useful for removing gutta percha in endodontic retreatment with reciprocating motion.14-18, 25  In the present study, WOG and RcPB were also used in continuous counterclockwise rotation, corresponding to the direction of the cutting edges. In general, when the practitioner decides on a rotary or reciprocating mechanical system, treatment is facilitated if all the endodontic procedures are performed with the same system. For this reason, these instruments were analyzed in continuous rotary and reciprocating motion to evaluate their speed in accessing root canals up to the WL in retreatment. Several authors have used mechanical instrumentation at the rotation speed indicated by the manufacturer of the instruments. For gutta-percha removal, this speed does not allow for a sufficiently fast action of the instruments, so some authors increased the speed to 500 rpm or more.7,8,11,13,17,18,20 Thus, a speed of 700 rpm was used in this study, both for PTN in continuous clockwise rotation and for WOG and RcPB in a counterclockwise direction. In the X Smart Plus motor, the torque cannot be modified in counterclockwise rotation; thus, the torque used was that allowed by the motor.

Likewise, PTN X3 (#30.07), WOG medium (#35.06), and RcPB R40 (#40.06) files were used because they have a size and taper compatible with the root canal previously prepared and filled, as is the case in retreatment.

The time used to penetrate the gutta percha up to the WL reported in different publications differs significantly.8,13,20,26 In this study, the time required to penetrate the gutta percha up to the WL with the instruments in continuous clockwise and counter-clockwise rotation was shorter than what has been reported by other authors.8,13,20,26 By changing the reciprocating motion of the WOG and RcPB instruments to continuous counterclockwise rotation, the speed of gutta-percha penetration significantly increased.

Contact of the cutting edges of the instruments with the gutta percha in the appropriate rotary movement favors penetration. In this sense, we agree with Azim, et al.,19 that continuous rotation is the appropriate motion. Our results agree with those of Azim, et al.,19 who found that the use of WOG in reciprocating motion increases the time of gutta-percha removal. Therefore, in the present study, this instrument was also used in continuous counterclockwise rotation, making it easier to penetrate the mass of obturation material.

Duncan and Chong7 considered that fracture of the instrument used for filling material removal is one of the most common risks during retreatment. In this study, two WOG and one RcPB fractured when used in reciprocating motion. We thought these fractures were caused by the greater pressure exerted for instrument progression into the gutta percha. Several publications note the fracture of different types of instruments during gutta-percha removal procedures in retreatment.8,9,19,26-28 However, no blockages or perforations were detected in the present study, perhaps because the evaluated roots had single and straight root canals.

Conclusion

According to the findings, we conclude that the time required to penetrate the gutta percha up to the WL was shorter with the PTN instruments in clockwise rotation as well as WOG and RcPB in counterclockwise rotation compared with WOG and RcPB in reciprocating motion.

Acknowledgments

The authors express their sincere appreciation to Professor Ricardo L. Macchi for his help with the statistical analysis.

Besides this study on three file systems, check out Dr. Nick Barker’s article on other aspects to consider when choosing a file system.

Gonzalo García, DDS, Denise Alfie, DDS, PhD, Pablo Alejandro Rodríguez, DDS, PhD, and Fernando Goldberg, DDS, PhD, are from the Department of Endodontics, School of Dentistry of the University of Buenos Aires, Argentina.

Disclosure: The authors deny any conflicts of interest related to this study.

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