Evaluation of the penetration time required by TruNatomy™ and ProTaper Next™ to reach the apical limit during gutta-percha removal in simulated curved and narrow canals of Endo Training Blocks

Clinical Articles

Drs. Gonzalo García, Denise Alfie, Juan Antonio Araujo, Claudia Hernández Restrepo, and Fernando Goldberg evaluated gutta-percha penetration times in curved and narrow root canals.

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Drs. Gonzalo García, Denise Alfie, Juan Antonio Araujo, Claudia Hernández Restrepo, and Fernando Goldberg discuss instruments that can be beneficial when faced with poorly instrumented and sealed curved and narrow canals

Abstract

Objective

To evaluate the time recorded by TruNatomy™ (TN) (Dentspy Sirona) and ProTaper Next™ (PTN) (Dentsply Sirona) systems for gutta-percha penetration up to the working length in simulated, narrow and curved canals of Endo Training Blocks  (ETBs).

Materials and methods

Twenty simulated canals were instrumented with PTN X1 and sealed with a single gutta-percha 20.04 cone and AH Plus® (Dentsply). The blocks were divided into two groups of 10 each.

Group 1: Gutta percha was drilled to working length with TN small.

Group 2: Gutta percha was drilled to the working length with PTN X1.

Both instruments were used at 700 rpm and 4 Ncm torque. Penetration time was recorded in each group. The data obtained was statistically evaluated with the Student’s t-test.

Results

No statistically significant differences were observed between the groups (p > 0.05).

Conclusion

PTN X1 and TN small can be used for gutta-percha penetration in the retreatment of narrow and curved canals.

Introduction

Nonsurgical endodontic retreatment is now a routine procedure at the dental office. Success depends on the adequate removal of the obturation materials used in the initial treatment in order to allow for proper re-instrumentation, disinfection, and sealing.1,2

Removal of the obturation materials is one of the most difficult steps. Its correct performance depends on the anatomical difficulties, the modifications of the original path of the root canal, and the characteristics of the materials used and their compaction.3-5 On the other hand, the presence of intracanal posts can further complicate this procedure.

For the removal of gutta percha, several instruments and procedures have been suggested: solvents, manual files, special design instruments, mechanized systems, ultrasound, and the combination of several of them.6 Numerous authors emphasize the difficulty of obtaining the total and complete removal of the obturation material that remains in the different thirds of the root canal system.4,5, 7-11

In curved and narrow canals that are poorly instrumented and sealed, the removal of the sealing material offers a unique challenge. In general, this intervention is performed with manual instruments and involves hard work and a long time. TruNatomy (TN) and ProTaper Next (PTN) are NiTi instruments that work in continuous rotation. These instruments have a heat treatment that gives them greater flexibility, fracture resistance, and cyclic fatigue.12,13

TN is a new rotary system designed to achieve more conservative preparations of the root canal. It consists of three instruments: small 20/04, prime 26/04, and medium 36/03. The PTN is a rotary system composed of 5 instruments: X1, X2, X3, X4, and X5 that correspond to the gauges of 17/04, 25/06, 30 /07, 40/06, and 50/06, respectively.

In the clinical cases of retreatment of curved and narrow canals, the use of mechanized instruments of low caliber and high flexibility would be appropriate.

The objective of the present study is to evaluate the time required by TN and PTN to penetrate the gutta percha and reach the apical limit in retreatment procedures in simulated curved and narrow canals of Endo Training Blocks (ETBs).

Materials and methods

Twenty ETBs (Dentsply Sirona, Ballaigues, Switzerland) with simulated curved canals (SCC) of circular section, 16 mm of working length (WL), ISO 0.15 gauge at apical level, and 2% continuous taper with approximately 40 degrees of curvature14  were used. SCC permeability was verified with a K-File No. 10 (Dentsply Sirona), and the WL was set at 16 mm. The blocks were then prepared to WL with an X1 instrument from ProTaper Next system (Dentsply Sirona) used with an X-Smart motor (Dentsply Sirona) following the manufacturer’s instructions. Subsequently, they were sealed with a single gutta-percha cone 20.04 caliber (Meta Biomed, ​​Co. Ltd., Korea) and AH Plus (Dentsply Sirona) (Figure 1). Samples were stored in 100% humidity at 37ºC for 10 days to allow the sealer to set.

Figure 1: Endo Training Block with the canal instrumented and obturated with gutta percha and AH Plus

Samples were divided into 2 groups of 10 units.

Group 1: The gutta-percha was penetrated until reaching the WL, with a Tru-Natomy small instrument (Dentsply Sirona) in continuous clockwise rotation at 700 rpm and a torque of 4 Ncm.

Group 2: The gutta-percha was penetrated until the WL with a ProTaper Next X1 instrument (Dentsply Sirona) in continuous clockwise rotation under the same conditions of group 1 (Figure 2).

Figure 2: Instruments TruNatomy small (top) and ProTaper Next X1 (bottom)

In both groups, the instruments penetrated the gutta percha with a constant crown-down motion until reaching the WL. The penetration maneuvers were performed by the same operator and the X-Smart Plus motor (Dentsply Sirona) was used.

Each instrument was used in three ETBs. The time required to reach the WL was recorded with a Tressa digital timer (Lat-Crom, China), and an Excel table was used to collect the data. For statistical evaluation the Student’s t-test was used.

Results

The summary of the results is described in Table 1.

Table 1: Descriptive summary Statistics TruNatomy™ ProTaper Next™ Media 11.90 10.42 Standard deviation 1.74 2.56 Minimum 8.81 7.31 Media 11.64 9.79 Maximum 15.35 16.84 Significance p > 0.05 Student's t-test

No statistically significant differences were observed between the groups (p > 0.05).

Removal of the obturation materials is one of the most difficult steps. Its correct performance depends on the anatomical difficulties, the modifications of the original path of the root canal, and the characteristics of the materials used and their compaction.

Discussion

During endodontic retreatment, penetration into the gutta-percha mass and its subsequent removal generally requires different procedures, which vary according to the compaction of the filling material, the apical limit, and iatrogenic or anatomical difficulties within the root canal.3 In this study, only the time needed to penetrate the gutta percha and reach the WL was analyzed. In straight and properly prepared canals, any instrument in rotational dynamics of caliber compatible to the root canal can penetrate and remove gutta percha more easily and efficiently.

In general, canals that are referred for retreatment present a poor primary preparation, and the obturation is made up of a small caliber gutta-percha cone and some sealer. If the path of the root canal is also curved, it is dangerous to penetrate and remove the gutta percha with rotary instruments of a greater taper than the one of the root canals. Consequently, the objective of the present study was to evaluate the penetration ability of instruments with reduced caliber and taper in simulated curved and narrow canals sealed with gutta percha. In that sense, the TN system, manufactured with NiTi SuperFlex™ (Vista Apex Dental Products, Racine, Wisconsin), has a flexibility that allows it to easily adapt to the curvature of the root canal without losing penetration capacity in the gutta-percha mass.

TN small and PTN X1 instruments were selected because of the SCC narrowness. The results obtained showed that the instruments used penetrated the gutta percha up to the WL in a similar time. Although the penetration time with PTN was shorter, the difference was not statistically significant. Similarly, comparing the penetration time with other studies, the results of this work showed greater speed to penetrate and reach the WL.15,16 This could be related to the lack of compaction that would facilitate the faster advance of the instrument.

Since penetration into the gutta-percha mass requires a greater pressure on the instrument, this difficulty was compensated by increasing its rotation speed to 700 rpm with a torque of 4 Ncm.16-18 TN and PTN have a similar cross-sectional design that promotes less contact with the dentinal walls. This would facilitate the gutta-percha removal to the coronal access. In this study, rotary instruments were used, considering that according to Azim, et al.,19 it is the most appropriate motion to penetrate gutta percha. Although some authors suggest the use of gutta-percha solvents to facilitate penetration in retreatments, others consider its use inappropriate to the extent that it softens the gutta percha, making it difficult to remove it later.10,15,20 In the present study, no solvents were used to avoid these inconveniences.

Different publications indicate the fracture of the instruments used during the removal procedure of the sealing material.2,19,21 It is important to note that in the TN group, one instrument presented an inelastic deformation during the first use without fracturing. There was no deformation or fracture of instruments in the PTN group.

Conclusion

The ProTaper Next X1 and TruNatomy small could be used for gutta-percha penetration in the retreatment of curved and narrow canals.

Acknowledgments

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

Read more about instruments that can facilitate gutta-percha penetration in this article: https://endopracticeus.com/a-comparative-study-of-the-penetration-time-of-different-instruments-and-kinematics-for-reaching-the-apical-limit-during-gutta-percha-removal-in-endodontic-retreatment/.

Gonzalo García, DDS, Denise Alfie, DDS, PhD, Juan Antonio Araujo, DDS, Claudia Hernández Restrepo, DDS, 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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