Efficacy of rotary and reciprocating single-file systems on different access outlines for gutta-percha removal in retreatment: An in vitro study.

INTRODUCTION: The aim of this study is to compare the effectiveness of reciprocating and continuous rotary nickel-titanium instruments during retreatment performed through two different access outlines.
METHODOLOGY: A total of 48 freshly extracted mandibular first and second premolars with single root and canal were selected. Initial root canal treatment was completed through a contracted endodontic cavity (CEC) design. Canals were instrumented with F2 ProTaper instrument, obturated with warm lateral condensation of gutta-percha with AH Plus sealer, and allowed to set for 30 days at 37°C and 100% humidity. For retreatment, specimens were divided into two groups (n = 24) on the basis of access outline, CEC or traditional endodontic cavity. Retreatment was initiated using ProTaper Retreatment instruments (D1-D3). Specimens were further divided (n = 12) and reinstrumented up to Neoniti 25/0.08 or WaveOne 25/0.08. Irrigation was performed using 3% sodium hypochlorite and 17% ethylene diamine tetraacetic acid. Retreatment time was recorded. Teeth were sectioned and photographed, and the percentage of remaining obturation material was measured.
RESULTS: Data were collected, and statistical analysis was performed using one-way analysis of variance and Tukey honestly significant difference multiple post hoc procedures (P < 0.05).
CONCLUSION: None of the systems completely removed the root filling material from root canals. However, ProTaper/Neoniti instruments removed more GP when compared to Protaper/WaveOne instruments with both the access outlines. Both the instruments with traditional access outline required less time for removal of obturating material when compared to CEC.

INTRODUCTION

The success of nonsurgical root canal retreatment depends on the complete evacuation of endodontic materials to allow efficient cleaning, shaping, and filling of root canal system.[1] Clark and Khademi suggested that conservative access design reinforces the tooth by preserving pericervical dentin and some amount of pulp chamber roof while maintaining its efficiency during instrumentation of root canal system.[2]

The use of NiTi rotary instruments proved to be more efficient than hand instruments in removing gutta-percha from root canals with lesser procedural errors.[3] ProTaper retreatment files have been used as an alternative to hand files for retreatment cases because of their ease and efficiency in removing gutta-percha.[4] Various authors have reported that ProTaper retreatment files alone leave around 10%–35% of the root fillings after their use. Therefore, use of supplementary files is recommended.[5]

Newly introduced file, Neoniti (Neolix, Châtres-la-Forêt, France) is a single-file rotary system with the continuous rotation, used both for shaping and retreatment of root canal system.[6] It consists of one C1 (25/0.12) and three A1 (with #20, #25, and #40 tip sizes) files. It is manufactured using a newly developed wire-cut electrical discharge machining process. These files undergo appropriate heat treatment that results in high flexibility and shape memory of this system.[6] WaveOne (Dentsply Tulsa Dental Specialties, Tulsa, OK) is a single-file reciprocating system, available in three different sizes, small (21/0.06), primary (25/0.08), and large (40/0.08).[7] It was reported that WaveOne (25/0.08) reciprocating files, when used alone to remove the root fillings; leave some residue within the root canal system.[5]

As suggested by Clark and Khademi, conservative access design increases the fracture resistance of teeth without compromising the instrumentation of root canal system.[8] Therefore, in this in vitro study, two novel rotary single-file systems were analyzed for retreatment efficacy in contracted endodontic cavity (CEC) and traditional endodontic cavity (TEC). The present study was based on the hypothesis that none of the systems completely removed the root filling material from root canals. However, ProTaper/Neoniti instruments removed more GP when compared to Protaper/WaveOne instruments with both the access outlines (TEC and CEC) and both the instruments with TEC outline required less preparation time.

METHODOLOGY

A total of 48, mandibular premolar teeth were collected from the Department of Oral and Maxillofacial surgery from our institution. Teeth with intact crowns, fully formed apices, single roots, and canals were included in the study. Exclusion criteria included as follows: teeth with root caries, fracture, previous root canal treatment, and internal resorption were discarded. All endodontic procedures were performed by a single operator under dental operating microscope with ×10.9 magnification (Seiler Revelation, St Louis, MO).

In the selected samples, access opening was performed to prepare CEC. In CEC preparation, access opening was done 1 mm buccal to central fossa [Figure 1a]. The buccolingual and mesiodistal extension of access cavity were minimized to preserve pericervical dentin. For uniform samples, the crowns were flattened (coronally 1–2 mm) and a final working length of 20 mm was standardized for each specimen. Root canals were prepared with a crown-down technique up to ProTaper F2 instrument (Dentsply Tulsa Dental Specialties). During shaping, each canal was irrigated between instruments with 2 ml of 3% sodium hypochlorite (NaOCl) (Niclor 5, Ogna, Milan, Italy) followed by a final flush of 17% ethylenediamine tetraacetic acid (Largal Ultra, Septodont, Saint Maitre, France) and saline. Root canals were dried with paper points (Dentsply Maillefer) and filled with 30/0.04 gutta-percha (Dentsply Maillefer) and AH Plus sealer (Maillefer, Dentsply, Konstanz, Germany) using warm lateral compaction technique.

Figure 1

Photographs of occlusal surface of mandibular premolars showing (a) contracted endodontic cavity design and (b) traditional endodontic cavity design

After temporary filling (Cavit, 3M-ESPE Seefeld, Germany), teeth were stored at 37°C in 100% humidity for 3 weeks to allow complete setting of the sealers. Teeth were radiographed (Radiography Digital System Kodak 6100, Rochester, NY, USA) in a buccolingual and mesiodistal direction to confirm the adequacy of root filling.

Retreatment procedure

For retreatment, teeth were divided into two groups of 24 each as follows:

Group 1 (n = 24) – contracted endodontic cavity

Group 2 (n = 24) – TEC: The CEC was further enlarged to the regular access design with an LA Axxess high-speed diamond (SybronEndo, Glendora, CA), [Figure 1b].

Teeth were further subdivided into two subgroups as follows:

Subgroup 1: retreatment with ProTaper files followed by reshaping with Neoniti file system – In all specimens, the bulk of the obturation material was removed with ProTaper retreatment instruments (Dentsply Tulsa Dental) at preset lengths: D1 (20/.09) for coronal one-third, D2 (25/0.08) middle for one-third, and D3 (20/0.07) for apical one-third at 600 rpm. Further teeth were reshaped with Neoniti C1 (25/0.12) orifice shaper followed by Neoniti A1 25/0.08 to the working length. The instruments were used passively at 300 rpm in X-smart endomotor in the presence of 3% NaOCl, with gentle pecking motions

Subgroup 2: retreatment with ProTaper files followed by reshaping with WaveOne system – After removing the bulk of the obturating material as in Group 1, WaveOne primary files 25/0.08 (Dentsply-Maillefer, Ballaigues, Switzerland), were used to remove the remaining residual material in X-Smart Plus endomotor (Dentsply Maillefer) in a reciprocating motion. Retreatment was considered complete when no gutta-percha or sealer was detected on the instrument surfaces or inside the root canal or dentinal walls.

Teeth were then sectioned using, a 30 mm diameter, 0.030 mm width double-sided diamond disk (AXIS; SybronEndo) in buccolingual direction under continuous distilled water irrigation to prevent debris from entering the root canal. Specimens were then photographed at 1:1 ratio (EOS Rebel T5i; Canon, Melville, NY). Adobe Photoshop CC 2014 (Adobe Systems Inc., San Jose, CA) was used to measure the total area of the root canal space, and the areas of remaining obturation material in millimeters squared for separate root canal thirds (apical, middle, and coronal), respectively [Figure 2].

Figure 2

Photographs of mandibular premolars split in buccolingual direction showing remaining obturation materials on root canal surface for different instrument and access design combinations: (a) contracted endodontic cavity-WaveOne, (b) contracted endodontic cavity-Neoniti, (c) traditional endodontic cavity-Waveone, and (d) traditional endodontic cavity-Neoniti

Thus, in this study, retreatment was initiated with the entire ProTaper retreatment series in all groups for bulk removal of gutta-percha from the canals and was followed with either Neoniti or WaveOne instruments.

Evaluation of percentage of residual filling material and operating time

The area of the canal and of the residual filling material was recorded, and the percentage of remaining filling material on canal walls was calculated with the following equation[9]

Area % of remaining filling material

Operating time – total retreatment time was recorded in minutes and seconds with a stopwatch.

Statistical analysis

The data were statistically analyzed using SPSS software version 20.0 (IBM Corporation, Armonk, NY, USA) and tested using analysis of variance followed by post hoc Tukey's test for multiple group comparison. A value of P < 0.05 was considered to be statistically significant.

RESULTS

Results revealed that significantly more time was required for retreatment with the CEC-WaveOne group when compared to other groups, P < 0.001 [Figure 3]. There was a highly significant difference between the instruments overall, with WaveOne showing more remaining obturation material on the root canal surface (P < 0.001). There was also a highly significant difference between CEC and TEC access designs overall, with CEC resulting in more obturation material remaining on the root canal surface (P < 0.02). The interaction between access design and instrument type showed that the combination of CEC-WaveOne presented significantly higher amounts of remaining obturation material on the canal surface when compared to TEC-WaveOne, CEC-Neoniti, and TEC-Neoniti (P < 0.001). When evaluating the canal thirds, all four access design-instrument combinations showed higher amounts of obturation material remaining in the apical and middle thirds when compared to the coronal third [Figures 4–6].

Figure 3

Comparison of time required in terms of (mean [standard deviation]) among all the four groups using analysis of variance test

Figure 4

Comparison of coronal values regarding (mean [standard deviation]) among all the four groups using analysis of variance test

Figure 6

Comparison of apical values regarding (mean [standard deviation]) among all the four groups using analysis of variance test

DISCUSSION

The main success of endodontic retreatment relies on the complete removal of root canal filling material to regain access to the apical foramen to facilitate the sufficient cleaning and shaping of entire root canal system.[10] In failed endodontic cases, obturating material harbor's necrotic tissue and bacteria which is responsible for periapical inflammation. Hence, complete removal of the obturating material is necessary to reduce the microbial burden within the canal.[11]

Human single-rooted mandibular premolar teeth with oval canals were chosen since they represent a major challenge for performing endodontic retreatment. High anatomical variability exists with respect to the shape, size, and dimensions of these teeth.[12] In this study, the teeth were standardized to 20 mm length, and hence that varying lengths could not exert an influence on the results. CEC is a conservative access design in which some chamber roof and pericervical dentin are preserved, minimizing the mesiodistal and buccolingual extension of the cavity.[13] The advantage of using a CEC design during retreatment in premolars is increased fracture resistance of the tooth along with effective reinstrumentation comparable with that of TEC.[13] A CEC access design in multirooted teeth has greater potential for sufficient space, allowing easier retrieval of gutta-percha because the access would be larger.[14] Moreover, the teeth which are indicated for retreatment usually would have received crowns after the initial root canal treatment, further weakening the root canal treated tooth. This fact further supports the importance of CEC in cases of retreatment as it preserves the compromised tooth structure by its conservative design. Selective retreatment cases also benefit from the conservative access design of the CEC, without any compromise in the instrumentation during retreatment. In our study, significantly more time was required for retreatment with the CEC-Waveone combination when compared to other groups. After obturation, the specimens were stored at 37°C and 100% humidity for 1 month to ensure the sealer was fully set.[15]

The ProTaper universal retreatment system was used for retreatment in this study. This system can remove large amounts of gutta-percha through spirals running around the instruments, which produce both cutting and softening actions. The negative cutting angle and the absence of radial land exert a cutting action as opposed to a planing action on the gutta-percha.[16]

WaveOne and Neoniti file systems were used for further guttapercha removal as well as for reshaping in respective groups. Reciprocating systems such as WaveOne produce a broader motion in the counterclockwise direction yet shorter in the clockwise direction, keeping the file more centered in the canal.[1718] This factor, together with the marked taper of the WaveOne files, creates a greater contact area between the instrument and gutta-percha, allowing filling removal that is as effective as that produced with continuous rotation.[19] Furthermore, instrument fracture through restrictive access was mitigated by WaveOne files which have high cyclic fatigue resistance when compared to the rotary file systems.[20]

Neoniti files have been used for root canal treatment as well as for retreatment cases.[6] The Neoniti rotary system has a nonhomogeneous rectangular cross-section and multiple taper in a single instrument.[21] The results revealed that the Neoniti instrument was most effective in removing gutta-percha. The better performance of Neoniti instrument may be attributed to its design. Furthermore, this single-file system required less time for retreatment than WaveOne file. Electrical discharge machining technology gives high flexibility which allows the files to work through CEC design without the risk of fracture. Neither evaluated instrumentation systems completely removed all obturation material from the root canals of mandibular premolars. These findings are in agreement with several studies that evaluated different instruments and systems for this purpose.[522]

In this study, canals were initially prepared to a 25/0.08 instrument and further enlarged apically in the retreatment phase to minimize the presence of residual filling material.[2324] Retreatment was initiated with the entire ProTaper retreatment series in all groups for bulk removal of gutta-percha and was followed with either WaveOne or Neoniti instruments to remove the residual gutta-percha within the canal and for reshaping the canal as well.

The study revealed that the use of WaveOne instruments through a CEC access design showed higher amounts of obturation material on the root canal walls, particularly in the apical and middle thirds [Figures 5 and 6]. A possible reason for this is that the constricted access and the design of the WaveOne instruments prevented the file from engaging the gutta-percha. The study results showed that if a contracted design is desired by the clinician during access, then Neoniti instruments can be preferred over WaveOne instruments with no deleterious effect on the overall amount of obturation material removal. However, regardless of the retreatment protocol or access design used, residual obturation material were evident on the root canal surface.

Figure 5

Comparison of middle values regarding (mean [standard deviation]) among all the four groups using analysis of variance test

CONCLUSION

Within the limitations of this in vitro study, neither retreatment protocol was able to render root canals free of obturation material. However, in the presence of a CEC access design, neoniti instruments removed more obturation material in single-rooted, oval-shaped canals. Thus, the results obtained was statistically similar across the instruments assessed, confirming the hypothesis of this study.

Financial support and sponsorship

Nil.

Conflicts of interest

There are no conflicts of interest.