Cone-beam computed tomography assessment of root canal transportation using WaveOne Gold and Neoniti single-file systems.

INTRODUCTION: The aim of this study was to compare canal transportation of two single-file systems, WaveOne Gold and Neoniti, using cone-beam computed tomography (CBCT).
METHODOLOGY: A total of 40 mesiobuccal canals of maxillary first molars with curvatures of 15°-30° were chosen and randomly divided into two experimental groups (n = 20). In both groups, glide path was established using ProGlider. In group 1, canals were shaped with WaveOne Gold and in group 2 with Neoniti A1, respectively. According to manufacturer's instructions, canal preparation was made. Canals were scanned before and after instrumentation using CBCT scanner to evaluate root canal transportation at 3, 5, and 7 mm from the apex. Data were statistically analyzed, and significance level was set at P < 0.05.
RESULTS: Mesiodistal and buccolingual transportation showed a statistically significant difference at 3 mm (P = 0.009) and 7 mm (P = 0.002), respectively, when instrumented with Neoniti than WaveOne Gold.
CONCLUSION: WaveOne Gold single reciprocation file respected original canal anatomy better than Neoniti single continuous file.

INTRODUCTION

The objective of endodontic treatment is to clean and shape the root canal system, maintaining its original configuration.[1] The curvature of the canal is considered to be a preeminent risk factor for procedural errors such as ledging, zipping, and transportation. This is due to the tendency of endodontic instruments to straighten within the canal during chemomechanical preparation.[2]

Development of nickel–titanium (NiTi) rotary files has been shown to significantly decrease errors such as canal transportation and deviation from the canal axis during preparation when compared to manual techniques, particularly in the apical area of the curved canal.[3] Despite the advantages of using NiTi rotary instruments, instrument separation is the most frequent procedural accident observed during their clinical use.[4]

A glide path is defined as a smooth, although possibly narrow, tunnel, or passage from the coronal orifice of the canal to the radiographic terminus or electronically determined portal of exit.[5] The maintenance of a glide path means having a smooth passage that is reproducible by files used successively in the canal.[6] Once established, a successful glide path permits unrestricted access to the apical part of the canal.[7] The glide path preparation performed with hand files can be very difficult and time-consuming, especially curved canals.[8] Recently, rotary pathfinding NiTi instruments have been introduced with the purpose of creating an initial glide path and eliminating the need for manual preflaring. The ProGlider single-file system (Dentsply Maillefer, Ballaigues, Switzerland) is manufactured from M-Wire alloy with 0.02 taper and 0.16 mm diameter at its tip.[9] The instrument is progressively tapered (up to 0.85) with an active part of 18 mm. ProGlider is recommended for use in continuous rotation (300 rpm; 2–5.2 Ncm torque) after canal patency has been verified with a size 10 K-file at working length (WL).[9]

Based on their motion, single-file rotary systems can be classified into rotating and reciprocating files.[10] WaveOne Gold (Dentsply Maillefer), is one of these newly introduced single-file systems with a reciprocating motion. WaveOne Gold instruments are manufactured utilizing a new proprietary thermal process, producing a superelastic NiTi file.[11] The gold process is a postmanufacturing procedure in which the ground NiTi files are Heat treated and slowly cooled. While this process gives the file its distinctive gold finish, more importantly, it considerably improves its strength and flexibility far in the excess of its predecessor, Waveone.[11] It is available in four sizes as follows: small (20.07, yellow), primary (25.07, red), medium (35.06, green), and large (45.05, white). Cross section of WaveOne Gold is a parallelogram with two 85 degrees cutting edge with alternate one and two-point contact.[12]

Recently another new single-file system, Neoniti (Neolix, France), has been introduced. Neoniti A1 is manufactured in three different sizes (20/0.08, 25/0.08 and 40/0.08) that are recommended to be used with speed of 300–500 rpm and torque limit of 1.5 N/cm. It is made by an electric discharge machining process, which offers many advantages such as progressive flexibility, sharp cutting edges, and built-in abrasive properties.[13]

To investigate the efficiency of instruments and techniques developed for root canal preparation, a number of methods have been used to compare canal shape before and after preparation. Cone-beam computed tomography (CBCT) is a modern and noninvasive diagnostic method with compact equipment, low-dose radiation and allows evaluation of detailed images using different settings.[14] It is useful in comparing the anatomy of root canal system before and after biomechanical preparation, allowing to detect deviations and transportation.[15]

METHODOLOGY

In the present study, 40 mesiobuccal roots of extracted maxillary first molar teeth with completely formed apices were collected from P.M.N.M. Dental College Bagalkot. Teeth having root curvature ranging from 15° to 30° were selected. Canal curvature was assessed by Schneider's technique and samples were standardized.[16]

Access cavities were prepared with access preparation kit (Dentsply, Maillefer, Ballaigues, Switzerland) and the root canals were negotiated using #10 K-file (Dentsply, Maillefer, Ballaigues, Switzerland). Distobuccal and palatal roots of all teeth were separated using diamond disc at the furcation level. A size #10 K file was placed in the canal until it was visible at the apical foramen and WL was established 1 mm short of this length. For more uniform samples, the crowns were flattened and a final WL of 18 mm was standardized for each specimen. Roots were embedded in acrylic blocks of 2.5 cm × 2.5 cm.

The teeth were randomly divided into two experimental groups (n = 20). For both the groups (n = 20), glide path was established using ProGlider. ProGlider (size 16,.02 taper) was used in the continuous rotation (300 rpm speed; 2–5.2 Ncm torque) until the WL. In group 1, teeth were prepared with WaveOne Gold, primary file (25/0.07) according to the manufacturer's instructions, installed on a handpiece powered by electric torque control motor (Silver, VDW, Munich, Germany) set on WaveOne Gold program.

In group 2 (n = 20), Neoniti C1 (25/0.12) was used for shaping of the coronal third with circumferential brushing motion (300 rpm speed; 2–5.2 Ncm torque). Further, Neoniti A1 (25/0.08) was used with alternating 2–3 circumferential wall brushing actions and 2–3 pecking motions till the WL. Neoniti A1 was used for middle and apical third enlargement of canals with speed of 300 rpm and torque of 1.5 N/cm.

The final apical preparation was standardized for all specimens at size 25. Instrumentation was done using Glyde (Dentsply Maillefer) as a lubricating agent. Canals were irrigated with 2 ml of 3% Sodium hypochlorite during instrumentation. Once the instrumentation was completed, 1 ml of 17% ethylenediamine tetraacetic acid (EDTA) was used for 3 min followed by a final irrigation with 2 ml of saline. Each instrument was used to prepare three canals and then, the files were discarded. Teeth were then scanned under the same condition as the initial scan and data were analyzed.

Image analysis

All the teeth were scanned using CBCT (NewTom VGi, QR SRL Co., Verona, Italy) with the following setup: 90 kVp, 3 mA, 0.1 mm × 0.1 mm × 0.1 mm voxel size and 0.1 mm axial thickness. The first section was at 3 mm from the apical end of the root (apical level), the second section at middle third (mid-root level) 5 mm from the apex and third section at the coronal third, 7 mm from the apex were recorded. After the initial scan, root canals were instrumented, and image analysis was performed using NNT Viewer software (NNT software corporation, Yokohama, Japan).

Cone-beam computed tomography measurements

The following formula was used for the calculation of canal transportation mesiodistally and buccolingually at each level for both the groups [Figure 1],[10]

Figure 1

Pre and Post-instrumentation Cone-beam computed tomography axial images

Mesiodistally = (m1-m2)-(d1-d2)

Buccolingually = (l1-l2)-(b1-b2)

Where,

Mesial (m1)/lingual (l1) is the shortest distance from the mesial/lingual edge of the root to the mesial/lingual edge of the uninstrumented canal.

Distal (d1)/Buccal (b1) is the shortest distance from the distal/buccal edge of the root to the distal/buccal edge of the uninstrumented canal.

m2/l2 is the shortest distance from the mesial/lingual edge of the root to the mesial/lingual edge of the instrumented canal.

d2/b2 is the shortest distance from the distal/buccal edge of the root to the distal/buccal edge of the instrumented canal.

According to this formula, a negative result indicates transportation towards the distal/buccal portion, a positive result towards the mesial/lingual portion and zero, the absence of transportation.

Statistical analysis

The inter-group comparison was made using independent sample t-test and Mann–Whitney U-test. The intragroup comparison was made using Friedman's test. SPSS software (SPSS version 17.0, SPSS, Chicago, IL, USA) was used for statistical analysis, and the level of significance was set at 0.05.

RESULTS

Intergroup comparison of mesiodistal transportation between the groups showed a statistically significant difference at 3 mm (P = 0.009) when instrumented with Neoniti than WaveOne Gold. There was no significance at 5 mm and 7 mm mesiodistally between the groups [Figure 2]. Intergroup comparison of buccolingual transportation between the groups showed a statistically significant difference at 7 mm (P = 0.002) when instrumented with Neoniti than WaveOne Gold. There was no significance at 3 mm and 5 mm buccolingually between the groups [Figure 3].

Figure 2

Mesiodistal canal transportation at different levels between the groups

Figure 3

Buccolingual canal transportation at different levels between the groups

Intragroup comparison of WaveOne Gold group showed a statistically significant difference at 5 mm (P = 0.047) than at 7 mm, buccolingually within the group [Figure 4]. However, there was no significance at 3 mm and 5 mm, 3 mm and 7 mm. Intragroup comparison of Neoniti group showed no statistically significant difference in mean canal transportation at 3 mm, 5 mm and 7 mm both mesiodistally and buccolingually within the group [Figure 5].

Figure 4

Mesiodistal and Buccolingual canal transportation at different levels within the WaveOne Gold group

Figure 5

Mesiodistal and Buccolingual canal transportation at different levels within the Neoniti group

DISCUSSION

The present study aimed to compare the root canal transportation using WaveOne Gold and Neoniti single-file systems in curved roots of maxillary first molars using CBCT. CBCT imaging is a noninvasive, relevant process for the analysis of canal geometry and shaping techniques.[17] In the present study, CBCT was used to evaluate the shaping performance of the tested groups.

Predictable endodontic success is dependent on three dimensional cleaning, shaping, and obturation of root canal system.[18] However, endodontic preparation in curved and narrow root canals is more challenging, with a tendency for the prepared canal to deviate away from its original axis leading to procedural errors such as ledging, zipping, and transportation.[19]

The creation of a glide path is essential to allow the proper action of NiTi instruments either used in a rotary or reciprocating motion.[20] A mechanical or manual glide path is key to reducing the effect of torsional stresses along the canal, the screwing effect of rotary instruments, and the risk of instrument failure.[21] Furthermore, a glide path created mechanically might be faster and associated with a lower prevalence and severity of postoperative pain.[22] The single use of endodontic instruments has further supported to reduce instrument fatigue and possible cross-contamination associated with the use of NiTi rotary instruments for canal instrumentation.[23]

The mesiobuccal root of maxillary first molars was chosen as they usually present with remarkable curvatures and have mesiodistal flattening.[24] Teeth having root curvature ranging from 15° to 30° were selected. Curved canals were selected for this study because they present greater challenges to instrumentation.[25] In the present study, three levels were chosen: 3, 5, and 7 mm. These measurements represent the apical, middle, and coronal thirds of root canals where curvatures with high vulnerability to iatrogenic mishaps typically exist.[17] The amount of canal transportation increases with apical preparation greater than size 25;[26] hence, the apical preparation was limited to size 25 file in the present study.

In the present study, at 3 mm mesiodistally, the transportation is more with Neoniti thanWaveOne Gold, which was statistically significant. Similar findings were reported by Yoo and Cho. where wave one reciprocating system maintains original canal contour better than files with continuous rotation, which tend to transport the outer canal wall of the curve in the apical part of the canal.[27] Berutti et al. have reported that reciprocating movement allows a more centralized chemomechanical preparation when compared to continuous rotary motion, especially in the apical third.[20] At 7 mm level, buccolingually, there was statistically significant transportation with Neoniti than WaveOne Gold. This could be attributed to the coronal preflaring with Neoniti C1, (taper-0.12) used in circumferential brushing motion. Similar findings were reported by Radwanski et al. where Waveone with reciprocating motion caused lesser transportation than protaper with continuous rotation.[28]

Buccolingually, wave one gold exhibited a significant canal transportation at 5 mm when compared to 7 mm, in intragroup comparison. This may be because wave one gold has a fixed taper from D1 to D3, a progressively decreasing percentage tapered design from D4 to D16.[29] According to yang et al., constant taper produced good centering ability compared to instruments with a progressive taper.[30] Neoniti did not exhibit any statistically significant transportation at 3 mm, 5 mm, and 7 mm, either mesiodistally or buccolingually, within the group. Cross section of Neoniti is a homothetic rectangle, the built-in abrasive property of the flutes, hard cutting edges, circumferential brushing motion in the middle, coronal third and pecking motion in apical third, may have led to aggressive cutting and caused canal transportation.[31]

CONCLUSION

Within the limitations of our study, it was concluded that WaveOne Gold single reciprocation file respected original canal anatomy better than Neoniti single continuous file.

Financial support and sponsorship

Nil.

Conflicts of interest

There are no conflicts of interest.