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Year : 2021  |  Volume : 39  |  Issue : 1  |  Page : 74-78

Synchrotron radiation-based micro-computed tomographic analysis of apical transportation of different Nickel–Titanium rotary systems in curved root canals: An in vitro study

1 Department of Conservative Dentistry and Endodontics, Government Dental College, Hyderabad, Telangana, India
2 Department of Conservative Dentistry and Endodontics, Mallareddy Dental College, Hyderabad, Telangana, India
3 RRCAT, Indore, Madhya Pradesh, India

Date of Submission09-Jan-2021
Date of Decision04-Feb-2021
Date of Acceptance02-Mar-2021
Date of Web Publication22-Apr-2021

Correspondence Address:
Dr. Pooja Yenubary
Government Dental College, Hyderabad, Telangana
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Source of Support: None, Conflict of Interest: None

DOI: 10.4103/jisppd.jisppd_16_21

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Background: In the last few decades, the availability of synchrotron sources has initiated revolutionary advances in X-ray imaging. Aims: The study aimed to evaluate the incidence of apical transportation after root canal preparation with ProTaper Gold (PTG), Hyflex electro discharge machining (HEDM), Reciproc (RPC), and WaveOne Gold (WOG) using synchrotron radiation-based micro-computed tomographic (SR–μCT) analysis. Materials and Methods: Forty mandibular molars were assigned to four experimental groups (n = 10) according to the file system used for the root canal preparation: Group 1: PTG (25/0.08), Group 2: HEDM (25/0.08), Group 3: RPC (25/0.08), and Group 4: WOG (25/0.07). The specimens were scanned on SR–μCT system before and after the root canal preparation. Apical transportation was assessed at 1, 2, 3, 4, and 5 mm section. Statistical Analysis: Two-way analysis of variance and Wilcoxon Mann–Whitney test was used. Results: No significant difference was found between the groups. Transportation in the mesial direction was of greater magnitude than distal transportation for all the files systems. Conclusion: SR–μCT can be used as a reliable diagnostic tool for further implications.

Keywords: Apical transportation, root canal preparation, synchrotron

How to cite this article:
Yenubary P, Anil C K, Singh B. Synchrotron radiation-based micro-computed tomographic analysis of apical transportation of different Nickel–Titanium rotary systems in curved root canals: An in vitro study. J Indian Soc Pedod Prev Dent 2021;39:74-8

How to cite this URL:
Yenubary P, Anil C K, Singh B. Synchrotron radiation-based micro-computed tomographic analysis of apical transportation of different Nickel–Titanium rotary systems in curved root canals: An in vitro study. J Indian Soc Pedod Prev Dent [serial online] 2021 [cited 2022 Dec 2];39:74-8. Available from: http://www.jisppd.com/text.asp?2021/39/1/74/314357

   Introduction Top

Cleaning and shaping of the root canal system are one of the purposes of endodontic therapy.[1] The fundamentals of root canal shaping are to maintain a tapering funnel from the coronal access cavity to the root apex preserving the original canal shape, sustaining the integrity and location of the apical canal anatomy.[2] However, procedural errors during instrumentation such as ledging, zipping, perforations, root canal transportation, and instrument separation may occur, especially when preparing curved canals.[3]

Several approaches have been used to assess the shaping ability of different NiTi rotary systems encompassing histological sections, plastic models, silicone impressions of instrumented canals, serial sectioning, radiographic comparisons, scanning electron microscopy, cone-beam computed tomography, and recently microtomography (micro computed tomographic [micro-CT]).[2],[4],[5],[6]

Indus-2 synchrotron source at Raja Ramanna Centre for Advanced Technology (RRCAT), Indore is an advanced X-ray imaging facility seen as an improvement over Indus-1 that has the distinction of being the first synchrotron generator of India. It is used to carry out absorption and phase-sensitive imaging and microtomography for material and medical science application. It uses techniques such as propagation-based and diffraction-enhanced phase imaging.[7] Another advantage is that the scans use a parallel beam geometry, allowing the reconstruction of the sample at a higher spatial resolution with reduced artefacts with respect to the use of polychromatic conventional sources with an increased signal-to-noise ratio. These sources allow faster image acquisition, better sensitivity, and higher resolution.[8],[9] Till date, no studies have compared the incidence of apical transportation of ProTaper Gold (PTG; Dentsply Tulsa Dental Specialties, OK, USA), Hyflex electro discharge machining (HEDM; Coltene/Whaledent AG, Altstatten, Switzerland), WaveOne Gold (WOG; Dentsply Maillefer, Ballaigues, Switzerland), and Reciproc (RPC; VDW, Munich, Germany) file systems in the root canals using a synchrotron radiation-based micro-CT (SRμCT).

   Materials and Methods Top

Sample selection

Forty human first mandibular molars, freshly extracted for different clinical reasons were used in the present study. All the Teeth were extracted using an atraumatic technique.[10] All roots were initially inspected with digital radiographs to detect and exclude teeth with any visible preexisting craze lines, cracks, and root canal obstructions. Only teeth with fully formed roots, closed apices, and two mesial root canals with independent foramina having moderate curvature (10°–20° curvature angle), analyzed through Schneider's technique[11] were selected. The specimens were decoronated to remove the distal roots using a low-speed saw (Isomet; Buhler Ltd, Lake Bluff, NY) with water cooling, leaving mesial roots with approximately 12 ± 1 mm in length to prevent the introduction of any confounding variables. All the roots were inspected with a dental operating microscope (Carl Zeiss, Jena, Germany) at ×24 to detect any new cracks formed. Four teeth with such findings were excluded and replaced. Canal patency was established with a size 10 K-file in the presence of Glyde (Dentsply Maillefer, Ballaigues, Switzerland). All teeth in which canal patency could not be established were excluded from the study and replaced with similar patent teeth. The specimens selected were then stored in 0.1% thymol solution at 5°C.

Experimental setup

The experiment has been performed at X-ray Imaging Beamline (BL-04), Indus-2 Synchrotron Source, RRCAT, Indore, India. Indus-2 is a third-generation synchrotron source operating at 200 mA current and 2.5GeV energy which provide broad radiation extending from infrared to hard X-ray. This beamline extracts a hard X-ray monochromatic beam using a silicon Si (111) double-crystal monochromator to expose the teeth samples. The projection images were acquired at 25 keV X-ray beam energy with a rotation step of 0.2°. The bright-and dark-field images were also acquired to correct the image noise. A very high-resolution (pixel size: 4.5 μm) photonic science charge-coupled device camera having field of view 18 mm × 12 mm is used to acquire the X-ray projection images. The sample was mounted on two high precision linear stages along with one angular stage on the top to rotate the sample as shown in [Figure 1]. The detector was mounted on three linear translation stage systems to align and optimize the imaging system. The acquired projection images were preprocessed, normalized, and reconstructed using a filtered back-projection algorithm to get the 3D slice images. Further, quantitative analysis of all slice images was done using the ImageJ software.[7]
Figure 1: Imaging Beamline experimental set up showing the detector and manipulation stages

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Root canal preparation

The surface of the roots was coated with a thin film of polyether impression material to simulate the periodontal ligament and placed coronoapically inside a custom-made jig to further streamline the coregistration process. Apical patency was confirmed by inserting a size 10 K-file into the root canal until its tip was visible at the apical foramen, and the working length (WL) was set 1.0 mm shorter of this measurement. The glide path was established with a size 15 K-file (Dentsply Maillefer) up to the WL, and the specimens were instrumented using X-smart Plus motor (Dentsply Maillefer, Ballaigues, Switzerland) They were randomly assigned into four experimental groups (n = 10):

Group 1

PTG (25/0.08): Root canals were prepared in a crown-down fashion with the aid of an X-Smart plus electric motor with torque control (Dentsply Maillefer) at 300 rpm. The PTG Shaping SX, S1, and S2 and finishing F1 and F2 files were sequentially used with a continuous in-and-out movement up to the WL as per the manufacturer's recommendation.

Group 2

HEDM (25/0.08): The canals in this group were shaped using X-Smart plus electric motor with torque control (Dentsply Maillefer) with HEDM file at 500 rpm and 2.5 Ncm torque in accordance with the manufacturer's instructions up to the WL.

Group 3

RPC (25/0.08): The R25 instrument was used with X-Smart Plus electric motor with torque control (Dentsply Maillefer) using in and out pecking motion in the “RPC ALL” mode with 350 rpm until reaching the WL of the canals as per the manufacturer's recommendation.

Group 4

WOG (25/0.07): The canals in this group were shaped with X-Smart plus electric motor with torque control (Dentsply Maillefer) using the WOG Primary NiTi file in the “WAVEONE ALL” mode with 350 rpm until reaching the WL as per the manufacturer's recommendation. In all the four groups, canal irrigation was consistent with 2 ml 2.5% NaOCl and saline alternatively. After preparation, a postoperative micro-CT scan of each specimen was performed with the above mentioned parameters.

Apical transportation evaluation

The five slices of interest for each tooth were determined by identifying the slice at which the apex of the tooth was first visible (0-mm mark) and then adding 29 slices per 1-mm increment. The same slices were compared pre- and post-instrumentation. The method according to Gergi et al.[12] was used, that measured the shortest distance from periphery of the canal to periphery of the root. The following formula: (X1-X2)-(Y1-Y2), where X1 represents the shortest distance from the mesial edge of the uninstrumented canal to the mesial edge of the root, Y1 is the shortest distance from the distal edge of the uninstrumented canal to the distal edge of the root, X2 is the shortest distance from the mesial edge of the instrumented canal to the mesial edge of the root, and Y2 is the shortest distance from the distal edge of the instrumented canal to the distal edge of the root was used, as shown in [Figure 2]. Pre- and postinstrumentation measurements were compared to assess the incidence and direction of apical transportation. A positive value represented mesial movement, whereas a negative value represented distal movement.[13]
Figure 2: Synchrotron radiation-based micro-computed tomographic scan with markings showing red lines denoting X1 and X2 (before preparation) and blue lines denoting X2 and Y2 (after preparation)

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Statistical analysis

All statistical analyses were performed using the SPSS software (ver. 20; SPSS, Inc., Chicago, IL, USA). Means and standard deviations were calculated for each group. Two-way analysis of variance was used to compare the differences in transportation between the 2 systems at each millimeter assessed. Wilcoxon Mann–Whitney test was used to assess significant differences between the four groups for mesial and distal directions. P < 0.05 was considered statistically significant.

   Results Top

No significant differences in apical transportation (P > 0.05) were found between the groups, as shown in [Table 1]. The mean transportation for groups PTG, HEDM, RPC, and WOG was calculated to be 1.53 ± 0.65, 1.56 ± 0.67, 1.31 ± 0.63, 1.23 ± 0.55 in the mesial direction and 1.34 ± 0.75, 1.40 ± 0.88, 1.24 ± 0.57, and 1.35 ± 0.78 in the distal direction, respectively. The mean transportation was toward the mesial wall for both file systems due to a positive value.
Table 1: Mean magnitude of apical transportation with standard deviation (μm)

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   Discussion Top

In the current study, the effect of four commonly used rotary and reciprocating NiTi file systems regarding the incidence of apical transportation during root canal preparation in curved root canals was evaluated. Extracted teeth were used because testing file systems in natural dentin are considered to be more beneficial than using standardized artificial canals[14] because of the hardness of the dentin. The study focused on the mesial canals of mandibular molars because they are the most frequently indicated for root canal endodontic treatment and constantly presented with apical curvatures which increases the level of instrumentation difficulty.[15] Evidence shows that NiTi rotary instruments enable the clinician to adequately and predictably prepare the root canal and decrease the risk of procedural errors. Various thermomechanical procedures in manufacturing and improvements in the composition of alloy aimed to improve the properties of NiTi files.[16] A number of studies have examined the apical transportation of rotary and reciprocation file systems. Few studies[17],[18] claimed that reciprocation produced less apical transportation than rotary systems and few studies showed vice versa.[19],[20] The present study is similar to studies[21],[22],[23] that showed no significant difference between rotary and reciprocating file systems in the incidence of apical transportation. Evidence shows that dimensions of instrument, metallurgical properties, design of instrument, and its application mode can all affect the amount of canal transportation during instrumentation.[24] PTG has a convex triangular cross-sectional design combined with the flute design with its progressive tapers sequence along with enhanced heat-treatment technology. The gold treatment intends to improve the mechanical properties compared to the conventional NiTi alloy.[2] Hyflex EDM is a new-generation single file system made of a controlled memory alloy using electrodischarge machining technology, which significantly improved its flexibility. Throughout their entire working part, they have three different horizontal cross sections: A quadratic in the apical region, trapezoidal in the middle and almost triangular in the coronal region.[25] RPC is made of a special NiTi-alloy called M-Wire that is created by an innovative thermal-treatment process. The benefits of this M-Wire NiTi are increased flexibility of the instruments and improved mechanical properties.[21] According to the manufacturer, WOG used in reciprocating motion is repeatedly heat treated and cooled, having parallelogram cross section, providing increased flexibility and cyclic fatigue resistance.[16] In our study, there was no significant difference in apical transportation due to these varied thermomechanical procedures in manufacturing and improvements in the composition of alloy. Recently, manufactured rotary systems of size 25 and taper varying from 0.06 to 0.08 have been used in instrumentation for curved canals with less transportation.[23] All groups of single-file system with size 25 apical diameter were used in this study for standardization to finalize all apical preparation with instruments of the same diameter. In addition, the taper was also selected with minimal variation with 0.08 for PTG, HEDM, RPC and 0.07 for WOG. However, in the present study, emphasis was made in using SR-μCT as a research tool for further dental research. In fact, one of the limitations of this in vitro study is the long duration which is required for the series of scans per sample.[7]

   Conclusion Top

Despite the limitations of this in vitro study, it may be concluded that both techniques induced similar apical transportation. We believe that using such method will boost the efficiency on the investigation of tooth-related defects over a large number of specimens.

Ethical clearance

The study was done on extracted teeth. There was no involvement of research participants.


The authors are thankful to Raja Ramanna Centre for Advanced Technology, Indore, India.

Financial support and sponsorship


Conflicts of interest

There are no conflicts of interest.

   References Top

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