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 Table of Contents  
Year : 2021  |  Volume : 33  |  Issue : 2  |  Page : 75-80

A comparative evaluation of canal transportation, centering ability, and volumetric increase in the curved canals using thermally treated three nickel-titanium rotary files: A cone-beam computed tomography study

Department of Conservative Dentistry and Endodontics, Sudha Rustagi College of Dental Sciences and Research, Faridabad, Haryana, India

Date of Submission02-Jan-2021
Date of Decision10-Feb-2021
Date of Acceptance05-Mar-2021
Date of Web Publication11-Jun-2021

Correspondence Address:
Dr. Meenu G Singla
Professor, Sudha Rustagi College of Dental Sciences and Research, Faridabad, Haryana
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Source of Support: None, Conflict of Interest: None

DOI: 10.4103/endo.endo_1_21

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Aims: The aim of this study was to evaluate and compare canal transportation (CT), centering ability (CA), and volumetric changes in the curved canals prepared using Hyflex Electrical Discharge Machining (HEDM), ProTaper Gold (PG), and NeoEndo Flex rotary file systems through cone-beam computed tomography (CBCT).
Materials and Method: Sixty mesiobuccal canals of maxillary molars were selected. Pre- and postinstrumentation CBCT scans were taken in the same position. CT and CA were calculated at 1 mm, 4 mm, and 7 mm from the apex; change in volume for the whole canal was measured and analyzed statistically.
Results: The results showed that mean CT of HEDM and NeoEndo was less than PG at all levels, with significant differences at 4 mm and 7 mm. Regarding CA, no significant differences were found among the file systems. PG showed maximum volumetric increase with no statistically significant differences between the groups.
Conclusion: All the experimental file systems respected the canal anatomy, although in the middle third, PG showed significantly more CT than HEDM and NeoEndo, whereas in the coronal third, PG showed significantly greater CT than NeoEndo. Regarding CA, no significant differences were found among the file systems. PG showed maximum volume of dentin removal.

Keywords: Canal transportation, centering ability, Hyflex Electrical Discharge Machining, NeoEndo, ProTaper Gold

How to cite this article:
Singla MG, Kumar H, Singh N. A comparative evaluation of canal transportation, centering ability, and volumetric increase in the curved canals using thermally treated three nickel-titanium rotary files: A cone-beam computed tomography study. Endodontology 2021;33:75-80

How to cite this URL:
Singla MG, Kumar H, Singh N. A comparative evaluation of canal transportation, centering ability, and volumetric increase in the curved canals using thermally treated three nickel-titanium rotary files: A cone-beam computed tomography study. Endodontology [serial online] 2021 [cited 2021 Oct 18];33:75-80. Available from: https://www.endodontologyonweb.org/text.asp?2021/33/2/75/318125

  Introduction Top

Shaping is considered a crucial phase in the root canal treatment, because it is not only aimed at removing remaining pulp tissue, microorganisms, and debris but also constitutes the preservation of the root canal anatomy.[1] The canal curvature is considered a principal risk factor for the procedural errors.[2] As the canal curvature increases, maintaining initial canal shape and direction becomes challenging which can lead to excessive dentin removal, straightening of canals, creation of ledge, or an elbow coronal to the apical seal and canal transportation (CT).[3] In general, it can be stated that more severely curved canal with shorter radius of curvature imposes the greater risk of transportation.[4]

CT is “the removal of canal wall structure on the outside curve in the apical half of the canal due to the tendency of files to restore themselves to their original linear shape during canal preparation.”[5] It may cause harboring of debris and residual microorganisms, destroys the integrity of the root, and reduces its fracture resistance.[4]

Centering ability (CA) is the ability to keep instruments centered to provide a correct enlargement, without excessive weakening of root structure.[6] More curved the root canal is, more constraint is the instrument and less centered it is in the canal. Along with CT and CA, change in the volume of the canal after instrumentation is also influenced both by the root canal anatomy and design of instrument.[7] The amount of dentin removed during the instrumentation is an important parameter to avoid procedural mishaps.[8]

Some of the causative factors associated with an increased risk of CT and CA in the curved canals include insufficiently designed access cavities, use of inflexible instruments, instrument design, and instrumentation technique.[4]

Instrumentation with stainless steel files has shown to produce undesirable results regardless of the technique or type of files used, owing to their inflexibility.[2] Due to the limitations of stainless steel instruments, such as risk of deviations in canal preparation and excessive time consumption, nickel–titanium (NiTi) instruments have become widely popular. NiTi instruments have higher flexibility and can be placed in canals with less lateral force.[9]

Lately, changes in metallurgy of NiTi instruments like “thermal treatment” has increased the reliability and effectiveness in controlling instrumentation, especially in curved canals. Some of the recently introduced thermally treated file systems include Hyflex Electrical Discharge Machining (HEDM), ProTaper Gold (PG), and NeoEndo flex (NE) rotary file system.

HEDM (Coltene/Whaledent AG, Altstätten, Switzerland) is produced by EDM, a noncontact machining procedure where the removal of material is performed by pulsating electric current discharge that flows between an electrode and workpiece, immersed in dielectric medium. This results in files being flexible and fracture resistant.[10]

PG (Dentsply, Tulsa Dental Specialties, Tulsa, OK, USA) presents with convex triangular cross-section and variable taper; exhibits exact geometries as ProTaper Universal (PU; Dentsply Maillefer, Ballaigues, Switzerland) file system.[11] The raw metal is repeatedly heated and cooled giving it a distinctive golden appearance along with considerably improved strength and flexibility.[12] Manufacturer's claim it to have improved CA, especially in the curved canals.

NE (Orikam Health-care India Pvt. Ltd) utilizes a proprietary heat treatment which provides it a unique flexibility.[3] These have alternating cutting edges which have two functions: (i) to eliminate screwing and blocking in continuous rotation and (ii) to reduce the working torque.[13]

Cone-beam computed tomography (CBCT) utilizes a cone-shaped X-ray beam and an area detector that captures a cylindrical volume of the data in one acquisition. Therefore, it becomes possible to analyze the shape of the canal before and after preparation.[14]

Very few studies about shaping ability of above-discussed rotary file systems are available in literature. Therefore, this study aimed to evaluate and compare shaping ability and volumetric changes in curved mesiobuccal canals of maxillary molars using three thermally treated rotary file systems through CBCT.

  Materials and Method Top

Sixty human maxillary permanent molars were included that had mesiobuccal canals with >30° curvature (Schneider's method). If two mesiobuccal canals were present, they had independent foramina and fully formed apices. Radiovisiographs were taken in both buccolingual and mesiodistal directions for identifying two separate mesiobuccal canals and calculating angle of curvature, radius of curvature and length of curved part of the canal.

r was calculated according to the formula: R = S/(2sinα)

k was calculated using formula: K = (4πα/360°) × r[15]

Data collected were subjected to the statistical analysis, to ensure sample homogeneity at baseline [Table 1].
Table 1: Data represented as mean±standard deviation

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Coronal access was made using an Endo-Access bur (Dentsply Mallifer) in a high-speed air rotor handpiece, and canal exploration was done. Patency was checked using #10 K-file. Samples were decoronated with a diamond disk to obtain standardized mesiobuccal root length of 14 mm. Working length was determined using #15 K file, established 1 mm short of foramen. The samples were embedded in resin molds of size 4 cm × 4 cm. Long axis of the specimens were parallel to the long axis of mold, to ensure standardization. Preinstrumentation images of each sample were recorded using CS 3D imaging software (CBCT-Carestream 9300 Premium, Carestream Health, Inc., Rochester, NY, USA) at three levels: 1 mm, 4 mm, and 7 mm from apex.

The samples were divided randomly into the three groups according to the file system used (n = 20):

Group I: Samples prepared using HEDM till OneFile (25/0.08).

Group II: Samples prepared using PG till F2 (25/0.08).

Group III: Samples prepared using NE till size 25/0.06.

Samples were irrigated with 2 ml of 5.25% sodium hypochlorite, followed by 1 ml of 17% ethylenediaminetetraacetic acid for the removal of smear layer and with a final flush of normal saline. Postinstrumentation, the samples were scanned under similar conditions as initial scans.

CT was determined by the comparative evaluation of linear measurements in the axial sections at above-mentioned levels in pre- and post-instrumentation scans using the following equation:

CT = (a1 − a2) − (b1 − b2), where

1 and a2- shortest distance from the mesial edge of the root to mesial edge of uninstrumented and instrumented canal, respectively, and b1 and b2- distance from the distal edge of the root to the distal edge of uninstrumented and instrumented canal, respectively. The result of “0” indicates no CT and other than 0 means transportation has occurred. Negative value indicates transportation toward distal and positive value indicates transportation toward mesial.

CA was determined using the following formula:[9]

CA = (a1− a2)/(b1− b2) or (b1− b2)/(a1− a2)

If differences are unequal, smaller value is considered as numerator. Therefore, values equal to 1 indicate perfect CA of instrument and values closer to 0 indicate instrument's lower ability to maintain the central axis of the canal.

Volume increase (mm3) was determined for each canal by subtracting uninstrumented canal volume from instrumented canal volume, using volume calculation tool of software – In vivo 5.2 licensed software (Anatomage, San Jose, CA, USA).

Statistical analysis

Data were collected and subjected to the analysis using the Statistical Package for the Social Sciences (SPSS) Statistics for windows, Version 21 (Armonk, NY: IBM Corp.). Overall group comparison was done using the one-way analysis of variance test, Kruskal–Wallis test, Mann–Whitney U-test, along with post hoc pairwise comparison using Tukey's test. Level of statistical significance was set at 0.05.

  Results Top

Canal transportation

At 1 mm, Group II showed the highest value followed by Group I and Group III which showed equivalent values. Differences among groups failed to reach the level of significance [Table 2].
Table 2: Inter-group comparison of canal transportation, centering ability and volumetric increase

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At 4 mm, mean CT in Group I and III was significantly less than Group II. Group I and III did not show any significant differences between them.

At 7 mm, the least value was found in Group III followed by Group I and Group II with significant differences between Group II and III.

Centering ability

At 1 mm, Group I and Group III showed similar values, which were higher than Group II. At 4 mm, Group I showed higher value than Group III followed by Group II. At 7 mm, Group III showed higher results followed by Group I and II.

No statistically significant differences were observed among the groups.

Volume increase

Maximum change in the canal volume among groups was shown by Group II, followed by Group I and III, with no statistically significant differences between them.

  Discussion Top

Transportation causes irreversible deleterious effects leading to loss of integrity of the root. Opting for NiTi instruments with high flexibility can provide improved adaptation of files in curved canals to provide fewer procedural errors.

NiTi alloys exist in two crystallographic forms, i.e., austenite and martensite, which determine its mechanical properties. These phases are interconvertible by heat and stress.[16] At higher temperature, Nitinol is in an austenitic phase which is stiff, hard, and possess superior superelastic (SE) properties. At the lower temperature, it is in martensitic phase which is soft, ductile, can be easily deformed and possess shape memory effect (SME).[17]

Therefore, manufacturers have been using complex procedures to modify alloy transformation temperatures such as austenite start (As), austenite finish (Af), martensite start (Ms), and martensite finish (Mf) temperature and consequently improve its mechanical performance. Af temperature for most conventional NiTi files is at or below room temperature, exhibiting austenitic phase during clinical use, whereas the Af of thermally treated files is above the body temperature and is mainly in the martensite phase that possess typical characteristics of SE and SME.[18]

Beside metallurgical processes, variations in cross-sectional design, taper, number of files, and sequence of instruments also affect shaping ability. Thus, this study was conducted to evaluate shaping ability of three heat-treated file systems with different design patterns, i.e., HEDM, PG, and NE.

According to the results of the present study, PG was found to cause highest transportation at all levels with significant differences at 4 mm on comparison with HEDM and NE and at 7 mm with NE. In a study by Gagliardi et al.,[11] PU showed increased cutting ability in the middle and coronal third. PG has a file design similar to PU, i.e., convex triangular cross section with sharp cutting edges but has different metallurgy due to heat treatment.[19] Thus, similar cutting ability of PG can be expected at middle and coronal third area which could further be responsible for increased transportation at 4 mm and 7 mm as in accordance with the findings of our study. Another study was conducted by Singh et al.[20] comparing shaping ability of PG and 2S and found that PG showed significantly higher CT than 2S at all levels.

HEDM showed almost similar findings of CT on comparison with NE at all levels while on comparison with PG showed lower values. In a study by Özyürek et al.[21] in which shaping ability of HEDM, Reciproc, and WaveOne Gold was evaluated, HEDM showed better results than Reciproc, while it showed similar results to WaveOne Gold at all thirds. This behavior of HEDM can be attributed to its manufacturing through EDM and built in shape memory, which reduces stress during preparation by changing their spiral shape, enabling better adaptation to original shape of canals. HEDM has a variable cross section; transitioning from roughly triangular near shaft, trapezoidal in the middle and rectangular at tip. Rectangular cross section provides more core material that provides resistance to breakage, i.e., strength and a combination of trapezoidal and triangular cross section provides flexibility. This unique combination could provide the better management of curved canals.[22],[23] Moreover, OneFile-shaping instrument of HEDM file system has a transitioning taper of 0.08/mm in its apical 4 mm that decreases to 0.04/mm along the file, which could contribute to increased flexibility resulting in the lower transportation in the middle third.[22]

In our study, PG and HEDM showed higher CT values than NE at cervical third. A study by Piheiro et al.[24] showed similar findings regarding CT in which PG and HEDM showed higher values at the cervical region among other thermally treated NiTi rotary files (ProDesign S, Hyflex CM, ProDesign Logic). NE showed the lowest transportation which was significantly less than PG. This can be attributed to the least taper of orifice enlargement instrument of 0.08 of NE and variable tapering file design of PG. SX file of PG exhibits nine increasingly larger tapers ranging from 0.035 to 0.19 between D1-D9, which has a further progressive design toward the shaft.[25] Lower transportation can also be credited to NE's proprietary thermal treatment which imparts it high flexibility and its design pattern, i.e., convex triangular cross-section with alternating cutting edges which prevents excessive dentin removal.[3],[13] Till date, no studies have been found which have evaluated transportation of NE.

In our study, all file systems showed transportation within the acceptable range at the apical level according to Wu et al.[26]

Regarding CA, at 1 mm HEDM and NE showed equivalent and highest CA; at 4 mm HEDM showed the best results and at 7 mm NE showed maximum CA while PG showed least values at all levels. Statistically nonsignificant differences were observed among tested groups. Similar findings were observed in a study by Bharti et al.[27] in which shaping ability of HEDM and ProTaper Next (PN) were compared, HEDM was found to maintain better CA than PN. Above-mentioned results can be attributed to the design of respective instruments along with their metallurgy.

Volume increase is likely a cumulative effect of coronal flaring, glide path preparation, and action of the final file. Tip diameter of all tested files was maintained at a standardized size of #25. According to the results, PG showed maximum volume increase and NE, the least. Thus, difference in tapers of instruments and design of final file could have led to these findings.

Higher values of volume increase in PG can be ascribed to its taper of the final file of 0.08, variable taper of orifice shaping instrument (0.035–0.19 [D1–D9]) and convex triangular cross section with sharp cutting edges which attributed to aggressive dentin removal. Orifice shaping instrument of HEDM has a taper of 0.12[22] which is lower than PG, resulted in less dentin removal than PG. Least values of NE can be attributed to the convex triangular cross section with alternating cutting edges, least taper of 0.06 of the final file and least taper of 0.08 of orifice shaping instrument as compared to PG and HEDM.

  Conclusion Top

Within the limitations of this study, it can be concluded that:

  • All file systems caused some degree of CT and not a perfectly centered preparation. In apical third, all tested file systems showed CT within the acceptable limit, where PG exhibited maximum values. In the middle third, PG showed significantly more CT than HEDM and NE, while in the coronal third, NE showed significantly less CT than PG
  • Most centered preparation at the apical level was shown by HEDM and NE, at middle level by HEDM and at coronal third by NE, with no statistically significant differences among the groups
  • PG showed highest volume increase, followed by HEDM and NE, with no statistically significant differences among the groups
  • NE file system can be credited for the preservation of dentin and maintaining original canal anatomy
  • Further research should focus on improving instrument design and metallurgy and test their impact on severely curved canals.


The authors thank the esteemed organization of Sudha Rustagi College of Dental Sciences and Research for providing the appropriate instruments, work environment, and research-oriented thinking.

Financial support and sponsorship


Conflicts of interest

There are no conflicts of interest.

  References Top

Shumilovich BR, Adunts LM, Rostovtsev VV, Kozhevnikov VV, Krukova SN. Comparative evaluation of the shaping ability of the three nickel-titanium rotary instruments using cone-beam computed tomography. Res J Pharm Biol Chem Sci 2018;9:708-15.  Back to cited text no. 1
Weine FS, Kelly RF, Lio PJ. The effect of preparation procedures on original canal shape and on apical foramen shape. J Endod 1975;1:255-62.  Back to cited text no. 2
Ahangar FA, Sajad M, Purra AR, Farooq R. Evaluation of centering ability of four thermally treated nickel titanium rotary files for root canal preparation in moderately curved root canals: An in vitro cone beam computed tomography assessment. Ann Int Med Den Res 2018;4:DE15-20.  Back to cited text no. 3
Schäfer E, Dammaschke T. Development and sequelae of canal transportation. Endod Topics 2009;15:75-90.  Back to cited text no. 4
American Association of Endodontists. Glossary of Endodontic Terms. 10th ed. Chicago: AAE; 2020.  Back to cited text no. 5
Shenoi PR, Luniya DA, Badole GP, Makade CS, Kubde R, Khode RT. Comparative evaluation of shaping ability of V-Taper 2H, ProTaper Next, and HyFlex CM in curved canals using cone-beam computed tomography: An in vitro study. Indian J Dent Res 2017;28:181-6.  Back to cited text no. 6
[PUBMED]  [Full text]  
Goldberg M, Dahan S, Machtou P. Centering ability and influence of experience when using WaveOne single-file technique in simulated canals. Int J Dent 2012;1-7.  Back to cited text no. 7
Deka A, Bhuyan AC, Bhuyan D. A comparative evaluation of root canal area increase using three different nickel-titanium rotary systems: An ex vivo cone-beam computed tomographic analysis. Contemp Clin Dent 2015;6:79-83.  Back to cited text no. 8
[PUBMED]  [Full text]  
Gambill JM, Alder M, del Rio CE. Comparison of nickel-titanium and stainless steel hand-file instrumentation using computed tomography. J Endod 1996;22:369-75.  Back to cited text no. 9
Pirani C, Iacono F, Generali L, Sassatelli P, Nucci C, Lusvarghi L, et al. HyFlex EDM: Superficial features, metallurgical analysis and fatigue resistance of innovative electro discharge machined NiTi rotary instruments. Int Endod J 2016;49:483-93.  Back to cited text no. 10
Gagliardi J, Versiani MA, de Sousa-Neto MD, Plazas-Garzon A, Basrani B. Evaluation of the shaping characteristics of ProTaper Gold, ProTaper NEXT, and ProTaper Universal in Curved Canals. J Endod 2015;41:1718-24.  Back to cited text no. 11
Al-Dhbaan AA, Al-Omari MA, Mathew ST, Baseer MA. Shaping ability of ProTaper gold and WaveOne gold nickel-titanium rotary file in different canal configurations. Saudi Endod J 2018;8:202-7.  Back to cited text no. 12
  [Full text]  
Tomer AK, Gupta R, Behera A, Mittal N, Raina AA, Ramachandran M, et al. An in vitro evaluation of remaining dentin thickness through CBCT using different file. Int J Appl Dent Sci 2018;4:09-13.  Back to cited text no. 13
Jain A, Asrani H, Singhal AC, Bhatia TK, Sharma V, Jaiswal P. Comparative evaluation of canal transportation, centering ability, and remaining dentin thickness between WaveOne and ProTaper rotary by using cone beam computed tomography: An in vitro study. J Conserv Dent 2016;19:440-4.  Back to cited text no. 14
[PUBMED]  [Full text]  
Schäfer E, Diez C, Hoppe W, Tepel J. Roentgenographic investigation of frequency and degree of canal curvatures in human permanent teeth. J Endod 2002;28:211-6.  Back to cited text no. 15
Thompson SA. An overview of nickel-titanium alloys used in dentistry. Int Endod J 2000;33:297-310.  Back to cited text no. 16
Zhou H, Peng B, Zheng YF. An overview of the mechanical properties of nickel–titanium endodontic instruments. Endod Topic 2013;29:42-54.  Back to cited text no. 17
Zupanc J, Vahdat-Pajouh N, Schäfer E. New thermomechanically treated NiTi alloys – A review. Int Endod J 2018;51:1088-103.  Back to cited text no. 18
Ruddle CJ, Machtou P, West JD. Endodontic canal preparation: New innovations in glide path management and shaping canals. Dent Today 2014;33:118-23.  Back to cited text no. 19
Singh S, Gupta T, Pandey V, Singhania H, Pandey P, Gangavane S. Shaping ability of two-shape and ProTaper Gold Files by using cone-beam computed tomography. J Contemp Dent Pract 2019;20:330-4.  Back to cited text no. 20
Özyürek T, Yılmaz K, Uslu G. Shaping ability of Reciproc, WaveOne GOLD, and Hyflex EDM single-file systems in simulated S-shaped canals. J Endod 2017;43:805-9.  Back to cited text no. 21
Coltene. The New NiTi File Generation: HyFlex; 2015. Available from: https://nam.coltene.com/pim/DOC/BRO/docbro31328-c-en-hyflex-edm-lettersenaindv1.pdf. [Last accessed on 2021 Mar 31].  Back to cited text no. 22
Singh H, Kapoor P. Hyflex CM and EDM files: Revolutionizing the art and science of endodontics. J Dent Health Oral Disord Ther 2016;5:385-7.  Back to cited text no. 23
Piheiro SR, ALcade MP, Gomes-Vivacqua N, Bramante CM, Vivan RR, Duarte MA, et al. Evaluation of apical transportation and centering ability of five thermally treated NiTi rotary systems. Int Endod J 2018;51:705-13.  Back to cited text no. 24
Ruddle CJ. The ProTaper advantage: Shaping the future of endodontics. Dent Today 2001;1-9.  Back to cited text no. 25
Wu MK, Fan B, Wesselink PR. Leakage along apical root fillings in curved root canals. Part I: Effects of apical transportation on seal of root fillings. J Endod 2000;26:210-6.  Back to cited text no. 26
Bharti R, Pandey P, Tikku AP, Chandra A. Comparative evaluation of canal transportation, centering ratio and volumetric changes associated with two rotary systems- ProTaper Next and Hyflex EDM – A CBCT study. Saudi J Oral Dent Res 2018;3:335-9.  Back to cited text no. 27


  [Table 1], [Table 2]


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