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 Table of Contents  
ORIGINAL ARTICLE
Year : 2019  |  Volume : 31  |  Issue : 2  |  Page : 138-143

Cone-beam computed tomography analysis of canal transportation and centering ratio of fifth-generation nickel-titanium rotary file systems in curved root canals


1 Department of Conservative Dentistry and Endodontics, Manubhai Patel Dental College and Hospital, Vadodara, Gujarat, India
2 Department of Conservative Dentistry and Endodontics, Government Dental College and Hospital, Ahmedabad, Gujarat, India

Date of Submission17-May-2019
Date of Decision22-Jul-2019
Date of Acceptance16-Oct-2019
Date of Web Publication09-Jan-2020

Correspondence Address:
Dr. Marsrat Ibrahim Kapadwala
B 401, Magnum Plaza, Behind Pratham Upvan, Off Sunpharma Road, Vadodara - 390 012, Gujarat
India
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Source of Support: None, Conflict of Interest: None


DOI: 10.4103/endo.endo_36_19

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  Abstract 


Aim: The aim of this study is to compare canal transportation and centering ratio using of Protaper Next (PTN) (Dentsply Maillefer, Ballaigues, Switzerland) and Revo-S (RS) (MicroMega, Besancon Cedex, France) compared to Protaper Universal (PTU) (Dentsply Maillefer, Ballaigues, Switzerland) nickel-titanium rotary file systems in curved root canals using cone-beam computed tomography.
Materials and Methods: Ninety maxillary mesiobuccal first molar uncalcified canals with mature apex, curvature of 20°–45° (the Estrela method) and minimum 20-mm length were selected. The samples were randomly divided into three groups of 30 teeth each, respectively, Group I PTU, Group II PTN, and Group III RS Rotary systems and Instrumented according to the manufacturers' instructions. Pre- and post-instrumentation cone-beam tomographic scan was performed in same position to calculate canal transportation and centering ability at 2 mm, 5 mm, and 8 mm from the root apex. Statistical analysis was performed with ANOVA and Post-hoc Tukey test.
Results: PTU had maximum mean canal transportation and minimum mean centering ratio at all levels, whereas PTN showed minimum mean canal transportation and maximum mean centering ratio. The results were statistically significant.
Conclusions: In terms of canal transportation and centering ratio in the middle and coronal third of the root, PTN and RS performed better than PTU. However, in apical third, PTN performed best among all other groups.

Keywords: Canal transportation, centering ratio, Protaper next, Revo-S


How to cite this article:
Kapadwala MI, Asthana G, Parmar GJ. Cone-beam computed tomography analysis of canal transportation and centering ratio of fifth-generation nickel-titanium rotary file systems in curved root canals. Endodontology 2019;31:138-43

How to cite this URL:
Kapadwala MI, Asthana G, Parmar GJ. Cone-beam computed tomography analysis of canal transportation and centering ratio of fifth-generation nickel-titanium rotary file systems in curved root canals. Endodontology [serial online] 2019 [cited 2020 Jan 19];31:138-43. Available from: http://www.endodontologyonweb.org/text.asp?2019/31/2/138/275458




  Introduction Top


Instruments during the canal preparation should not deviate from the original pathway or else result in canal transportation.[1] Maintaining the canal centering is difficult in curved canals compared to straight canals,[2] as during instrumentation, procedural errors such as transportation of the apical foramen or the creation of zips, elbows, ledges can occur which may lead to loss of working length (WL), perforation, and separation of instruments.[3]

Transportation of the canal can occur due to the lack of flexibility and the centering ability of the instruments or due to the instrumentation technique used. Ni-Ti rotary files have significantly altered the canal shaping procedure as different changes have been introduced through consecutive generation of files. Superelsticity and shape memory of the present generation files causes less transportation in curved canal and maintains its shape.[4]

New concept fifth-generation Ni-Ti files, Protaper next (PTN), and Revo-S (RS) have been introduced with asymmetric off-centered cross sections for the root canal shaping. The PTN (Dentsply Maillefer, Ballaigues, Switzerland) is a Ni-Ti rotary file system and the manufacturer claimed that it has significant design features, which causes file to remain centered within the canal.

The RS Ni-Ti file system is another fifth-generation file with asymmetrical triangular cross section introduced by MicroMega (Besançon, France). This smaller off-centered cross-section allows more flexibility by generating snake-like swaggering movement and offers a better ability to negotiate curves.

Hence, the purpose of this in-vitro study was to evaluate canal preparation using these, novel fifth-generation PTN and RS rotary file systems compared with Protaper universal (PTU) for canal transportation and centering ability using cone-beam computed tomography (CBCT).


  Materials and Methods Top


Sample selection and preparation

Ninety curved maxillary molars extracted for periodontal or prosthetic reasons were selected for this study after taking ethical clearance (IECGDCH/CONS.3/2014). Radiographs of teeth in both the buccolingual and mesiodistal directions were taken for sample selection. Only teeth with closed apices and no significant calcifications were included. Tissue fragments and calculus were removed using ultrasonic scaler. About 0.5% NaOCl was used in wide-mouthed plastic jars for initial collection and storage medium. After immersing in the NaOCl for at least half an hour to dissolve organic tissue, then liquids were discarded and the teeth were transferred into separate jars containing physiologic saline. Access opening was done with No 2-round carbide bur (SS White, Lakewood, New Jersey) and Endo-Z bur (Dentsply Maillefer, Ballaigues, Switzerland). Distobuccal and palatal roots of all the teeth were separated using a diamond disc and contra-angled micromotor handpiece at the furcation. To determine the WL, a size #10 K-file was inserted into the remaining mesiobuccal canal until it was visible at the apical foramen. The WL of each canal was calculated to be 1 mm less than the length obtained by the initial file. The selected teeth were embedded in 5cm × 5cm circular silicon putty block. The putty block was then placed on the acrylic template that was mounted on the CBCT machine and arrows were drawn on the block as well as on the template to guide the reposition of the block for the postoperative scan. Thus, pre- and post-operative positioning of the samples was standardized. The embedded teeth were scanned using CS 9300 Carestream CBCT scanner with tube voltage of 75 KV and tube current of 6.3 MA for 20 s. The sections were 90-μthickness from apex to the canal orifice. Canal curvature angle and radius were measured according to the method described by Estrela et al. using CBCT scan [Figure 1]a.[5] Curvatures between 20° and 45° and radius between 3 mm and 8 mm were selected. According to radius, canal curvature was classified as Small radius (r ≤ 4 mm): severe curvature; Intermediary radius (r > 4 and r ≤ 8 mm): moderate curvature; Large radius (r > 8 mm): mild curvature.[5] Teeth that did not meet the criteria of this angle and radius (mild curvature) were excluded from the study.
Figure 1: (a) Measurement of canal curvature by Estrela's method by cone beam computed tomography. (b) Illustration of measurements of shortest mesial and distal distance from the canal orifice

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The specimens were randomly allocated to 1 of 3 groups (n = 30) based on the canal curvature angle and radius. Biomechanical preparation was done with torque controlled endomotor Endomate DT (NSK) using 5 ml of 3% sodium hypochlorite (Prime Dental, Maharashtra, India) as intermittent irrigation after each file. Group I was instrumented using PTU (Dentsply Maillefer, Ballaigues, Switzerland) with SX, S1, S2, F1, and F2 (Speed-300 rpm, Torque-2.5 Ncm). Group II was instrumented using PTN (Speed-350 rpm, Torque-2 Ncm) X1 and X2(Dentsply Maillefer, Ballaigues, Switzerland), and Group III was instrumented using RS system (MicroMega, Besancon Cedex, France) SC1, SC2 and SU (Speed-300 rpm, Torque-0.8 Ncm) according to the manufacturer's instructions. In all three groups, final filing was up to 25 size at apex with 6% taper. All the files were used for single time only. There was no instrument separation in any of the samples in all the groups. All the samples in all the groups were prepared by the same operator after canal preparation; each canal was irrigated with 2 ml of 17% EDTA for 1 min. Final irrigation was done with 2 ml of 3% sodium hypochlorite. Postinstrumentation scan was done using the same parameters as preoperative scan.

Evaluation of canal transportation and centering ratio

The amount of canal transportation was determined by measuring the shortest distance from the edge of uninstrumented canal to the most peripheral part of the root at 2 mm, 5 mm, and 8 mm (mesial and distal) and then comparing this with the same measurements obtained from the instrumented images [Figure 1]b.[6],[7]

The following formula was used for the calculation of transportation at each level for both the Groups:

([A1 − A2] − [B1 − B2]).

where, A1 is the shortest distance from the mesial edge of the curved root to the mesial edge of the uninstrumented canal. B1 is the shortest distance from distal edge of the curved root to the distal edge of the uninstrumented canal. A2 is the shortest distance from the mesial edge of the curved root to the mesial edge of the instrumented canal. B2 is the shortest distance from distal edge of the curved root to the distal edge of the instrumented canal. According to this formula, a result of '0' indicates no canal transportation. A result other than '0' means that transportation has occurred in the canal.

According to Gambill et al.[8] “The mean centering ratio” indicates the ability of the instrument to stay centered in the canal. This ratio was calculated for both the groups at each level using the following ratio:



Or



If these numbers are not equal, the lower figure is considered as the numerator of the ratio. According to this formula, a result of '1' indicates perfect centering. Intergroup comparison of all the specimens was made.

Statistical analysis

Statistical analysis was performed using ANOVA and Post-hoc Tukey test with the help of Statistical Packages for Social Sciences version 18.0 (SPSS Inc., Chicago, Illinois, USA) by considering P < 0.05 as statistically significant.


  Results Top


[Table 1] shows mean, standard deviation, and standard error values of canal transportation and centering ratio at three different levels of all groups. [Table 2] shows post-hoc tukey HSD test for transportation and centering ratio at three different level between all groups. Significant (P < 0.05) results are shown with red color. Hence, for both canal transportation and centering ratio, PTN performed significantly better than PTU in all 3 level (2, 5, 8 mm from apex). However, there were no significant differences between PTN and RS instruments in the apical, middle third of root.
Table 1: Mean standard deviation and standard error values of canal transportation and centering ratio at three different level of three rotary system groups

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Table 2: Post-hoc tukey honestly significant difference test for transportation and centering ratio at three different level between all groups

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  Discussion Top


Root canal shaping is one of the most important steps in canal treatment. It is essential in determining the efficacy of all subsequent procedures, including chemical disinfection and root canal obturation. Shaping is largely influenced by highly variable root canal anatomy. Opposed to most root canals that are curved, the endodontic instruments are made from straight blanks. They have a tendency of straightening the canal during preparation.[9] These aberrant results of root canal shaping make it difficult for clinicians to remove infected tissues and achieve a properly sealed root canal obturation and might consequently increase the risk for root canal treatment failure.[10] Many factors have been identified that exert an impact on the incidence of canal transportation and canal centering ability including file design and metallurgy.[11] Hence, here we have compared the canal transportation and centering ratio caused by different file generations, design, and metallurgy as PTU is the second-generation file system, whereas PTN and RS are the fifth-generation file systems having different metallurgy and cross-section designs.

In our study, we selected natural teeth as there were certain drawbacks of using rotary instruments in resin blocks. Hülsmann et al. reported that the use of simulated canals in resin blocks does not reflect the results of the instruments in root canals of natural teeth because of the hardness and abrasion behavior of acrylic resin and root dentine may not be identical.[12]

Mesiobuccal root canals of extracted maxillary molars were used in the present study as they usually present an accentuated curvature and mesiodistal flattening.[13] These characteristics are additional shortcomings during chemo-mechanical instrumentation which make cleaning and shaping of these canals difficult specifically isthmus areas.[12]

PTN showed the most promising result among the three groups. This result was similar to the result observed by Saberi et al. and Elnaghy.[14],[15] Various studies show similar results that PTN is better in terms of transportation and centering ratio when compared with PTU.[16],[17],[18] This may be due to decreased flexibility of PTU. The flexibility of the instrument depends on complex interrelationships between different parameters such as instrument design, core diameter, pitch, metallurgical properties, and surface treatments of instruments. An increase in taper is related to the increase in core diameter, increase in the force applied against the walls and decrease in flexibility as in PTU.[19] The results are obtained in conformity to Bonaccorso et al.,[20] and Javaheri and Javaheri [21] who found PTU to produce more apical transportation than any other instrument.

PTN showed the least transportation and maximum centering ratio at 2 mm (P < 0.05) because they remove less amounts of dentin compared with other instruments, with an apical taper of 0.08. This may be because of the offset asymmetric cross-section design of this instrument, and progressive percentage tapers on a single file.[22] The off-set design further minimizes the engagement between the file and dentin.[23] Moreover, PTN instruments are manufactured from M-Wire alloy, which has been proposed to improve file flexibility and resistance to cyclic fatigue while retaining cutting efficiency.[24]

In our study at apical third PTN showed minimum transportation and maximum centering ratio, but in middle and cervical third, PTN and RS showed similar better results. This can be attributed to the beneficial effects of instrumentation techniques of both the files, which are fifth-generation off-set files having asymmetrical cross-section. This increases the available volume for upward debris elimination. Both have modified guiding tip, progressive pitch and variable taper of 6° along the length. The comparable apical transportation was less and mean centering ability was superior of RS than PTU which may be due to asymmetrical cutting profile of RS which facilitates penetration by a snake-like swaggering movement and offers a root canal shaping and apical finishing that is closely adapted to the anatomical and ecological criteria of the canal. Furthermore, RS has one cutting edge which makes it less aggressive as compared to others.[25]

Apical transportation of more than 300 μm can have a negative impact on the seal of the obturation and subsequent treatment failure.[26] In this study, we found that at any level the transportation did not exceed the critical limit. Thus, we can say that all three files are safe to use and will not cause transportation beyond the critical limit.

However, this study does not agree with the Bürklein et al.,[11] Saber et al.[27] and Capar et al.[22] who evaluated the transportation produced by different files systems including PTN, PTU and concluded that no significant differences were found between the file systems in terms of canal transportation. These studies might have demonstrated a significant difference if more sample size, angle, and uniform distribution of angle and radius had been done.


  Conclusions Top


Within the limitation of this study, we found in terms of canal transportation and centering ratio, in the apical, middle, and coronal third of the root, PTN performed best among all three files. In middle and apical third, RS also showed comparable results with PTN. This is an in vitro study, therefore, it is possible that the inferences from the study might not correlate completely, with similar situations clinically. Further studies are needed to clarify the clinical performance of the new fifth-generation files.

Financial support and sponsorship

Nil.

Conflicts of interest

There are no conflicts of interest.



 
  References Top

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Schäfer E. Cleaning and shaping the root canal. Dent Clin North Am 1974;18:269-96.  Back to cited text no. 1
    
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Schäfer E, Tepel J, Hoppe W. Properties of endodontic hand instruments used in rotary motion. Part 2. Instrumentation of curved canals. J Endod 1995;21:493-7.  Back to cited text no. 2
    
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Deplazes P, Peters O, Barbakow F. Comparing apical preparations of root canals shaped by nickel-titanium rotary instruments and nickel-titanium hand instruments. J Endod 2001;27:196-202.  Back to cited text no. 3
    
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Ingle JI, Himel VT, Hawrish CE, Glickman GN. Endodontic cavity preparation. In: Ingle JI, Bakland LK, editors. Endodontic. 5th ed. Ontario, Canada: BC Decker; 2002. p. 502.  Back to cited text no. 4
    
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Estrela C, Bueno MR, Sousa-Neto MD, Pécora JD. Method for determination of root curvature radius using cone-beam computed tomography images. Braz Dent J 2008;19:114-8.  Back to cited text no. 5
    
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Guelzow A, Stamm O, Martus P, Kielbassa AM. Comparative study of six rotary nickel-titanium systems and hand instrumentation for root canal preparation. Int Endod J 2005;38:743-52.  Back to cited text no. 6
    
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Scha¨ Fer E, Dammaschke T. Development and sequelae of canal transportation. Endod Top 2009;15:75-90.  Back to cited text no. 7
    
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Peters OA. Current challenges and concepts in the preparation of root canal systems: A review. J Endod 2004;30:559-67.  Back to cited text no. 9
    
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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. 10
    
11.
Bürklein S, Schäfer E. Critical evaluation of root canal transportation by instrumentation. Endod Top 2013;29:110-24.  Back to cited text no. 11
    
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Hülsmann M, Gressmann G, Schäfers F. A comparative study of root canal preparation using flexMaster and HERO 642 rotary Ni-Ti instruments. Int Endod J 2003;36:358-66.  Back to cited text no. 12
    
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Taşdemir T, Aydemir H, Inan U, Unal O. Canal preparation with hero 642 rotary Ni-Ti instruments compared with stainless steel hand K-file assessed using computed tomography. Int Endod J 2005;38:402-8.  Back to cited text no. 13
    
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Saberi N, Patel S, Mannocci F. Comparison of centring ability and transportation between four nickel titanium instrumentation techniques by micro-computed tomography. Int Endod J 2017;50:595-603.  Back to cited text no. 14
    
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Elnaghy AM. Cyclic fatigue resistance of ProTaper next nickel-titanium rotary files. Int Endod J 2014;47:1034-9.  Back to cited text no. 15
    
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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. 16
    
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Wu H, Peng C, Bai Y, Hu X, Wang L, Li C. Shaping ability of ProTaper universal, WaveOne and ProTaper next in simulated L-shaped and S-shaped root canals. BMC Oral Health 2015;15:27.  Back to cited text no. 17
    
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Pasqualini D, Alovisi M, Cemenasco A, Mancini L, Paolino DS, Bianchi CC, et al. Micro-computed tomography evaluation of ProTaper next and BioRace shaping outcomes in maxillary first molar curved canals. J Endod 2015;41:1706-10.  Back to cited text no. 18
    
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Kim HC, Kwak SW, Cheung GS, Ko DH, Chung SM, Lee W. Cyclic fatigue and torsional resistance of two new nickel-titanium instruments used in reciprocation motion: Reciproc versus WaveOne. J Endod 2012;38:541-4.  Back to cited text no. 19
    
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Bonaccorso A, Cantatore G, Condorelli GG, Schäfer E, Tripi TR. Shaping ability of four nickel-titanium rotary instruments in simulated S-shaped canals. J Endod 2009;35:883-6.  Back to cited text no. 20
    
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Javaheri HH, Javaheri GH. A comparison of three Ni-Ti rotary instruments in apical transportation. J Endod 2007;33:284-6.  Back to cited text no. 21
    
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Capar ID, Ertas H, Ok E, Arslan H, Ertas ET. Comparative study of different novel nickel-titanium rotary systems for root canal preparation in severely curved root canals. J Endod 2014;40:852-6.  Back to cited text no. 22
    
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24.
Lopes HP, Gambarra-Soares T, Elias CN, Siqueira JF Jr., Inojosa IF, Lopes WS, et al. Comparison of the mechanical properties of rotary instruments made of conventional nickel-titanium wire, M-wire, or nickel-titanium alloy in R-phase. J Endod 2013;39:516-20.  Back to cited text no. 24
    
25.
Deepak J, Ashish M, Patil N, Kadam N, Yadav V, Jagdale H, et al. Shaping ability of 5th generation Ni-Ti rotary systems for root canal preparation in curved root canals using CBCT: An in vitro study. J Int Oral Health 2015;7:57-61.  Back to cited text no. 25
    
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[PUBMED]  [Full text]  
27.
Saber SE, Nagy MM, Schäfer E. Comparative evaluation of the shaping ability of ProTaper next, iRaCe and hyflex CM rotary NiTi files in severely curved root canals. Int Endod J 2015;48:131-6.  Back to cited text no. 27
    


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