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Year : 2020  |  Volume : 32  |  Issue : 2  |  Page : 67-71

Centering ability of three different mechanized files while instrumenting oval canals

Department of Conservative Dentistry and Endodontics, Nair Hospital Dental College, Mumbai, Maharashtra, India

Date of Submission14-Nov-2019
Date of Decision21-Feb-2020
Date of Acceptance13-Mar-2020
Date of Web Publication18-Jun-2020

Correspondence Address:
Ajinkya Mansing Pawar
301, Department of Conservative Dentistry and Endodontics, Nair Hospital Dental College, Mumbai - 400 008, Maharashtra
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Source of Support: None, Conflict of Interest: None

DOI: 10.4103/endo.endo_77_19

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Purpose: The present study evaluated the centering ability of rotary ProTaper NEXT (PTN; Dentsply Tulsa Dental, Tulsa, OK), reciprocating WaveOne (WO; Dentsply Maillefer, Ballaigues, Switzerland) and vibratory Self-Adjusting File (SAF; ReDent Nova, Ràanana, Israel) when used for instrumenting mandibular premolars with oval canals.
Materials and Methods: Ninety oval canals (confirmed using radiovisography, buccolingual dimensions were × 2.5 the mesiodistal canal dimensions) were acquired, preinstrumentation cone-beam computed tomography (CBCT) was taken, and divided into three groups (n = 30) for root canal instrumentation: group 1 – PTN; Group 2 – WO; and Group 3 – SAF. The samples were then subjected to postinstrumentation CBCT. The pre- and postinstrumentation scans were compared at 3 mm, 6 mm, and 9 mm from the apex to obtain the centering ability ratio of the three files. The data collected were analyzed using the one-way analysis of variance test and Duncan's multiple comparison tests.
Results: The ratio obtained at 6 mm and 9 mm from the apex did not differ for the mesiodistal dimensions (P > 0.05), but a significant difference was observed when the buccolingual dimensions were considered (P < 0.001). The PTN and WO instrumentation were associated with a very high ratio for buccolingual dimensions. However, SAF instrumentation resulted in well-centered preparation for both the dimensions at 6 mm and 9 mm (P < 0.001). At 3 mm from the apex, the files did not differ in canal preparation (P > 0.05).
Conclusion: The SAF instrumentation results in centered preparation when used for instrumenting nonround root canals.

Keywords: Canal-centering ability, cone-beam computed tomography, instrumentation, oval canals, reciprocating files, rotary files

How to cite this article:
Pawar AM. Centering ability of three different mechanized files while instrumenting oval canals. Endodontology 2020;32:67-71

How to cite this URL:
Pawar AM. Centering ability of three different mechanized files while instrumenting oval canals. Endodontology [serial online] 2020 [cited 2020 Oct 24];32:67-71. Available from: https://www.endodontologyonweb.org/text.asp?2020/32/2/67/287073

  Introduction Top

Root canal instrumentation has always been challenging because of the complexity of the root canal anatomy and its associated variations. The horizontal dimensions of the root canal are classified as a round, oval, long oval, flattened, and irregular.[1] It is a well-known fact that the canals are rarely circular and often oval.[2] In teeth with oval cross-section, it is preferable to use an instrument that can maintain the original anatomy of the root canal, preserve maximum dentin thickness, and enhance the cleaning of buccal and lingual recesses.[3]

Although root canal preparation instruments have been progressively developed and optimized, a complete mechanical debridement of the root canal system is rarely achievable.[4],[5] Rotary/reciprocating instruments, regardless of their type and form produce a preparation with a round outline, which in most cases does not coincide with the outline of the root canal.[6] Similarly, popular manual instrumentation techniques, such as the “balanced force” technique, usually implement a rotation movement of files, which also results in creating a round root canal preparation.[7] Consequently, incomplete shaping is usually observed when the canal outline deviates from a round form. Oval canals, which are the simplest deviation from a round outline, can be found in all types of teeth. The oval outline is more pronounced in the mid root and decreases toward the apex, where the outline is almost round.[2]

Many preparation techniques and instruments have been advocated to facilitate the preparation of oval root canals.[8],[9],[10] Nevertheless, incomplete preparations were observed in most studies, as the files did not remain centered.[8],[9],[10],[11],[12],[13],[14]

This study was an attempt to carry out an ex vivo evaluation, the centering ability of three different file systems: ProTaper NEXT (PTN; Dentsply Tulsa Dental, Tulsa, OK) (rotary), WaveOne (WO; Dentsply Maillefer, Ballaigues, Switzerland) (reciprocating), and Self-Adjusting Files (SAFs; ReDent Nova, Ràanana, Israel) (vibratory). Cone-beam computed tomography (CBCT; ProMax three-dimensional [3D] Mid Planmeca Oy, Helsinki, Finland) was used as the main experimental tool to evaluate the centering ability of the files when used for root canal instrumentation in oval canals.

  Materials and Methods Top

A total of 90 single-rooted mandibular premolars with fully formed apices and single oval canals confirmed by taking periapical radiographs by exposing both mesiodistal and buccolingual sides (buccolingual dimensions were × 2.5 the mesiodistal canal dimensions) were selected. The teeth were then mounted on wax blocks stabilizing them and exposed to preinstrumentation CBCT scan.

After the preinstrumentation scan, the specimens were subjected to a standard oval access cavity preparation followed by checking the canal patency using 10# K-File. All the specimens facilitated the placement of #25 K-file passively till the apex (large canals). The samples were then randomly divided into three groups (n = 30) for root canal instrumentation: Group 1 – rotary PTN (PTN X1, X2, X3, and X4; Dentsply Tulsa Dental, Tulsa, OK); Group 2 – reciprocating WO (WO Large; Dentsply Maillefer, Ballaigues, Switzerland); and Group 3 – SAF (SAF 2 mm; ReDent, Raanana, Israel). The shaping procedure for the files in all three groups was carried out according to the manufacturer's instructions.


Group 1 – ProTaper NEXT instrumentation

A total of 30 teeth were instrumented by rotary PTN instruments, used according to the manufacturer's instructions using a gentle in-and-out motion with a torque-controlled endodontic motor (X-Smart Plus, Dentsply Maillefer, Ballaigues, Switzerland) at 300 rpm and a torque of 2.6 Ncm. The orifice of the canal in each sample was flared using Gates-Glidden (GG) drills (1–3), followed by the use of X1, X2, X3, and X4 files. The canal was irrigated after each file using 2.5% sodium hypochlorite (NaOCl; Prime Dental Products, Mumbai, India). Ethylenediaminetetraacetic acid (EDTA; Prime Dental Products, Mumbai, India) gel was used as a lubricant for each file. The instrumentation was carried out till the ×4 (40.06) file reached the apex. After the completion of the shaping procedure, a final flush was applied using 5 mL 17% EDTA for 1 min and 5 mL 2.5% NaOCl for 1 min followed by the final rinse with 5 mL distilled water.

Group 2 – WaveOne instrumentation

A total of 30 specimens were instrumented by WO Large files (40/0.08, Dentsply Maillefer, Ballaigues, Switzerland) using X-Smart Plus Endo Motor (Dentsply–Maillefer). The large WO file was selected according to the manufacturer's instructions; if a # 20 K-file or larger reached the apex passively. In all the samples, #25 K-file reached the working length passively. The root canal orifices were flared using GG drills as in Group 1. WO instrumentation with pecking motion followed this. After every three pecks, the file was withdrawn, cleaned off debris, the canal was irrigated, recapitulated by a # 15 K-file, and the file was re-introduced into the canal again. The canal was irrigated with 2.5% NaOCl (Prime Dental Products, Mumbai, India). The instrumentation was carried out in the above manner until the file reached its working length. After completion of the shaping procedure, the canal underwent a final flush as in Group 1.

Group 3 – Self-adjusting file instrumentation

A total of 30 specimens were instrumented by the 2 mm SAF with an in-and-out transline motion using EndoStation (SAFpro; ReDent Nova, Ràanana, Israel) which is a preprogramed endomotor which is designed to use the SAF at a frequency of 5000 movements/min with an amplitude of 0.4 mm. Continuous irrigation with 2.5% NaOCl (Prime Dental Products, Mumbai India) was applied through the file using the inbuilt peristaltic pump at a rate of 4 mL/min. The instrumentation was carried out in each sample for 4 min. After instrumentation, a final flush was applied as in Group 1.

Following the instrumentation of all the three groups, the samples were exposed to a second CBCT scan for obtaining postinstrumentation images. The pre- and postinstrumentation scans obtained underwent 3D reconstruction using Blender version 2.69 (Blender Foundation, Netherlands) for further analysis.

Cone-beam computed tomography scan specifications

The pre- and postinstrumentation CBCT scans were done using ProMax 3D Mid (Planmeca Oy, Helsinki, Finland). The samples were mounted onto wax blocks for stabilizing them and were exposed to the CBCT imaging with 90 kv and 8 mA with a field of view of 4.5 cm × 4.5 cm and an isotropic resolution of 0.1 mm, resulting in approximately 400–450 slices per root with the exposure time being 12.28 s. The measurements of the samples in the results were calculated using inbuilt software Romexis version 3.20 (Planmeca Oy, Helsinki, Finland).

Centering ability calculation

Centering abilities of the three different files when used for shaping root canals were carried out using a formula proposed by Gambill et al.,[14] a mesiodistal ratio a1-a2/b1-b2, and as the canals were oval, another variant of buccolingual ratio (c1-c2/d1-d2) was added [the measurements are illustrated in [Figure 1]. If the numbers were not equal, the lower figure was taken as the numerator. The result of these ratios to 1 indicates the perfect centering of the file. The above measurements were recorded in millimeters (mm) for the coronal, middle, and apical thirds.
Figure 1: Schematic diagram exhibiting oval canal and marking of values for calculating the centering ability of the files for mesiodistal as well as buccolingual parameters. Color RED denotes preinstrumentation, and BLUE denotes postinstrumentation

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Statistical analysis

Data analysis was done using the Statistical Package for the Social Sciences Software (SPSS) version 20 (SPSS Inc., Chicago, IL, USA). Quantitative data are presented with the help of mean and standard deviation. Comparison between the study groups was made with the help of the one-way analysis of variance test and Duncan's multiple comparison tests. P < 0.05 is taken as significant level difference.

  Results Top

At 6 mm and 9 mm sections from the apex, for the mesiodistal dimensions, the ratios were not statistically significant different between the three files. However, for the buccolingual dimensions at these two levels, the ratios exhibited a significant difference (P < 0.001). At the 3 mm from the apex, there was no difference seen (P > 0.05) between the files [Figure 2]. Duncan's multiple comparison tests to find out the most significant group revealed that PTN and WO exhibited significantly high ratio buccolingually, suggesting the failure of the files to reach the canal recesses. Overall ratios (mesiodistal and buccolingual) were close to one in Group 3 (SAF instrumented) for sections at 6 mm and 9 mm from the apex. The mean-wise presentation of the data is shown in [Figure 3].
Figure 2: Representative images of the pre- and post-operative centering ability of the files after instrumenting oval canals at 6 and 3 mm from the apex. (a) ProTaper NEXT, (b) WaveOne, and (c) Self-Adjusting File. Color RED denotes preinstrumentation, and BLUE denotes postinstrumentation

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Figure 3: The mean-wise comparison of the ratios for centering ability in the coronal, middle, and apical sections. At 9 mm, 6 mm, and 3 mm from the apex the files remained well centered in the mesiodistal dimensions. Nevertheless, there was a significant difference between the groups considering the buccolingual dimensions. The self-adjusting file among the three files tested was the only file, which remained well centered in both the dimensions (P < 0.01)

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  Discussion Top

Canal shaping is a critical aspect of endodontic treatment because it influences the outcome of subsequent phases of the root canal irrigation, obturation, and the overall success of the treatment itself. There has been constant development and evolution in the endodontic instruments to result in the most desired shape for ease of obturation and also preventing any endodontic mishaps. This evolution overcame the limitations of conventional hand files such as stiffness, more cutting of the outer walls in curved root canals, and also the tedious and time-consuming factor.[15]

A study design that allows for standardization and facilitates simulation of the clinical situation is desirable when evaluating the quality of the root canal preparation. CBCT allows increased precision and acceptable resolution to produce a 3D image with no destruction of the sample, with before and after comparison of the samples.[16] Hence, a nondestructive method by CBCT imaging was used for evaluation in the presentin vitro study.

Complete mechanical debridement of the root canal system is rarely achieved.[4],[5] One of the main reasons is the geometrical asymmetry of the root canal; incomplete shaping is usually observed when the canal outline deviates from a round form. Wu and Wesselink [17] determined that it may be difficult to instrument the entire wall in teeth with oval-shaped canals and that uninstrumented buccal and/or lingual recesses may remain. Flat oval root canals are common in the distal roots of lower molars, upper and lower bicuspids, and lower incisors and canines.[2] Oval canals have been described, as those exhibiting a maximum cross-sectional diameter of up to two times greater than the minimum diameter; long oval canals have a maximum diameter of 2–4 times greater than the minimum diameter.[1] In canals with these anatomical conditions, hand and rotary instruments have been reported to leave untouched fins or recesses.[8],[11]

Nickel–Titanium (Ni-Ti) rotary endodontic files leave around 40%–60% of the oval root canal surface unaltered is reported in the literature.[13],[18],[19] De Deus et al.[20] and ElAyouti et al.[12] have also reported the ineffectiveness of rotary endodontic files in shaping long oval and flat canals. Weiger et al.[11] reported that even with the most meticulous preparation, between 44% and 68% of the canal surface remained unprepared in long oval canals, resulting in noncentered root canal instrumentation. Currently used rotary/reciprocating files imposed a circular “bore-”shaped preparation on these kinds of canals. When compared with rotary Ni–Ti instrumentation, SAF has been reported to leave less unprepared area and is significantly more effective in disinfecting oval canals in vitro.[6] In the current study, SAF resulted in a well-centered preparation of oval canals in mesiodistal and buccolingiual dimensions, thus addressing most of the root canal perimeter. However, the rotary and reciprocating file resulted in better mesiodistal preparation but exhibited a higher ratio buccolingually. SAF is hollow and gets compressed in an unprepared canal, thus enabling the file to adapt to the cross-sectional shape of the canal. This property is well appreciated while treating irregularly shaped root canals. In cases with oval canals, the file gets compressed mesiodistally, where the dimensions are smaller, leading to buccolingual expansion.[6],[21] Paqué et al.[13] studied the efficacy of shaping oval root canals in distal roots of mandibular molars and found that SAF left 23% of the canal wall unaffected by the procedure, whereas rotary files when used with circumferential motion and brushing, almost left 69% of the canal wall unaffected by the procedure. The results in the current study with rotary instrumentation do not come as a surprise, because it has already been widely demonstrated that rotary instruments in reaming motion do not prepare all root canal walls, especially in oval-shaped canals. Both rotary and reciprocating instruments tend to actively pack canal recesses with debris [6],[22] and this effect is more pronounced when reciprocating files are used as compared with a traditional multifile system.[23] Such packed debris cannot be washed out even with passive ultrasonic irrigation.[22],[23] Consequently, such packed debris prevents root-filling material from adapting to the canal wall in uninstrumented canal recesses.[20] In contrast, the SAF system has been reported to effectively instrument and clean such recesses [20] and is almost free of the debris packing phenomenon.[23] In the apical third, all files resulted in a well-centered preparation (P > 0.05), as most root canals present a circular cross-section at the apical third.[2]

  Conclusion Top

The SAF cleaning-shaping-irrigation system resulted in significantly more centered preparation, addressing almost entire perimeter of nonround (oval) canals, compared to rotary and reciprocating instrumentation.

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Conflicts of interest

There are no conflicts of interest.

  References Top

Jou YT, Karabucak B, Levin J, Liu D. Endodontic working width: Current concepts and techniques. Dent Clin North Am 2004;48:323-35.  Back to cited text no. 1
Wu MK, R'oris A, Barkis D, Wesselink PR. Prevalence and extent of long oval canals in the apical third. Oral Surg Oral Med Oral Pathol Oral Radiol Endod 2000;89:739-43.  Back to cited text no. 2
Hülsmann M, Peters OA, Dummer PM. Mechanical preparation of root canals: Shaping goals, techniques and means. Endod Top 2005;10:30-76.  Back to cited text no. 3
Uzun O, Topuz O, Aydýn C, Alaçam T, Aslan B. Enlarging characteristics of four nickel-titanium rotary instrument systems under standardized conditions of operator-related variables. J Endod 2007;33:1117-20.  Back to cited text no. 4
Rödig T, Hülsmann M, Kahlmeier C. Comparison of root canal preparation with two rotary NiTi instruments: ProFile. 04 and GT Rotary. Int Endod J 2007;40:553-62.  Back to cited text no. 5
Metzger Z. The self-adjusting file (SAF) system: An evidence-based update. J Conserv Dent 2014;17:401-19.  Back to cited text no. 6
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Metzger Z, Solomonov M, Kfir A. The role of mechanical instrumentation in the cleaning of root canals. Endo Topics 2013;29:87-109.  Back to cited text no. 10
Weiger R, ElAyouti A, Löst C. Efficiency of hand and rotary instruments in shaping oval root canals. J Endod 2002;28:580-3.  Back to cited text no. 11
ElAyouti A, Chu AL, Kimionis I, Klein C, Weiger R, Löst C. Efficacy of rotary instruments with greater taper in preparing oval root canals. Int Endod J 2008;41:1088-92.  Back to cited text no. 12
Paqué F, Balmer M, Attin T, Peters OA. Preparation of oval-shaped root canals in mandibular molars using nickel-titanium rotary instruments: A micro-computed tomography study. J Endod 2010;36:703-7.  Back to cited text no. 13
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. 14
Zarei M, Javidi M, Erfanian M, Lomee M, Afkhami F. Comparison of air-driven vs. electric torque control motors on canal centering ability by ProTaper NiTi rotary instruments. J Contemp Dent Pract 2013;14:71-5.  Back to cited text no. 15
Mao T, Neelakantan P. Three-dimensional imaging modalities in endodontics. Imaging Sci Dent 2014;44:177-83.  Back to cited text no. 16
Wu MK, Wesselink PR. A primary observation on the preparation and obturation of oval canals. Int Endod J 2001;34:137-41.  Back to cited text no. 17
Paqué F, Ganahl D, Peters OA. Effects of root canal preparation on apical geometry assessed by micro-computed tomography. J Endod 2009;35:1056-9.  Back to cited text no. 18
Barbizam JV, Fariniuk LF, Marchesan MA, Pecora JD, Sousa-Neto MD. Effectiveness of manual and rotary instrumentation techniques for cleaning flattened root canals. J Endod 2002;28:365-6.  Back to cited text no. 19
De-Deus G, Reis C, Beznos D, de Abranches AM, Coutinho-Filho T, Paciornik S. Limited ability of three commonly used thermoplasticized gutta-percha techniques in filling oval-shaped canals. J Endod 2008;34:1401-5.  Back to cited text no. 20
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