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Table of Contents   
ORIGINAL RESEARCH  
Year : 2014  |  Volume : 25  |  Issue : 3  |  Page : 279-283
Refinement influence in the cleaning efficacy of rotary nickel-titanium Mtwo ® instruments in oval-shaped canals by means of optical microscopy


1 Brazilian Navy, Rio de Janeiro, RJ, Brazil
2 Department of Proclin, School of Dentistry, Rio de Janeiro State University, Rio de Janeiro, RJ, Brazil

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Date of Submission04-Jun-2013
Date of Decision02-Aug-2013
Date of Acceptance16-Nov-2013
Date of Web Publication7-Aug-2014
 

   Abstract 

Objective: This study evaluated the cleaning efficacy of the rotary nickel-titanium Mtwo ® by means of optical microscopy in oval-shaped root canals and compared refinement influence using ultrasonic files or Hedströem files.
Materials and Methods: Twenty mandibular incisors were accessed, included in epoxy resin blocks, and cut transversely at 3, 6, and 9 mm from the apex. Teeth were instrumented using rotary nickel-titanium Mtwo. Digital images of the root cross sections were obtained before and after instrumentation with a digital camera attached to an optical microscope. Subsequently, samples were randomly divided into two groups for refinement. Group I was refined using ultrasonic files #30 and group II with Hedströem files #30. Final digital images of cross sections after refinement were captured and analyzed. The boundaries for the uninstrumented perimeter were measured by the software ImageTool 3.0. The data obtained were statistically analyzed by analysis of variance (ANOVA) and t-test.
Results: Mtwo instrumentation produced 41.48% of the uninstrumented perimeter. The final refinement using Hedströem and ultrasonic files decreased the uninstrumented perimeter. Significant differences (t-test, P = 0.00) were found at the three thirds after the final refinement, except for the apical third that was enhanced by Hedströem file. However, there was no statistical difference between the two refinement techniques used (P > 0.05). Mtwo instrumentation was not capable of cleaning and shaping the entire perimeter of the root canals walls.
Conclusions: The final refinement, either with ultrasonic files or with Hedströem files, resulted in significantly less uninstrumented perimeter.

Keywords: Instrumentation, Mtwo ® file, nickel-titanium file, oval canal, refinement

How to cite this article:
Pontes CM, Sassone LM, Murad CF, Fidel RS, Vilhena FS. Refinement influence in the cleaning efficacy of rotary nickel-titanium Mtwo ® instruments in oval-shaped canals by means of optical microscopy. Indian J Dent Res 2014;25:279-83

How to cite this URL:
Pontes CM, Sassone LM, Murad CF, Fidel RS, Vilhena FS. Refinement influence in the cleaning efficacy of rotary nickel-titanium Mtwo ® instruments in oval-shaped canals by means of optical microscopy. Indian J Dent Res [serial online] 2014 [cited 2020 Jul 6];25:279-83. Available from: http://www.ijdr.in/text.asp?2014/25/3/279/138286
Success of endodontic treatment relies on a sequence of operatory procedures including cleaning and shaping the root canal system. All disinfection processes performed by hand or mechanical instrumentation are associated with the use of antibacterial irrigating solutions, promote microbiologic control of the root canal system, and remove organic pulp tissue and debris. Furthermore, they provide a conic progressive shape toward the apex, which offers a conducive shape for three-dimensional filling of the root canals and all accessory canals. [1] Moreover, adequate chemomechanical preparation should help in equal dentin removal from all root canal walls, producing a uniform debridement and avoiding excessive thinning of the root structure. [2]

Anatomic complexities might be present at root canals, making it difficult to clean properly and fill the entire root canal space, such as oval-shaped canals, isthmus, and accessory canals. Due to these anatomic variations, instrumented recesses may remain after preparation. [3]

Many instruments and instrumentation techniques have been recommended in order to reduce the working time, and simplify and, above all, improve root canal preparation. Rotary nickel-titanium (NiTi) instruments are able to maintain the canal pathway even in severely curved canals, and canal preparation with these instruments is substantially faster than with hand preparation. [4]

The new Mtwo ® rotary NiTi instruments (VDW, Munich, Germany) present an S-shaped cross-sectional design and a non-cutting safety tip. Due to the variable and increasing taper, the files are allowed to work to the full working length (single-length technique). [5] Thus, these instruments are characterized by a positive rake angle with two cutting edges, which are claimed to cut dentine effectively with less energy. Mtwo instruments have an increasing pitch length from the tip to the shaft, which reduce debris accumulation and attain effective cutting action with less risk of fracture. The higher pitch allows a more delicate cut in the apex and a more aggressive cut at the coronal third, maintaining the original canal curvature. [5],[6],[7],[8]

In circular root canals, NiTi rotary files consistently produce a rapid round preparation with less transportation, centered and with less dentin loss when compared to stainless steel instruments. [9] In oval canals, cleaning and shaping become more complex; even after root canal preparation, few areas may remain uninstrumented. Additionally, NiTi rotary files may create a larger flare on one side of the canal wall due to the tendency of creating round preparations. [3]

The use of post-instrumentation adjuvants that allow cleaning the areas that are beyond the reach of the instrumentation, such as Hedströem files and ultrasonic irrigating files, might be of great help. The use of ultrasonics in endodontics has become more popular over the years and has expanded to several applications, which include access and root canal final refinement, increasing the efficacy of irrigating solutions, locating calcified canals, and removing pulp stones and intracanal obstructions and root canal and retrograde preparations. [10]

The aim of this investigation was to evaluate, by means of optical microscopy, the cleaning efficacy of the rotary NiTi Mtwo instrumentation in oval root canals (uninstrumented recesses). Another purpose of this study was to assess whether the final refinement had an influence on the cleanliness of root canals prepared by Mtwo system using ultrasonic files or Hedströem files.


   Materials and methods Top


Sample selection and preparation

Twenty freshly extracted single-rooted human mandibular incisors with a mesiodistal-flattened root were selected for this study. After extraction, the teeth were immersed in 5.25% sodium hypochlorite (NaOCl) for 30 min and stored in 0.1% thymol solution. Before experimental procedures, the teeth were washed thoroughly in water for 24 h. Only single root canals, radiographically confirmed, were used in this study. Periapical radiographs were taken in buccolingual and mesiodistal directions in each tooth. Teeth with oval-shaped canals were selected only when the ratio of the mesiodistal: buccolingual diameter was 3:1 at 5 mm from the apex. [3]

Access to the root canal system was prepared and the patency of each canal was confirmed by inserting a size 15 file (Dentsply-Maillefer, Ballaigues, Switzerland) through the apical foramen (AF). The working length was established by deducting 1 mm from the canal length, with all teeth presenting the same length. Roots were grooved at 3, 6, and 9 mm from the apex and had the crown and AF protected with utility wax. The teeth were included in epoxy resin blocks, centered, and the long axis of the teeth was positioned perpendicular to the horizontal plane and the crowns were exposed until the cementoenamel. Two holes were drilled in the resin block at each side and two self-tapping bolts were screwed through the holes. The bolts were removed and the resin blocks were cut in three locations at 3, 6, and 9 mm from the apex, resulting in four blocks representing the apical, middle, and cervical thirds of the root, and the tooth crown. Sections were made using a low-speed saw (Isomet; Buhler Ltd, Lake Bluff, NY, USA) with a diamond disk (diameter 125 mm × 0.35 mm × 12.7 mm), with continuous water irrigation in order to prevent overheating. Subsequently, the sections were reassembled and the self-tapping bolts were again screwed through the holes, ensuring a root canal space closed system. Consequently, the segments of each tooth can be separated from each other and each third can be analyzed separately [Figure 1].
Figure 1: Resin blocks after the cross-sections are cut

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Root canal lumen was filled with utility red wax, and all segments were examined under a light optical microscope (DF Vasconcelos, São Paulo, Brazil) and images of initial anatomy of each section were acquired at ×20 magnification as Tagged Image File Format (TIFF) images. Image data were saved for posterior analysis.

Instrumentation procedures and images acquisition

The specimens (N = 20) were instrumented using the engine-driven Endo Pro Torque (VK Driller Equipamentos Elétricos Ltda, São Paulo, Brazil) at 300 rpm and 2 N/cm and Mtwo rotary NiTi instruments (VDW, Munich, Germany), with all teeth inserted at the apparatus. The patency of each canal was confirmed by inserting a size 15 K-file through the AF. Following the manufacturer's instructions, all Mtwo instruments were used to the full length of the canals (single-length technique), with a gentle in-and-out motion. The instrumentation sequence was as follows:

  • A 0.04 taper size 10 instrument
  • A 0.05 taper size 15 instrument
  • A 0.06 taper size 20 instrument
  • A 0.06 taper size 25 instrument
  • A 0.05 taper size 30 instrument
  • A 0.04 taper size 35 instrument.


Once the instrument had negotiated to the end of the canal and had rotated freely, it was removed. During preparation, the canals were rinsed with 1 ml of 5.25% NaOCl delivered by a 10-ml syringe after each file, and patency was verified with a 10 K-file (Dentsply-Maillefer).

All root canal preparations were completed by one operator. All instruments were used to enlarge four canals only. Prior to and after the instrumentation procedure, the three root segments were separated and the segments were observed through a light optical microscope, whilst images were taken with a digital camera (Nikon Coolpix, Nikon, Japan).

Teeth were again inserted in the apparatus and randomly divided into two groups for final refinement: Group I (n = 10) with ultrasonic files and group II (n = 10) with Hedströem files. Final refinement of group I was conducted with #30 ultrasonic file at the Enac ultrasonic unit (Osada Enac, Tokyo, Japan), with potency set at 3, and the file was used for 3 min for each tooth, with 1 min of continuous flush of irrigation and aspiration of distilled water, followed by 1 min of irrigation with 5.25% NaOCl and finally 1 min with distilled water. In group II, manual instrumentation with Hedströem file #30 was performed during the time required for the entire root canal circumference to be instrumented. Final refinement was conducted 1 mm short of the working length in both groups. Root canals were rinsed with 1 ml of 5.25% NaOCl after each file.

After the final preparation, the root segments were again separated and the prepared root canal space was filled with utility red wax. The root canal spaces of all segments were viewed through a light optical microscope and images were taken with a digital camera and saved as TIFF images [Figure 2].
Figure 2: (a) Representative image of a cross section showing the prepared root canal space filled with utility red wax. (b) Image of a cross section viewed by ImageTool 3.0 program

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Image analysis and processing were completed using the software ImageTool 3.0 (UTHSCSA, San Antonio, TX, USA) [Figure 2]. Through this software, images of the initial perimeter (mm) of each root canal of all samples could be measured and compared to the measurements of the post-instrumentation perimeter images. The uninstrumented areas (mm) in the root canals of groups I and II were also analyzed. The percentage of uninstrumented perimeter was calculated. Statistical analysis was performed with analysis of variance (ANOVA) and t-test through the software Primer for Windows 4.0. The level of significance in all tests was set at P < 0.05.


   Results Top


There was 41.48% of uninstrumented perimeter in all root canals instrumented with Mtwo rotary files. All canals remained patent following instrumentation, and no Mtwo instrument had fractured or was permanently deformed during canal enlargement. Statistical analysis showed a significant difference in each third (P = 0.0) when comparing the initial and the final perimeters of the cervical, medium, and apical thirds [Table 1].
Table 1: Comparison of the initial and the final perimeters (mm) after Mtwo instrumentation and after the final refinement with ultrasonic file and Hedströem file (H-file) of the cervical, medium and apical thirds


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In general, the use of a final refinement resulted in significantly less uninstrumented perimeter when compared to canal preparation with Mtwo (P < 0.05). [Figure 2] and [Figure 3] show the section images of the prepared root canal. In the samples with final refinement by ultrasonic files (group I), the mean percentage of uninstrumented perimeter was 16.72%, and in the samples with final refinement by Hedströem files (group II), it was 26.66%. Comparison of the uninstrumented perimeter of each third for both refinement techniques and Mtwo instrumentation showed significant differences (P = 0.00) at the three thirds after the final refinement, except for the apical third enhanced by Hedströem file (group II) (P = 0.10) [Table 2] and Graph 1]. However, no statistical difference was found between the two final refinement techniques used (P > 0.05).
Figure 3: (a) Canal wall preparation with Mtwo files at the middle third of the root. (b) Canal wall preparation with Mtwo files and refinement with Hedströem files. (c) Canal wall preparation with Mtwo files and refinement with passive ultrasonic irrigation

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Table 2: Comparison of the perimeter of the cervical, medium, and apical thirds after the final refinement with ultrasonic file and Hedströem file


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   Discussion Top


Success of the endodontic treatment depends on the efficacy of the therapeutic procedures, as the cleaning and shaping of root canal system, which is aimed to remove all pulpal tissue, microorganisms, debris, and necrotic tissue remaining, and in promoting a conic progressive shape toward the apex. Furthermore, it enables a tridimensional filling and repair of periapical tissues. [1],[4] Root canal preparation is considered to be one of the most important phases of endodontic therapy. Therefore, several techniques and instruments, including NiTi rotary instruments, have been proposed to improve root canal cleanliness. [2]

It may be postulated that irregularly shaped canals may be more difficult to clean and shape properly, leaving uninstrumented areas that are beyond the reach of the mechanical action of endodontic instruments. [3] In agreement with this, rotary NiTi instruments may leave uninstrumented recesses in oval and flattened canals due to their tendency to produce round preparations. [3],[11] Reminiscent bacteria may survive in these recesses and put the treatment outcome at risk. This in vitro study not only evaluated the cleaning ability of Mtwo instrumentation, but also compared two different approaches used after chemomechanical preparation procedures to improve the cleanliness of the root canal system. Mandibular incisors with oval canals were used in this study due to their irregular anatomy. [3]

Recent studies have demonstrated the cleaning and shaping of root canal system through radiographs, photographs, and scanning electron microscope (SEM) analysis. However, there are few studies using real root canals in the extracted teeth, which were designed to evaluate Mtwo instrumentation before and after root canal cleaning and shaping procedures on the same specimen. The methodology used in this study was modified from those described previously by Grande et al. and Bramante et al., which effectively compared root canal anatomy of instrumented and uninstrumented canals, from cross sections. [12],[13],[14]

In order to reduce the working time and produce a more effective canal preparation, new instruments have been proposed with different designs, alloys, and tapers that increase elasticity and deformation resistance, in order to promote an easier and better shaping of irregularly shaped root canals. Previous studies reported that Mtwo instruments prepared curved canals rapidly without substantial change in the working length, preserving the original canal curvature and displaying excellent cleaning abilities. [5],[6],[8] Schäfer et al. evaluated the efficacy of Mtwo, K3, and Race instrumentation on the basis of a score evaluation for debris and smear layer using SEM. The use of Mtwo instruments resulted in significantly less remaining debris, presenting "few small conglomerations" for the apical third and "very few debris particles" for the middle and coronal thirds. Corroborating with that result, a study showed that Mtwo instruments achieved significantly better results in root canal cleanliness than the other instruments in the apical third of the canals. [14]

On the other hand, the present study results demonstrated that some areas on the intracanal walls may be left uninstrumented by using only Mtwo system, leaving 41.48% of uninstrumented perimeter. The different results obtained in our study may be due to the irregular anatomy of the selected teeth samples. However, when a final refinement was made, the mean perimeter of uninstrumented recesses decreased significantly to 16.72% in group I (ultrasonic files) and 26.66% in group II (Hedströem files).

The difficulty in effectively cleaning and disinfecting irregularly shaped canals led clinicians to pursue alternative methods or supplementary procedures to enhance root canal cleanliness. Supplementary approaches such as activation of irrigant solution have been proposed to improve root canal disinfection after canal instrumentation has been completed. Among the methods available, passive ultrasonic irrigation is probably the most used. [15],[16] Ultrasonic irrigation shows better canal debridement efficacy over the use of needle irrigation alone. Ultrasonic irrigation increases the efficacy of irrigating solutions [10],[16] and enhances significantly the chemical and mechanical action of NaOCl, improving the cleanliness of uninstrumented areas of the root canal, [17] as it increases tissue dissolution. [18],[19] Studies have reported that passive ultrasonic irrigation of the root canal, performed after instrumentation with NiTi rotary files, was capable of reducing dentin debris and smear layer of the root canal walls. [19],[20]

Our results demonstrated that final refinement with 3 min of ultrasonic irrigation and Hedströem files decreased significantly uninstrumented recesses in oval canals. Nevertheless, no technique completely cleaned the whole canal perimeter. Grecca et al. evaluated the efficiency of rotary, manual, and ultrasonic root canal instrumentation techniques in flattened root canals filled with dye. Authors' findings demonstrated that no instrumentation technique was 100% efficient to remove the dye, including K3 ® and ProTaper ® rotary systems, ultrasonic crown-down technique, and progressive manual technique. [21] Direct comparisons cannot be made because of the differences in methodological design - different instruments, lower NaOCl concentration, absence of a final refinement, and less time of ultrasonic instrumentation. Although the uninstrumented perimeter of each third for both refinement techniques demonstrated significant differences to Mtwo, the study findings revealed no significant differences in the root canal preparation at all thirds (P < 0.05) when comparing Hedström files to ultrasonic files. Conclusions on whether, once obturated, these differences will affect the final clinical success cannot be drawn and further long-term clinical studies are required to investigate this.

Under the conditions of the present ex vivo evaluation, the following conclusions can be drawn: (i) Mtwo instrumentation is not capable of cleaning the entire perimeter of root canals walls; (ii) the final refinement using Hedströem and ultrasonic files decreased uninstrumented perimeter of root canal walls, ensuring more efficient cleanliness; and (iii) the refinement with either ultrasonic or Hedströem files is equally effective for cleaning oval canals after instrumentation with rotary NiTi Mtwo.

 
   References Top

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3.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. 3
    
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6.Veltri M, Mantovani ML, Pini P, Balleri P, Grandini S. A comparative study of Endoflare-Hero ® shaper and Mtwo NiTi instruments in the preparation of curved root canals. Int Endod J 2005;38:610-6.  Back to cited text no. 6
    
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8.Bürklein S, Hiller C, Huda M, Schäfer E. Shaping ability and cleaning effectiveness of Mtwo versus coated and uncoated EasyShape instruments in severely curved root canals of extracted teeth. Int Endod J 2011;44:447-57.  Back to cited text no. 8
    
9.Glossen CR, Haller RH, Dove SB, del Rio CE. A comparison of root canal preparations using Ni-Ti hand, Ni-Ti engine driven, and K-flex endodontic instruments. J Endod 1995;21:146-51.  Back to cited text no. 9
    
10.Plotino G, Pameijer CH, Grande NM, Somma F. Ultrasonics in Endodontics: A review of the literature. J Endod 2007;33:81-95.  Back to cited text no. 10
    
11.Wu MK, Van Der Sluis LW, Wesselink PR. The capability of two hand instrumentation techniques to remove the inner layer of dentine in oval canals. Int Endod J 2003;36:218-24.  Back to cited text no. 11
    
12.Grande NM, Plotino G, Butti A, Messina F, Pameijer CH, Somma F. Cross-sectional analysis of root canals prepared with NiTi Rotary instruments and stainless steel reciprocating files. Oral Surg Oral Med Oral Pathol Oral Radiol Endod 2007;103:120-6.  Back to cited text no. 12
    
13.Bramante CM, Fidelis NS, Assumpção TS, Bernardineli N, Garcia RB, Bramante AS, et al. Heat release, time required, and cleaning ability of Mtwo ® and ProTaper universal retreatment systems in the removal of filling of material. J Endod 2010;36:1870-3.  Back to cited text no. 13
    
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15.van der Sluis LW, Wu MK, Wesselink PR. The efficacy of ultrasonic irrigation to remove artificially placed dentine debris from human root canals prepared using instruments of varying taper. Int Endod J 2005;38:764-8.  Back to cited text no. 15
    
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19.van der Sluis LW, Vogels MP, Verhaagen B, Macedo R, Wesselink PR. Study on the influence of refreshment/activation cycles and irrigants on mechanical cleaning efficiency during ultrasonic activation of the irrigant. J Endod 2010;36:737-40.  Back to cited text no. 19
    
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Correspondence Address:
Luciana Moura Sassone
Department of Proclin, School of Dentistry, Rio de Janeiro State University, Rio de Janeiro, RJ
Brazil
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Source of Support: None, Conflict of Interest: None


DOI: 10.4103/0970-9290.138286

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    Figures

  [Figure 1], [Figure 2], [Figure 3]
 
 
    Tables

  [Table 1], [Table 2]

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