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 Table of Contents  
ORIGINAL ARTICLE
Year : 2016  |  Volume : 13  |  Issue : 2  |  Page : 68-72

Shaping ability of single versus multi file rotary Ni-Ti systems in curved root canals


1 Department of Endodontics, Faculty of Dentistry, Misr International University, Cairo, Egypt
2 Department of Endodontics, Faculty of Dentistry, Ain Shams University, Cairo, Egypt

Date of Submission26-Mar-2016
Date of Acceptance24-Jul-2016
Date of Web Publication23-Aug-2016

Correspondence Address:
M F Obeid
Department of Endodontics, Faculty of Dentistry, Ain Shams University, Cairo
Egypt
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Source of Support: None, Conflict of Interest: None


DOI: 10.4103/1687-8574.188910

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  Abstract 


Objectives
The aim of this study is to compare the shaping ability (straightening of curved root canals, apical transportation, preparation time) of single and multi-file rotary systems during the preparation of curved root canals in extracted human molar teeth.
Methods
Sixty mandibular molars were divided according to the instrument used into three groups of 20 teeth each: group PTU (ProTaper Uneiversal), group PTN (ProTaper Next) and group OS (One Shape). Using standardized pre- and post-instrumentation radiographs, straightening of canal curvature was determined using image analysis software. A double-digital standardized radiographic technique was used to determine apical transportation. Preparation time was also recorded. Data were analysed using one-way analysis of variance (ANOVA) and post hoc Tukey's test, and significance was set at P < 0.05.
Results
During root canal preparation, no instruments fractured. The use of PTN resulted in significantly less canal straightening followed by OS then PT. There were no significant differences between the three groups with respect to apical transportation. PTN were significantly faster than PTU and OS.
Conclusion
Under the conditions of this study, ProTaper Next Protaper Universal and One Shape instruments respected original canal curvature and were safe to use. Protaper Next was the fastest among them.

Keywords: apical transportation, Canal straightening, One Shape, ProTaper Next, Shaping ability


How to cite this article:
Ghobashy A, Nagy M M, Obeid M F. Shaping ability of single versus multi file rotary Ni-Ti systems in curved root canals. Tanta Dent J 2016;13:68-72

How to cite this URL:
Ghobashy A, Nagy M M, Obeid M F. Shaping ability of single versus multi file rotary Ni-Ti systems in curved root canals. Tanta Dent J [serial online] 2016 [cited 2017 Dec 16];13:68-72. Available from: http://www.tmj.eg.net/text.asp?2016/13/2/68/188910




  Introduction Top


Root canal preparation is considered as one of the most important steps in endodontic treatment as it determines the efficacy of all subsequent steps [1]. Maintaining the original canal shape is associated with better endodontic outcomes [2].

Previous studies have shown that canal transportation leads to inappropriate dentine removal, with a high risk of straightening the original canal curvature and forming ledges in the dentine wall [3],[4] thus one of the main objectives in canal preparation is to maintain the location of the apical foramen as well as the canal curvature to allow adequate filling [5].

Nickel titanium (NiTi) rotary instruments have proven efficiency in achieving optimal root canal shaping [2],[6], with less straightening of curved root canals [7]. This can be explained by the super elasticity of NiTi rotary files that allow less lateral forces to be exerted against the canal walls [2],[8].

ProTaper Universal (PTU)1 is a multi-file system based on a sequence of files in different sizes. It combines multiple progressive taper over the length of the cutting blades, convex triangular cross sections, and noncutting tips [9] that adequately maintain the original canal curvature [10]. The ProTaper system is widely used in many countries and appears in the curricula of undergraduate dental schools thus it was used as the standard system in our study. It has three shaping and five finishing files with a total of 5 files minimally to finish root canal preparation.

One of the drawbacks of NiTi instruments is that they may fracture in clinical practice, mainly because of flexural and torsional stresses [11],[12]. Also, It was shown that instrumentation with rotary nickel-titanium (NiTi) instruments could potentially cause dentinal cracks [13].

To reduce that, manufacturers began to focus on other methods to increase the resistance to file separation and minimize dentinal defects.

Protaper Next (PTN)2 is the second generation of Protaper Universal system. Its design features include variable tapers and an off-centered rectangular cross section giving a unique asymmetric rotary motion. The manufacturer declarations that this enhances canal shaping efficiency [14]. This system is manufactured from M-Wire NiTi alloy that is proven for increased flexibility and resistance to cyclic fatigue [15]. It requires fewer instruments to fully prepare the canal and tended to cause fewer dentinal cracks compared with the ProTaper Universal instrument [16].

The latest advances in canal preparation techniques have moved toward single file concept to simplify instrumentation protocols and avoid the risk of cross-contamination. Moreover, the use of only one NiTi instrument is more cost-effective, and the learning curve is considerably reduced [17].

OneShape files 3 are used in a traditional continuous rotation motion. They have an asymmetric cross-sectional geometry (a triangle cutting edge in the apical part, 2 cutting edges in the coronal part, and a cross-section that progressively changes from 3 to 2 cutting edges between the apical and coronal parts); this design offers an optimal cutting action [18].

Investigations of the effect of multi-file and single file concept on the canal geometry are important; however, little information exists. Thus, we aimed to evaluate and compare the shaping ability (straightening of curved root canals, apical transportation, preparation time) of single and multi-file rotary systems during the preparation of curved root canals in extracted human molar teeth. The null hypothesis tested was that there is no difference in the shaping ability between the tested rotary NiTi systems.


  Materials and Methods Top


Sample preparation

Sixty extracted human mandibular molars were collected and stored in normal saline. Only molars with completely formed roots, closed apices and curved mesial roots were included in this study. Curettes were used to remove calculus mechanically from the root surfaces. Then teeth were immersed 1 hour in 3% sodium hypochlorite to disinfect them for operator safety.

Standard coronal access cavity was prepared in all teeth using Endo-Access bur 4 in a high-speed hand-piece then patency was confirmed by size 10 K-file 1. Any non-patent tooth was immediately replaced. The working length (WL) of the canal was established 1 mm short of where the file tip exits onto the root canal surface.

The distal roots with its respective coronal part were sectioned at the furcation level using a low-speed diamond saw 5 in conjunction with water then discarded.

An initial size 15 K-file 1 was placed in the mesiobuccal canal of the sample which was then mounted in a radiographic mount made of silicone based impression material 6 to fix their position. The X-ray cone 7 was aligned perpendicular to the root canal with the aid of paralleling device 8. The exposure time was identical for all radiographs with constant source-to-film and object-to-film distances to get an initial digital radiograph. The curvature of each canal was measured according to Schneider SW [19], from its corresponding periapical radiograph and recorded for later use.

Root canal instrumentation

The teeth were randomly divided into three groups (n = 20). Homogeneity of the groups with respect to the degree of the curvature was evaluated using ANOVA. All samples were prepared by the same operator using a gentle pecking up and down motion with an electric and torque-controlled endodontic motor 9 following the manufacturers' recommendations for each system.

In Group 1: Protaper Universal files (PTU) were used in which SX was used at two-thirds of the WL, S1 and S2 at WL –1 mm and F1, F2 and F3 at the WL. Once the instrument had negotiated the full WL and rotated freely, it was removed. The rotational speed of 300 rpm and 200 g cm torque was adjusted according to the manufacturer's instructions.

In Group 2: Protaper Next (PTN) files were used in the sequence X1, X2 and X3 corresponding to sizes 17/04, 25/06 and 30/07 respectively, to the WL with a rotational speed of 300 rpm and 200 g cm torque according to the manufacturer's instructions.

In Group 3: One Shape (OS) files (size 30/06) (Micro-Mega) were used at the manufactures recommended speed 350-450 rpm and 2.5 N. cm torque in pecking motion till reaching WL.

All Canals were irrigated with 2.25% NaOCl after each instrument, delivered by means of a gauge 27 needle. The time elapsed until the last instrument reached the working length in each group was recorded as working time. It included the time for instrument change and irrigation. This was measured with a stopwatch by two different observers at the same time.

At the end of the mechanical preparation the final rotary file was placed again in its corresponding canal at WL and the prepared samples were repositioned in the same mount and a final radiograph was taken with the same procedure described previously.

Evaluations

An examiner who was blind to all experimental groups carried out assessment of the canal straightening. It was determined as the difference in canal curvatures before and after instrumentation. To assess apical transformation, the final and the initial radiograph of each sample were superimposed using Adobe Photoshop 10 then compared by ImageJ analysis software 11 and the apical transportation at 0.5 mm short of the WL was measured.

An analysis of variance (ANOVA) and post hoc Tukey's test were used for comparisons of the three groups. The level of statistical significance was set at P < 0.05.


  Results Top


No instrument fractured during root canal instrumentation. With all instruments, no canal showed overextension or under-extension of the master apical rotary file. Statistical analysis of mean values for canal straightening, apical transportation and preparation time is summarized in [Table 1]. There was no statistical significant difference between all groups in respect to canal straightening, the use of PTN resulted in significantly less canal straightening followed by OS then PT. There were no significant differences between
Table 1: Statistical analysis of mean and standard deviation values for changes in canal curvature, transportation and preparation time for experimental groups

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the three groups with respect to apical transportation. PTN were significantly faster than PTU and OS.


  Discussion Top


The assessment of whether a single file used in rotation motion is proficient to maintain the original location of the canal and permit uniform enlargement in all directions is a significant concern before accepting the single file concept. Thus, evaluating apical transportation as well as canal straightening among single and multi-file systems is a worthwhile investigation of this promising approach.

Previous studies have shown that preserving the original canal shape minimizes the risk of canal transportation with a subsequently lower incidence of canal curvature straightening, the formation of ledges, and irregular apical enlargement [20]. The prevention of apical transportation and irregular foramen widening results in a well-sealed root filling with less extrusion of debris, reduced postoperative discomfort [21],[22],[23].

Sixty extracted, human molars were selected for this in vitro study. Yet, the use of extracted teeth with complex root anatomy and variable dentin structure) compromised standardization of the experimental groups, natural teeth provide conditions close to clinical situation [24].

Each system was used according to the manufacturer instructions. The final apical preparation was determined to be size 30 as larger preparations can result in canal straightening and undesirable weakening of the tooth structure, whereas smaller preparations may leave tissue remnants and infected dentin behind [25].

Several techniques can be used to evaluate the shaping ability of NiTi instruments. Serial sectioning technique is one of them but it is invasive, restricted to predetermined levels [26] and resulted with unknown loss of material [27]. The radiographic technique is non-invasive but only shows two-dimensional changes [28]. Yet, Katz and Tomase confirmed that apical transport displays the greatest changes in the mesiodistal dimension [29]. Hence, the radiographic method used by Schafer et al. [30] was applied in our study to determine canal transportation.

Despite the better flexibility of NiTi systems, the tendency to straighten during instrumentation is still a factor where the observed direction of transportation was always moving toward the convex or outer portion of the curvature.

The results of our study were in agreement with previous studies detailing magnitude and direction of apical transportation [30],[31]. Wu et al. [33] concluded that apical transportation exceeding 300 mm may have a negative impact on the sealing of the obturation. None of the transportation values measured in this study surpassed this limit.

The results of our study was in agreement with Dhingra et al. [33] that showed that PTN resulted in less canal transportation, this was attributed by the author to the presence of only two points of the rectangular cross section of PTN that touches the wall of the root canal during preparation which causes negligible transportation and more centered preparations.

Also Capar et al. [34] investigated six rotary file systems (ProTaper Next, ProTaper Universal, classical (old) One Shape, Reciproc, Twisted File Adaptive, SM2, and WaveOne) and reported no significant difference among the six groups in terms of transportation, canal curvature. These findings are consistent with the results of the present study. This may be explained as the systems were non-cutting (apical rounded safe tip) systems, leading to minimal apical transportation in curved canals [35].

Another finding of the present study was that the canal transportation values at the 2-mm level were in the range 0.07-0.09 mm. These values are less than the 'critical' canal transportation value of 0.3-mm defined by Wu et al. [21].

The least time taken for preparation was with OS as only one file was used followed by PTN because most of the teeth needed preparation only up to X2 and PTU was the last.


  Conclusions Top


Based on the results obtained following the described ex vivo approach, it can be concluded that ProTaper Next Protaper Universal and One Shape instruments respected original canal curvature and were safe to use. Protaper Next was the fastest among them.

Financial support and sponsorship

Nil.

Conflicts of interest

There are no conflicts of interest.

 
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