Comparison of canal transportation and centering ability of rotary protaper, one shape system and wave one system using cone beam computed tomography: An in vitro study.

AIM: The aim of the present study was to compare the canal transportation and centering ability of Rotary ProTaper, One Shape and Wave One systems using cone beam computed tomography (CBCT) in curved root canals to find better instrumentation technique for maintaining root canal geometry.
MATERIALS AND METHODS: Total 30 freshly extracted premolars having curved root canals with at least 10 degrees of curvature were divided into three groups of 10 teeth each. All teeth were scanned by CBCT to determine the root canal shape before instrumentation. In Group 1, the canals were prepared with Rotary ProTaper files, in Group 2 the canals were prepared with One Shape files and in Group 3 canals were prepared with Wave One files. After preparation, post-instrumentation scan was performed. Pre-instrumentation and post-instrumentation images were obtained at three levels, 3 mm apical, 3 mm coronal and 8 mm apical above the apical foramen were compared using CBCT software. Amount of transportation and centering ability were assessed. The three groups were statistically compared with analysis of variance and Tukey honestly significant.
RESULTS: All instruments maintained the original canal curvature with significant differences between the different files. Data suggested that Wave One files presented the best outcomes for both the variables evaluated. Wave One files caused lesser transportation and remained better centered in the canal than One Shape and Rotary ProTaper files.
CONCLUSION: The canal preparation with Wave One files showed lesser transportation and better centering ability than One Shape and ProTaper.

INTRODUCTION

Root canal shaping is a key stage of endodontic treatment with a predictive success factor if performed properly. Ideally, root canal shaping should create a continuous tapered preparation from crown to apex while maintaining the original path of the canal and keeping the foramen size as small as practical.[1] These objectives are difficult to achieve by using stainless steel hand instrumentation.[2] Thus, the introduction of rotary nickel titanium (Ni-Ti) instrumentation in endodontics was an important step in optimal root canal shaping procedure in root canal treatment.[3] This approach is quick, safer and more accuracy-oriented, with a lower risk of procedural errors compared to hand instrumentation.[4] Despite ongoing research aimed at consolidating a safe instrumentation technique, the one that promotes effective cleaning and shaping does not cause root canal transportation. The need to enlarge curved canals and at the same time preserve dental anatomy will always involve the challenge of selecting appropriate endodontic instruments. After the introduction of instruments manufactured from Ni-Ti alloys,[5] there was a significant improvement in the quality of root canal shaping, with predictable results and less iatrogenic damage, even in severely curved root canals.[6] In the past few years, important modifications to the design and manufacturing process of rotary instruments have been proposed with the aim of increasing their reliability, effectiveness and safety.[78] Ni-Ti rotary instruments such as ProTaper (Dentsply Maillefer, Ballaigues, Switzerland) have a modified cross-sectional design that resembles a K-File configuration as compared to other rotary instruments. With this cross-sectional design, it cuts dentine more electively, and may therefore reduce torsional loads. However more aggressive cutting could produce increased canal transportation.[9] Other than clinical guidelines, little information exists about these instruments. However, the risk of fracture of Ni-Ti rotary files is still a concern among clinicians.[1011] A 2008 publication described a single file technique using asymmetric reciprocation.[12] The objectives of this new technique were to reduce the working time and cost and to improve safety of the shaping procedure. Recently, Wave One (Dentsply Maillefer, Ballaigues, Switzerland), a reciprocating file system with a dedicated motor mechanism has been introduced. Wave One files are made of a special Ni-Ti alloy called M-wire that is created by an innovative thermal treatment process.[12] The benefits of M-wire are increased flexibility of the instruments and resistance to cyclic fatigue.[13] The system is designed to be used with a dedicated reciprocating motion.[14] A large rotating angle in the cutting direction (counter-clockwise) determines that the instrument advances in the canal and engages dentin into its flute to cut, while the smaller angle in the opposite direction (clockwise) allows the file to immediately disengage and safely progress along the canal path, thus reducing the screwing effect and file separation with ease.[15] Centering ability is influenced by the design of the instrument (taper, flexibility and type of alloy) and the root canal anatomy. The instrument receives lesser constraint and is more centered in cases of straighter root canals. Conventional analytical methods may employ reassembly techniques,[16] which evaluate cross-sections of root canals before and after preparation. Recently, microcomputed tomography (mCT) was introduced to evaluate the cross-sectional anatomy of roots, and also three-dimensional shapes of canals at resolutions as high as 36 mm.[171819] In addition, three-dimensional analysis using mCT indicated that canal transportation was more pronounced when shaping narrow curved canals than wider specimens.[18]

The study aims to assess the shaping potential of ProTaper instruments, One Shape system and Wave One system; and to evaluate the effect of normal canal anatomy on the final outcome of the shaped canal using different variables.

MATERIALS AND METHODS

Specimen selection

The present study consisted of 30 freshly extracted mandibular premolars with fully formed apices having angles of curvature within 0-10 degrees (according to Schneider method)[20] that had been extracted for periodontal and/or prosthetic or orthodontic reasons. The teeth were stored in saline at 4°C until use. Access cavities were prepared with round diamond burs (Diatech Dental AG, Heerbrugg, Switzerland). A size 10 K-Flexofile (Dentsply Maillefer) was placed into the canal until it was visible at the apical foramen, and the working length (WL) was established 1 mm short of this length.

Roots were embedded into modeling wax, which was simulated in mandibular arch form. The teeth were randomly divided into three experimental groups. All teeth were scanned by cone beam computed tomography (CBCT) to determine the root canal shape before instrumentation. Three sections from each tooth were obtained. The first two sections were taken 3 mm from the apical end of the root (apical level) and 3 mm below the orifice from the coronal level (15 mm from the apex) followed by a section at the mid-root level (8 mm from the apex). After initial scans, root canals were instrumented by the same operator using a standardized technique. All root canals of experimented teeth were instrumented to the WL with sizes 10, 15, 20 K-files by using a step-back technique. Canals that were larger than ISO size 20 were discarded.

Specimens in Group 1 (n = 10) were prepared with Rotary ProTaper files (Dentsply Maillefer) using 128:1 reduction geared hand piece powered by electric motor according to manufacturer's recommendations.

Specimens in Group 2 (n = 10) were prepared with One Shape file system according to manufacturer's recommendations.

Specimens in Group 3 (n = 10) were prepared with Wave One system, which has a tip size of 0.25 mm and a taper of 0.08 in apical 3 mm. It was used in slow in and out pecking motions. The flutes of the used instruments were cleaned using gauze soaked in 70% ethyl alcohol after three in and out movements. Each instrument was discarded after use in two canals, as per manufacturer's instructions.

After the use of each file, canals were irrigated with 3 mL of a 5.25% NaOCl solution in all the groups. Glyde (Dentsply Maillefer) was used as a lubricant during instrumentation, and after root canal instrumentation was completed, 1 mL of 17% ethylene diamine tetra-acetic acid was used for 1 min followed by a final flush of 3 mL of NaOCl. All instruments in Group 1 (ProTaper) and Group 2 (One Shape) were discarded after use in five canals, whereas in Group 3 (Wave One) was discarded after use in two canals.[21] It was as per recommendations by manufacturers.

Evaluation of canal transportation

The amount of canal transportation was determined by measuring the shortest distance from the edge of uninstrumented canal to the periphery of the root (mesial and distal) and then comparing this with the same measurements obtained from the instrumented images.[22] All values were measured by two evaluators and a mean value was taken.

The following formula was used for the calculation of transportation: J (a1-a2)-(b1-b2) j, where a1 is the shortest distance from the mesial edge of the root to the mesial edge of the uninstrumented canal, b1 is the shortest distance from distal edge of the root to the distal edge of the uninstrumented canal, a2 is the shortest distance from the mesial edge of the root to the mesial edge of the instrumented canal, and b2 is the shortest distance from distal edge of the root to the distal edge of the instrumented canal [Figure 1]. According to this formula, a result other than 0 indicates that transportation has occurred in the canal.[22]

Figure 1

Schematic representations of measurements of image cross sections

One-way analysis of variance followed by post hoc Tukey honestly significant difference (HSD) test were conducted to explore a significant difference in mean degree of canal transportation between the three shaping procedures. The level of significance was set at a = 0.05.

Evaluation of centering ability

The mean centering ratio indicates the ability of the instrument to stay centered in the canal.[13] It was calculated for each section by using the following ratio: (a1-a2)/(b1-b2) or (b1-b2)/(a1-a2). If these numbers are not equal, the lower figure calculated is considered as the numerator of the ratio. According to this formula, a result value of 1 indicates perfect centering.[22] One-way analysis of variance followed by Tukey HSD multiple comparisons was conducted to look at a significant difference in mean centering ratio between the three shaping procedures. The level of significance was set at a = 0.05.

CBCT picture of three different techniques are as follows [Figures 2: A1-6, B1-6, C1-6].

Figure 2

A1- CBCT image of wave one system at apical 3 mm (pre-instrumentation). A2- CBCT image of wave one system at apical 8 mm (pre-instrumentation), A3- CBCT image of wave one system at coronal 3 mm (pre-instrumentation) A4- CBCT image of wave one system at apical 3 mm (postinstrumentation). A5- CBCT image of wave one system at apical 8 mm (post-instrumentation). A6- CBCT image of wave one system at coronal 3 mm (post-instrumentation). B1- CBCT image of rotary protaper at apical 3 mm (preinstrumentation). B2- CBCT image of rotary protaper at apical 8 mm (pre-instrumentation). B3- CBCT image of rotary protaper at acoronal 3 mm (pre-instrumentation). B4- CBCT image of rotary protaper at apical 3 mm (postinstrumentation). B5- CBCT image of rotary protaper at apical 8 mm (post-instrumentation). B6- CBCT image of rotary protaper at coronal 3 mm (post-instrumentation). C1- CBCT image of one shape system at apical 3 mm (preinstrumentation). C2- CBCT image of one shape system at apical 8 mm (pre-instrumentation). C3- CBCT image of one shape system at coronal 3 mm (pre-instrumentation). C4- CBCT image of one shape system at apical 3 mm (postinstrumentation). C5- CBCT image of one shape system at apical 8 mm (post-instrumentation). C6- CBCT image of one shape system at coronal 3 mm (post-instrumentation)

RESULTS

Canal transportation

The mean transportation for Group 1 at 3 mm apical, 3 mm coronal and 8 mm apical was −0.076 mm, −0.098 mm and −0.13 mm, respectively. The mean transportation for Group 2 at 3 mm apical, 3 mm coronal and 8 mm apical was −0.04 mm, −0.18 mm and −0.105 mm, respectively. The mean transportation for Group 3 at 3 mm apical, 3 mm coronal and 8 mm apical was −0.014 mm, −0.012 mm and −0.056 mm, respectively [Table 1].

Table 1

Distribution of mean and SD values of apical transportation at 3 mm apical, 3 mm coronal and 8 mm apical in groups 1, 2 and 3

Centering ability

The mean centering ratio for Group 1 at 3 mm apical, 3 mm coronal and 8 mm apical was 0.543, 0.48 and 0.39, respectively. The mean centering ratio for Group 2 at 3 mm apical, 3 mm coronal and 8 mm apical was 0.45, 0.46 and 0.29, respectively. The mean centering ratio for Group 3 at 3 mm apical, 3 mm coronal and 8 mm apical was 0.37, 0.60 and 0.285, respectively [Table 2].

Table 2

Distribution of mean and SD values of centering ability at 3 mm apical, 3 mm coronal and 8 mm apical in groups 1, 2 and 3

DISCUSSION

In modern day endodontics so much has been debated about efficient disinfection of the root canal space with considerable removal of dentin.[2324] At the same time, the importance of preserving the natural root canal anatomy after its instrumentation has been discussed and researched upon.[25] Professionals need to balance well between the concepts of controlled instrumentation and removal of contaminated dentin.

This study evaluates the canal transportation and centering ability of three different file systems, which are Rotary ProTaper, One Shape system and Wave One system. The results obtained suggested that all the three systems used in this study for canal transportation and centering ability showed significant variations. It has been highlighted from various literatures that the canal centering ability is better within Ni-Ti instruments, instruments with less cross-sectional area and instruments with non-cutting tips.[2627]

However, there are studies suggesting that there is an increased tendency for canal transportation as the diameter of the files increases.[28] Hence, greater taper of more than 0.06 should be avoided for apical enlargement especially in curved canal. The occurrence of up to 0.15 mm of canal transportation has been considered acceptable and should not be above 0.30 mm at the apical end.[6] In the present study, the three groups showed canal transportation of −0.04 mm to −0.076 mm, which is within the acceptable range.

Rotary ProTaper files (Group 1) were used with a 128:1 reduction geared hand piece produced by electric motor according to manufacturing instructions. These files have advantages such as increased flexibility and cutting efficiency. The cutting efficiency increases due to the triangular cross-section of the instrument. Each instrument creates its own crown-down effect and the larger conicity creates space for the smaller ones thus maintaining the canal curvature with a small risk of apical transportation.[29]

In this study, ProTaper showed more canal transportation and less centering ability compared to other groups. Similar results were seen in the study conducted by Maitin et al (2013) where the shaping ability of four different rotary endodontic instruments was compared (group I — ProTaper, group II — K3, group III — Race, group IV — MTWO) using spiral CT. They concluded that canal prepared with ProTaper had more canal transportation at all the three levels of root canal.[9]

One Shape system (Group 2) has advantages such as it is a single-use, single-file system and has better cutting efficiency on continuous rotation pertinent to its cross-sectional design. It has a variable cross-section at three different levels, which progressively changes from 3 to 2 cutting edges. An additional advantage of anti-breakage control is a safety bonus, which would help the instrument to unwind to avoid separation.[30]

Wave One system (Group 3) has advantages such as single-use, single-file system to shape the root canal completely. The specially designed Ni-Ti files work in a similar but reverse “balanced force” action[12] using a pre-programmed motor to move the files in a back and forth “reciprocal motion.” It is manufactured using M-wire technology thus improving strength and resistance to cyclic fatigue to approximately four times in comparison with other brands of rotary Ni-Ti files.[31]

In the study conducted by Dhingra et al (2014), the canal curvature modification after instrumentation with One Shape rotary file and Wave One primary reciprocating file was compared, and it was concluded that canal prepared with Wave One file preserved canal shape, respected the anatomical J-shape and produced a continuously tapered funnel.[14]

Results showed that CBCT scanning is an efficient method for the assessment of root canal instrumentation techniques for its accuracy. Canal transportation and centering ability have been studied with several methodologies, but CBCT is the most used methodology at the present time because it does not require the destruction of the specimen and is reproducible. It allows the capture of several images and provides detailed information of the root canal before, during and after biomechanical preparation.[22313233]

The advantages of CBCT include three-dimensional rendition, geometrically precise images, increased sensitivity and specificity for caries, periodontal and peri-apical lesions, patient comfort, no intra-oral placement of film or sensor and soft tissue interpretation.[34]

Overall in all the three sections, Wave One system (Group 3) showed less canal transportation and better centering ability followed by One Shape (Group 2) and ProTaper (Group 1).

CONCLUSION

Within the limits of this study, all the three groups showed significant difference and it was found that Wave One single-file reciprocation has better centering ability and less canal transportation than One Shape and ProTaper.