Comparative evaluation of the canal curvature modifications after instrumentation with One Shape rotary and Wave One reciprocating files.

AIMS: This study compared the canal curvature modifications after instrumentation with One Shape (Micro Mega) rotary file and Wave One primary reciprocating file (Dentsply Maillefer, Ballaigues, Switzerland).
MATERIALS AND METHODS: Thirty International Organization for Standardization 15, 0.02 taper, Endo Training Blocks (Dentsply Maillefer) were used. In all specimens working length (WL) was established at the reference point 0. Glide path was achieved with Path-File 1, 2 and 3 (Dentsply Maillefer) at the WL. Group 1 were shaped with One Shape file and group 2 with Wave One files. Pre and post-digital images were superimposed, processed with Corel draw Graphic Suite X5 (Corel Corporation, Ottawa, Canada), Adobe Photoshop CS3 (Adobe Systems Inc., San Jose, CA) and Solid works student Edition software (Dassault Systems Solid Works Corp, S.A., Velizy, France).
RESULTS: Mean was more for Wave One compared with One Shape. One-way ANOVA and t-test showed a significant difference between One Shape and Wave One at 5% level of significance (P < 0.05).
CONCLUSIONS: Canals prepared with Wave One file preserved canal shape, respected the anatomical shape of J-shaped canal and produced a continuously tapered funnel.

INTRODUCTION

Root canal shaping is one of the most important steps in canal treatment.[1] It is essential in determining the efficacy of all subsequent procedures, including chemical disinfection and root canal obturation.[2] This “ideal” preparation can be a difficult task to achieve in severely curved root canals or S-shaped canals, especially with traditional stainless steel hand instruments.[34] Nickel-titanium (NiTi) instruments have been marked as a way to overcome these shortcomings. NiTi-alloy has the advantages of super elasticity and the shape memory effect,[5] which can maintain the original canal curvature and create a tapered root canal shape. Root canal working length (WL) may be defined as the distance from a coronal reference point to the point of which canal preparation and obturation should terminate. Success has been found to be greatest in teeth in which the obturation material extended to within 2 mm of the radiographic apex but did not extend beyond the radiographic apex.[6]

Canal curvature is suspected to be the predominant risk factor for instrument failure because of flexural stresses and cyclic fatigue.[127] The clinician can do very little to prevent or reduce such stresses. The reciprocating motion of the NiTi rotary instrument has been shown to decrease the impact of cyclic fatigue compared with rotational motion.[8910] Therefore, it has been recently proposed that the single-file shaping technique may 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.[10]

Now-a-days simplifying endodontic procedures with complete safety and effectiveness is our primary concern. Micro-Mega now offers One Shape, the one and only NiTi instrument in continuous rotation for quality root canal preparations. One Shape allows for curved canal negotiation with an instrumental and easy dynamic. Its non-working (safety) tip ensures an effective apical progression avoiding obstructions which are often preceded by instrument separation. Quality root canal shaping can be achieved with one single instrument with remarkable design. A root canal treatment is approximately 4 times faster than a conventional treatment with One Shape file. Overall duration of treatment is shortened. Simplification of the endodontic instrument sequence is possible.

The new Wave One NiTi single-file system has been recently introduced by Dentsply Maillefer (Ballaigues, Switzerland).[11] The system is designed to be used with a dedicated reciprocating motion motor. It consists of 3 single-use files: Small (International Organization for Standardization [ISO] 21 tip and 6% taper) for fine canals, primary (ISO 25 tip and 8% taper) for the majority of canals and large (ISO 40 and 8% taper) for large canals. The files are manufactured with M-Wire (Dentsply Tulsa Dental Specialties, Tulsa, OK) NiTi alloy.[12]

The purpose of this study was to compare the canal curvature modification of the Wave One Primary file with One Shape file system.

MATERIALS AND METHODS

Thirty ISO 15, 0.02 taper, J shaped Endo Training Blocks (Dentsply Maillefer) were used. The canal in the blocks were marked from 0 to 11 at an interval of 1 mm taking 0 as the termination/reference point for the WL. Each simulated canal was colored with Indian ink injected with a syringe. Each specimen was mounted on a stable support consisting of a rectangular slot the size of the specimen (30 mm × 10 mm) and a support for a digital camera (Nikon D70; Nikon, Tokyo, Japan) positioned centrally and at 900 to the specimen. Digital images of all specimens before instrumentation were obtained and saved as JPEG files. Specimens were then randomly assigned to 2 different groups (n = 15 each). WL was established in the canals until reference point 0 with a #10-K file (Dentsply Maillefer).

In group 1, the glide path was created with PathFile 1, 2 and 3 (Dentsply Maillefer) at the full WL until reference point 0 using Glyde (Dentsply Maillefer) as the lubricating agent. Each canal was shaped using OneShape rotary file till the WL (reference point 0) with the X-Smart Plus motor (Micro mega) set to 350 rpm and a 5-Ncm torque with a 16:1 contraangle. Canal patency was checked with a #10 K-file (Dentsply Maillefer) before the glide path, after the glidepath, before using OneShape rotary file and after OneShape rotary file.

In group 2, the glidepath was created with PathFile 1, 2 and 3 at the full WL till reference point 0 by using Glyde as the lubricating agent. Canals were shaped with Wave One Primary reciprocating files using a pecking motion till WL.

The reciprocating motor X-Smart Plus (Dentsply Maillefer) of the Wave One file was used with the manufacturer configuration setup. Canal patency was checked with a #10 K file (Dentsply Maillefer) before the glidepath, after the glidepath and before using WaveOne Primary and after shaping with WaveOne Primary.

New instruments were used in each specimen. After instrumentation, all specimens in each group were repositioned in the slot and photographed as described previously. By using digital imaging software Corel draw Graphic Suite X5 (Corel Corporation, Ottawa, Canada), Adobe Photoshop CS3 (Adobe Systems Inc. San Jose, CA) and Solid works student Edition software (Dassault Systems Solid Works Corp, S.A., Velizy, France) the pre and post-instrumentation images were processed and superimposed.

The processing of the images was done in the following steps:

Step 1 — Alignment and auto color: Alignment of the axis of blocks done with reference to the scales in the toolbox of Corel draw Graphic Suite X5 (Corel Corporation, Ottawa, Canada). Then, auto color is performed which is an image correction tool which provides better visibility and maintains the color gamut difference per pixel.

Step 2 — Inversion of images: One image is set to inversion mode to differentiate the properties of both images from each other while overlapping using Adobe Photoshop CS3 (Adobe Systems Inc. San Jose, CA).

Step 3 — Orbit shifting and superimposition with respect to the reference line: Superimposition is the placement of an image on top of an already-existing image (inversion mode) to add to the overall image effect. During the development of images, a reference measurement was undertaken into consideration for the experimental analysis based on the perpectual analysis with respect to the reference line. This is known as orbit shifting.

Step 4 — Degree of angle of curvature-One shape: Two reference points were assumed to precisely calculate the angle of curvature. Two intersection points were defined for OneShape and the angles for the same were calculated via solid works student Edition software (Dassault Systems Solid Works Corp, S.A., Velizy, France). The Angular calculation was based on the principle of geometry. Furthermore, the angles were confirmed using the trigonometric formulas for each block.

Step 5 — Degree of angle of curvature-Wave One: This is calculated in a similar manner as step 4.

Pre and post-digital images were superimposed, processed with Corel draw Graphic Suite X5 (Corel Corporation, Ottawa, Canada), Adobe Photoshop CS3 (Adobe Systems Inc. San Jose, CA) and solid works student Edition software (Dassault Systems Solid Works Corp, S.A., Velizy, France). Statistical analysis was performed with mean, standard deviation, one way ANOVA, (P < 0.05) t-test and Karl Pearson's correlation coefficient.

RESULTS

Mean for the angle of curvature was more for wave-one when compared to OneShape. Mean value for WaveOne was 62.227 when compared with 61.68 for OneShape. Standard deviation for WaveOne was 0.5922 and for OneShape 0.8273 respectively [Table 1].

Table 1

Comparison between one shape and wave one

DISCUSSION

The purpose of this study was to compare the ability of 2 NiTi instruments, the WaveOne primary and OneShape, in canal curvature modification after instrumentation. In the present study, simulated canals were chosen to standardize the conditions. Much care should be taken in the extrapolation of the results to the use of real roots due to the difference between resin and dentin.[1314] In this study, geometric variations of canal curvature in the middle plane of standardized resin blocks were analyzed through a 2-dimensional photographic method. Simulated root canals have been widely used to allow a direct analysis of post instrumentation changes in canal curvature and thus to evaluate the tendency of these techniques to maintain the original canal anatomy under standardized conditions.[15]

Ni-Ti alloys have been found to be 2-3 times more elastic than similarly manufactured stainless steel files. This property may allow Ni-Ti files to negotiate curved canals with less lateral stress but do not allow the precurving of Ni-Ti files. Whether the physical tendency of Ni-Ti files to remain straight, prevents ideal instrumentation or whether their high flexibility allows a better negotiation of curved canals despite the inability to precurve, still remains questionable.[16]

Previous studies have shown that preserving the original canal shape with a less invasive approach minimizes the risk of canal transportation with a subsequently lower incidence of canal curvature straightening, the formation of ledges and irregular apical enlargement.[1718] The prevention of apical transportation and irregular foramen widening may also lead to a well-sealed root filling with less extrusion of debris and reduced post-operative discomfort.[192021] Preservation of the original canal shape and the lack of canal aberrations are associated with increased antimicrobial and sealing efficiency[22] and reduced weakening of the tooth structure. Besides canal anatomy, other factors contribute to optimal mechanical instrumentation outcomes, such as instrument design, instrumentation sequence, rotational speed, operator's experience and the use of irrigants.[123] Recently, a new WaveOne NiTi single-file reciprocating system has been introduced to simplify root canal preparation. Only one single shaping file is required to provide the canal with an adequate size and taper. The main characteristics of this system are single use, a reciprocating action and M-Wire technology alloy manufacturing.

Even more recently, One Shape file has been introduced in which complete canal shaping is possible with only one single file in continuous rotation. The main advantages of this file are unique, sterile, economic and innovative. As a result of clinical use and extensive publication, continuous rotation is a principle known and recognized for almost 20 years. The advantages of the reciprocating motion are based on the physics law of action and reaction applied to root canal instrumentation, which results in a balanced force, as theorized by Roane et al.[24] The reciprocating movement minimizes torsional and flexural stresses, increases the canal centering ability and reduces the taper lock within the number of instrument cycles within the root canal. Recent studies showed that an alternating rotary movement is a valid option to optimize endodontic instrumentation by reducing the risk of instrument fracture and root canal deformity.[8] The use of the reciprocating motion instead of the continuous rotation method could be advantageous in terms of stresses and the time required for the preparation of curved root canals with a single use of a NiTi file.[10] In our study, the single-file technique used with the reciprocating motion enhanced the canal centering ability, leading to less invasive root canal preparation. Deviation from the original curvature can lead to excessive or inappropriate dentine removal, straightening of the canal and creation of a ledge in the dentinal wall, a biomechanical defect known as elbow, which forms the coronal to the elliptical-shaped apical seal, canals with hourglass appearance in cross-section, which requires stripping and over-preparation that weakens the tooth, resulting in fracture of the root.

The single use of endodontic instruments was recently recommended to decrease instrument fatigue and possible cross contamination, reducing the number of NiTi rotary instruments required for canal preparation. The single-file technique was also suggested as being cost-effective. The WaveOne technique is both a single-file and single-use concept. As stated, it is a single-file concept given that one single file is able to transition a secured canal to a well-shaped canal, in most instances. Further, appreciate that a single WaveOne file is frequently used to prepare multiple canals in a single furcated tooth, performing a significant amount of work. The WaveOne concept must be considered a single-use concept due to the obvious stress and wear on the active portion of the file. In conclusion, within the limits of this study, the new WaveOne NiTi Primary reciprocating single-file better maintained the original canal anatomy, with less modification of the canal curvature compared with OneShape continuous rotation file. Further investigations are needed to understand whether the better performance of the instrument may be attributed to the reciprocating motion, the variable section design, the Wire alloy or the reverse cutting blades, or a combination of these variables.[25]