Comparison of shaping ability of the Reciproc Blue and One Curve with or without glide path in simulated S-shaped root canals

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Restor Dent Endod. 2022;47.e3

Publication date (electronic) : 2022 December 28

doi : https://doi.org/10.5395/rde.2022.47.e3

Vincenzo Biasillo^1,†, Raffaella Castagnola^1,†, Mauro Colangeli¹, Claudia Panzetta², Irene Minciacchi¹, Gianluca Plotino³, Simone Staffoli⁴, Luca Marigo^1,‡, Nicola Maria Grande^1,‡

¹Department of Operative Dentistry and Endodontics, Fondazione Policlinico Universitario A. Gemelli – IRCCS, School of Dentistry, Università Cattolica del Sacro Cuore, Rome, Italy.

²Physics Department, Università Cattolica del Sacro Cuore, Rome, Italy.

³Private practice, Rome, Italy.

⁴Department of Oral and Maxillo-Facial Science, Sapienza University of Rome, Rome, Italy.

Correspondence to Raffaella Castagnola, DDS, PhD. Adjunt Professor, Department of Operative Dentistry and Endodontics, Fondazione Policlinico Universitario A. Gemelli – IRCCS, School of Dentistry, Università Cattolica del Sacro Cuore, Largo Agostino Gemelli 8, Rome 00168, Italy. raffaellacastagnola@inwind.it

^†Vincenzo Biasillo and Raffaella Castagnola equally contributed to this work.

^‡Luca Marigo and Nicola Maria Grande equally contributed to this work.

Received 2021 March 03; Revised 2021 April 02; Accepted 2021 April 12.

Abstract

INTRODUCTION

The introduction of nickel-titanium (NiTi) rotary instruments has improved root canal preparation. NiTi alloy has the advantages of super-elasticity and shape memory effects, which allows the maintenance of the original canal curvature and creates a tapered root canal shape [1]. The reciprocating motion and single-file NiTi systems allow root canal preparation to be developed by using a single instrument, thereby requiring less time than full-sequence rotary systems [2]. The reciprocating motion of these NiTi systems relieves stress on the instrument by counter-clockwise (cutting action) and clockwise (release of the instrument) movements, thereby extending their durability and increasing their resistance to cyclic fatigue in comparison with systems that use continuous rotation motion [3].

A large percentage of root canals can be prepared with one instrument and without a preliminary glide-path [45]. In barely curved root canals or S-shaped canals, root canal preparation can be a difficult task [67]. During the shaping of curved root canals, especially double curved canals, several procedural errors can occur, including apical transportation, zips, ledges, root perforations, loss of working length, straightening of the root canal, or deviation from the original path [8]. In particular, regarding apical transportation, the use of increasingly greater diameter files decreases the angle of curvature, owing to the tendency to move towards the outer wall of the root canal and leading to a non-instrumented inner dentin wall in the apical third, which may result in a worse prognosis for treatment [910].

The glide-path is usually formed manually with stainless-steel instruments, but in recent years, NiTi mechanical instruments have been created dedicated exclusively to this task [11]. Compared to manual preparation, the mechanical glide-path technique has been shown to significantly reduce the procedural time, decreasing post-operative pain and flare-ups, while preserving the morphology of the original root canal [121314].

Reciproc Blue (RB; VDW, Munich, Germany) is a single-file that employs reciprocating motion and kinematics identical to those of Reciproc M-wire but uses an innovative heat treatment that transforms its molecular structure [15]. Thus, this novel system is much more flexible than its predecessor [16]. R-Pilot files (VDW), which are made of M-wire alloy, are engine-driven files for glide-path preparation and designed for use with reciprocating motion [17]. One Curve (OC; Micro Mega, Besancon, France) is a single-use, rotary file that enables shaping of the full length of the canal with a single instrument directly to the apex, manufactured from heat-treated NiTi alloy and characterized by a variable blade shape along its axis [18]. One G (Micro Mega) is a mechanical glide-path instrument with an asymmetrical cross-section. The 3 cutting edges are situated on 3 different radiuses relative to the canal axis with space for debris elimination, cutting action for the pre-enlargement of the canal and snake-like behavior [19].

Similar characteristics of the alloy (heat-treated NiTi alloy) and being single instrument but with different motions (reciprocating and rotating) make these instruments very suitable for comparison. The purpose of this study was to assess the effect of a preliminary glide-path formed by mechanical instruments (R-Pilot and One G) on the shaping ability (centering ability, maintenance of the original canal curvatures and area of instrumentation) of 2 single-file systems (RB and OC) in artificial root canals with double curvature.

MATERIALS AND METHODS

Forty simulated S-shaped root canals made of clear resin were used for this study, with an apical diameter of 0.10 mm and taper 0.00 (Endo training Blocks, VDW). The artificial canal had 2 curvatures, with a coronal angle of 30° and an apical angle of 20°. A size K-file was inserted inside the artificial canal until the tip was visible at the apex and the working length was determined. The artificial canals were prepared with OC (group OC), One G and OC (group GOC), RB (group RB), R-Pilot and RB (group PRB). The instruments were used by a single operator for canal preparation following the indications of the manufacturers, specific for each type of file used. The Reciproc Gold Motor was used (VDW) in reciprocating movement for the RB and R-pilot instruments and in continuous rotation (300 RPM, Torque 2,5 N/cm²) for the OC and One G instruments. Saline solution was used as an irrigant during instrumentation. Then, the artificial canals were scanned using the Epson Perfection V330 photo scanner at times T0 and T1, before and after instrumentation, respectively. The scans were saved in JPEG format at 4,800 × 8,600 pixels and 12,800 dpi resolution.

AutoCAD analysis

The images were analyzed using the AutoCAD program (version 23.0, 2018). Four levels were defined (D1, D2, D3, and D4), drawn along the entire length and perpendicular to the root canal, at the beginning of the canal (D1), in the center of the first curvature (D2, 7 mm from the apex), in the center of the second curvature (D3, 2 mm from the apex) and at the apex (D4, 0 mm from the apex) (Figure 1). For each scan, the contours of the canal were traced and a line was made through the center to indicate the central axis. After superimposing the sample image before instrumentation (T0) and after instrumentation (T1), the distance was measured between the center of the root canal in T0 and the center of the canal in T1 of all samples (centering ability). The distance was taken in the 4 levels already defined (D1, D2, D3, and D4) (Figure 2).

Figure 1

The 4 levels defined in the artificial canals: The beginning of artificial canal (D1); the center of the first curvature (D2); the center of the second curvature (D3); apex level (D4).

Figure 2

Superimposition of the artificial canal before (red) and after shaping (blue) and the measurement of centering ability (yellow line).

The area of the canal (mm²) from D1 to D4 was measured at T0 and T1 and the difference of the 2 measurements was calculated (ΔA). Then, the angles of the 2 curvatures of the artificial canal were measured before and after instrumentation (Δ1, Δ2), following the Cunningham and Senia method to evaluate the curvature modifications (Figure 3) [20]. A file was inserted inside simulated S-shaped root canals. Four points were determined: point ‘a’ at canal orifice, point ‘b’ and ‘c’ where the instrument deviated from the straight edge, point ‘d’ at apical foramen. Three lines were drawn and the angles formed by the intersection of the 3 lines were measured as the canal curvature.

Figure 3

The angles of the 2 curvatures (angle 1, green; angle 2, blue).

RESULTS

The results are shown in Tables 1 and 2. Regarding centering ability, the 2-way ANOVA test for D1 showed the use of a single-file technique without glide-path preparation (RB and OC groups) yielded better performance than the use of the glide-path file before the single-file (PRB and GOC groups) (p < 0.05), and for D2, there was a statistically better result for the OC system (OC and GOC groups) than the RB system (RB and PRB groups) in terms of centering ability (p < 0.05).

Table 1

Centering ability

Table 2

Deviation of original canal curvatures (°) and area of instrumentation (mm²)

In general, for D3 and D4 the 2-way ANOVA test showed the use of the glide-path improved the centering of the shaping (p < 0.05), moreover in D4, the RB system (RB and PRB groups) showed a better canal centering ability than the OC system (OC and GOC groups) (p < 0.05). Moreover, according to the 2-way ANOVA test, the final area after instrumentation (ΔA) showed that the OC system removed less material than the Reciproc system (p < 0.05).

Regarding centering ability, the Tukey-test for D1 and D2 showed no statistically significant differences among the groups (p > 0.05). In D3, among the groups, PRB yielded better results than RB (p < 0.05). Among the groups in Δ1, RB showed better results than OC while in Δ2, no differences were found in the 2 systems used (p > 0.05).

DISCUSSION

In endodontics, considerable attention has always been paid to the phase of obtaining the glide-path as a mandatory clinical step to improve the safety and efficiency of NiTi instruments and to increase the life of the instrument by decreasing the fracture rate and preventing inaccurate shaping [212223]. Many authors, especially in the past, have emphasized the idea that coronal enlargement and preliminary manual preflaring are fundamental to obtain the glide-path and therefore allow safer use of NiTi rotating instruments [21222425]. However, the entry into the world of "single-file" endodontics as well as having produced the enormous advantage of simplifying the operating sequence, reducing the number of steps for root canal preparation and, therefore, working times [226]. According to some authors, made the creation of a preliminary glide-path unnecessary to avoid screwing and torsional fracture of the instruments for root canal preparation [427].

As already done in many previous studies, simulated canals were used to standardize the experimental conditions [132829]. The S-shaped canals, which present a greater difficulty for instrumentation, were used to highlight the differences in the performance of the instruments. However, the use of resin blocks is a limitation of this study. In fact, differences in the hardness of artificial resin and dentinal walls can affect the results. The microhardness of resin materials used for artificial canals is included in a range from 20 to 22 kg/mm², while the hardness of dentin is 35-40 kg/mm near the pulp space. In this respect, the force applied to remove dentin of natural teeth is double that for the resin. Moreover, the size of resin chips may be different from natural dentin chips by determining difficulties to remove the debris in the resin canal and so, blockages of the apical root canal space [30]. Zhang et al. [31] also described in resin blocks the heat generation during instrumentation can soften the resin material and binding of instrument cutting blades.

The analysis of the samples using AutoCAD software allowed to accurately evaluate the anatomy of the artificial canals before and after instrumentation and to superimpose them to precisely measure the differences between the 2 times (T0 and T1) at which the samples were analyzed (Figure 4). Better centering abilities were evident for the single-file instruments (OC and RB groups) in D1 compared to the glide-path groups (RPB and GOC groups). The use of a preliminary glide-path in the coronal part of the artificial canal probably caused major deviation from the center of the canal. The brushing motion of the glide-path instrument performed by operator may not have been homogeneous throughout the circumference of the coronal part of the artificial canal. Regarding D3 and D4, the glide-path groups (GOC and PRB groups) showed a better centering ability than the groups without a preliminary glide-path (OC and RB respectively). Keskin et al. [32] affirmed that glide-path preparation with a Proglider instrument improved the shaping ability of the RB R25 instrument. In contrast with our results, Bürklein et al. [33] reported that glide-path preparation had no impact on the centering ability of rotary and reciprocation systems in resin blocks double curved. In the apical part of the canal (D4), the RB system had a better performance than the OC system. This result is confirmed by several studies that have reported that instruments with reciprocating motion have better centering ability than those with continuous rotation motion [34353637].

Figure 4

The 4 simulated resin blocks groups after superimposition, R-Pilot and Reciproc Blue (RPB) (A), Reciproc Blue (RB) (B), One Curve (OC) (C), One G and One Curve (GOC) (D).

The ΔA of the OC system showed that this file removed less resin compared with the RB system. The higher area could be related to the higher apical taper of the RB system. Furthermore, Özyürek et al. [38] found that the Reciproc 25 removed a statistically significantly higher amount of resin from every canal zones when compared with the WaveOne gold and Hyflex EDM in double curved resin block. The RB system (RPB and RB groups) better maintained the first canal curvature (Δ1) than the OC system (OC and GOC groups), but no differences were found for the apical curvature (Δ2). The reciprocating motion may have positively influenced these results. In fact, Dhingra et al. [39] reported that the WaveOne NiTi Primary reciprocating single-file better maintained the original canal anatomy, reducing deviations in the canal curvature compared with the OneShape continuous rotary file system.

CONCLUSIONS

Under the conditions of the present study, glide-path preparation improved the centering ability of both the single-instruments in the apical part of the canal in resin blocks with S-shaped canals, regardless of reciprocating or rotational movement. In addition, RB with or without the use of the glide-path file showed better centering ability in the apical part and higher respect of the canal curvature of the artificial canal in comparison with OC.

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