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ORIGINAL ARTICLE
Year : 2021  |  Volume : 11  |  Issue : 1  |  Page : 14-18

Evaluation of the surface nanoscale changes of R-phase, M-wire nickel-titanium instruments after use in extracted molars: An in vitro study


Department of Restorative Dental Sciences, College of Dentistry, Taibah University, Al Madinah Al Munawarah, Saudi Arabia

Date of Submission04-Feb-2020
Date of Decision03-Mar-2020
Date of Acceptance24-Mar-2020
Date of Web Publication09-Jan-2021

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Source of Support: None, Conflict of Interest: None


DOI: 10.4103/sej.sej_18_20

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  Abstract 


Introduction: The objective was to explore the impact of root canal instrumentation on the surface nanoscale characteristics of M-wire (ProTaper Next®[PTN]) and R-phase (twisted file [TF]) nickel–titanium (NiTi) instruments.
Materials and Methods: Endodontic cleaning and shaping was performed on the curved canals of the mesial roots of mandibular extracted molars (n = 32). Canal curvatures ranged from 20° to 30° according to the Schneider method. PTN and TF NiTi instruments were used for this purpose. The surface parameters of NiTi instruments were evaluated before and after the root canal instrumentation using a Dektak three-dimensional nanoscale surface profiler. An analysis of variance and Student's t-test were used to determine the significance of various parameters of the NiTi instruments before and after the root canal instrumentation. The statistical significance level was set at P < 0.05.
Results: There were no significant differences in the root mean square roughness (Sq), average roughness value (Sa), and peak to valley height (Sz) in flutes between the instruments (P > 0.05) or in the Sq in blade location. However, the Sa and Sz in blade location were significantly greater for TF than PTN. The TF instruments had greater surface roughness than PTN. The PTN instruments exhibited minor surface cracks, while TF instruments exhibited cracks and microcavities.
Conclusion: Endodontic instrumentation altered the surface characteristics; the surface distortion was significantly greater for the TF instruments than the PTN instruments.

Keywords: M-wire, nickel–titanium, ProTaper Next, R-phase, Twisted File


How to cite this article:
Ghabbani HM. Evaluation of the surface nanoscale changes of R-phase, M-wire nickel-titanium instruments after use in extracted molars: An in vitro study. Saudi Endod J 2021;11:14-8

How to cite this URL:
Ghabbani HM. Evaluation of the surface nanoscale changes of R-phase, M-wire nickel-titanium instruments after use in extracted molars: An in vitro study. Saudi Endod J [serial online] 2021 [cited 2021 Jan 23];11:14-8. Available from: https://www.saudiendodj.com/text.asp?2021/11/1/14/306603




  Introduction Top


Nickel–titanium (NiTi) rotary instruments are commonly used for endodontic cleaning and shaping and are known for their unique functional and mechanical properties such as pseudoelasticity and shape memory effects. However, due to their brittle nature, the spontaneous fracture of NiTi instruments during cleaning and shaping remains a major concern.[1] To overcome such shortcomings, a variety of thermomechanically treated instruments have been developed, aiming the manufacturing of martensitic phase NiTi alloy that are comparatively stable during the course of clinical applications. The recently developed heat-treated NiTi rotary instruments, including SybronEndo, R-phase NiTi, (Orange, CA, USA), and M-wire (Dentsply, Tulsa, USA) exhibited remarkably improved physical and mechanical properties in contrast to the standard NiTi instruments.[2],[3] In addition, endodontic instrument systems vary based on manufacturing modifications. For example, the ProTaper Next® (PTN) (Dentsply Maillefer, Ballaigues, Switzerland) instruments utilize a rectangular cross-section design that offers improved mechanical strength and facilitates exceptional asymmetric rotary motions, resulting in effective cleaning and shaping. In contrast, M-wire NiTi instruments were manufactured to provide improved flexibility and cyclic fatigue resistance.[4],[5] Recently, Elnaghy reported the improved cyclic fatigue of the PTN compared to the ProTaper Universal (Dentsply Maillefer, Ballaigues, Switzerland) and HyFlex CM (ColteneEndo/Whaledent, Inc., Cuyahoga Falls, OH) instruments.[4]

Another recently developed NiTi engine-driven “Twisted File System” (TF; SybronEndo, Orange, CA), fabricated using a twisting method, demonstrated improved fracture resistance, and compared to the ground instruments.[2],[6] Kim et al. reported specific surface textures and microstructures in TF comprising longitudinal grains of the R-phase of the NiTi alloy that, in turn, facilitates enhanced flexibility and fracture resistance. In addition, lack of transverse-running micro-grooves diminishes crack initiation and propagation in these instruments.[7] Based on these facts, it is evident that the mechanical properties and associated factors are crucial to endodontic efficacy and must be considered during the selection of cleaning and shaping systems.[8] To date, no reports have compared the nanoscale surface properties of TF and PTN endodontic instruments before and after the endodontic cleaning and shaping. Therefore, the current study aimed to explore the impact of root canal instrumentation on the surface nanoscale characteristics of M-wire (PTN) and R-phase (TF) NiTi rotary instruments. In addition, the flute and cutting blades' areas of intact PTN and TF instruments were qualitatively analyzed for cracks or deformations.


  Materials and Methods Top


This study was approved by the Institutional Research Ethics Committee at the College of Dentistry, Taibah University (Ref# TUCDREC/20200129/HGhabbani).

Endodontic rotary instruments

A total of eight new sets of PTN (Group 1) and TF (Group 2) NiTi instruments (four sets in each group) were used to run the experiment.

To exclude any manufacturing defects, the NiTi instruments were carefully examined using a microscope (Leica DM6000, Leica Microsystems, Wetzlar, Germany) at × 50 magnification.

Root canal cleaning and shaping

Endodontic cleaning and shaping was performed on curved canals (canal curvatures ranged from 20° to 30°) of the mesial roots of extracted mandibular molar teeth (n = 32) as previously described by Schneider?.[9] All teeth were extracted because of periodontal or prosthetic reasons. The extracted teeth used in this study had a closed apex and patent canal. Third molars, molars with open apices or severe curvature (more than 30°), and roots with previous root canal therapy and internal or external resorption were excluded from the study. The teeth were decrowned at the cementoenamel junction. Then, the working length (1 mm short of the apical foramen) was determined using a K-file (size #10; Dentsply Maillefer, Ballaigues, Switzerland) followed by NiTi instrumentation according to the manufacturers' guidelines (X1 17/0.04 and X2 25/0.06 for PTN and TF 25/0.04 and 25/0.06). The instrumentation of each root canal was performed by an experienced endodontist using ~ 20 mL of sodium hypochlorite (3%) as an irrigator. Following the completion of root canal instrumentation, each instrument was cleaned using an enzymatic cleaning solution in the ultrasonic cleaner, sterilized for 4 min (30 psi; 134°C), and dried. Each instrument was used for the cleaning and shaping of four canals, then discarded after three-dimensional (3D) scanning. Each instrument was scanned at the same position before and after the root canal instrumentation where it fixed at glass slide in of the same position each scanning.

Quantitative analysis of surface characteristics

The NiTi instruments were evaluated before and after the endodontic instrumentation as described previously by AlRahabi and Atta using a 3D nanoscale surface profiler (Dektak 150, Veeco Instruments Inc., Tucson, AZ, USA).[10] For this purpose, an area (100 μm × 100 μm) 3 mm coronal to each instrument's tip was scanned, focusing on the cutting blade and associated flutes component. The characteristics of the following three amplitude parameters were determined:

  • Average roughness value (Sa) that is defined as the arithmetic means of the peaks' height and valleys' depth from the mean line
  • Root mean square roughness (Sq) that is defined as the height distribution in relation to the mean line
  • Peak to valley height (Sz) measured over the entire profile (ISO 25178-2).


Data analysis

The data were analyzed using IBM SPSS software (v. 21.0, IBM Corp., Armonk, NY, USA). An analysis of variance and Student's t-test were used to determine the significance of various parameters (Sa, Sq, and Sz) of the NiTi instruments before and after the endodontic instrumentation. The significance level was set at P < 0.05.


  Results Top


The quantitative data (Sa, Sq, and Sz) of the PTN and TF instruments are presented as means ± standard deviations [Table 1] and [Table 2].
Table 1: The quantitative analysis of surface roughness parameters (average roughness value, root mean square roughness, and peak to valley height) ProTaper Next and Twisted File nickel-titanium instruments' cutting blade and flute before root canal instrumentation

Click here to view
Table 2: The quantitative analysis of surface roughness parameters (average roughness value, root mean square roughness, and peak to valley height) ProTaper Next and Twisted File nickel-titanium instruments' cutting blade and flute after root canal instrumentation

Click here to view


Preinstrumentation assessment revealed a significant difference in the Sa, Sq, and Sz values (P < 0.05) between the instruments. The TF instruments had the highest values in the blade and flute locations, with the exception of the Sz value in the blade where there was no significant difference (P > 0.05) between PTN and TF.

Postinstrumentation assessment revealed no significant differences in the Sq, Sa, and Sz values in the flutes between PTN and TF (P > 0.05). Similar findings were observed in the Sq in blade location. However, the blade location in the Sa and Sz parameters was greater for the TF instruments than the PTN instruments.

The qualitative analysis indicated that the TF instruments had greater surface roughness than the PTN instruments. In addition, the PTN instruments exhibited minor surface cracks, while the TF instruments exhibited cracks and microcavities [Figure 1].
Figure 1: Three.dimensional evaluation of a flute and blade areas of a ProTaper Next and Twisted File. (a) ProTaper Next before the root canal instrumentation, (b) ProTaper Next after the root canal instrumentation, (c) Twisted File before the root canal instrumentation and (d) Twisted File after the root canal instrumentation

Click here to view



  Discussion Top


The present study investigated the impact of root canal instrumentation on surface nanoscale characteristics of two different NiTi systems manufactured with different methods, M-wire thermal treatment technology (PTN), and R-phase thermal treatment technology (TF). The surface characteristics of these instruments were compared by nanoscale surface profilometry before and after the root canal instrumentation.

Due to differences in hardness between resin and dentin, the extracted teeth were used in this study to simulate the clinical usage of NiTi instruments. The microhardness of resin blocks is 20–24 kg/mm2 and that of dentin is 35–40 kg/mm2.[11]

The endodontic instrumentation of four canals did not produce any visible cracks or deformations on the PTN and TF instruments' surface.

The results of this study revealed that the roughness of intact TF is more than the roughness of intact PTN. The differences were just in Sa and Sz values in the blade where TF has the greater values. There are no previous studies compared the surface roughness of PTN and TF, but one study compared the effects of irrigating solutions on the nanostructure alterations of TF, Hero Shaper RaCe, and GTX instruments. The intact TF and Hero Shaper instruments had the significant highest roughness values. In addition, the NaOCl increased the surface roughness of TF and Hero Shaper instruments significantly more than that of RaCe and GTX.[12]

The characterization of the surface features of NiTi instruments is considered a crucial indicator for assessing the instruments' safety.[13] The surface features of NiTi instruments have been evaluated by several methods such as scanning electron microscope (SEM) and atomic force microscope (AFM),[5],[14] the 3D optical noncontact surface profiling system,[15] and the 3D stylus profiler.[10] In addition to surface roughness, SEM and AFM are commonly utilized for the assessment of surface topographies of NiTi instruments.[5],[14] SEM provides two-dimensional images, and therefore, lacks interpretation of quantitative and 3D surface topography imaging data.[16] Although the AFM analysis provides 3D imaging data, it can only evaluate a very small surface area and requires a flat specimen that may not be feasible for NiTi instruments.[15]

The 3D stylus profiler is a beneficial technique for the quantitative and qualitative evaluation of the surface characteristics of endodontic instruments[10] and was, therefore, used in the present study.

However, optical profilometry has a number of limitations and is associated with various factors, including specimens' optical constants, surface height, and slopes. In addition, scattering of the light results from deep surface valleys and diffracts from the fine surface features, which adversely affects the accuracy of 3D optical profilometry.[17] In contrast, the surface stylus profiler functions by applying a light force using a contact mode stylus sensor and analyses the surface topography with precision and minimal noise.[18] The stylus profiler facilitates a nanoscale vertical (~0.5 nm) and lateral resolution (~100 nm) corresponding to the stylus tip size.[19]

The 3D nanoscale surface profiler (Dektak 150, Veeco Instruments Inc., Tucson, AZ, USA) technology reveals difficult shapes and overcomes steep slopes, improving accuracy to within 0.25°. Similarly, the low-force option improves stylus sensitivity to 0.03 mg to enable nondestructive characterization of delicate surfaces. Also, additional analysis capabilities have been added, such as histogram and advanced automation program summary for pass/fail analysis.[10]

AlRahabi and Atta[10] used a 3D nanoscale surface profiler to compare the surface topographies and nanoscale profiles of intact and used WaveOne, WaveOne Gold, Reciproc, and Reciproc blue NiTi instruments. They concluded that 3D stylus profiler provided valuable assessments of the surface topographies of NiTi instruments. Ferreira et al.[15] describe noncontact 3D optical profilometry as a new method for the assessment of nanoscale alterations in the surface topography of NiTi endodontic instruments, where this technique enables a more comprehensive understanding of the effects of wear on the surface of instruments.

Grinding is commonly used for the industrial fabrication of NiTi instruments. Cold working during the grinding of NiTi alloys exerts stresses on grains and leads to the formation of deformities, including metal folds, pits, and fissures.[20] Such surface irregularities on NiTi instruments are considered potential areas of stress concentration and lead to crack initiation and ultimately instrument fractures after continuous cyclic fatigue.[21] Resistance to cyclic fatigue can be increased by reducing the surface roughness and vice versa.[22] However, increasing the surface roughness reduces the cutting efficiency of endodontic instruments and enhances the likelihood of instrument separation.[23]

There are not many studies comparing PTN and TF, but the shaping ability was compared and revealed that PTN preserved the original curvature of the canal better than the TF instruments.[24] In the present study, the TF instruments remained intact and exhibited greater surface roughness than the PTN.

In terms of comparative qualitative analysis, the PTN instruments' surfaces displayed minor cracks, in contrast to the TF instruments' surfaces that had cracks and microcavities following instrumentation. These findings may be consistent with the results of the study by Elnaghy and Elsaka, indicating that PTN had better resistance to torsional stresses and wear than did TF.[25]

The clinical significance findings of this study are that four canals can be prepared safely whether PTN or TF is used. There is a need to evaluate different types of NiTi instruments to prepare more than four canals in addition to evaluate canal curvature on surface nanoscale changes.

This study was an in vitro study, which is considered to be one of the limitations of this study, along with the lack of methods used to compare different NiTi instruments. In addition, only four canals were prepared by each instrument.


  Conclusion Top


The nanoscale surface profilometry of PTN and TF was altered after the endodontic instrumentation despite no visible cracks or deformations on the instruments. The 3D stylus profiler is a useful method for assessing the surface topography of endodontic instruments for clinical safety.

Acknowledgment

I would like to thank Dr. Raghied M Atta, Associate Professor, College of Engineering, Taibah University, for his efforts in scanning the study sample, as well as I would like to thank Editage (www.editage.com) for English language editing.

Financial support and sponsorship

Nil.

Conflicts of interest

There are no conflicts of interest.



 
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Alrahabi M, Zafar MS. Assessment of apical transportation caused by nickel-titanium rotary systems with full rotation and reciprocating movements using extracted teeth and resin blocks with simulated root canals: A comparative study. Niger J Clin Pract 2018;21:772-7.  Back to cited text no. 11
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Uslu G, Özyürek T, Yilmaz K. Comparison of alterations in the surface topographies of HyFlex CM and HyFlex EDM nickel-titanium files after root canal preparation: A three-dimensional optical Profilometry study. J Endod 2018;44:115-9.  Back to cited text no. 13
    
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Ferreira F, Barbosa I, Scelza P, Russano D, Neff J, Montagnana M, et al. A new method for the assessment of the surface topography of NiTi rotary instruments. Int Endod J 2017;50:902-9.  Back to cited text no. 15
    
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Alapati SB, Brantley WA, Svec TA, Powers JM, Mitchell JC. Scanning electron microscope observations of new and used nickel-titanium rotary files. J Endod 2003;29:667-9.  Back to cited text no. 20
    
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Nair AS, Tilakchand M, Naik BD. The effect of multiple autoclave cycles on the surface of rotary nickel-titanium endodontic files: An in vitro atomic force microscopy investigation. J Conserv Dent 2015;18:218-22.  Back to cited text no. 23
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