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| ORIGINAL RESEARCH |
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| Year : 2022 | Volume
: 13
| Issue : 2 | Page : 53-56 |
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Dentinal Defects Induced by Offset and Alternating Contact Endodontic Rotary Files: An In Vitro Study
Abeer A Abass, Haidar T Fadhil, Firas S. O Albaaj
Department of conservative dentistry, College of Dentistry, Mustansiriyah University, Baghdad, Iraq
| Date of Submission | 04-Oct-2021 |
| Date of Decision | 25-Feb-2022 |
| Date of Acceptance | 20-Apr-2022 |
| Date of Web Publication | 12-Jul-2022 |
Correspondence Address:
Firas S. O Albaaj
Department of conservative dentistry, College of Dentistry, Zayona 712, Baghdad
Iraq
 Source of Support: None, Conflict of Interest: None  | Check |
DOI: 10.4103/denthyp.denthyp_138_21
Objective: Dentinal defects during root canal preparation could lead to treatment failure and tooth extraction. Many rotary files are manufactured with asymmetric cross sections or alternating cutting edges to minimize contact with the canal wall. Decreasing contacts may generate low stresses and, hence, fewer dental defects during root canal instrumentation. This study aimed to evaluate the incidence of dentinal defects induced by ProTaper Next, Wave One Gold (Dentsply Maillefer, Ballaigues, Switzerland), and iRace (FKG Dentaire SA, La Chaux-de-Fonds, Switzerland) in comparison to the symmetric file HyFlex CM (Coltene-Whaledent, Allstetten, Switzerland). Materials and Methods: Sixty extracted single-rooted premolars with round canals were selected for this study. All teeth were decoronated and divided into four experimental groups according to the tested file systems. In each group, 15 canals were prepared with the crown down technique using a speed and torque recommended by manufacturers. The root samples were then sectioned horizontally at 3, 6, and 9 mm from the apex and examined under a stereomicroscope to evaluate the presence or absence of dentinal defects. Data were statistically analyzed with SPSS software using a chi-square test. Results: Dentinal defects were observed at all canal levels following all methods of instrumentation. ProTaper Next showed the lowest values of dentinal defects, whereas Hyflex CM displayed the highest values. Conclusion: Files with few contacts with the canal wall decreased the number of dentinal defects compared to the HyFlex CM file, with a nonsignificant difference being observed.
Keywords: Alternating contact files, dentinal defects, offset files, root canal instrumentation
How to cite this article:
Abass AA, Fadhil HT, Albaaj FO. Dentinal Defects Induced by Offset and Alternating Contact Endodontic Rotary Files: An In Vitro Study. Dent Hypotheses 2022;13:53-6 |
| Introduction | |  |
The aim of root canal instrumentation is to remove infected tissues and shape the root canal into a smooth conical lumen while maintaining the original canal path and anatomy.[1] The instrumentation process is a critical phase that can affect endodontic treatment prognosis. Incorrect instrumentation can induce errors, such as canal stripping and preformation, or complications such as dentinal crack and root fracture.[2] Apart from iatrogenic factors, criteria such as file design and the type of alloy used to fabricate these files have been reported to directly impact the incidence and severity of such errors and complications.
Dentinal defects occur when stresses applied to a dentinal wall exceed the tensile stress limit of dentine.[3] Manufacturer attempts to reduce these stresses have been seen in developing files with asymmetrical cross sections, files with variable tapers, and files with alternating contact edges. These designs could reduce the screw-in effect of the file in the canal and, hence, reduce the tensile forces on the dentinal wall. Rotary ProTaper Next files are produced with asymmetrical rectangular cross sections with two-point contacts with the canal wall and progressive/regressive tapers.[4] Reciprocating Wave One Gold files are produced with an offset parallelogram-shaped cross section design and gold-wire technology characteristics to control the unfavorable effect of high stresses observed during canal preparation with the first-generation files.[5]
iRace is a rotary file with an asymmetrical triangular cross-section design and sharp cutting edges. The file is electromechanically polished to improve cyclic and torsional fatigue resistance. The file works with full rotation and an alternating cutting action to minimize stresses on dentine and wedging in the canal.[6] Furthermore, the file is designed with a thin core that can provide increased flexibility and more space to remove debris coronally, as claimed by the manufacturer.[6],[7]
HyFlex CM files have a symmetrical convex-triangular cross section making contact with the canal wall with three points at any given cross section.[8] The files are manufactured from a heat-treated NiTi alloy to ensure high flexibility during navigation of a curved canal.[9]
This study aimed to evaluate the incidence of dentinal defects induced by ProTaper Next, Wave One Gold, and iRace compared with HyFlex CM using a stereomicroscope.
| Materials and Methods | | |
Sixty extracted single-rooted premolars were collected for this study following the approval of the Research Ethics Committee of the College of Dentistry, Mustansiriyah University. Remnants of periodontal ligaments were cleaned with a periodontal scaler (Acteon, Aquitaine, France). Teeth with severely curved roots, calcified root canals, or an additional canal were excluded. The crowns were sectioned with a diamond disc under water cooling, leaving roots of 15 mm in length. Root surfaces were examined with a stereomicroscope under 24× magnification to discard roots with preexisting cracks or craze lines. Roots were stored in distilled water at 4°C until use. The root samples were randomly divided into four groups of 15 samples each. The working length was estimated at 0.5 mm short of the apical foramen. Apical patency was established utilizing a #15 K-file (Dentsply Maillefer, Ballaigues, Switzerland). To facilitate the removal of roots during the testing procedure, they were wrapped with aluminum foil and inserted into a cylindrical metal mold containing silicon impression material (President dental, Allershausen, Germany). Canal instrumentation was made in a crown-down brushing motion with the speed and torque set according to manufacturer recommendations [Table 1].
File flutes were cleaned of dentinal debris with an endodontic sponge following every three in-out strokes. Each file was used to prepare five canals. To irrigate the canal during preparation with each instrument, 1 mL of 2% sodium hypochlorite solution (Cerkamed, Stalowa Wola, Poland) was used. Canal patency was regularly maintained with the #15 K-file.
After preparation, the samples were removed from the set silicon impressions, and the foils were discarded. Using a dental surveyor, the roots were placed centrally in clear acrylic resin in a cylindrical plastic mold to control root sectioning. Sample sectioning was performed at 3, 6, and 9 mm from the apex using a diamond disc under water cooling. Sections were then coded by the authors and visualized by two blind examiners using the stereomicroscope at 24× magnification. Dentinal defects, including cracks and craze lines, were recorded as “0 = no defect” and “1 = defect” according to the classification used by Milani et al. with modification.[10] Data were statistically analyzed with SPSS (V. 24) (SPSS Inc., Chicago, IL, USA) using a chi-square test at a significance level of P < 0.05 (α = 0.049) and a 95% confidence interval.
| Results | | |
The distribution and frequency of dentinal defects for each group are presented in [Table 2]. The distribution of dentinal defects at each root level is provided in [Table 3]. | Table 2 Distribution and frequency of dentinal defects induced by each file system
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 | Table 3 Distribution of dentinal defects induced by file systems at each root level
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All tested file systems induced defects on dentine at all canal levels. The difference was nonsignificant among groups (P > 0.05). ProTaper Next induced the lowest number of dentinal defects, whereas HyFlex CM showed the highest number. A significant difference (P < 0.05) was found between apical and middle levels of the HyFlex CM group, and a nonsignificant difference was noted among the different levels of the other groups (P > 0.05).
| Discussion | | |
Recently, several NiTi rotary file systems have been developed with various cross-sectional and longitudinal designs. Variations in file geometry have demonstrated different levels of tensile stress on the canal wall during the instrumentation process.[11],[12] The goal of the present study was to assess to what extent offset and alternating contact NiTi rotary file systems including ProTaper next, Wave One Gold, and iRace induce dentinal defects compared with the symmetrical HyFlex file system.
The current study revealed that all file systems induced dentinal defects at the three root levels. This finding agrees with the results of other studies that relied on the same stereomicroscope methodology.[13],[14] However, the results contradict those of other studies that relied on noncontact assessments of root dentine using microCT. For instance, Katanec et al. and De-Deus et al. found that rotary files did not generate new dentinal cracks; rather, cracks were observed in the pretreatment phase.[15],[16] Tooth extraction, storage conditions, and tooth sectioning are factors that could generate dentinal defects apart from root canal instrumentation in vitro. Hence, it may be that the preoperative evaluation of external root surfaces with a stereomicroscope cannot detect preexisting cracks or craze lines located deep in the root structure. Such a methodology shortcoming could cause false-positive results of dentinal defects following root canal instrumentation.
In the current study, ProTaper Next, Wave One Gold, and iRace files produced similar percentages of dentinal defects. These results agree with the findings of Saberi et al., where both ProTaper Next and iRace files caused similar dentinal defect percentages.[17] A previous finding showed that files with a larger taper or driven with high torque and a reciprocating motion can generate high tensile stress on the canal wall.[13] In this study, the large taper and high torque used with the reciprocating Wave One Gold file were not recognized as factors that aggravate dentinal defects, potentially because these aggravating factors are compensated by the offset design, which offers one or two contact points with the canal wall at any given cross section.[5] This notion is further supported by Pedullà et al., who found that the Wave One Gold file induced significantly fewer dentinal defects than the conventional Wave One file with the symmetrical cross section.[18]
In our study, files with an asymmetrical cross section or with alternating cutting edges produced fewer defects than the symmetrical HyFlex CM files did. This result is consistent with the work of Shori et al., where files with more contact points showed more defects in the canal wall.[19] HyFlex CM has three contact points, which could add more foci of stresses on root canal dentine when compared with the fewer contact points of the other files. Furthermore, less contact with the canal wall could leave more spaces, as claimed by manufacturers. These spaces can facilitate debris removal and reduce debris packed in canal recesses, permitting more unrestricted file movement. Additionally, HyFlex CM files have a fixed taper, which increases the possibility of file wedging and, hence, stresses in the canal.[20]
| Conclusion | | |
Within the limitations of this in vitro study, the offset and alternating contact file systems induced fewer dentinal defects than did the symmetric file system, but these differences were not significant.
Financial support and sponsorship
Nil.
Conflicts of interest
There are no conflicts of interest.
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[Table 1], [Table 2], [Table 3]
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