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ORIGINAL ARTICLE
Year : 2022  |  Volume : 40  |  Issue : 2  |  Page : 188-194
 

An in vitro comparative evaluation of dentinal crack formation caused by three different nickel–titanium rotary file systems in primary anterior teeth


Department Paediatric Dentistry, Pacific Dental College and Hospital, Udaipur, Rajasthan, India

Date of Submission04-Mar-2022
Date of Decision29-Mar-2022
Date of Acceptance02-Apr-2022
Date of Web Publication15-Jul-2022

Correspondence Address:
Dr. Dinesh Rao
Department of Paediatric Dentistry, Pacific Dental College and Hospital, Udaipur - 313 024, Rajasthan
India
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Source of Support: None, Conflict of Interest: None


DOI: 10.4103/jisppd.jisppd_100_22

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   Abstract 


Context: Cleaning and shaping of the canals damages the root dentin which becomes a gateway to dentinal cracks and thereby causes failure of the treatment. Aim: The aim of this study was to assess and compare dentinal crack formation caused by three different nickel–titanium (NiTi) rotary file systems in primary anterior teeth. Settings and Design: The present in vitro study is an experimental, comparative study. Materials and Methods: One hundred fifty extracted primary anterior teeth were included in this study. The teeth were randomly divided into five groups. Group 1: Pedoflex rotary file system, Group 2: Prime Pedo rotary file system, Group 3: Kedo-S2 rotary file system, Group 4: K-files, and Group 5: no instrumentation. Roots were sectioned and viewed under a stereomicroscope for the presence of any cracks. Statistical Analysis Used: The data were analyzed using the Chi-square test and Kruskal–Wallis test. Results: In the coronal, middle, and apical thirds, Group 2 showed a maximum number of crack formations in the middle third (57%), followed by Group 3 (43.3%) and Group 1 (36.7%). Groups 4 and 5 showed no crack formation in all the root sections. The middle third showed a maximum number of crack formations compared to the coronal and apical thirds. Conclusions: Rotary systems render various benefits with an acceptable success in comparison to conventional hand instrumentation. Within the limitation of this study, it was found that Pedoflex rotary file system was the best with the least number of crack formations.


Keywords: Dentinal cracks, nickel–titanium rotary files, primary teeth


How to cite this article:
Bhagyashree B, Rao D, Panwar S, Kothari N, Gupta S. An in vitro comparative evaluation of dentinal crack formation caused by three different nickel–titanium rotary file systems in primary anterior teeth. J Indian Soc Pedod Prev Dent 2022;40:188-94

How to cite this URL:
Bhagyashree B, Rao D, Panwar S, Kothari N, Gupta S. An in vitro comparative evaluation of dentinal crack formation caused by three different nickel–titanium rotary file systems in primary anterior teeth. J Indian Soc Pedod Prev Dent [serial online] 2022 [cited 2022 Aug 12];40:188-94. Available from: http://www.jisppd.com/text.asp?2022/40/2/188/351035





   Introduction Top


The primary objective of endodontic treatment is the elimination of microorganisms from the root canal system, which is achieved through the removal of vital tissues, residual necrotic material, infected dentin, and debris.[1] Although the morphology of root canals in primary teeth renders endodontic treatment challenging, the use of stainless steel instrument for canal preparation has been the “gold standard” for many years. However, preparation of narrow curved canals by manual stainless steel files is time-consuming and difficult, with limited apical enlargement, thereby reducing the efficacy of irrigation and obturation and also causing fewer aberrations, such as the ledge and zip formations, canal transportations, and perforations.[2]

The development of nickel–titanium (NiTi) alloys has allowed the use of rotary instruments in pediatric endodontic treatment. Biomechanical preparation with rotary files in primary teeth has gained popularity when the first case was reported by Barr et al.,[3] using profile 4% taper rotary files. Since then the repetition of using different rotary NiTi systems for instrumentation of the primary root canal is developing among pediatric practitioners. When compared to the permanent teeth, the rotary instrumentation is faster in primary teeth, due to the smaller root canal length. It also favors a patient's cooperation by reducing the treatment time for shaping the canals which is one of the highest challenges in pediatric endodontics. Although instrumentation with NiTi rotary instruments having active cutting edges and larger taper produce significant forces on root dentin during instrumentation, this may lead to root dentinal defects or root microcracks which have the potential to develop into root fracture, thus reducing the long-term prognosis of endodontically treated teeth and also may result into tooth loss.[4],[5],[6],[7],[8]

Thus, the physical and mechanical properties of NiTi rotary file systems may affect the incidence of cracks on the dentinal surface. Many studies have examined dentinal crack formation caused by NiTi files during root canal preparation in permanent teeth.[2],[4],[9],[10],[11] A comprehensive literature search revealed that no study examined the dentinal crack in primary teeth, which were caused by pediatric NiTi rotary files. Therefore, this study aimed to evaluate and compare the dentinal crack formation caused by three different NiTi rotary file systems in primary anterior teeth.


   Materials and Methods Top


Ethical clearance was obtained, before conducting the study, from the Ethical Committee, Pacific Dental College and Hospital, Udaipur (Ref. No. PDCH/20/EC-216). The study was conducted for about 6 months.

In the current in vitro study, 150 radiographically confirmed single-rooted extracted primary teeth with a minimum root length of 9 mm were included. The roots were visually inspected to rule out any evidence of root fracture and open apex. The collected teeth were cleared of all bloodstains, soft-tissue tags, hard bony spicules, and calculus adherent to the root. Teeth were then rinsed and stored in normal saline at room temperature until use.

The teeth were decoronated with a low-speed diamond disc, underwater coolant. All teeth were observed under a stereomicroscope at ×1 to exclude the cracks. A single layer of aluminum foil was used to cover the roots of the teeth and each tooth was embedded into acrylic resin set in an acrylic tube. The root and the aluminum foil were removed from the tube. The roots were immediately inserted into light-body silicon-based material, which acts like a periodontal ligament. The apical 3 mm of the root was exposed and immersed in water during instrumentation to prevent dehydration of the root. The study materials were randomly grouped into five with each containing thirty extracted primary anterior teeth [Figure 1].
Figure 1: (a) Decoronation of crown structure, (b) Covering the root with aluminum foil, (c) Application of light-body silicon-based material, (d) Root insertion into acrylic tube, (e) Horizontal sectioning of the root, (f) Observation of cracks under stereomicroscope

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  • Group 1 (n = 30): the biomechanical preparation was carried out with Pedoflex rotary file system. Initially, a glide path preparation was carried out up to the working length using #15 and #20 K-files. Pedoflex rotary file was used in the following sequence: #20 4% taper-16 mm, #25 4% taper-16 mm
  • Group 2 (n = 30): the biomechanical preparation was carried out with the Prime Pedo rotary file system. Initially, a glide path preparation was carried out up to the working length using #15 and #20 K-files. Prime Pedo rotary file used in the following sequence: starter 8% taper-16 mm, P1 #15, 6% tape-18 mm and P2 #25, 6% taper-18 mm
  • Group 3 (n = 30): the biomechanical preparation was carried out with Kedo-S2 rotary file system. Initially, a glide path preparation was carried out up to the working length using #15 and #20 K-files and then the canal was prepared using Kedo-S2 single rotary file system with P1 16 mm file
  • Group 4 (n = 30): the root canals were prepared manually using K-files. Instrumentation was done up to file #25 in the apical third, and then, the step-back technique was followed to prepare the middle and coronal thirds of the canal
  • Group 5 (n = 30): left untreated.


In all the samples, apical patency was established by introducing #15 K-file into the root canal until its tip was visible at the apical foramen and the working length was set 1.0 mm shorter than this measurement. Each instrument was replaced after preparing five teeth. Copious irrigation was carried out with 1% sodium hypochlorite and normal saline solutions between instruments.

All roots were cut horizontally at 3 mm and 6 mm from the apex. To prevent artifacts by dehydration, the teeth were kept moist in distilled water throughout experimental procedures. Sections were viewed under a stereomicroscope for the presence of dentinal defects. Defects were classified using Wilcox et al.,[12] classification as no defect, fracture, and all other defects.

  • Score 0 (no defect): Assigned when radicular dentin was devoid of any lines or cracks in both the root canal's external and internal surfaces
  • Score 1 (fracture): Assigned when the tooth has cracks that were extending from the root canal space to the outer root surface
  • Score 2 (other defects): Assigned when the cracks did not extend from the root canal to the outer root surface and the internal and external craze lines as well as partial cracks.


The results were tabulated by counting the number of defects in each group. An intergroup comparison of microcracks was performed using Pearson's Chi-square test and Kruskal–Wallis test. A comparison between the number of microcracks at the coronal, middle, and apical third of each file system was performed using the Wilcox classification. The level of significance was set at P < 0.05.


   Results Top


Intergroup comparison of dentinal cracks reveals that in the coronal third, a maximum number of dentinal cracks were seen in Group 2 (30%), followed by Group 3 (23.3%), whereas Group 1 (13.3%) showed the least number of dentinal cracks. In the middle third, a maximum number of dentinal cracks were seen in Group 2 (57%), followed by Group 3 (43.3%), whereas Group 1 (36.7%) showed the least number of dentinal cracks. In the apical third, Group 2 (10%) showed a maximum number of dentinal cracks, followed by Group 3 (6.70%) [Figure 2]. Among all three rotary file systems used, the minimum amount of crack was observed in the apical third of Group 1, whereas the middle third area of Group 2 exhibited the maximum amount of cracks. However, Groups 4 and 5 showed no crack formation at any level [Figure 3] and [Table 1], [Table 2], [Table 3].
Figure 2: Group 1 showing no cracks in the coronal, middle, and apical third (a-c), Group 2 showing the highest amount of cracks in the middle, coronal, and apical third (d-f), Group 3 showing cracks in middle, coronal, and apical third (g-i)

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Figure 3: Group 4 showing other defects in coronal, middle, and apical third (a-c) respectively, Group 5 showing other defects in the middle, coronal, and apical third (d-f), respectively

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Table 1: Comparison of dentinal crack formation in coronal third in all five groups

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Table 2: Comparison of dentinal crack formation in the middle third in all five groups

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Table 3: Comparison of dentinal crack formation in apical third in all five groups

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When compared within the groups, there was a significant association between apical, middle, and coronal thirds for Groups 1, 2, and 3 (P < 0.05), whereas Groups 4 and 5 indicated a nonsignificant association between their apical, middle, and coronal thirds (P > 0.05).


   Discussion Top


Residual dentin thickness is the measure of mechanical limits of instrumentation to enlarge the canal diameter to approximately predetermined values that would not significantly weaken the dentinal walls.[13] After completion of all the intraradicular procedures, at least 1 mm of sound radicular dentin should remain in all aspects of the root along its entire length.[14] Excessive removal of the radicular dentin may result in strip perforation as well as vertical root fractures.[15] In addition, unnecessary enlargement of the canal can reduce the dentinal thickness and weakens the tooth structure. Root canal preparation using rotary files creates a variable degree of rotational forces on the dentinal walls, which generates microcracks or craze lines. The extent of these defects rests upon various precipitating factors, such as constant or progressive taper, constant or variable pitch, cross-sectional geometry, tip design, and flute form of the instrument.[16]

The present study aimed to evaluate the dentinal microcracks during the biomechanical preparation of primary teeth. Samples were stored in purified filtered water. According to Saber and Schafer,[17] this medium causes the smallest changes in dentin over time. Decoronation of all the specimens was done using a diamond disc which eliminates some variables, such as the anatomy of the coronal area and access to the root canals allowing a more reliable comparison between endodontic treatment techniques.[18] Arias et al.[18] stated that no artificial material was found to completely reproduce the viscoelastic properties of the periodontal ligament. In the present study, acrylic blocks and a silicone-based material were used to simulate bone and the periodontal ligament, which is more reliable than using only acrylic blocks.[19] Canals were prepared with Pedoflex rotary files, Prime Pedo rotary files, and Kedo-S2 rotary files using a torque control motor. All these files are developed for cleaning and shaping primary teeth.[20] Kedo-S2 pediatric rotary file system (fourth generation) is a single-file system, with a total length of 16 mm. This file system provides higher cervical enlargement and restricted apical preparation with the progressive taper than the constantly fixed taper.[8] Another file system used in this study was Prime Pedo rotary files (third generation) which consist of four files (Starter, P1, P2, and Endosonic file) and have a triangular cross-section, heat-treated, and controlled memory, whereas Pedoflex rotary files (third generation) consist of three files # 20-4%, #25-4%, and #30-4% and have a unique file design with efficient cutting efficiency and flexibility. About 1% NaOCl solution was used as the irrigation solution for protecting the microstructure of the dentin to make sure that the dentinal cracks were primarily related to the mechanical preparation.

Stainless steel hand K-files had been used for biomechanical preparation in many previous studies, and thus, it served as a positive control group in the present study.[21],[22] In the present study, no fracture was observed in this group. This is similar to the results found by Çiçek et al.,[23] where hand K-files did not produce microcracks at any level in permanent teeth.

However, no other study has examined dentinal cracks caused by pediatric NiTi rotary files during root canal preparation in the primary anterior. Yoldas et al.[16] observed that rotary files induced the maximum number of cracks in the permanent teeth. Similar observations were noted in the current study, as all the rotary files show some amount of crack formation in the primary anterior teeth. Files with a high taper caused higher stress levels on canal walls.[24] In corroboration with this finding, this study revealed that the Prime Pedo and Kedo-S2 file with a high taper caused more dentin cracks, whereas Pedoflex files caused less dentin cracks than Prime Pedo and Kedo-S2 file; this is believed to originate from the low taper of Pedoflex files.

Dentinal crack is related not only to the design of the instrument but also to its instrument's kinematics.[25] Manufacturers recommend different speeds and torque settings for different diameters of files. An earlier study done by Gambarini[26] suggested that if a high-torque motor is being used, the instrument-specific torque limit is often exceeded, thus increasing the risk of intracanal fracture. In support with these findings, this study revealed that the Prime Pedo and Kedo-S2 file with a higher torque caused more dentin cracks, and Pedoflex files with a low torque caused less dentin cracks. Another study done by Dane et al.[27] suggested that high-torque settings caused more dentinal cracks than low-torque settings. Similar results were found in this study in which Prime Pedo files with higher torque settings resulted in a higher amount of crack.

In the present study, it is found that the canals instrumented with full sequence systems (Pedoflex file system) showed less cracks than single-file systems (Kedo-S2 file system), in which single file causes more stress generation leading to crack formation. The study results are similar to the results of Bürklein et al.[28] that reciprocating single files created more defects than files used in full sequence. Özyürek et al.[29] and Versluis et al.[30] stated that during the instrumentation procedure, the stresses generated at the middle, and coronal thirds were three times more prevalent than at the apical level in accordance with this result, a similar result was found in the present study. The lowest incidence may be due to the preparation of the oval canal led to a substantial reduction in circumferential stresses at the canal wall, particularly in the apical one-third where the canal was enlarged to a smooth round shape.

Very few studies were conducted to evaluate the dentinal crack formation caused by NiTi rotary files in primary teeth. Panda et al.[21] instrumented primary teeth using different file systems and found that stainless steel hand K-files and self-adjusting file instruments resulted in fewer dentinal damage than the ProTaper Universal files. Özyürek et al.[29] observed more dentinal cracks in primary molars, tested with the NiTi file system compared to the control group. However, the current study showed that Pedoflex rotary file system was the best with the least number of crack formations.

Limitation of the study

The standardization of speed, as well as torque settings for different file systems, might be a limitation of the present study. Moreover, it was difficult to standardize the downward force used during each instrumentation and teeth with straight root canals without anatomical complexities. These may not always reproduce a true clinical presentation.


   Conclusions Top


Within the limitations of the present study, the following conclusions were made:

  1. Different kinds of rotary systems can cause damage to the root dentin resulting in crack formation
  2. No cracks were observed with stainless steel hand K-files though the use of hand files is more time-consuming; it results in lesser cracks and cleaner canal walls
  3. Between the rotary file groups Pedoflex rotary system showed fewer dentinal crack formations, followed by Kedo-S2 rotary system and the highest cracks were observed in the Prime Pedo rotary system
  4. Maximum cracks were seen in the middle third followed by the coronal third and least were observed in the apical third.


Financial support and sponsorship

Nil.

Conflicts of interest

There are no conflicts of interest.



 
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Zuckerman O, Katz A, Pilo R, Tamse A, Fuss Z. Residual dentin thickness in mesial roots of mandibular molars prepared with Lightspeed rotary instruments and Gates-Glidden reamers. Oral Surg Oral Med Oral Pathol Oral Radiol Endod 2003;96:351-5.  Back to cited text no. 13
    
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Katz A, Wasenstein-Kohn S, Tamse A, Zuckerman O. Residual dentin thickness in bifurcated maxillary premolars after root canal and dowel space preparation. J Endod 2006;32:202-5.  Back to cited text no. 14
    
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Yoldas O, Yilmaz S, Atakan G, Kuden C, Kasan Z. Dentinal microcrack formation during root canal preparations by different NiTi rotary instruments and the self-adjusting file. J Endod 2012;38:232-5.  Back to cited text no. 16
    
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Saber SE, Schäfer E. Incidence of dentinal defects after preparation of severely curved root canals using the Reciproc single-file system with and without prior creation of a glide path. Int Endod J 2016;49:1057-64.  Back to cited text no. 17
    
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    Figures

  [Figure 1], [Figure 2], [Figure 3]
 
 
    Tables

  [Table 1], [Table 2], [Table 3]



 

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