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Table of Contents
ORIGINAL ARTICLES
Year : 2022  |  Volume : 6  |  Issue : 2  |  Page : 74-79

Effect of smear layer on calcium hydroxide removal from root canal using different systems: An ex-vivo study


Department of Conservative Dentistry and Endodontics, VYWS Dental College and Hospital, Amravati, Maharashtra, India

Date of Submission18-Oct-2021
Date of Decision12-Jan-2022
Date of Acceptance03-Apr-2022
Date of Web Publication12-Jul-2022

Correspondence Address:
Akshita G Rathi
Department of Conservative Dentistry and Endodontics, VYWS Dental College and Hospital, Amravati 444602, Maharashtra
India
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Source of Support: None, Conflict of Interest: None


DOI: 10.4103/SDJ.SDJ_104_21

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  Abstract 

Background: For successful multi-visit endodontic treatment, clinicians often use calcium hydroxide as an intracanal medicament, and it is necessary to completely remove it from canal before obturation. Presence or absence of a smear layer may play an important role in the removal of calcium hydroxide from root canal systems. Objectives: This study aimed to evaluate the effect of the smear layer on the removal of calcium hydroxide from root canal walls using manual files, ultrasonic files, and an EndoActivator System under a stereomicroscope and to evaluate the effect of sodium hypochlorite solution and ethylenediaminetetraacetic acid (EDTA) solution with sodium hypochlorite solution on the removal of the smear layer from root canals during biomechanical preparation. Methods: A total of 80 extracted premolars were decoronated. They were divided into groups and subgroups, and then further evaluation was performed. Root canal instrumentation was done using #25, 0.06 taper nickel-titanium rotary files (Neoendo, Orikam, Gurgaon, India) using the crown-down technique. Samples were divided into two groups: Group A (with a smear layer) and Group B (without a smear layer), for the placement of calcium hydroxide. They were then divided into three subgroups to evaluate the removal of calcium hydroxide from root canal walls using manual files, ultrasonic files, and an EndoActivator and were examined under a stereomicroscope at magnification 10× with image analysis software. Statistical analysis was performed using analysis of variance and Tukey’s post-hoc test. Results: The removal of calcium hydroxide from dentinal walls was significantly better in Group B (p <0.05) than in Group A in cervical, middle, and apical third of the canals. Conclusion: Removal of calcium hydroxide was more efficient in Group B (smear-free) than in Group A (with a smear layer), regardless of the technique used. A comparison of the techniques showed that ultrasonic files were more efficient in removing calcium hydroxide than manual files and EndoActivator System in both study groups.

Keywords: EndoActivator System, manual files, ultrasonic files


How to cite this article:
Heda AA, Manwar NU, Rathi AG, Deshmukh G, Rahul N, Tekam DA, Bhatia CM. Effect of smear layer on calcium hydroxide removal from root canal using different systems: An ex-vivo study. Sci Dent J 2022;6:74-9

How to cite this URL:
Heda AA, Manwar NU, Rathi AG, Deshmukh G, Rahul N, Tekam DA, Bhatia CM. Effect of smear layer on calcium hydroxide removal from root canal using different systems: An ex-vivo study. Sci Dent J [serial online] 2022 [cited 2022 Aug 19];6:74-9. Available from: https://www.scidentj.com/text.asp?2022/6/2/74/350755




  Background Top


Root canal treatment aims to eliminate bacteria from the root canal system and to prevent reinfection. For successful endodontic treatment, it is necessary to ensure that the root canal is sterile. The removal of debris by using mechanical instrumentation alone may not always succeed in obtaining a complete cleaning due to morphological and physical barriers. Therefore, cleaning with chemical solutions is an important aid.[1],[2]

It has been reported that bacteria may survive inside a root canal even after careful chemomechanical preparation.[3] Intracanal medications (ICMs) may indirectly contribute to healing the affected periapical tissues.[4],[5] ICMs may be used for a number of purposes, such as to reduce or prevent inter-appointment pain and to provide supplementary coronal seal in temporary restorations.[6] Calcium hydroxide is commonly used as an ICM, especially in cases of apical periodontitis.[7]

Calcium hydroxide has been widely used as an ICM to disinfect the root canal system because of its alkaline pH.[8],[9],[10] Calcium hydroxide has been routinely used as an inter-appointment intracanal due to its ability to control the bacteria in the canal environment, dissolve soft tissue debris, and promote drying of weeping per apical lesions, and because of its good biocompatibility.[11],[12]

Previous reports have demonstrated that remnants of calcium hydroxide reduce the bond strength of resin-based sealer to the root canal dentin,[13] interfere with the sealing ability of a silicon-based sealer,[14] increase apical leakage of gutta-percha root fillings when zinc oxide-eugenol sealer is used,[15] interact with eugenol-based sealers,[16] and prevent penetration of sealer into dentinal tubules.[17] Thus, it is necessary to completely remove calcium hydroxide from the root canal before filling the root canal.[8]

As is well known, a smear layer is created during root canal instrumentation. It may be beneficial because it reduces the permeability of dentin and prevents or slows penetration of bacteria into the dentinal tubules.[18]

It was shown that rotary nickel titanium (Ni-Ti) instruments simplify the removal procedure from a curved root canal.[19] Sonic-activated devices, such as an EndoActivator System, have been introduced to improve the irrigation phase.[20],[21] However, it was found that no technique can completely remove calcium hydroxide medicament from root canals.[20],[22]

Thus, this study aimed to evaluate the influence of the smear layer on the removal of calcium hydroxide from a root canal using three different techniques: manual files, ultrasonic files, and an EndoActivator System.


  Materials and Methods Top


This study was conducted in the Department of Conservative Dentistry and Endodontics at VYWS Dental College and Hospital, Amravati, Maharashtra, India, after receiving approval from the local Ethics Committee. The stereomicroscopic study was conducted at VNIT, Nagpur, India.

Tooth selection

The present ex-vivo research study included 80 single-rooted extracted human permanent premolars. The selection of the sample was based on the following inclusion and exclusion criteria.

Inclusion criteria

Single-rooted permanent mandibular premolars, having a single canal, with fully developed apices that were indicated for extraction due to orthodontic/periodontal reasons, were selected for the study.

Exclusion criteria

Permanent mandibular premolars having more than one root and one canal, not having fully developed apices, having calcification or internal resorption, with a carious lesion or restoration, were excluded from the study.

Root canal preparation

The length of the teeth was standardized at 16 mm from the apex using a vernier caliper, and each tooth was decoronated using a diamond disk and a straight handpiece (NMD, Ghaziabad, India). The patency of the root canals was obtained using a 10 K-file (Mani, Yokohama, Japan). The working length was then recorded for each canal using a Root ZX apex locator (J Morita, Tokyo, Japan). The coronal portions of the canals were enlarged with Gates Glidden (Mani, Japan). All the root canals were instrumented up to size 25 using 0.06 taper Ni-Ti rotary files (Neoendo Orikam, Gurgaon, India) with a crown-down technique. The root canals were irrigated intermittently with 1 mL of 5.25% sodium hypochlorite solution (5.25% NaOCl) in between using each of the hand and rotary instruments.

The 80 prepared specimens were divided randomly into two groups: Group A (with a smear layer) and Group B (smear-free); each group contained 40 teeth.

Experimental groups

Group A: The canals were treated with 5 mL of 5.25% sodium hypochlorite solution (5.25% NaOCl) (Rahul Photographic Company Pvt. Ltd, India.) as the final irrigation before placement of calcium hydroxide.

Group B (smear-free group): The canals were treated with 5 mL of 17% EDTA (Prime Dental, India) for 1 min, followed by 5 mL of 5.25% NaOCl as the final irrigation before placement of calcium hydroxide.

Five samples from both groups were stored as negative controls and the canals were not filled. The teeth in the negative control group were viewed with a scanning electron microscope to confirm the presence/absence of a smear layer.[23]

Placement of calcium hydroxide

The root canals from Group A and Group B were dried with sterile absorbent paper points (Meta-BioMed, Chungcheongbuk-do, Korea) after final irrigation. Calcium hydroxide paste was made by mixing calcium hydroxide powder (Neelkanth, Jodhpur, India) with saline on a glass slab. This paste was then placed in the root canals using a size 25 Lentulo spiral dental instrument (Mani, Japan). After placing calcium hydroxide in the root canals, the access cavities were temporarily sealed with MD-Temp Plus (Meta Biomed Chungcheongbuk-do, Korea). The samples were then stored in a laboratory incubator (U-Tech, Mumbai, India) for 7 days to allow the calcium hydroxide paste to set under static conditions.

Removal of calcium hydroxide

After the samples were stored in an incubator for 7 days, five filled specimens from both groups (Group A and Group B) were stored as positive controls. Each group was then divided into three subgroups of 10 samples each, as follows:

Subgroup I: Calcium hydroxide was removed with a manual file (size 25 K file, master apical file; Mani, Japan).

Subgroup II: Calcium hydroxide was removed with an ultrasonic file (Woodpecker, Guangxi, China) (20 U file).

Subgroup III: Calcium hydroxide was removed with an EndoActivator System (Dentsply Sirona, NC, USA) (25/.04 non-cutting polymer tip).

Removal of calcium hydroxide was performed in each group (n = 10) as follows.

Subgroup I

First, a manual file no. 25, 2% K-file was placed through the working length using circumferential filing for 1 min with 1 mL of 5.25% NaOCl. Finally, the root canals were irrigated using 3 mL of 5.25% NaOCl for 1 min and then dried with paper points.

Subgroup II

The root canals were irrigated with 1 mL of 5.25% NaOCl solution and ultrasonically agitated using a no. 20 U-file at 2 mm from the working length; the file was attached to the ultrasonic unit. The total activation time was 1 min. Finally, the canals were irrigated with 3 mL of 5.25% NaOCl and then dried with paper points.

Subgroup III

The root canals were agitated by an EndoActivator System set at 10,000 cycles per min for 20 s between irrigation (1 mL of NaOCl) using a size 25/.04 non-cutting polymer tip. The total activation time was 1 min, and the respective device was inserted and activated at 2 mm from the working length. Finally, the canals were irrigated with 3 mL of 5.25% NaOCl and then dried with paper points.

Examination

The teeth were split longitudinally along the buccal-palatal plane. To fracture the teeth into two halves, all the roots were longitudinally grooved on external surfaces using a diamond disk, avoiding penetration of the root canals, and sectioned longitudinally using a hammer and a chisel. The sectioned teeth were then examined under a stereomicroscope (Wuzhou New Found Instrument Co., Ltd, Jiayuan, China, Model: XTL 3400E, Magnification: 10×) with image analysis software (Chroma Systems Pvt. Ltd, India, Model: MVIG 2005, VNIT, India).

Statistical analysis

Statistical analysis was performed using analysis of variance (ANOVA) and Tukey’s post-hoc test.


  Results Top


Remnants of calcium hydroxide were found in all the experimental groups, regardless of the absence/presence of a smear layer or the removal technique that was used. The positive control group revealed complete coverage of the canal walls with calcium hydroxide, in contrast to the negative controls.

The removal of calcium hydroxide from the dentinal walls was significantly better in Group B (P<0.05) than in Group A in cervical, middle, and apical third of the canals [Figure 1].
Figure 1: Comparison of the mean values of the remaining calcium hydroxide in all subgroups

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Comparison of the remaining calcium hydroxide in Group A (with smear)

Tukey’s post-hoc test showed a statistically significant difference in terms of the pairwise comparison of the manual files, ultrasonic files, and the EndoActivator System in Group A (with a smear). The dependent variable was apical, middle, and coronal part in the efficacy of manual files, ultrasonic files, and EndoActivator System for the removal of calcium hydroxide from root canals in Group A. The ANOVA was statistically significant [F= 543.897, F= 639.082, F=325.741 (P = 0.0001), respectively] [Table 1].
Table 1: One-way ANOVA in Group A (with smear)

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Comparison of the remaining calcium hydroxide in Group B (smear-free)

Tukey’s post-hoc test showed a statistically significant difference in terms of the pairwise comparison of the manual files, ultrasonic files, and EndoActivator System in Group B (smear-free). A comparison of the ultrasonic files and the EndoActivator System in the apical third of the root canal walls in Group B showed that the difference between these two techniques was not significant. The dependent variable was apical, middle, and coronal part in the efficacy of manual files, ultrasonic files, and EndoActivator System for the removal of calcium hydroxide from root canals in Group B. The ANOVA was statistically significant [F= 31.734, F= 1143.374, F=932.897 (P = 0.000), respectively] [Table 2].
Table 2: One-way ANOVA in Group B (smear-free)

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From the data mentioned earlier, it can be concluded that removal of calcium hydroxide was more effective in Group B (smear-free) than in Group A (with smear), independent of the technique used. [Figure 1] shows a comparison of the mean values of the remaining calcium hydroxide in both the groups. Moreover, ultrasonic files and the EndoActivator System are more efficient than manual files in removing calcium hydroxide in both groups. Ultrasonic files remove calcium hydroxide in the smear-free group (Group B) more efficiently in the coronal and middle third of the root canal walls, but in the apical third both ultrasonic files and the EndoActivator System are equally efficient.

[Figure 1] shows a comparison of all the subgroups in the study. The removal of calcium hydroxide was more effective in Group B (smear-free) than in Group A (with a smear). Moreover, ultrasonic files and the EndoActivator System were more efficient than manual files in removing calcium hydroxide in both the groups. Ultrasonic files removed calcium hydroxide in Group B (smear-free) more efficiently in the coronal and middle third of the root canal wall. In the apical third of the root canal wall, the ultrasonic files and EndoActivator System were equally efficient.


  Discussion Top


Root canal treatment is a procedure in which an inflamed or infected pulp is removed and the inside of the tooth is cleaned, disinfected, and then filled and sealed with restorative material.[24] Success in endodontic treatment was originally based on the triad of debridement, thorough disinfection, and obturation of the root canal system.[25]

Some studies advocated for the importance of maintaining a smear layer after canal preparation, and other studies provided strong evidence to prove that a smear layer acts as a seal to the dentinal tubules and minimizes the risk of bacterial and the toxin invasion by altering dentinal permeability.[26],[27]

Conversely, some authors promoted the significance of removing the smear layer as it contains necrotic tissue, bacteria, and their by-products.[28],[29],[30] A smear layer can act as a reservoir for further microbial irritants and may serve as a substrate for microorganisms to survive, multiply, and then proliferate deep inside the dentinal tubules.[31],[32]

ICMs should be given for completely disinfecting the root canals.[33] If the root canal is not dressed properly with ICMs between visits, residual bacteria may increase in same number as before treatment began.[34] Calcium hydroxide has been considered to be an ideal ICM material.[35]

In the present study, we compared the removal of calcium hydroxide from Group A (with smear) and Group B (smear-free). The samples from Group A were treated with 5.25% NaOCl and the samples from Group B were treated with 5 mL of 17% EDTA for 1 min, followed by 5 mL of 5.25% NaOCl. There were 40 samples in each group. Five samples from each group were used as the negative controls and were not filled by calcium hydroxide. The teeth in the negative control group were viewed with a scanning electron microscope.

Three different techniques were used: manual files, ultrasonic files, and an EndoActivator System. The percentage of the calcium hydroxide-coated surface area was examined under a stereomicroscope.

The ultrasonic files were found to be the most effective in removing calcium hydroxide in Group B (smear-free). An irrigant solution in conjunction with ultrasonic vibration was directly associated with removal of organic and inorganic debris from the root canal walls.[34] The ultrasonic files also showed better removal of calcium hydroxide than the EndoActivator System in both the groups, but those files had about the same efficiency in the apical third of the root canal walls in Group B.

The efficiency in eliminating calcium hydroxide from root canals by the EndoActivator System in combination with irrigation may be due to its primary function, which has been reported to produce vigorous intracanal fluid agitation through acoustic streaming and cavitation.[36],[37] This sonic system has been reported to improve penetration, circulation, and the flow of the root canal irrigant into the more inaccessible sites of the root canal system.[38] In the present study, the EndoActivator System was found to be less effective than the ultrasonic files in removing calcium hydroxide in both the groups, except for the apical third of the root canal wall in Group B, in which not much difference was seen between the EndoActivator System and the ultrasonic files. Consequently, it was found that ultrasonic files are more efficient than the EndoActivator System and manual files.

Thus, the presence or absence of a smear layer affects the removal of calcium hydroxide. The removal of calcium hydroxide was better in the smear-free group (Group B) than the smear layer group (Group A), regardless of the technique that was used. A comparison within groups showed that the ultrasonic files were more efficient than the EndoActivator System and the manual files. Thus, the most effective removal of calcium hydroxide was seen in Group B when ultrasonic files were used. While we evaluated the effect of a smear layer on the removal of calcium hydroxide using different techniques, there are a number of confounding factors in the oral environment, thus the result of this study cannot be completely generalized to clinical conditions.


  Conclusion Top


Based on the results of the present ex-vivo study, it can be concluded that the removal of calcium hydroxide was more efficient in the smear-free group (Group B) than the group with a smear layer (Group A), regardless of the technique that was used. Ultrasonic files were found to be more efficient in removing calcium hydroxide than manual files and the EndoActivator System in both the groups.


  Supplementary Data Top


Table 3: Comparison of the remaining calcium hydroxide in Group A (with smear)

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Table 4: Comparison of the remaining calcium hydroxide in Group B (smear-free)

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    Tables

  [Table 1], [Table 2], [Table 3], [Table 4]



 

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