Efficacy of new irrigating solution on smear layer removal in apical third of root canal: A scanning electron microscope study.

AIMS: The aim of this in vitro study is to evaluate and compare the smear layer removal efficacy of etidronic acid-based irrigating solution with others in the apical third of the root canal.
MATERIALS AND METHODS: Forty human single-rooted mandibular premolar teeth were taken and decoronated to standardize the canal length. After biomechanical preparation, teeth were randomly divided into four groups (n = 10) and the final irrigation was carried out with tested irrigants. Group I: normal saline (negative control); Group II: 5.25% sodium hypochlorite (NaOCl) with surfactant and 17% ethylenediaminetetraacetic acid (EDTA) with surfactant; Group III: freshly mixed BioPure MTAD; and Group IV: freshly mixed Chloroquick solution. The teeth were split into two halves and observed under a scanning electron microscope to analyze the amount of smear layer present. STATISTICAL ANALYSIS: Data were analyzed using the Kruskal-Wallis test and Mann-Whitney test.
RESULTS: Group II (5.25% NaOCl with surfactant followed by 17% EDTA with surfactant) showed least smear layer scores (1.1 ± 0.3162). This was followed by Group III (MTAD) (2.2 ± 0.4216) and then Group IV (Chloroquick) (2.4 ± 0.5164).
CONCLUSION: Sequential use of 5.25% NaOCl with surfactant and 17% EDTA with surfactant was found to be the most efficient than MTAD and Chloroquick in the removal of smear layer in the apical third of root canal.

INTRODUCTION

Root canal treatment is an element of routine dental practice, which aims to preserve teeth in a healthy and functional condition by removing diseased pulp tissue, managing internal infection, and preventing its recurrence. Treatment should balance the need to eliminate microorganism and organic matter from the pulp space, with the imperative to minimize harm to the host and the dental hard tissues. During cleaning and shaping procedure, mechanical instrumentation leads to the formation of an amorphous, granular, and irregular layer covering root dentin and occluding the orifices of dentinal tubules known as “smear layer” that contains organic and inorganic material.[1] The smear layer prevents the penetrations of intracanal medicament and sealers into the dentinal tubules. Hence, removal of smear layer improves the fluid-tight seal during obturation of the root canal systems.[2]

Mechanical instrumentation, therefore, must be supplemented by irrigation to keep the canal wall lubricated, to remove/kill microorganisms, and to dissolve pulp remnants and infected predentin from root canals and ramification.[3] Irrigation has a major influence on removal of smear layer as well.[4] A number of chemicals have been investigated as irrigants to remove the smear layer, for example, sodium hypochlorite (NaOCl), ethylenediaminetetraacetic acid (EDTA), citric acid, etc.

BioPure MTAD disinfects as well as effectively removes smear layer after biomechanical preparation.[5]

Etidronic acid or etidronate (1-hydroxyethylidene-1, 1-bisphosphonate) has been suggested as a possible alternative to EDTA or citric acid.[6] Recently, a new formulation of 18% etidronic acid with 5% NaOCl has been commercially available as “Chloroquick.” Till date, no study has been conducted with this combination.

Hence, the aim of this in vitro study was to compare the smear layer removal efficacy of etidronic acid-based irrigating solution with others in the apical third of the root canal.

MATERIALS AND METHODS

Forty extracted human single-rooted mandibular premolar teeth, for an orthodontic treatment purpose, were selected for this study. The study protocol was approved by ethical institutional board. The presence of a single root canal in each tooth was confirmed on radiographs. All the teeth were decoronated to get the flat reference point and to standardize the root canal length of 14 mm. Patency of the root canal was established by passing a stainless steel number 15 K-file (Mani, Japan) just beyond the apex of all canals. When the tip of the file was visible at the apex, 1 mm short of the file length was considered to be the working length. Canals were prepared using ProTaper Universal rotary system (Dentsply Maillefer, Ballaigues, Switzerland) with torque-controlled motor (X-smart, Dentsply Maillefer, Ballaigues, Switzerland) according to the manufacturer's specifications. Each canal was prepared up to an apical preparation of #F3. About 2 ml solution of 3% NaOCl (Vishal dentocare Pvt., Ltd., India) was used as an irrigant between each subsequent file size in all experimental groups using 5 ml syringe (BD, India) and 30-gauge side-vented needle (Miraject Endotech Luer, Hager & Werken, Germany). For effective irrigation in the apical third of root, the needle was inserted till 1 mm short of the apex.

All specimen teeth were randomly divided into four groups according to the type of final irrigant used. To determine the effects of final irrigating solutions on the surface of root canals after instrumentation, the canals were treated with 5 ml of the respective irrigant for 3 min with the flow rate of 1.7 ml/min approximately.

Group I control (n = 10): 10 samples were irrigated with 0.9% normal saline solution (Abaris Healthcare Pvt. Ltd., Rajpur, India)

Group II (n = 10): 10 samples were irrigated with 5.25% NaOCl with surfactant followed by 17% EDTA with surfactant (Cerkamed, Stalowa Wola, Poland)

Group III (n = 10): 10 samples were irrigated with freshly prepared Biopure MTAD solution (Dentsply, Tulsa Dental, USA)

Group IV (n = 10): 10 samples were irrigated with freshly prepared Chloroquick solution (Neelkanth Dental and Surgical Factory, Jodhpur, India).

The canals were then dried with paper points (Sure-endo, Gyeonggi-do, Korea). Nonpenetrating grooves were made using diamond disc (Summadisk, Shofu Inc., Japan) in all specimen teeth longitudinally on the buccal and lingual aspects. The teeth were then longitudinally split into two halves using chisel and mallet. The half containing the greater part of the apex was selected as the representative sample for each group and then evaluated under scanning electronic microscope (JSM-7600F, JEOL Ltd., Tokyo, Japan) at ×500 magnification.

Scanning electron microscope evaluation

The photomicrographs of each sample were evaluated by another experienced operator who was totally blind to the protocol.

The amount of smear layer remaining on the surface and dentinal tubules was scored according to following 5-score system.[7]

Score 1: Clean root canal wall having only few small debris particles

Score 2: Few small agglomerations of debris covering the root canal wall

Score 3: Many agglomerations of debris covering < 50% of the root canal wall

Score 4: Many agglomerations of debris covering >50% of the root canal wall

Score 5: Complete or nearly complete root canal wall covered by debris.

RESULTS

Statistical analysis was done using Kruskal–Wallis test and Mann–Whitney test using software version SPSS 18.0 version (SPSS Inc., Chicago, IL, USA) as shown in Tables 1 and 2, respectively. Significance for all statistical tests was predetermined at P < 0.05 (significance level α = 5%). Hence, for all the tests, P value was considered for statistical significance.

Table 1

Comparison of mean scores of smear layer removal from apical third of radicular dentin wall using Kruskal-Wallis test

Table 2

Mann-Whitney test was carried out for pair wise significant differences in the presence of smear layer from apical third of radicular dentin wall

All tested irrigants exhibited the ability to remove smear layer from the apical third of the canal except normal saline solution [Figure 1]. Group II (5.25% NaOCl with surfactant followed by 17% EDTA with surfactant) showed least smear layer scores (1.1) when compared to others. This was followed by Group III (MTAD) (2.2) and then Group IV (Chloroquick) (2.4). There was no statistical significance between Group III and Group IV.

Figure 1

Scanning electron microscope photomicrograph (×500) for all groups. (a – Group I; b – Group II; c – Group III; d – Group IV)

DISCUSSION

The primary purpose of irrigation is to flush out loose debris and remove organic and inorganic material, that is, smear layer from the root canal system.[8] Combination of irrigants are recommended to remove organic and inorganic material from canal interstices.[910]

All the samples were irrigated using needle and syringe technique because it can control the volume, depth of penetration, and the flow/rate of irrigation in the apical third of the canal.[11] To avoid confounder in the final results, any type of agitation or activation of irrigating solution was avoided.

In this study, Group II showed best results where 5.25% NaOCl with surfactant followed by 17% EDTA with surfactant was used. This may be due to the synergistic effect of combination of 5.25% NaOCl and 17% EDTA. NaOCl dissolves organic matter of smear layer (pulpal remnants, bacteria, and infected predentin), while EDTA dissolves inorganic portion.[1213] Benzalkonium bromide was used as surfactant in both the solutions by manufacturers. Palazzi et al. showed that solution modified with surfactants had significantly lower surface tension than its normal composition,[14] thereby increasing their adaption to dentin and penetration into the dentinal tubules.[15]

BioPure MTAD is available in two components. Citric acid solution was mixed with doxycycline powder just before use, according to manufacturer's instructions. This group (Group III) showed the second best results due to the presence of 4.25% citric acid which is a chelator. In addition, the detergent (0.5% polysorbate 80) decreases the surface tension and increases the penetrating ability of MTAD.[5] The synergistic action of citric acid, doxycycline, and detergent led to the removal of smear layer.[59]

The result of the current study are in accordance with Torabinejad et al., who verified that 1% NaOCl preceding MTAD can dissolve the organic portion of smear layer that covers the dentinal tubules after instrumentation. This allows MTAD to dissolve the inorganic portion of the smear layer, penetrate into dentinal tubules, and decalcify them.[16]

Chloroquick solution is available in 2-vial system. 18% etidronic acid and 5% NaOCl solution were mixed with each other, according to the manufacturer's instruction. Freshly mixed Chloroquick was found to be less efficient in removing the smear layer among all the tested groups. 18% etidronic acid is a weak chelating agent than 17% EDTA and citric acid solution, studied and quoted by Tartari et al.[17] and De-Deus et al.[18] According to De-Deus et al., this combination required approximately 300 s to completely remove the smear layer due to its slow and weak action on inorganic contents,[19] which was not as per our study protocol. Chloroquick solution does not contain surfactant.

CONCLUSION

Within the limitations of this study, it can be concluded that combination of 5.25% NaOCl with surfactant and 17% EDTA with surfactant proved superior than MTAD and Chloroquick solutions, for smear layer removal.

Financial support and sponsorship

Nil.

Conflicts of interest

There are no conflicts of interest.