Effect of different final irrigating solutions on smear layer removal in apical third of root canal: A scanning electron microscope study.

AIM: The aim of this in vitro study is to compare the smear layer removal efficacy of different irrigating solutions at 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 to 14 mm. They were prepared by ProTaper rotary system to an apical preparation of file size F3. Prepared teeth were randomly divided into four groups (n = 10); saline (Group 1; negative control), ethylenediaminetetraacetic acid (Group 2), BioPure MTAD (Group 3), and QMix 2 in 1 (Group 4). After final irrigation with tested irrigants, the teeth were split into two halves longitudinally and observed under a scanning electron microscope (SEM) for the removal of smear layer. The SEM images were then analyzed for the amount of smear layer present using a three score system. STATISTICAL ANALYSIS: Data are analyzed using the Kruskal-Wallis test and Mann-Whitney U-test.
RESULTS: Intergroup comparison of groups showed statistically significant difference in the smear layer removal efficacy of irrigants tested. QMix 2 in 1 is most effective in removal of smear layer when compared to other tested irrigants.
CONCLUSION: QMix 2 in 1 is the most effective final irrigating solution for smear layer removal.

INTRODUCTION

Successful endodontic therapy depends on thorough chemo-mechanical preparation as well as three-dimensional obturation that provides a complete sealing of the root canal system.[1]

During cleaning and shaping procedure instrumentation with various root canal instruments leaves an amorphous, granular, and irregular layer covering root dentin known as smear layer that contains inorganic and organic material. The first researchers to describe the smear layer on the surface of instrumented root canals were McComb and Smith.[2] The smear layer may adversely affect the disinfection of dentin walls while blocking irrigants and sealants from entering dentinal tubules. In addition, it may increase post obturation microleakage, and may serve as a source of nutrients for some species of intra-canal microbiota.[3]

Removal of smear layer after root canal instrumentation and before canal obturation improves the adaptation of root filling materials to the canal walls, resulting in a superior seal.[4] So far the most commonly used method of smear layer removal has been the chemical method using chelating agents, with ethylenediaminetetraacetic acid (EDTA) being the most common agent used.[5] The most advocated combination of 17% EDTA plus 5.25% NaOCl removes the smear layer completely in the coronal and middle thirds but is less effective in the apical third.[6]

For effective removal of smear layer apart from EDTA new irrigating agents such as QMix 2 in 1, MTAD, have been introduced as final irrigants.

The aim of the present study is to evaluate the smear layer removal efficacy of different final irrigating solutions.

MATERIALS AND METHODS

Forty human single-rooted mandibular premolar teeth were selected for this study. They were decoronated to get the stable reference point and to standardize the root canal length of 14 mm. All specimen teeth were randomly divided into four groups as follows:

Group 1: Saline.

Group 2: EDTA.

Group 3: BioPure MTAD.

Group 4: QMix 2 in 1.

Patency of the root canal is established by passing a stainless steel number 15 K-file (Kendo, Germany) just beyond the apex of all canals. Working lengths were determined by subtracting 1 mm from that length. Canals were prepared using ProTaper rotary system (Dentsply Maillefer, Ballaigues, Switzerland). Each canal was prepared up to an apical preparation of #F3. Three percent NaOCl (Vishal dentocare Pvt., Ltd., India) irrigant was used between each subsequent file size in all experimental groups while saline was the sole irrigant in Group 1.

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. The irrigating solution was delivered using a 30-gauge side-vented needle (Dentsply Tulsa Dental, Tulsa, OK, USA) passively placed to within the apical third of the root canals.

The canals were then dried with paper points. Nonpenetrating grooves were made in all specimen teeth at the cement-enamel junction (CEJ) and longitudinally on the buccal and lingual aspects. The teeth were then longitudinally split into two halves using chisel and mallet and the half containing the greater part of the apex was selected as the representative sample for each group and they were evaluated under scanning electronic microscope.

Scanning electron microscope evaluation

Coded samples were mounted on metallic stubs, gold sputtered and viewed under a scanning electron microscope (SEM). Photographs at magnifications of ×1000 were taken for each specimen in the apical third (4 mm from root apex). The images at ×1000 magnification were then analyzed for the amount of smear layer present [Figures 1a, b and 2a, b]. The amount of smear layer remaining on the surface of the root canal and dentinal tubules was scored according to a three score system developed by Torabinejad et al.[7]

Figure 1

(a) Scanning electron microscope picture of saline, (b) Scanning electron microscope picture of ethylenediaminetetraacetic acid

Figure 2

(a) Scanning electron microscope picture of MTAD, (b) Scanning electron microscope picture of QMix 2 in 1

Score 1: No smear layer — No smear layer was detected on the surface of the root canal, and all tubules were open.

Score 2: Moderate smear layer — No smear layer on root canal walls but tubules contained debris.

Score 3: Heavy smear layer — Smear layer covered the root canal wall surface and the tubules.

RESULTS

Statistical analysis was done using Kruskal-Wallis H test and Mann-Whitney U-test using software version SPSS 17.0 version (SPSS Inc., Chicago) [Tables 1 and 2]. The results showed that QMix 2 in 1 (Group 4) showed least smear layer scores (1.30 ± 0.48) when compared to others. This was followed by MTAD (2.00 ± 0.00), EDTA (2.40 ± 0.52), and saline showed highest smear layer scores (3.00 ± 0.00).

Table 1

Smear layer scores for experimental groups

Table 2

Comparison between groups

DISCUSSION

During mechanical instrumentation smear layer formation occurs on the root canal dentinal wall occluding dentinal tubules, for efficient disinfection and sealing of the root canal system its removal is necessary.[8]

Irrigation is an important step during and after instrumentation for effective removal of smear layer and also for lubrication of root canal system.[9]

NaOCl is the traditional irrigant which is used most commonly, however due to its inability to remove inorganic part of smear layer other irrigants were introduced.[10] There are different final irrigating solutions which are used after instrumentation for effective smear layer removal.

QMix 2 in 1 is a new root canal irrigating solution, and it contains a mixture of a bisbiguanide an antimicrobial agent, a polyaminocarboxylic acid, a calcium-chelating agent, saline, and a surfactant.[11]

Eliot et al.[12] evaluated the effectiveness of the three different formulations of QMix on the removal of canal wall smear layer and compared to a standard solution of 17% EDTA. SEM analysis showed the effectiveness of all three QMix formulations were superior to EDTA in smear layer removal and exposure of dentinal tubules in the root canal system in single-rooted teeth.

Kolosowski et al. analyzed the precipitate formation on the surface and in the tubules of dentin irrigated with sodium hypochlorite and a final rinse of chlorhexidine or QMix and concluded no precipitates or PCA were detected with QMix and NaOCl in dentinal tubules.[13]

Stojicic et al.[14] evaluated efficacy of a novel root canal irrigant, QMix, against Enterococcus faecalis and its ability to remove smear layer was examined, using SEM. It was concluded that QMix and NaOCl were superior to CHX and MTAD under laboratory conditions in killing E. faecalis and ability to remove smear layer by QMix was comparable to EDTA. This was also supported by studies done by Ballal et al.,[15] who showed that wetting of root canal dentin was better with QMix 2 in 1 due to its low surface tension. These studies correlate with our study; QMix 2 in 1 showing better smear layer removal compared with other final irrigating solutions and there is a significant difference among all the groups.

Dai et al.,[16] evaluated the Smear and debris scores of QMix in the coronal third, middle third, and apical third of root canals using two versions of QMix 2 in 1 (QMix I [pH = 8], QMix II [pH = 7.5]) using SEM. It was concluded that the two versions of the experimental antimicrobial (QMix) are as effective as 17% EDTA in removing canal wall smear layers from the entire root canal space in straight root canals after the initial use of NaOCl as the initial rinse.

BioPure MTAD is a mixture of tetracycline isomer (3% doxycycline), 4.25% citric acid, detergent (0.5% polysorbate 80). MTAD has smear layer removal and antimicrobial properties. In this product, doxycycline hyclate is used instead of its free-base doxycycline monohydrate, to increase the water solubility. It is considered to be clinically effective and a biocompatible endodontic irrigant.[17]

In this study MTAD shown to be next to QMix 2 in 1 in removing smear layer, this may be because of its low surface tension (34.5 mJ/m2), These results correlate with the study conducted by Paul et al.,[18] who showed that MTAD is better irrigating solution removing smear layer even in apical third.

Shenoy et al.,[19] compared the smear layer removal efficacy of Tublicid plus, MTAD, EDTA and found that Tublicid plus and MTAD are better when compared to EDTA.

CONCLUSION

Within the limitations of this study, it was observed that among the final irrigating solutions used QMix 2 in 1 displayed effective smear layer removal when compared to EDTA, MTAD and Saline.

Financial support and sponsorship

Nil.

Conflicts of interest

There are no conflicts of interest.