Concentration and time-dependent effect of initial sodium hypochlorite on the ability of QMix and ethylenediaminetetraacetic acid to remove smear layer.

AIMS: The aim of this study was to compare the ability of 17% ethylenediaminetetraacetic acid (EDTA) and QMix with different concentrations and time exposures of initial sodium hypochlorite (NaOCl) to remove the smear layer from the root canals.
MATERIALS AND METHODS: Eighty maxillary central incisors were used. After instrumentation, the teeth were divided into eight experimental groups according to the initial and final rinse. About 2.5% and 5% NaOCl were used during instrumentation and for 1 or 3 min was used as postinstrumentation initial irrigants, and 17% EDTA and QMix used as final irrigants. The apical and middle parts of the specimens were observed by scanning electron microscope. STATISTICAL ANALYSIS USED: Data were analyzed using the Kruskal-Wallis, Mann-Whitney, and Friedman's test.
RESULTS: Regardless of the type of final irrigant, QMix allowed more smear layer removal than EDTA after using 5% initial NaOCl for 3 min. In the apical part of the root canal walls, the smear layer was not completely removed.
CONCLUSION: QMix and EDTA were similarly effective in smear layer removal at the middle parts of the root canal regardless of the concentration and time exposure of initial NaOCl, while none of the irrigation protocols was able to remove smear layer at the apical parts.

INTRODUCTION

Root canal preparation results in the formation of 2–5 μm thick superficial smear layer containing organic and inorganic materials that packed into dentinal tubules up to 40 μm.[1] The smear layer can harbor bacteria and so its removal is required for the root canal treatment.[2] It also compromises disinfection of dentinal tubules by preventing penetration of disinfecting solutions into dentinal tubules.[3] Furthermore, its presence interferes the adhesion of obturation materials to dentin walls.[4]

The combined use of sodium hypochlorite (NaOCl) and chelating agent such as ethylenediaminetetraacetic acid (EDTA) has been used to eliminate both organic and inorganic parts of the smear layer.[5] EDTA has been reported to cause high degree of decalcification on the root canal dentin[6] while inactivating the active agent of NaOCl.[7] However, it does not prevent recolonization of the bacteria.[8]

For the dual effect on the removal of smear layer and disinfecting of the root canals, an alternative final irrigation solution, QMix (Dentsply Tulsa Dental, Tulsa, OK, USA) containing a mixture of a polyaminocarboxylic acid, chelating agent, and bisbiguanide antimicrobial agent has been suggested.[910] Due to its detergent content, QMix decreases surface tension and increases wettability to allow better intracanal delivery and improved adhesion of root canal sealers.[11] A review of the current studies showed a lack of reports regarding the different concentration and time exposure of the initial NaOCl irrigation on the smear layer removal effect of QMix. For this reason, the objective of the present study was to compare the ability of QMix with different concentrations and time exposures of initial NaOCl to remove the smear layer from the root canals compared with the influence of 17% EDTA.

MATERIALS AND METHODS

Test solutions

The irrigation solutions tested were 2.5% and 5% NaOCl, 17% EDTA and QMix. EDTA disodium salt was obtained from Sigma Chemical Co., (St. Louis, MO, USA) and was prepared by diluting the dehydrated salt of EDTA to obtain a concentration of 17% (weight/volume); the pH was adjusted to 7.5 by addition of NaOH.

Specimen selection and preparation

Eighty maxillary central incisors from the patients aged 45–65 years, extracted for periodontal reasons, were stored in 0.1% thymol solution until use. After access cavity preparation, a#15 K-file (Dentsply Maillefer, Zurich, Switzerland) was inserted into each canal until its tip was visible at the apical foramen. The roots were decoronated to obtain a standardized length of 17 mm from the anatomic apex. The working length (WL) was determined by reducing 1 mm from the measured length. The root apex was closed using cyanoacrylate glue to simulate a closed root apex. The root canals were prepared by ProTaper Rotary Files (Tulsa Dental Products, Tulsa, OK, USA) up to the size of ProTaper F3. The teeth were then randomly assigned into eight experimental groups (n = 10) as follows: Group 1: 3 min 5% NaOCl, followed by QMix; Group 2: 3 min 5% NaOCl, followed by EDTA; Group 3: 1 min 5% NaOCl, followed by QMix; Group 4: 1 min 5% NaOCl, followed by EDTA; Group 5: 3 min 2.5% NaOCl, followed by QMix; Group 6: 3 min 2.5% NaOCl, followed by EDTA; Group 7: 1 min 2.5% NaOCl, followed by QMix; and Group 8: 1 min 2.5% NaOCl, followed by EDTA.

All irrigants were delivered using a 30-gauge side-vented needle (Max-i-Probe, Dentsply, Rinn, Elgin, IL, USA) from 1 mm of WL. The same concentration of 1 mL of NaOCl was used between each file, and 5 mL was used as the postinstrumentation initial irrigant. Five milliliter of EDTA or QMix for 2 min was delivered as final irrigant. The root canals were irrigated with 5 mL of distilled water and dried with sterile paper points.

Scanning electron microscopic evaluation

The access of root canals was protected with a cotton pellet, and two longitudinal grooves were prepared in each root without perforating the canal to facilitate splitting of each root into two longitudinal halves. Each root half was labeled at 3 and 6 mm from the apical foramen for apical and middle root canal evaluation. The specimens were mounted on aluminum stubs, gold sputtered, and evaluated under scanning electron microscope (EVO, 50; Carl Zeiss NTS GmbH, Oberkochen, Germany). The first scan was made at a magnification of ×30, and then the images of dentin surfaces were taken at the magnifications of ×2000 at previously labeled 3 and 6 mm. Therefore, two images of each level were obtained for each tooth, providing twenty images per canal level/group. Two investigators scored the smear layer at the middle and apical parts of the root canals in a blinded manner. To evaluate the degree of smear layer removal, a four-scale scoring system[12] was used: 1, no smear layer, with all tubules cleaned and opened; 2, few areas covered by smear layer, with most tubules cleaned and opened; 3, smear layer covering almost all the surface, with few tubules opened; and 4, smear layer covering all the surfaces.

Data were analyzed using the SPSS Software (Version 21.0; Chicago, IL, USA). The interexaminer reliability for the scanning electron microscopic evaluation was verified by kappa test (kappa value = 0.85). Kruskal–Wallis test was used for differences among groups, while Mann–Whitney U-test was used for pair comparisons 5% (P = 0.05). The Friedman's test was used to analyze the results of the middle and apical root part of the same specimen.

RESULTS

There was no smear layer on the most of the canal surfaces at the middle part of the root canals [Figure 1]. QMix caused more smear layer removal than 17% EDTA after using 5% NaOCl for 3 min (P < 0.05). However, no significant difference was observed when 2.5% NaOCl was used as the initial irrigant (P > 0.05). There was no statistically significant difference in the smear layer removal from the middle part of the root canal walls by each final irrigation solution with the increasing time exposure of the initial NaOCl (1 vs. 3 min) (P > 0.05). Regarding the concentration of initial NaOCl, 5% NaOCl increased the smear layer removal efficiency of QMix as compared to 2.5% NaOCl concentration (P < 0.05), while no significant difference was observed for EDTA solution (P > 0.05) [Figure 2].

Figure 1

Representative scanning electron microscopic images of middle part of the root canals treated with 2.5% or 5 sodium hypochlorite for 1 or 3 min, followed by 17% ethylenediaminetetraacetic acid or QMix for 2 min (×2000). No smear layer observed on the root canal walls and dentinal tubules were clean and patent

Figure 2

Smear removal scores of experimental groups at middle parts of root canals (n = 20) based on the four-level scoring system. Score 1 - No smear layer; 2 - Few areas covered by smear layer; 3 - Smear layer covering almost all the surface, with few tubules opened; 4 - Smear layer covering all the surfaces. Five percent or 2.5% sodium hypochlorite was applied for 1 or 3 min as an initial final irrigant, followed by ethylenediaminetetraacetic acid and QMix. QMix caused more smear layer removal than ethylenediaminetetraacetic acid after using 5% sodium hypochlorite for 3 min. Five percent sodium hypochlorite resulted in more smear layer by QMix as compared to 2.5% sodium hypochlorite regardless of time (P < 0.05)

In the apical part of the root canal walls, the smear layer was not completely removed by 17% EDTA and QMix after using initial NaOCl (P > 0.05) and severe smear layer was observed on the surface of most of the root canals [Figure 3]. With increasing concentration or application time of initial NaOCl did not affect the smear layer removal score at the apical part (P > 0.05) [Figure 4].

Figure 3

Representative scanning electron microscopic images of apical part of the root canals treated with 2.5% or 5 sodium hypochlorite for 1 or 3 min, followed by 17% ethylenediaminetetraacetic acid or QMix for 2 min (×2000). Severe smear layer on the root canal walls was observed

Figure 4

Smear removal scores of the experimental groups at apical parts of root canals (n = 20) based on the four-level scoring system. Score 1 - No smear layer; 2 - Few areas covered by smear layer; 3 - Smear layer covering almost all the surface, with few tubules opened; 4 - Smear layer covering all the surfaces. In the apical part of the root canal walls, heavy smear layer was observed regardless of the final irrigation solutions

DISCUSSION

As a main root canal irrigant, NaOCl is widely used during root canal treatment due to its unique capacity to dissolve necrotic tissue remnants and excellent antimicrobial potency.[5] It has been indicated that the removal of organic material and mechanical impact on dentin is dependent the concentration of NaOCl.[13] The present study indicates that the smear layer removal effect of QMix was increased with the high concentration of NaOCl, while the effect of EDTA was similar regardless of the concentration of NaOCl. The results also demonstrated that the effectiveness of the smear layer removal with QMix was statistically higher from that of 17% EDTA when 5% NaOCl for 3 min is used as an initial irrigant. On the other hand, there was no concentration or time-dependent effect of initial NaOCl for the smear layer removal capacity of 17% EDTA in consistency with previous studies.[6]

QMix has been reported to remove smear layer as effectively as 17% EDTA after using 5.25% NaOCl.[14] However, open apex root model was used in the previous study, while the apex of the root canals was closed in the present study to mimic clinical situation. In the present study, we observed the similar finding for 5% NaOCl for 1 min or 2.5% NaOCl for 1 or 3 min at the middle part of the root canals. QMix caused more smear layer removal after using 5% NaOCl for 3 min as compared to 17% EDTA. However, the smear layer was not completely removed in the apical part of the root canals regardless of final irrigant used. On the other hand, severe erosion of the dentinal tubules of a root canal treated with 5.25% NaOCl as a root canal irrigant and 17% EDTA as a final irrigant for 5 min was reported.[15] From a cleansing perspective, lower concentrations of NaOCl retain tissue dissolution capacity and are effective in cleaning root canals.[16] Furthermore, it has been reported that the aggressiveness of EDTA in causing canal wall erosion is attributed to the prolonged use of NaOCl.[17] Overall, the present study suggested the lower concentration of NaOCl with short application time for clinical usage.

The irrigation solutions require sufficient working time to be effective. About 17% EDTA for 2 min has been suggested to remove the smear layer from root canal walls.[18] In addition, increasing the application time of 17% EDTA has been known not to improve smear layer removal.[19] For this reason, in this study, we fixed the application time of 17% EDTA and QMix for 2 min.

The debridement in the apical part of root canals has always been a challenge. In fact, in the present study, none of the final irrigation solutions was able to completely remove the smear layer from the apical part of the root canal walls. This finding is in agreement with previous studies indicating that irrigating solutions are less effective in the apical part of root canals.[14] The likely explanation for this result could be inadequate penetration of the irrigation solutions into the apical part of the root canal during irrigation.[20] More wide diameter of coronal and middle parts of the root canals allow higher volume of irrigants and better flow of the solution that improve the efficiency of the smear layer removal.[15] Nevertheless, in this study, heavy smear layer was still observed in the apical parts of most of the root canal walls. Crumpton et al.[21] showed that the smear layer was efficiently removed with a final rinse of 1 mL of 17% EDTA for 1 min followed by 3 mL of 5.25% NaOCl. On the contrary, this protocol has been reported not to be efficient to completely remove the smear layer, especially in the apical part.[22] In addition, in our study, the combined use of 2 mL of 17% EDTA for 2 min and 5 mL of 5% NaOCl was still not found to completely remove the smear layer in the apical part. For this reason, it is important to bear in mind that activating the irrigating solutions with an ultrasonic tip in the apical parts of root canals seems to be essential.[23] Under the conditions of this study, it could be concluded that 2.5% NaOCl for 1 or 3 min, followed by 17% EDTA or QMix for 2 min removes more smear layer from the middle part of the root canals. Ultrasonic activation of new irrigation solutions should be further evaluated to increase the smear layer removal from the apical part of the root canals.

Financial support and sponsorship

Nil.

Conflicts of interest

There are no conflicts of interest.