A comparative evaluation of smear layer removal by using edta, etidronic acid, and maleic acid as root canal irrigants: An in vitro scanning electron microscopic study.

AIM: The purpose of this study is to evaluate and compare the efficacy of 17% EDTA, 18% etidronic acid, and 7% maleic acid in smear layer removal using scanning electron microscopic image analysis.
MATERIALS AND METHODS: Thirty, freshly extracted mandibular premolars were used. The teeth were decoronated to obtain working length of 17mm and instrumentation up to 40 size (K file) with 2.5% NaOCl irrigation between each file. The samples were divided into Groups I (17% ethylenediaminetetraacetic acid (EDTA)), II (18% etidronic acid), and III (7% maleic acid) containing 10 samples each. Longitudinal sectioning of the samples was done. Then the samples were observed under scanning electron microscope (SEM) at apical, middle, and coronal levels. The images were scored according to the criteria: 1. No smear layer, 2. moderate smear layer, and 3 heavy smear layer. STATISTICAL ANALYSIS: Data was analyzed statistically using Kruskal-Wallis analysis of variance (ANOVA) followed by Mann-Whitney U test for individual comparisons. The level for significance was set at 0.05.
RESULTS: The present study showed that all the three experimental irrigants removed the smear layer from different tooth levels (coronal, middle, and apical). Final irrigation with 7% maleic acid is more efficient than 17% EDTA and 18% etidronic acid in the removal of smear layer from the apical third of root canal.

INTRODUCTION

Three-dimensional cleaning, shaping, and a proper obturation with adequate seal of the root canal system are the main goals of root canal treatment. Complete debridement, with smear layer removal is an asset and could help to achieve a successful outcome of the root canal treatment.[1] Smear layer contains both organic and inorganic components. The smear layer has been recommended to be removed as it may be having mixture of bacteria and their byproducts.[23] Also it may prevent the penetration of irrigants and intracanal medicaments into the dentinal tubules and prevent the close adaptation and adherence of sealer cement onto canal walls.[456]

Ultrasonic instruments, lasers, and chelating agents have been used for chemical and mechanical debridement during root canal treatment for the smear layer removal.[7] Ethylenediaminetetra acetic acid (EDTA) is the most frequently used chelatorin endodontics.[8] Several studies have shown that the use of a combination of sodium hypochlorite (2.5-5%) and EDTA (10-17%) is particularly effective in the removal of organic and inorganic debris.[910] EDTA is a Ca2+ chelating agent, and therefore capable of removing smear layer. It has been found that a final flush of EDTA can open up the dentinal tubules, and thus it increases the number of lateral canals to be filled.[11]

Etidronic acid (also known as 1-hydroxyethylidene-1,1-bisphosphonate or HEBP) is abiocompatible chelator that can be used in combination with sodium hypochlorite and have adequate calcium chelating capacity.[12] Bisphosphonates are highly biocompatible chelators systemically administered in patients suffering from osteoporosis or neoplastic diseases involving osteolytic bone destruction.[13]

Maleic acid is a mild organic acid used as an acid conditioner in adhesive dentistry.[14] It has been found to possess the smear layer removing quality when used as an acid etchant in restorative dentistry.[15] Ballal et al., have suggested 7% maleic acid as a mild organic acid and found to acquire the smear layer removing high quality from root canal dentine and to be more effective than EDTA at the apical third of root canal.[16]

The present study evaluates and compares the efficiency of 17% EDTA, 18% etidronic acid, and 7% maleic acid in their ability to remove smear layer following root canal instrumentation on human extracted tooth using scanning electron microscope (SEM).

MATERIALS AND METHODS

Selection of samples

Ethical clearance was taken before starting the study. Thirty freshly extracted single rooted human mandibular premolars were collected. They were caries free and had single canal and mature apex. Teeth with cracks or fracture lines were eliminated after examining using loops.

Teeth preparation for the study

Buccal and proximal radiographs were taken to ensure that the teeth had only single canal. The teeth were cleaned of debris and soft tissue remnants and were stored in saline solution. The samples were then autoclaved.

An open-end model was used in our study. The teeth were decoronated to obtain uniform working length of 17 mm for all samples using a diamond disk (D&Z, Darmstadt, Germany). The root canals were accessed and the initial coronal preparation was done with Gates-Glidden drills (Dentsply Maillefer, Ballaigues, Switzerland) up to number 3 size. Standardized crown down technique with sequentially sized K files (Densply-Maillefer, Ballaigues, Switzerland) is used up to size 40 with 2.5% NaOCl irrigation (Novo Dental Product, India) between each file, followed by irrigation with 5 ml of saline.

The samples are divided into Groups I, II, and III containing 10 samples each.

Group I- 17%EDTA irrigation (Merck, Germany).

Group II- 18% etidronic acid irrigation (Cublen K8514 GR:Zschimmer &Schwarz, Germany).

Group III- 7% maleic acid irrigation (Merck, Germany).

Then each sample was irrigated with 5 ml of each irrigant for 1 min. All the irrigants were freshly prepared and standardized. According to the groups, irrigants were delivered into the root canals with a side vented endodontic irrigating needle (RC Twents, Prime Dental Products, Mumbai, India) until the working length using manual technique. And the final irrigation was done with 5 ml of distilled water for each sample.

Teeth preparation for sem analysis

The canals were dried with absorbent paper points and the entrance to each of the canals was protected with a cotton pellet. Diamond discs were used to cut deep grooves on the buccal and lingual surfaces of the roots, without perforating the root canals. The roots were then split with a chisel and mallet. One half of each tooth is selected and prepared for SEM examination.

Sem analysis

The specimens were dehydrated by ethyl alcohol: 30% for 10 min, 50% for 20 min, 70% for 20 min, 90% for 30 min, 100% for 30 min, and 100% for 30 min. After that the specimens were mounted on coded stubs, air dried, placed in a vacuum chamber, and sputter-coated with a 300 Agold layer. The specimens were then analyzed using a SEM (Cam scan MV 2300, Oxford Instrument, UK). The dentinal surfaces were observed at cervical, middle, and apical thirds with a magnification of ×2,000 for the presence/absence of smear layer and visualization of the entrance to dentinal tubules. Photomicrographs (×2,000) of these areas on each of the coronal, middle and apical thirds were taken [Figures 1-3].

Figure 1

(a) SEM image of group I at coronal third. (b) SEM image of Group I at middle third. (c) SEM image of Group I at apical third. SEM = Scanning electron microscope

Figure 3

(a) SEM image of Group III at coronal third. (b) SEM image of Group III at middle third. (c) SEM image of Group III at apical third

(a) SEM image of Group II at coronal third. (b) SEM image of Group II at midddle third. (c) SEM image of Grup II at apical third

The removal of smear layer was evaluated by a teaching faculty, who was blind to the irrigation regimens employed for each group. The scores were attributed according to the rating system developed by Torabinejad et al.:[17]

No smear layer (no smear layer on the surface of the root canal: All tubules were clean and open).

Moderate smear layer (no smear layer on the surface of the root canal, buttubules contained debris).

Heavy smear layer (smear layer covered the root canal surface and the tubules).

Statistical methods

Statistical Package for Social Sciences (SPSS) version 16 was used for analysis:

Kruskal-Wallis analysis of variance (ANOVA) was used for intragroup comparisons.

Mann-Whitney U test was used for intergroup comparisons.

RESULTS

All irrigants tested, removed smear layer effectively form coronal and middle third [Figure 4]. At the apical third, all irrigants showed poor smear layer removing property, but maleic acid (Group III) showed comparatively better results than EDTA (Group I) and etidronic acid (Group II) at the apical third [Table 1]. There was no significant difference between etidronic acid and EDTA. Intragroup comparison showed highly significant difference in coronal against apical region in EDTA group, significant difference in coronal vs apical and middle vs apical in etidronic acid group. In maleic acid group also, we found a significant change in coronal-middle and coronal-apical regions [Table 2].

Figure 4

Mean smear layer removal by different irrigants at coronal, middle, and apical levels. EDTA = Ethyelenediaminetetra acetic acid

Table 1

Mann-Whitney U test for intergroup comparison at apical third

Table 2

Mann–Whitney U test for intergroup comparison of EDTA, etidronic acid, and maleic acid

DISCUSSION

Straight single-rooted and single canal mandibular premolar were selected with root length of approximately 20-22 mm and curvature less than 5 degrees according to Schneider in order to avoid anatomic variation and to maintain standardization, which was confirmed using radiograph as suggested by Wu et al.[18] Standardized crown down technique was followed for preparation of root canal using K-files up to size 40 reaching full working length which facilitates penetration of irrigants to the apical third and produces a greater reduction in remaining bacteria and dentin debris as compared with smaller preparation.[19]

We used a 27-gauge needle tips (Endo EZE; Ultradent Products Inc., South Jordan, UT, USA), which can penetrate more deeply into theapical one-third because of the small bore size. Endo-EZE irrigating needles have a unique anti-obturating end with side venting, which increases the contact of the irrigant to the canal walls and prevents the forceful passage of irrigants through the apical foramen and have increased the efficiency of the irrigant in smear layer removal from root canals.

In the present study, 2.5% NaOCl was used for the chemomechanical preparation between each instrument, which could also remove the organic contents of smear layer. This is similar to a study which shows that diluted form of NaOCl is not inferior to higher concentration of NaOCl in removal of organic part of smear layer.[20]

In the present study; EDTA, etidronic acid, and Maleic acid were used for the removal of inorganic components of smear layer. Hasheminia et al.,[21] concluded that 1 min application of 17% EDTA was more effective than erbium-yttrium aluminium garnet (Er:YAG) laser in SL removal. Calt and Serper'sinvestigation on 1 and 10 min application time has shown that the ability of 17% EDTA in 1 min application time is agreeable and prevents harmful consequences such as excessive erosion, enlargement of dentinal tubule openings, and deterioration of the dentinal surface.[22] Studies were done on the efficacy of removal of smear layer using 18% etidronic acid and was found to be effective.[10] It was reported that maleic acid when used at a higher concentration than 7% caused damage to the intertubular dentin and at 7% was effective in removing the smear layer.[23]

In the present study, all the three irrigants (17% EDTA, 18% etidronic acid, and 7% maleic acid) removed the smear layer effectively from coronal and middle third with statistically no significant difference between them. In the apical third, 7% maleic acid showed better smear layer removing property than 17% EDTA and 18% etidronic acid. This is in agreement with various other studies that have reported EDTA to be effective in smear layer removal only in coronal and middle thirds, but not in the apical third.[16]

In a study published recently, maleic acid was found to be more effective than EDTA in removing smear layer, even though apical preparation was performed up to ISO size 40. This might be due to high surface tension of 17% EDTA (0.0783 N/m) in contrast with that of 7% maleic acid (0.06345 N/m). The efficacy of EDTA decreases over a time because of the decrease in pH, but maleic acid is highly acidic and it has a better demineralizing effect in shorter period of time.[16]

Paque et al., reported that dentin in the apical third of the root canal is sclerosed; hence, EDTA may not have such a pronounced action on sclerosed dentin in apical third.[24] Etidronic acid is a weak chelator and in a study 9 and 18% was used to remove smear layer;18% concentration provided better results, and hence the higher concentration was used in our study.[25] Etidronic acid was found to have smear layer removal efficacy in coronal and middle third as equal to that of EDTA and maleic acid. But it showed less smear layer removal in the apical third when compared with maleic acid. This might be because of the lesser chelating action of etidronic acid than maleic acid. The lower efficacy of etidronic acid on sclerosed dentin can also be an attributing factor. EDTA and maleic acid showed interactions with NaOCl, when used together it reduced the expected properties of NaOCl, whereas etidronic acid can be used in combination with NaOCl without any loss of actions related to both irrigants.[1126]

Other than SEM, the smear layer can also be scored by using digital image analysis. It can overcome the potential evaluator bias, requires less time, and other parameters of interest like density and average diameter of dentinal tubules can be measured; but SEM was opted in this study because it is a commonly available tool for evaluating the smear layer.[16]

The present study was done in vitro, so the results obtained do not necessarily allow any definite actions of the tested substances in situ. Blood, tissue remnants, and a multitude of other variables may affect the actions of agents under investigation in the root canal system. Curved canals can be more challenging and makes effective cleaning of the root canal system more difficult. Deeper penetration of the needle takes place in the single-rooted premolar tooth because of wider canals; therefore, results may vary in posterior teeth with narrow canals. Nevertheless, further long-term clinical studies are necessary to confirm these results and evaluate their relevance to treatment outcome.