Saudi Endodontic Journal

: 2017  |  Volume : 7  |  Issue : 3  |  Page : 170--175

Comparative evaluation of ethylenediaminetetraacetic acid, maleic acid, and peracetic acid in smear layer removal from instrumented root canal system: A scanning electron microscopic analysis study

Roshni Butala, Pradeep Kabbinale, Vasudev Ballal 
 Department of Conservative Dentistry and Endodontics, Manipal College of Dental Sciences, Manipal University, Manipal, Karnataka, India

Correspondence Address:
Pradeep Kabbinale
Department of Conservative Dentistry and Endodontics, Manipal College of Dental Sciences, Manipal University, Manipal - 576 104, Karnataka


Introduction: The aim of this study was to assess the ability of 7% maleic acid, 0.5% peracetic acid (PAA), and 17% ethylenediaminetetraacetic acid (EDTA) in removing smear layer from root canal system of human teeth using scanning electron microscopic analysis (SEM). Materials and Methods: Thirty-five non-carious human anterior teeth with single roots were selected for the study. Chemo-mechanical preparation was done using crown down technique with irrigation of 2.5% NaOCl after every instrument use. Depending on the final irrigation solution, the samples were divided randomly into three experimental groups and one control group: (1) The maleic acid group: 07% (n = 10), (2) the PAA group: 0.5% (n = 10), (3) the EDTA group: 17% (n = 10), and (4) the control group: 0.9% saline (n = 5). These teeth were then evaluated using SEM analysis for the absence or presence of smear layer, thereby analyzing their cleaning effectiveness in the coronal, middle, and apical thirds of the root canal system. The inter examiner's reliability was verified with the use of Kappa test. The data of the score for intragroup comparison and intergroup comparison for evaluation of the presence or absence of smear layer were statistically analyzed by Pearson Chi-square test. The level of statistical significance was set at P < 0.05. Results: In the coronal thirds of the root canal, there was no statistically significant difference between the EDTA and the maleic acid groups when evaluated for their efficacy at smear layer removal. Whereas, maleic acid performed significantly better than PAA and EDTA in removing smear layer from middle and apical thirds of the root canal system. Conclusion: A final irrigation with 7% maleic acid is more efficacious than 17% EDTA and 0.5% PAA when used as a smear layer removal agent in the apical third of the root canal system.

How to cite this article:
Butala R, Kabbinale P, Ballal V. Comparative evaluation of ethylenediaminetetraacetic acid, maleic acid, and peracetic acid in smear layer removal from instrumented root canal system: A scanning electron microscopic analysis study.Saudi Endod J 2017;7:170-175

How to cite this URL:
Butala R, Kabbinale P, Ballal V. Comparative evaluation of ethylenediaminetetraacetic acid, maleic acid, and peracetic acid in smear layer removal from instrumented root canal system: A scanning electron microscopic analysis study. Saudi Endod J [serial online] 2017 [cited 2020 Aug 15 ];7:170-175
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Microorganisms in the root canal system are considered to play a major role in the pathogenesis of apical periodontitis.[1] The complete obliteration of root canal space with an inert filling material and creation of a fluid tight seal are the goals for successful endodontic therapy. It is imperative for the endodontic filling material to adhere closely to the tooth structure for the creation of this seal. This, however, is impaired by the formation of smear layer after mechanical instrumentation of the root canal.[2],[3] The endodontic smear layer which is amorphous and irregular in structure contains organic components such as microorganisms and their metabolic products, necrotic debris, pulp tissue, and odontoblastic processes as well as inorganic components like dentin debris.[4]

There have been controversial reports over the maintenance or removal of this endodontic smear layer. While some suggest that its persistence will alter dentinal permeability by blocking the dentinal tubules thus limiting bacterial or toxin penetration,[5],[6],[7] others believe that it can harbor bacteria and cause leakage thus necessitating its entire removal from the root canal walls.[8],[9],[10] This loosely adherent structure is also known to prevent adaptation of endodontic sealers to canal walls as well as interfere with penetration of irrigants and intracanal medicaments into the dentinal tubules.[11],[12],[13],[14]

Several techniques have been employed for the removal of smear layer ranging from the use of chelating agents and ultrasonics to lasers during root canal therapy.[15] Current methods to remove the smear layer might involve the use of a chelating agent during irrigation or as a final rinse in combination with other irrigants having tissue dissolving properties.[16]

Ethylenediaminetetraacetic acid (EDTA), a calcium chelating agent is used routinely in endodontics for the removal of smear layer.[17] The combination of sodium hypochlorite (2.5%–5%) and EDTA (10%–17%) has been proven to be successful in the removal of organic and inorganic debris.[18],[19] Studies have stated that a final irrigation of the root canal with EDTA can open up the dentinal tubules thereby increasing the number of lateral canals to be filled eventually by the sealer.[20]

Maleic acid is used as an acid conditioner in adhesive dentistry.[21] This mild organic acid is found to remove smear layer from the surface of teeth.[22] Ballal et al. have shown that smear layer removal from the apical third of the root canal was performed better using 7% maleic acid than EDTA.[23]

Peracetic acid (PAA) is one of the most potent disinfectants. It has been used as a single endodontic irrigant in the former German democratic republic.[24] It has antibacterial, sporicidal, antifungal, and antiviral effects.[24] It has been used for the elimination of biofilm formation in various areas.[25],[26] The acetic acid content seems to cause inorganic material dissolution while also forming water soluble complexes with calcium. It has been shown that 2.25% PAA solution is comparable with 17% EDTA at removing the smear layer.[19] The caustic effect of 2.25% PAA on oral mucosa has led to its use in lower concentrations such as 0.5%.[26]In vitro studies done by Lottanti et al. and De-Deus et al. have proven that 0.5% PAA is effective in removal of smear layer.[19],[27]

The aim of the present study is to evaluate and compare the efficiency of 7% maleic acid, 0.5% PAA, and 17% EDTA to remove smear layer following instrumentation of root canal system.

 Materials and Methods

Ethical clearance was attained for the use of human extracted teeth (IEC 342/2016). Thirty-five non-carious anterior teeth with type I canal anatomy and straight roots were selected for the study. Radiographs were taken to ascertain the presence of single, non-calcified canal with mature apex. Teeth showing the presence of resorption or obturation of root canal system were excluded from this study. The teeth were cleaned with a brush to remove the superficial soft tissues following which they were stored in 0.2% sodium azide (Sigma Chemical Co., St. Louis, MO, USA) at 4°C.

A standardized root length of 14 mm was achieved by decoronation of the samples at the cementoenamel junction. Following this, the samples were randomly divided into three experimental groups (n = 10) and one control group (n = 5). A no. 10 K file (Mani Inc., Tochigi Ken, Japan) was used to assess the working length. It was inserted into each canal until it was just visible at the apical foramen (observed under magnifying loupes) and 1 mm was subtracted from this point. Thereafter, the apices were sealed using sticky wax. The canals were prepared using ProTaper nickel titanium rotary instruments (Dentsply/Tulsa Dental, Tulsa, OK, USA) to size F4 in a crown-down technique. Throughout the preparation, canals were irrigated with 2.5% NaOCl (KMC Pharmacy, Manipal, Karnataka, India) solution for 1 min using 29-gauge Navi Tip side vented needle (Ultradent products Inc., South Jordan, UT, USA) after every instrument change. The needle was introduced 1 mm short of the working length for all samples by adjusting the rubber stopper on the needle to the desired length.

The final irrigation sequence in each group was as follows:

Group 1: 5 ml of 7% maleic acid was used for 1 min (KMC Pharmacy, Karnataka, India)Group 2: 5 ml of 0.5% PAA was used for 1 min (National Peroxide Ltd., India)Group 3: 5 ml of 17% EDTA was used for 1 min (Presvest Denpro, India)Group 4: 5 ml of 0.9% saline was used for 1 min (Fresenius Kabi Pvt. Ltd., India).

Thereafter, drying of canals was carried out using sterile paper points (Dentsply-Maillefer, Ballaigues, China). Longitudinal grooves were prepared on the buccal and lingual surfaces of each root by using a diamond disc (Horico, Germany) at a slow speed. Care was taken not to penetrate the root canal. A chisel was used to split the root into two halves. The specimens were dehydrated using 100% ethyl alcohol and placed in furnace at 60°C for 24 h. The samples were manually marked at the coronal (10–12 mm from apex), middle (6–7 mm from apex), and apical (1–2 mm from apex) thirds of each specimen before the scanning electron microscopic analysis (SEM) analysis. The samples were mounted on metallic stubs followed by gold sputtering using an ion sputter. These samples were then examined under scanning electron microscope (JEOL Ltd., USA) for the presence or absence of smear layer. Several photomicrographs were taken at ×1500, 20 kV magnification to observe the surface morphology of the canal walls. These were evaluated by two independent examiners unaware of the experimental groups to which the samples belonged.

The images were scored according to the criteria given by Torabinejad et al.:[28]

1 = No smear layer (no smear layer on the surface of the root canal; all tubules were clean and open)2 = Moderate smear layer (no smear layer on the surface of the root canal, but tubules contained debris)3 = Heavy smear layer (smear layer covered the root canal surface and the tubules).

The inter examiner's reliability was verified using the Kappa test. The data of the score for intragroup comparison and intergroup comparison to evaluate the presence or absence of smear layer were statistically analyzed by Pearson Chi-square test. The level of statistical significance was set at P < 0.05.


Kappa results displayed a fair (0.41) agreement between the two examiner values for scoring smear layer in the coronal, middle, and apical thirds of the root canal.

[Figure 1] represents the comparative percentage of smear layer removal at the coronal, middle, and apical thirds of the root canal by the test irrigants.{Figure 1}

There was a highly significant difference between the maleic acid, PAA, and EDTA groups in removing the smear layer in the apical third of the root canal (P < 0.05). No significant difference was noted between the EDTA and the maleic acid groups in smear layer removal from the coronal third. Both of these irrigants along with sodium hypochlorite removed smear layer efficiently in the coronal third of the instrumented root canal walls. PAA removed smear layer equivalent to that removed by saline in the coronal third but in the apical and middle third; it performed better than saline. However, in the middle and apical third, maleic acid performed significantly better when compared to EDTA or PAA [Figure 2]. In EDTA and PAA treated specimens there was moderate smear layer present, and in some areas, peritubular dentinal erosion was observed [Figure 3] and [Figure 4]. In the control (saline) group, there was the presence of excessive smear layer in the coronal, middle, and apical thirds of the root canal walls.{Figure 2}{Figure 3}{Figure 4}


Endodontic smear layer formed during root canal instrumentation has been shown to significantly increase apical leakage, thus necessitating its removal to facilitate close adaptation of gutta-percha to the root canal wall.[12] In addition, this non-homogeneous structure may disintegrate around leaky filling margins resulting in the formation of voids between root canal wall and the filling material.[8]

In this study, 2.5% NaOCl was used for the chemo-mechanical preparation between each instrument, which could also remove the organic contents of smear layer. This is in accordance to a study which stated that diluted NaOCl is as effective as a greater concentration of NaOCl for the removal of an organic component of smear layer.[28]

The outcome of this research revealed that 7% maleic acid was better in the removal of smear layer than 17% EDTA and 0.5% PAA in the middle and apical thirds of the root canal. In the coronal third, both maleic acid and EDTA were equally effective without any statistical difference between them. This is in agreement with other studies.[28],[29] In this study, the apical part of canal preparation was done up to ISO size no. 40 which is in consensus with other studies stating that larger apical preparation as compared to a smaller preparation produces a greater reduction in remaining bacteria and dentin debris.[30] Even though the apical preparation was performed up to ISO size no. 40, EDTA and PAA were not able to remove smear layer effectively when compared with 7% maleic acid.

This might be related to the differences in surface tension between 17% EDTA (0.0783 N/m) and 7% maleic acid (0.06345 N/m).[23] EDTA is a chelating agent effective at a neutral pH and thus is independent of a high hydrogen ion concentration to cause decalcification. A decrease in pH in dentin is due to the exchange of calcium by hydrogen which is responsible for a reduced efficacy of EDTA over time.[31] Maleic acid has a better demineralizing effect within a shorter period as it is highly acidic.

It has been reported by Paqué et al. that the apical dentin of root canal is sclerosed [31] thus, minimizing the action of EDTA. Recent studies have stated a reduction in the mineral and noncollagenous proteins (NCPs) component of dentin by EDTA facilitating removal of calcium ions as well as calcium bonded to NCPs. This decreased content of NCPs causes a lower degree of decalcification effect of EDTA in the apical part of the root canal.[32]

In this study, 0.5% PAA was inefficacious in removal of the smear layer when compared to maleic acid and EDTA. This was in contrast to a study by Lottanti et al. who investigated the effects of 2.25% PAA and EDTA on the smear layer in their study and found comparable results between the irrigants.[19] De-Deus et al. indicated that PAA solutions in various concentrations could dissolve the smear layer as quickly as 17% EDTA solutions. It may be due to acetic acid present in the PAA. They also found dentin erosion after the use of 2.25% PAA solutions in the root canals. They found that PAA in low concentration (0.5%) did not cause irritation of oral mucosa and was able to eliminate the smear layer, hence in this study, we preferred to use 0.5% PAA.[27] PAA is relatively cytotoxic. Nevertheless, it is considered to be an alternative to sodium hypochlorite for drinking water disinfection.[33]

The irrigating needle was introduced 1 mm short of working length for all the samples by adjusting the stopper on Navi Tip irrigation needle [34] and is dependent on fluid flow rate. However, it is difficult to standardize and control the fluid flow rate during syringe needle irrigation.[35]

Other than conventional SEM, the smear layer can also be evaluated using digital image analysis, micro-computed tomography, atomic force microscopy, environmental SEM, and co-site optical microscopy.[27] However, SEM was opted in this study because it is a commonly available tool for evaluating the smear layer.

The results obtained in this study may be confined to only single-rooted teeth with almost straight root canal configuration. Curved canals can be more challenging and make effective cleaning of the root canal system more difficult. Deeper penetration of the needle takes place in the single-rooted anterior 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.


The apical third is deemed as an important area for the complete disinfection of the root canal system. Within the limitations of this study, it can be stated that a 1-min application of 7% maleic acid as a final irrigant is highly efficacious for the removal of smear layer when used in the apical third of the root canal system.

Financial support and sponsorship


Conflicts of interest

There are no conflicts of interest.


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