Comparative analysis of smear layer removal by conventional endodontic irrigants with a newly experimented irrigant-fumaric acid: A scanning electron microscopic study

Abstract

Introduction:

This study was aimed to evaluate the efficacy of 17% ethylenediaminetetraacetate (EDTA), 7% maleic acid and 0.7% fumaric acid in smear layer removal from the root canal walls.

Materials and Methods:

Forty single-rooted mandibular premolars were collected and prepared till F3 rotary ProTaper file with 1 ml of 3% of sodium hypochlorite after each instrument change. Samples were randomly divided into 4 groups according to the final irrigating solution: 17% EDTA, 7% maleic acid, 0.7% fumaric acid, and 0.9% saline. The samples were prepared for scanning electron microscope analysis to observe smear layer removal at coronal, middle, and apical third level of root canal system.

Results:

At coronal third level, fumaric acid was equally efficient in smear layer removal when compared to maleic acid and EDTA without any significant difference between them. At the middle third, fumaric acid showed significantly better results than maleic acid followed by EDTA. At the apical third, both fumaric acid and maleic acid were equally effective without any significant difference between them but both showed significantly better results than EDTA.

Conclusion:

Fumaric acid can be tried as a new irrigating agent for smear layer removal in root canal system.

INTRODUCTION

Formation of smear layer during root-canal treatment is an inevitable process[1] which contains organic and inorganic components that include remnants of odontoblastic processes, necrotic tissues, bacteria and their by-products.[2]

The presence of such layer not only hinders the penetration of intracanal medicaments, sealers, root canal irrigants and obturating materials into the dentinal tubules[3] but also increases the risk of microleakage and bacterial infection[4] which leads to the failure of endodontic treatment. Therefore, the smear layer should be completely removed to increase the fluid tight seal of the root canal system[5] to enhance the endodontic success.

Since, there is no single irrigating solution which can completely eliminate both organic and inorganic components of the smear layer; a combination of different root canal irrigants along with root-canal instrumentation is used.[6] Till date, sodium hypochlorite (NaOCl) has been routinely used to dissolve the organic part of smear layer whereas, inorganic part is removed with chelating agents such as ethylenediaminetetraacetate (EDTA), smear clear, citric acid, biopure MTAD (mixture of a tetracycline isomer, citric acid, and a detergent), and maleic acid.[7,8]

The most commonly used combination includes NaOCl and EDTA for the effective removal of smear layer;[9] however, Ballal et al.[8] reported that 17% EDTA was less efficient in the apical level of the root-canal when used for 1 min and when used for more than 1 min, may cause erosion of both inter- and peri-tubular dentin reducing the microhardness of dentin.[10,11]7% maleic acid efficiently removed the smear layer at the apical level when used in combination with NaOCl.[8]

Fumaric acid (Butene-1,4-dioic acid) which is a trans isomer of maleic acid[12] has spectacular properties of being nontoxic, anti-carcinogenic, anti-inflammatory, and growth modulatory potential.[13] Hence, this new irrigating solution was experimented to remove the smear layer from the root canal system in the present study. Fumaric acid is a well-known key intermediate product in citric acid cycle during glucose metabolism, and its esters have been used successfully for the treatment of psoriasis and multiple sclerosis.[14,15] Till date, there is no single study published evaluating the effect of fumaric acid for the removal of smear layer from the root canal system. The purpose of this study was to evaluate the efficacy of 17% EDTA, 7% maleic acid, and 0.7% fumaric acid followed by 3% NaOCl as final irrigant in smear layer removal at coronal, middle, and apical levels of the root canal system by scanning electron microscope (SEM).

MATERIALS AND METHODS

Forty extracted human noncarious mandibular premolars with single-canal and straight roots were selected. Radiographs were taken to confirm single canal and absence of any type of resorption, cracks, fractures, and calcifications. Ultrasonic scaling was done to remove the calculus and soft tissues and kept in 0.1% thymol solution until use. Samples were randomly divided into three experimental groups (n = 10 each) and one control group (n = 10).

Preparation of the root canal

The teeth were decoronated to a standardized length of 13 mm and working length was determined by inserting an ISO #10 K file (Mani, Japan) until it was just visible at the apical foramen and then keeping it short by 1 mm.

Root canal instrumentation was performed along with 1 ml of 3% NaOCl (Pyrex, Faridabad, India) irrigating solution after each instrument change for 1 min. Cleaning and shaping was done till rotary F3 ProTaper file (Dentsply, Maillefer, Switzerland).

Irrigating solutions: 0.7% fumaric acid, 7% maleic acid, and 17% EDTA were freshly prepared in the Department of Pharmacology, Mahadevappa Rampure Medical College, Gulbarga, Karnataka, India.

After root canal preparation, the samples were randomly divided into four groups:

1. Group 1–5 ml of 17% EDTA for 1 min

2. Group 2–5 ml of 7% maleic acid for 1 min

3. Group 3–5 ml of 0.7% fumaric acid for 1 min

4. Control group – 5 ml of 0.9% saline for 1 min.

Root canal irrigants were delivered with 5-ml syringe of 26 G beveled needle with Luer lock system (Unolok), by keeping the needle short by 1–2 mm of the working length. The irrigants were activated using ultrasonic needle size #25K (SATELEC, France) according to manufacturer's instructions.

In all the groups, the final irrigation was done using 5 ml of 3% NaOCl for 1 min followed by 5 ml of distilled water for 1 min, to remove any precipitate formed during the cleaning and shaping process and then dried with sterile paper points (Dentsply, Maillefer, Switzerland).

The access cavity was closed with sterile cotton pellet. Longitudinal grooves were prepared on the buccal and lingual surfaces of each root with a slow-speed silicon carbide disc without penetrating the root canal. Each tooth was then carefully split into two halves using chisel and mallet and stored in distilled water until use.

Scanning electron microscopic analysis

Samples were dehydrated and mounted on aluminum metal stubs, sputtered with gold, and analyzed under field emission SEM (ULTRA 55, Field Emission SEM [Karl Zeiss] with EDS, GERMANY) at the apical, middle, and coronal thirds of each root for the presence or absence of smear layer at ×3000. The photomicrographs were evaluated by two independent evaluators who were unaware of the groups to which the samples belonged.

Scoring was done according to the criteria given by Torabinejad et al.[9]

Score 1 = no smear layer (no smear layer on the surface of root canal, all the tubules were clean and open).

Score 2 = moderate smear layer (no smear layer on the surface of root canal but tubules contained debris).

Score 3 = heavy smear layer (smear layer covered the root canal surface and the tubules).

The scores obtained were statistically analyzed with two-way analysis of variance test using STATISTICA 7.1 software (StatSoft Tulsa, Oklahoma 74104, USA) for the presence or absence of smear layer in all the groups; P values were compared with a statistical significance of <0.05.

RESULTS

In the present study, at all the cross-sectional levels (coronal, middle, and apical) a significant difference was observed between the control group and the experimental groups except a nonsignificant difference between the control and EDTA group at the apical third [Table 1].

Table 1.

The mean value and standard deviation of all the groups at the apical, middle, and coronal third level of the root canal

In the coronal third, no or small amount of smear layer was detected, with all the dentinal tubules wide open in all the experimental groups. There was no statistically significant difference noticed among EDTA, maleic acid, and fumaric acid group; experimentally, both fumaric acid and maleic acid has shown better results than EDTA.

In the middle third, small amount of smear layer with only few blocked dentinal tubules were detected in the fumaric acid and maleic acid group. Whereas, EDTA group has shown moderate amount of smear layer with part of open dentinal tubules. There was a significant difference between fumaric acid and Maleic acid group (P < 0.05) whereas, a highly significant difference was noticed between fumaric acid and EDTA group (P < 0.001). No significant difference was found between maleic acid and EDTA group. However, maleic acid has shown better smear layer removing property than EDTA experimentally.

In the apical third, moderate amount of smear layer with partially blocked dentinal tubules were detected in the fumaric acid and maleic acid group. Whereas EDTA group showed heavy smear layer with very few open dentinal tubules. There was a very highly significant difference between fumaric acid and EDTA group (P < 0.0001) whereas significant difference was noted between maleic acid and EDTA group (P < 0.05). Fumaric acid and maleic acid were equally effective in removing the smear layer without any statistical difference. However, fumaric acid showed better results than maleic acid experimentally [Figures 1 and 2].

Figure 1.

Photomicrographs show the removal of smear layer at coronal, middle, and apical third level of root canal walls by EDTA, maleic acid, fumaric acid, and control groups at the magnification of ×3000 by scanning electron microscope

Figure 2.

Bar diagram representation comparing the means of all the groups at coronal, middle, and apical third

DISCUSSION

Difficulty in complete removal of the smear layer from the root canal system is well-known and it led to the use of combination of irrigants;[16] however, it is still a challenge because of the complex anatomy of the root canal system. In an urge to find a better irrigating solution, we have experimented 0.7% fumaric acid which is a trans isomer of maleic acid. 0.7% fumaric acid was chosen as 0.7% is the maximum amount of fumaric acid which is soluble in water at room temperature. About 17% EDTA and 7% maleic acid was chosen as they cause erosion of the peri- and inter-tubular dentin when used at higher concentration.[7,10,11]

The results of the present study are in accordance with Ballal et al.[8] for smear layer removing property of maleic acid and EDTA, where maleic acid has shown significantly better smear layer removing property at the apical third area of root canal walls. It may be due to the fact that the properties of EDTA are self-limiting because of the neutral pH. Since 99% of EDTA exist as EDTAHNa3, exchange of Ca⁺⁺from dentin will occur by H⁺ion and subsequently decrease in pH, hence increase in acidity; so, the effect of EDTA decreases with increase in acidity.[17]

It can be explained by two existing reactions:[18]

EDTAH^3- + Ca⁺² = EDTACa^2- + H      (1)

EDTAH^3- + H = EDTAH₂^2-      (2)

Unlike EDTA, Fumaric acid and Maleic acid depend on hydrogen ion concentration for their demineralization affect as they are organic acids. After calculation, pH of 0.7% fumaric acid and 7% maleic acid was obtained as 2.70 and 3.06, respectively. Since dentin demineralization occurs at pH 4–5[19] so both fumaric acid and maleic acid can well demineralize and remove the smear layer.

Recent studies have shown that neutral EDTA solution can reduce the Ca⁺⁺as well as noncollagenous proteins (NCP) and as the concentration of NCP decreases in the apical third zone of root dentin, EDTA may have a lesser degree of decalcification in the apical third area of root canal.[20] Also since apical third of root canal is sclerosed, EDTA may not be efficient enough to remove the smear layer at neutral pH.[21] Other attributing factor for limited demineralization of EDTA may be due to its higher molecular size[19] than that of fumaric acid and maleic acid since larger molecules will bind to less number of Ca⁺⁺into the narrow canals.

Fumaric acid has shown significantly better smear layer removal, may be because, two carboxylic groups are always opposite to each other in their three-dimensional orientation and can bind with more of Ca⁺⁺present in intraradicular dentin than the cis form of maleic acid where the carboxylic group (-COOH) are always at the same side and when 1 proton (H⁺) is removed from them, a strong intramolecular H-bonding is formed with the nearby remaining carboxyl group and can bind with less number of Ca⁺⁺present in the intraradicular dentin.

Fumaric acid is poorly absorbed after oral intake: It is nontoxic, anticarcinogenic, anti-inflammatory, nonabsorbable, biocompatible and growth modulatory in action. Therefore, fumaric acid was experimented as a root canal irrigant to remove smear layer in the field of endodontics.

CONCLUSION

1. Within the limitation of this study, it can be concluded that 1 min of 0.7% fumaric acid followed by 3% of NaOCl has better smear layer removing property than 7% maleic acid and 17% EDTA and can be efficiently used as a final irrigating solution for the removal of smear layer from the apical third of root-canal system

2. Biologic and physical properties of fumaric acid have to be evaluated within the root canal system and at the periapical tissues before considering it in clinical use

Further studies in vitro as well as in vivo are needed with larger sample size and with different clinical situations for its use.

Financial support and sponsorship

Nil.

Conflicts of interest

There are no conflicts of interest.