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ORIGINAL ARTICLE  
Year : 2019  |  Volume : 22  |  Issue : 3  |  Page : 223-227
Efficacy of different endodontic irrigation protocols on shear bond strength to coronal dentin


Department of Restorative Dentistry, Faculty of Dentistry, Erciyes University, Kayseri, Turkey

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Date of Submission06-Dec-2018
Date of Decision12-May-2019
Date of Acceptance13-Jun-2019
Date of Web Publication03-Jul-2019
 

   Abstract 

Aim: The purpose of this study was to evaluate the effect of etidronic acid on bond strength to coronal dentin.
Materials and Methods: A total of 75 human mandibular molars were sectioned 3 mm below the occlusal surface and then randomly divided into five groups according to irrigation solution used (n = 15): Group 1: 5 ml 2.5% sodium hypochlorite (NaOCl) +5 ml distilled water; Group 2: 5 ml 2.5% NaOCl + 5 ml 17% ethylenediaminetetraacetic acid (EDTA); Group 3: 10 ml mixture of 5% NaOCl and 18% 1-hydroxyethylidene-1,1-bisphosphonate (HEBP); Group 4: 5 ml mixture of 5% NaOCl and 18% HEBP + 5 ml 17% EDTA; and Group 5: 5 ml mixture of 5% NaOCl and 18% HEBP + 5 ml distilled water. Thereafter, Clearfil SE bond was applied to the dentin surfaces and then, composite build-ups were created using Tygon tubes for the microshear bond strength test. Data were analyzed using the one-way analysis of variance and Tukey test.
Results: When compared to Groups 3, 4, and 5, Groups 1 and 2 showed significantly higher bond strength values (P < 0.05). However, there was no statistically significant difference between Groups 1 and 2 and between Groups 3, 4, and 5 (P > 0.05).
Conclusion: HEBP adversely affected the bond strength of the tested adhesive to coronal dentin.

Keywords: Coronal dentin; endodontic irrigation; etidronic acid; microshear bond strength

How to cite this article:
Arslan S, Balkaya H, Çakir NN. Efficacy of different endodontic irrigation protocols on shear bond strength to coronal dentin. J Conserv Dent 2019;22:223-7

How to cite this URL:
Arslan S, Balkaya H, Çakir NN. Efficacy of different endodontic irrigation protocols on shear bond strength to coronal dentin. J Conserv Dent [serial online] 2019 [cited 2019 Aug 20];22:223-7. Available from: http://www.jcd.org.in/text.asp?2019/22/3/223/262020

   Introduction Top


The success of endodontic treatment depends on effective cleaning, shaping, and proper obturation of root canals. During the complete debridement of root canals, smear layer removal is important and could help to achieve a successful outcome of the root canal treatment.[1] Smear layer contains both organic and inorganic components. Furthermore, the smear layer may be containing mixture of bacteria and byproducts of them, and hence, it has been recommended to be removed. Moreover, it may prevent the penetration of irrigation solutions and intracanal medicaments into the dentin tubules and prevent the close adaptation and adhesion of the sealer onto the canal walls.[2],[3]

Sodium hypochlorite (NaOCl) is widely used for antibacterial activity, lubrication, and removing organic remnants in smear layer during endodontic treatment. Ethylenediaminetetraacetic acid (EDTA) removes the inorganic part of the smear layer and it is commonly used as chelating agents.[4] The combined application of NaOCl and EDTA may reduce the dissolution capacity and antimicrobial properties of NaOCl due to reduced free chlorine.[5] Furthermore, the combined application of this irrigation solutions can cause erosion of the dentin surface.[6] However, the elasticity modulus and flexure strength of dentin may reduce with prolonged exposure time of root dentin to EDTA.[7] This reduction can adversely affect the physical and mechanical properties of the dentin and ultimately increase the risk of root fracture.[8] The weak chelating agents such as etidronic acid (1-hydroxyethylidene-1,1-bisphosphonate [HEBP]) have a minimal effect on dentin walls, and they can still reduce the smear layer. Furthermore, when used in combination with NaOCl, HEBP does not affect its proteolytic or antimicrobial properties.[4],[9] However, in contrast to EDTA, HEBP cannot be used alone for the final rinse because it is a weak-decalcifying agent. For this reason, it is recommended that HEBP be mixed with NaOCl for using as a more complete root canal irrigant. This combination is favorable in that this solution keeps the hypochlorite-hypochlorous acid equilibrium toward hypochlorite, which has better tissue dissolution capacity than hypochlorous acid and also has less cytotoxicity.[10],[11]

Adhesive systems divided into two major groups according to interaction with the smear layer and etching procedure as self-etch adhesive and etch-and-rinse adhesive. Etch-and-rinse adhesives remove the smear layer while the smear layer is modified by self-etch adhesives and incorporates into the structure of the hybrid layer.[12],[13]

Irrigation solutions which were used during the root canal treatment and the adhesive system used for postendodontic restoration affect the bond strength. The irrigation solutions in contact with coronal dentin may alter the structure of the dentin and thus effect the sealing of postendodontic coronal restoration.[14],[15] Although there are so many studies that evaluated the effects of irrigation solutions such as NaOCl and EDTA on the bond strength to coronal dentin, the studies about the effects of HEBP on the bond strength of coronal dentin are insufficient and there is no study yet about the effect of HEBP on composite resin's bond strength. Therefore, the aim of this in vitro study is to evaluate the effect of HEBP on the bond strength of composite resin to deep coronal dentin. The null hypothesis was that the effect of etidronic acid would have no difference from the other tested endodontic irrigants on microshear bond strength to coronal dentin.


   Materials and Methods Top


Tooth selection and preparation of the samples

The research protocol of this in vitro study was approved by the Institutional Ethics Committee (approval number: 2017/290) before conducting the study. In the present study, 75 noncaries human mandibular molar teeth extracted for periodontal reasons were collected, immersed for 2 weeks in chloramine-T solution (0.5%) at room temperature and then stored in normal saline solution until used. The periodontal tissue residues and calculus were gently removed with curettes and an ultrasonic scaler (Cavitron; Dentsply, York, PA, USA). The teeth were sectioned 3 mm below the occlusal surface with a low-speed diamond saw to obtain deep coronal dentin surface. Thereafter, the teeth were placed in auto-polymerizing acrylic resin (Imicryl, Konya, Turkey) using PVC (polyvinyl chloride) rings with 2 cm diameter and 2 cm length, leaving the flat surface exposed. The exposed surfaces of teeth were ground with 600 and 800 grit SiC papers under running water to obtain flat dentin surfaces and then, teeth were randomly divided into five groups (n = 15) according to the irrigation protocol used.[16]

  • Group 1 (G1): 5 ml 2.5% NaOCl for the first irrigation and 5 ml distilled water as the final rinse
  • Group 2 (G2): 5 ml 2.5% NaOCl for the first irrigation, and 5 ml 17% EDTA as the final rinse
  • Group 3 (G3): 5 ml mixture of 5% NaOCl and 18% HEBP (1:1) for the first irrigation, and the same mixture as the final rinse, totally 10 ml (5 ml + 5 ml)
  • Group 4 (G4): 5 ml mixture of 5% NaOCl and 18% HEBP (1:1) for the first irrigation, and 5 ml 17% EDTA as the final rinse
  • Group 5 (G5): 5 ml mixture of 5% NaOCl and 18% HEBP (1:1) for the first irrigation, and 5 ml distilled water as the final rinse.


In the current study, to prepare 5 ml of 2.5% NaOCl solution, 2.5 ml of 5% NaOCl (Werax; Spot Dis Deposu AŞ, İzmir, Turkey) was added into 2.5 ml of deionized water. Furthermore, 17% EDTA (Werax; Spot Dis Deposu AŞ, Izmir, Turkey) used in this study was ready solution. The 60% etidronic acid solution (Sigma-Aldrich, St. Louis, USA) was diluted to 18% with distilled water and then, diluted solution was mixed with 5% NaOCl in a ratio of 1:1.[4]

Before the irrigation protocols, an approximately 1 cm high frame was formed around the teeth with polyvinyl siloxane impression material (Zetaplus; Zhermack, Badia Polesine, Italy). Each irrigation application time was 2 min. After the irrigating procedures, the dentin surfaces were rinsed with 5 ml distilled water for 2 min and gently dried using an air syringe. Clearfil SE Bond (Kuraray, Osaka, Japan) primer was applied for 20 s to the sample surfaces, dried with mild air for 5 s and then, the bonding agent was applied to the samples, made a uniform bond film using a gentle air flow and light cured for 10 s with a LED light source (VALO, Ultradent, USA). After adhesive resin polymerization, the composite build-ups were created using Tygon tubes with an internal diameter of 0.8 mm and a height of 1 mm on the center of the bonded area with Charisma Smart composite (Heraeus Kulzer, Hanau, Germany). The samples were stored in distilled water at 37°C for 24 h before the microshear bond test.

Microshear bond strength test and failure analysis

Tygon tubes were carefully removed using a scalpel, and the specimens were subjected to a universal testing machine (Instron, Canton, MA, USA). A 0.25-mm thick wire loop was placed around the composite resin cylinders in contact semi-peripherally, followed by shear forces being applied to the adhered composite resin cylinders at a crosshead speed of 1 mm/min until failure. Maximum loads at the moment of bond failure were recorded as Newtons (N) and then, the bond strength values were calculated in megapascals (MPa) by dividing this value to the bonding surface area. The debonded areas were explored under a stereo microscope (DV 4; Zeiss, Jena, Germany) at ×25, and failure modes were classified as adhesive failure, cohesive failure, and mixed failure.

Field emission scanning electron microscopy

To observe the irrigated sample surfaces under a field emission scanning electron microscope (FE-SEM), one tooth surface was prepared for G1, G2, G3, G4, and G5. The samples were critical point dried, and prepared dentin surfaces were coated with gold palladium. Thereafter, the surfaces of the samples examined using FE-SEM (GeminiSEM 500, Zeiss, Germany) at 3–5 kV and a working distance of 5–8 mm.

Statistical analysis

The data were analyzed using the statistical software (SPSS Statistics 22.0; SPSS Inc., IL, USA). The Kolmogorov–Smirnov and Shapiro–Wilk tests were used to test the normal distribution. The One-way analysis of variance and Tukey's honestly significant difference tests were used to analyze the differences between groups at 0.05 significance level.


   Results Top


The mean microshear bond strength values and the standard deviations of the groups are shown in [Table 1]. There were significant differences between microshear bond strengths of the groups tested (P < 0.05). The lowest bond strength values were found in the groups used HEBP among all groups (G3, G4, and G5). The multiple comparison test showed that there was a statistically significant difference between G1 with G3, G4, and G5 and between G2 with G3, G4, and G5 (P < 0.05). There was no statistically significant difference between G1 with G2 and between G3, G4, and G5 (P > 0.05).
Table 1: The mean microshear bond strength values (megapascals) and the standard deviations of the groups

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In the FE-SEM examination, it was observed that the samples of the groups containing etidronic acid had precipitate on the dentin surface and in dentin tubules for G3, G4, and G5 [Figure 1]. In G1, smear layer was seen on the surface and in dentin tubules, whereas in G2, smear plugs were seen in dentin tubules [Figure 2].
Figure 1: Field emission scanning electron microscopy images of G3, G4, and G5 dentin surfaces after irrigation (×3000)

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Figure 2: Field emission scanning electron microscopy images of G1 and G2 dentin surfaces after irrigation (×3000)

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The results of failure modes are presented in [Table 2]. Adhesive failure was frequently observed in the samples. Cohesive failure was not observed in any sample, and mixed failure was more seen in G1 and G2.
Table 2: Failure modes of the groups

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   Discussion Top


An intact coronal seal is important for successful endodontic therapy. However, coronal dentin is subjected to various medicaments, irrigants, which has different surface tensions, wettability, and different action mechanism, and these factors with regional differences in dentin structure make the bonding more difficult.[17],[18]

In the present study, the effect of etidronic acid used as a chelating agent in endodontic treatment on microshear bond strength was evaluated. The null hypothesis was rejected because the bond strengths of the groups containing HEBP were significantly lower than NaOCl and NaOCl + EDTA groups.

There are several methods such as microtensile and microshear for evaluating the bond strength of the dental materials to tooth structures. In the present study, microshear bond strength test was used. This technique has some superiorities because it is easier, there is no obligation to take sections from the samples after bonding of the composite resin and therefore, bond strength will not be reduced due to the slicing procedure. Besides, standard tooth regions could be selected, preserving uniformity of the testing area.

Actually, endodontic therapy is the chemomechanical debridement of the root canals. An ideal endodontic irrigation material should have high antimicrobial activity, dissolve necrotic tissue, remove smear layer, and have low systemic toxicity.[9] NaOCl and EDTA are widely used irrigation solutions during root canal preparation. NaOCl has low surface tension, antibacterial activity, and dissolves organic structure. However, sodium chloride and oxygen are decomposed from NaOCl and this oxygen inhibits polymerization of the adhesive system.[19] In addition, the residues of irrigation solutions and their products could be diffused into the dentin tubules. Therefore, the residual chemicals may interact with the adhesive system and affect the monomer polymerization and decrease the bond strength. EDTA is a chelating agent, and it was reported that its demineralizing effect is strong, may cause softening of the dentin, enlargement of the dentinal tubules, and denaturation of collagen fibrils. Furthermore, EDTA causes erosion on the dentin surface when increase application time,[20] and these features of EDTA may negatively affect bonding and sealing.

Recently, etidronic acid has been introduced as an equivalent of EDTA to simplify and reduce the irrigation time. During the root canal preparation, this solution can be mixed with NaOCl solutions without losing the desired features of two components.[4]

In previous studies,[15],[21] it was evaluated that the effect of different irrigation regimens on the bond strength of dental adhesive to pulp chamber dentin and coronal dentin. They reported that it was observed similar bond strength values following NaOCl and NaOCl + EDTA treatments. These findings are consistent with our study, which NaOCl and NaOCl + EDTA groups showed similar bond strength values.

The groups containing HEBP had lower bond strength values in this study. Direct comparison with other studies was not possible because there was not any study evaluated the effect of HEBP on composite resin's bond strength to coronal dentin. However, there were studies that evaluated the effect of HEBP solution on bond strength of a resin sealer and resin cement.

In a study, which all the test groups had 1.3% NaOCl as initial rinse and followed by specific final rinse for each group (respectively, distilled water, 17% EDTA, and 18% HEBP and MTAD), it was evaluated that the effects of different final irrigants on the shear bond strength of resin-based sealer to coronal dentin.[22] The authors reported that NaOCl + EDTA showed the highest bond strength value which was followed by HEBP and it has been associated with the formation of less demineralized dentin zone of HEBP (soft chelating agent) compared to EDTA.

Egilmez et al.[23] investigated that the effect of tetracycline HCl, chlorhexidine digluconate, and HEBP on bond strengths of two self-adhesive resin cements (Clearfil SA Cement, RelyX Unicem) to coronal dentin, and it was concluded that the application of topical HEBP solution treatment could have adverse effects on bond strength of RelyX Unicem to dentin. In this study, it was thought that the reason for the significant decrease in bond strength of RelyX Unicem might be related to the difference in contents of these self-adhesive cements. These findings are consistent with our study in which HEBP adversely affected the bond strength of resin composite to dentin.

The adhesion of the dental materials is directly affected by the application mode (together or separately) and order of the irrigation agents.[15] The NaOCl slowly degrades the collagen fibrils because collagen fibrils covered by the hydroxyapatite on mineralized dentin are less vulnerable to the effects of NaOCl. If HEBP and NaOCl are used together, the action area of HEBP increases and NaOCl occurs more deproteination on the dentin surface.[22] In addition, HEBP has low surface tension like NaOCl, so it has high diffusion capacity into the dentin and their remnants diffused into the dentin tubules.[24] Moreover, it was observed that the samples of the groups containing etidronic acid had precipitate in the dentin surface and dentin tubules [Figure 1] in our study. These collagen degradations, etidronic acid precipitates, and irrigation solution's remnants may have prevented the adhesive penetration, polymerization, and formation of hybrid layer, and therefore, the groups containing HEBP may have shown low bond strength values in our study.

In all tested groups, adhesive failure type was predominantly observed. More mixed failure was seen in G1 and G2 than other groups. The cohesive failure of adhesive material is related to the high bond strength values, predicting effective bonding.[25] However, in this study, cohesive failure was not observed in any sample.


   Conclusion Top


In this in vitro study, it was shown that using etidronic acid as an irrigation solution caused to decrease the microshear bond strength. Although it is an advantage that the NaOCl-etidronic acid mixture can be used as a single irrigant during instrumentation, adversely affecting the bond strength is a major drawback. However, additional studies which investigate the effects of etidronic acid on coronal dentin should be performed.

Acknowledgments

This study was supported by the Erciyes University Scientific Research Projects Foundation (TSA-2018-7731).

Financial support and sponsorship

Nil.

Conflicts of interest

There are no conflicts of interest.

 
   References Top

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Correspondence Address:
Dr. Hacer Balkaya
Department of Restorative Dentistry, Faculty of Dentistry, Erciyes University, Melikgazi, Kayseri 38039
Turkey
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Source of Support: None, Conflict of Interest: None


DOI: 10.4103/JCD.JCD_502_18

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