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Aust Endod J 2015; 41: 135–139

ORIGINAL RESEARCH

Effect of final irrigation protocols on push-out bond strength of an epoxy resin root canal sealer to dentin Fernanda Leal, DDS, MSc1; Renata Antoun Simão, MSc, PhD2; Sandra Rivera Fidel, DDS, MSc, PhD1; Rivail Antônio Sérgio Fidel, DDS, MSc, PhD1; and Maíra do Prado, DDS, MSc, PhD2 1 Department of Endodontics, UERJ – State University of Rio de Janeiro, Rio de Janeiro, Brazil 2 Department of Metallurgic and Materials Engineering, Federal University of Rio de Janeiro, Rio de Janeiro, Brazil

Keywords chlorhexidine, dental bonding, EDTA, QMix root canal irrigant, sodium hypochlorite. Correspondence Dr Maíra do Prado, Centro de Tecnologia, Cidade Universitária, Bloco F, Sala F-211, Ilha do Fundão, Rio de Janeiro, RJ CEP 21941-972, Brazil. Email: [email protected] doi:10.1111/aej.12114

Abstract The purpose of the present study was to evaluate the effect of different final irrigation protocols on push-out bond strength of an epoxy resin root canal sealer to dentin. Eighty single-rooted anterior teeth were used. The root canals were partially prepared using a rotary system and the final diameter was standardised using a #5 Gates-Glidden drill prior to the push-out bond test. During chemomechanical preparation, 5.25% NaOCl or 2% CHX gel was used. For smear layer removal, 17% ethylenediaminetetraacetic acid (EDTA) or QMix 2 in 1 was applied for 3 min. As final irrigant, 1 mL of NaOCl, CHX solution or distilled water was used. On conclusion of preparation, canals were filled with gutta-percha/AH Plus sealer. Bond strength was measured by the push-out test. Data were statistically analysed by Kruskal–Wallis and Mann–Whitney U-tests. The group NaOCl/EDTA/NaOCl showed significantly higher bond strength values than other groups. In all groups, there were mainly mixed failure patterns. It can be concluded that 5.25% NaOCl proved to be the best solution for the final irrigation when combined with EDTA. The final irrigation protocols affect the push-out bond strength of AH Plus to dentin.

Introduction The success of endodontic treatment depends on cleaning, disinfection and shaping of the root canal system (1). For this purpose, different chemical substances are used during and after use of the different instruments (2). Sodium hypochlorite (NaOCl) is the most common irrigant used during chemomechanical preparation due to its ability to dissolve organic tissue and effective antimicrobial properties (3–5). Chlorhexidine (CHX) has been used because it is an effective antimicrobial agent with substantivity. Because CHX lacks the tissue-dissolving capabilities of NaOCl, the latter has been suggested as a final irrigant (6). Furthermore, its use as final irrigant is capable of favouring the wettability of resin-based sealers on dentine surfaces (7) and prevent coronal microleakage (8,9).

© 2015 Australian Society of Endodontology

During chemomechanical preparation, an irregular amorphous layer known as the ‘smear layer’ is formed on the root canal walls. It contains inorganic and organic substances that include fragments of odontoblastic process, microorganisms and necrotic debris. Its removal improves the adaptation of filling materials to root canal dentin, decreases apical and coronal microleakage, and facilitates the diffusion of the irrigant solutions and intracanal medication into the root canal system (10,11). Because NaOCl and CHX are incapable of removing the smear layer, the adjunctive use of a chelating agent or acids is recommended. The most common irrigant used for this purpose is ethylenediaminetetraacetic acid (EDTA) (6). Recently, an EDTA-based formulation was developed as final rinse solution. QMix (Dentsply Tulsa Dental, Tulsa, OK, USA) contains EDTA, chlorhexidine and a surfactant 135

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Table 1 Protocols of irrigation

Groups

Chemical auxiliary substance

Smear layer removal

Final flush

1 2 3 4 5 6 7 8

5.25% NaOCl 5.25% NaOCl 5.25% NaOCl 5.25% NaOCl 2% chlorhexidine gel 2% chlorhexidine gel 2% chlorhexidine gel 2% chlorhexidine gel

17% EDTA 17% EDTA QMix QMix 17% EDTA 17% EDTA QMix QMix

5.25% NaOCl Distilled water 5.25% NaOCl Distilled water 2% chlorhexidine solution Distilled water 2% chlorhexidine solution Distilled water

EDTA, ethylenediaminetetraacetic acid.

agent. This solution exhibits a lower level of toxicity than 17% EDTA (12), which also has low toxicity and antimicrobial activity associated with the ability to remove the smear layer (13–16). The aim of the present study was to evaluate the effect of different final irrigation protocols, associated with NaOCl or chlorhexidine during chemomechanical preparation, on push-out bond strength of an epoxy resin root canal sealer to dentin. The null hypothesis tested was that these final irrigation protocols had no influence on the sealer–dentin bond strength.

Materials and methods The present study was approved by the Ethics Committee of Pedro Ernesto College Hospital and the teeth were obtained from the teeth storage of Endodontic Department of Rio de Janeiro State University.

Sample preparation Eighty single-rooted anterior teeth with straight root canal and mature root apex were used. The teeth were accessed by means of #1014 and EndoZ burs (Kg Sorensen, São Paulo, SP, Brazil). A size 15 K-file (Dentsply Maillefer, Ballaigues, Switzerland) was used to verify patency of the canals and to determine the total length of the root canals. Patency was verified when the file exceeded the apex, and the working length was established at 1 mm short of the apical foramen. After this, the roots were divided into groups of 10 according to the irrigation regimen (Table 1). The root canals were prepared using ProTaper rotary instruments (Dentsply Maillefer, Ballaigues, Switzerland) in the sequence SX, F1, F2 and F3. During preparation, before the insertion of each file, 1 mL of 5.25% NaOCl solution (Mil Fórmulas, Rio de Janeiro, RJ, Brazil) or 2% CHX gel (Mil Fórmulas) was used as the auxiliary chemical substance. On conclusion of instrumentation, a #5 Gates-Glidden bur was used in the full length of the root 136

canal until there was no resistance from the root canal wall. The use of #5 Gates-Glidden bur aimed to standardise root canal preparation and eliminate its taper. After that, the push-out plunger was inserted into the root canal to guarantee that it was slightly smaller than the root canal final diameter. For smear layer removal, 17% EDTA (Mil Fórmulas) or QMix 2 in 1 (Dentsply Tulsa Dental) was applied for 3 min. The chelating solutions were renewed every 1 min (1 mL/min). As final irrigant, 1 mL of 5.25% NaOCl, 2% CHX solution or distilled water (control) was used. During these steps, the apices of all the teeth were sealed with utility wax (Technew, Rio de Janeiro, RJ, Brazil) to prevent flow through them and to allow an effective reverse flow of the irrigant, simulating clinical conditions. The root canals were dried with paper points (Dentsply-Maillefer, Rio de Janeiro, RJ, Brazil). The canals were filled with gutta-percha cones ML (Odous De Deus, Belo Horizonte, MG, Brazil) and AH Plus sealer (Dentsply, Petropolis, RJ, Brazil). Radiographs were taken at different angulations to verify the presence/absence of voids in the filling mass and the quality of the filling procedure. To allow the materials to set properly, all roots were kept on gauze pads at 37°C and 100% relative humidity for 1 week.

Push-out assessment Each root was horizontally sectioned with a slow-speed, water-cooled diamond saw (Isomet 2000; Buehler, Lake Bluff, IL, USA) to produce two discs approximately 1 mm thick for each root third (i.e. apical, middle and coronal). Due to the impossibility of standardising all samples, the coronal discs and the last apical disc were discarded. A total of four discs from the middle and apical thirds were evaluated. A load was placed on the filling material by means of a plunger 1.30 mm in diameter, which provided the most extensive coverage over the filling material, without touching the canal wall. Although a GatesGlidden bur was previously used to eliminate root canal taper, the coronal face of the discs were marked to ensure that the plunger push was from the apical to coronal direction. Loading was performed in a universal testing machine (DL200MF; EMIC, São José dos Pinhais, PR, Brazil) at a cross-head speed of 1 mm min−1 until bond failure occurred. Debonding values (maximum load) were used to calculate the push-out strength in megapascals (MPa) according to the following formula:

Push-out bond strength ( MPa ) =

Maximum load ( N ) Adhesion area ( mm 2 )

The bond area was calculated by using the following formula:

© 2015 Australian Society of Endodontology

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Table 2 Bond strength values and failure patterns of the experimental groups Bond strength (MPa)

Failure pattern (n)

Discussion

Groups

Mean ± SD

Adhesive

Cohesive

Mixed

1. 2. 3. 4. 5. 6. 7. 8.

9.30 ± 3.02A 7.41 ± 3.09B,C 7.87 ± 3.65B 6.98 ± 3.83B,C,D 6.29 ± 2.50C,D 6.09 ± 3.15D 6.64 ± 3.03B,C,D 5.87 ± 2.27D

5 5 8 29 7 16 3 10

12 2 6 1 2 4 0 0

23 33 26 10 31 20 37 30

NaOCl/EDTA/NaOCl NaOCl/EDTA/DW NaOCl/QMix/NaOCl NaOCl/QMix/DW CHX/EDTA/CHX CHX/EDTA/DW CHX/QMix/CHX CHX/QMix/DW

Different superscript letters indicate statistically significant values (P < 0.05). EDTA, ethylenediaminetetraacetic acid.

π ( R + r ) ⎡⎣(h2 + ( R − r ) ⎤⎦

2 0 .5

where π = 3.14, R is the coronal radius, r is the apical radius and h is the slice thickness. The thickness of each slice was measured with a digital caliper (Starret Indústria e Comércio Ltda., São Paulo, SP, Brazil) and the total bonding area for each root canal segment was measured with a magnifying stereoscope (Carl Zeiss Microscopy GmbH, Munich, Germany) equipped with the AxioVision 4.8 software program (Carl Zeiss Microscopy GmbH). The images were then examined to determine the failure pattern (17): (i) adhesive, at the filling material/ dentin interface; (ii) cohesive, within filling material; or (iii) mixed failure.

Statistical analysis Data were analysed using Kolmogorov–Smirnov, Kruskal–Wallis and Mann–Whitney U-tests (P < 0.05).

Results Table 2 shows the mean and standard deviation values of the bond strength and failure pattern associated with the different experimental groups. Group 1 (NaOCl/EDTA/ NaOCl) showed significantly higher bond strength values than the other groups. When the groups in which NaOCl was used as chemical auxiliary substance were compared, final irrigation with NaOCl after EDTA application showed the best results. The other groups (2–4) showed no significant differences. When 2% CHX gel was used during instrumentation, the final irrigation protocols showed no significant differences.

© 2015 Australian Society of Endodontology

All groups, except group 4, exhibited a mixed failure pattern. Group 4 presented an adhesive failure pattern.

In the current study, the null hypothesis tested was rejected. The protocol in which NaOCl/EDTA/NaOCl were associated showed the highest bond strength value when compared with the other experimental groups. This protocol is usually used in daily clinical practice because of its capacity to remove the inorganic (by EDTA) and organic (by NaOCl) components of smear layer (18). This fact may also explain the present results, that is, the NaOCl/EDTA/NaOCl protocol caused further exposure of the dentinal tubules and probably allowed greater sealer penetration into them. In the NaOCl groups, when distilled water was used as final irrigant, and EDTA and QMix as the last active irrigant, similar bond strength values were found. Aranda-Garcia et al. (14) and Dai et al. (15) observed that protocols using NaOCl during preparation, and EDTA or QMix as final rinse showed similar smear layer and debris removal capacity. Thus, exhibiting the same extension of surface for sealer penetration, justifying the similar results of push-out bond strength of the present study. Similar to our results, Aranda-Garcia et al. (14) observed similar push-out bond strength values when EDTA and QMix were used as final irrigant, after the use of NaOCl. In the chlorhexidine groups (groups 5–8), lower bond strength values were observed. CHX lacks the tissuedissolving capabilities and its absence of proteolytic action, which makes the dentinal surface more hydrophilic (19,20). As AH Plus is a hydrophobic sealer (21), it can be unfavourable to sealer penetration and bond strength. Furthermore, the organic component of the smear layer was not removed; this resulted in a surface covered by the organic components of smear layer, which may also have interfered in the bond strength. When CHX solution was used as final irrigation, it had no additional influence on the bond strength values. This result is in agreement with previous studies that did not observe a positive influence of chlorhexidine used as final irrigant on the bond strength (2,22). The present experimental protocols are somewhat different from protocols employed in previous studies (2,14,15,22–25). There are differences such as the active solution sequence, the use of an inert solution between the active irrigants and the volume. Although, the main focus of the present study was to evaluate the final irrigation protocol. In the present study, no inert solution was used between the active solutions. This may have created a 137

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chemical smear layer that occluded the dentinal tubules and allowed less effective sealer penetration, thus resulting in lower bond strength values (23,24). Although, the results found by Magro et al. (25) showed that the presence of a chemical smear layer did not affect the bond strength. The higher bond strength values observed in the present study when compared with those reported by other studies (26,27) might be explained by the root canal preparation (using a #5 Gates-Glidden bur) associated with the large plunger diameter used for the push-out test (28). Pane et al. (29) evaluated the range of variables commonly encountered with root filling materials on pushout strength. The specimen orientation, different punch sizes and different root canal diameters were examined. The authors stated that even slight root curvature will result in sections that are not perfectly perpendicular to the applied load, and also that the canal diameter varies among teeth and from coronal to apical sections within the same tooth with differing punch sizes used. Their results demonstrated that load profiles were strongly influenced by the orientation and no effects of punch diameter were observed when the diameter was 90% of the root canal. In the present study, teeth with curved root canal were not used and the root canal standardisation by using #5 Gates-Glidden bur on conclusion of the instrumentation was intended to obtain the same root canal diameter in all root thirds and eliminate its taper. This experimental set-up used the same punch size for all specimens. However, during the specimen preparation, it could be noted that it was not possible to create a perfect circular shape in all of the root canal thirds. For this reason, the samples of coronal thirds were discarded. As the variables regarding the push-out test were eliminated in this study, the quite large standard deviations observed in Table 2 can be associated with other variables related to the dentin pattern, that is, the number of dentin tubules and the age of the tooth (30–32). This source of extraneous variance could not be eliminated. As regards the failure pattern, in the present study, it was predominantly mixed (excluding group 4). This result is partially in agreement with Aranda-Garcia et al. (14) who observed that the mixed failure mode was predominant for both NAOCl/EDTA and NaOCl/QMix groups when the AH Plus/gutta-percha system was used.

Conclusion The final irrigation protocols affected the push-out bond strength of an epoxy resin root canal sealer to dentin. When 17% EDTA was applied prior to NaOCl used as 138

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final irrigant, higher bond strength values were observed than with application of QMix.

Acknowledgements We would like to thank Jackson Belmiro (PEMM), Luiz Lima and Antonieta Middeia (CETEM) for the technical support. The Brazilian Agency Capes supported this work. The authors deny any conflicts of interest.

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Effect of final irrigation protocols on push-out bond strength of an epoxy resin root canal sealer to dentin.

The purpose of the present study was to evaluate the effect of different final irrigation protocols on push-out bond strength of an epoxy resin root c...
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