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ORIGINAL ARTICLE
Year : 2022  |  Volume : 25  |  Issue : 3  |  Page : 336-341

The efficacy of different sealer removal protocols on the microtensile bond strength of adhesives to a bioceramic sealer-contaminated dentin


1 Department of Restorative Dentistry, Faculty of Dentistry, Cukurova University, Adana, Turkey
2 Department of Endodontics, Faculty of Dentistry, Cukurova University, Adana, Turkey

Date of Submission03-Jun-2021
Date of Acceptance13-Sep-2021
Date of Web Publication16-Mar-2022

Correspondence Address:
Dr. Z G Bek Kurklu
Department of Restorative Dentistry, Faculty of Dentistry, Cukurova University, Sarıcam, Adana
Turkey
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Source of Support: None, Conflict of Interest: None


DOI: 10.4103/njcp.njcp_1575_21

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   Abstract 


Background: The optimal bonding of adhesives to dentin requires the sealer to be completely removed from the dentinal walls. Aim: This study compared the efficacy of different sealer removal protocols on the microtensile bond strengths (MTBS) of single-step adhesives to a calcium silicate-based bioceramic root canal sealer-contaminated dentin. Materials and Methods: Standardized box-shaped Class I cavities were prepared in human lower third molars (N = 50). All cavities were contaminated with a bioceramic root canal sealer (Endosequence BC Sealer, Brasseler, Savannah, USA), except the control group (G1) cavities. For the experimental groups, contaminated dentin surfaces were wiped with a dry cotton pellet (G2), wiped with a cotton pellet saturated with water (G3), rinsed with the air/water spray (G4), and passively applied aqueous ultrasonic energy with an ultrasonic scaler (G5) before the restoration procedure. All the cavity surface was restored with a one-bottle universal adhesive and composite resin. All the specimens were subjected to both thermocycling (2,500 thermal cycles from 5 to 55°C, with a 30-s dwelling time and a 10-s transfer time) and mechanical loading (50 N load for 100,000 cycles). The restored specimens were sectioned into resin-dentin beams for MTBS evaluation. Additional specimens were prepared for the scanning electron microscopy (SEM) to examine the dentin-adhesive interface (n = 10). Results: No significant difference was found between the mean bond strengths of the groups. In SEM examination, no residual sealer was found in any group. Conclusion: Calcium silicate-based bioceramic sealer was removed from the dentin surface with all removal protocols when evaluated with MTBS after the thermal and mechanical cycle tests.

Keywords: Bond strength, coronal seal, mechanical load, root canal sealers, SEM


How to cite this article:
Bek Kurklu Z G, Yoldas H O. The efficacy of different sealer removal protocols on the microtensile bond strength of adhesives to a bioceramic sealer-contaminated dentin. Niger J Clin Pract 2022;25:336-41

How to cite this URL:
Bek Kurklu Z G, Yoldas H O. The efficacy of different sealer removal protocols on the microtensile bond strength of adhesives to a bioceramic sealer-contaminated dentin. Niger J Clin Pract [serial online] 2022 [cited 2022 Aug 19];25:336-41. Available from: https://www.njcponline.com/text.asp?2022/25/3/336/339717




   Introduction Top


Coronal restorations are very important for increasing the success of the root canal treatment[1],[2],[3] as they prevent bacterial invasion and endotoxin infiltration from the coronal direction by creating an additional barrier to the canal orifice and occluding the pulp chamber.[4]

Different modes of adhesive can be used in the restoration of the endodontic access cavity. One bottle of self-etch adhesive with relatively easy application and low technical precision is used for coronal sealing immediately after the root canal filling.

The bond strength of the adhesives is lower when the dentin surface is contaminated by a zinc oxide eugenol-based sealer[5],[6] or resin-based sealer residues.[7],[8],[9] Furthermore the remnants can also cause tooth discoloration,[10] thereby, creating aesthetic issues for the patient. There are studies reporting the chemical solvents such as ethanol, acetone, amyl acetate, sodium chlorite, or isopropyl alcohol to be used for removing the root canal sealer residues from the endodontic access cavities.[7],[8],[9],[11],[12]

Bioceramic root canal sealers have entered dentistry in recent years and have been presented to the market with features such as the osteoinductive effect,[13] hardening of tissue fluids, long-term antibacterial effect,[14],[15],[16] biocompatibility,[17],[18],[19],[20] long working time, and expansion in the root canal.[21]

The bonding of calcium silicate-based bioceramic canal sealers to root dentin[22],[23] and gutta-percha[24] was evaluated. However, it is not known how the bioceramic pastes are removed and how they affect the adhesion of self-etch adhesives on coronal dentin. The aim of this study is to evaluate the different removal techniques of calcium silicate-based canal sealers from the endodontic access cavities.

The null hypothesis of this study is that cleaning contaminated dentin with a calcium silicate-based bioceramic canal sealer with different removal protocols does not cause the deterioration of the strength of the resin-dentin bonds created by self-etching adhesives.


   Materials and Methods Top


Sixty freshly extracted, erupted, non-carious, non-restored, uncracked human lower third molars were gathered by the Non-Invasive Clinical Research Ethics Committee of the Cukurova University Faculty of Medicine, dated 13.03.2020, numbered 42, and stored in a solution of 0.5% chloramine-T for 3 months at 4°C. Informed consent forms were signed by all the patients. The procedures used in this study adhere to the tenets of the Declaration of Helsinki. Furthermore, teeth of nearly equal size and similar occlusal anatomy were selected. The sample size was determined according to the Academy of Dental Materials guidance.[25]

The teeth were embedded in a self-curing acrylic resin, and standardized uniform box-shaped Class I cavities (4 mm × 4 mm × 4 mm) were prepared with a high-speed handpiece under air-water spray using cylindrical flat-end medium grit diamond burs. The burs were replaced after every five preparations. The teeth were randomly divided into five groups according to the removal protocol (n = 10 per group). The remaining 10 teeth were used for scanning electron microscopy (SEM) analysis. The cavity of the control group (G1) was not contaminated with the canal sealer. The teeth in the experimental groups were dried with an air stream. Approximately a 1-mm-thick layer of calcium silicate-based Endosequence BC Sealer (Brasseler, Savannah, GA, USA) was injected on the surface of the dentin at the base of the cavity and left for 5 min. According to the removal protocol, uncured sealer remnants were removed from the cavities as follows: G2—A dry cotton pallet, 2 × size nr. 2, was used to scrub the access cavity walls for 5 s, the same process was repeated by new a dry cotton pallet, G3—a wet cotton pallet, size nr. 2, was used to scrub the access cavity walls for 5 s, the same process was repeated by new a wet cotton pallet, G4—the access cavity walls were rinsed with the air/water spray from a dental unit for 5 s, and G5—by passively applying aqueous ultrasonic energy without any contact with the canal walls for 5 s with the ultrasonic scaler (PiezonMaster 400, EMS, Nyon, Switzerland).

After the removal of the canal sealer, the cavity surface was restored with a one-bottle universal adhesive (G-Premio BOND, GC, Tokyo, Japan) and in two 2-mm-thick vertical layer composite resins (G-ænial posterior, GC, Tokyo, Japan) according to the manufacturer's instructions. Each layer was cured with 900 mW/cm2 light intensity for 20 s (Elipar Freelight, 3M-ESPE, MN, USA). All the restored specimens were stored for 7 days at 37°C in distilled water to allow for complete residual sealer setting and were then subjected to both thermocycling and mechanical loading in a chewing simulator. The mechanical loading was performed with a 50 N load for 100,000 cycles. The load was vertically applied on the central fossa of the molar with a steel ball (6 mm in diameter) at a frequency of 1.6 Hz. A 0.5-mm sliding movement was also applied during the loading. Thermocycling was performed for 2,500 thermal cycles in deionized water from 5 to 55°C, with a 30-s dwelling time and a 10-s transfer between temperature baths.

After simulating aging, the restored teeth were sectioned into three or four 1-mm-thick slices perpendicular to the bonded surface using a slows-peed diamond saw (Diamond cutt-off Wheel MOD15, Struers, Rødovre, Denmark) underwater irrigation (Accutom 10, Struers, Rødovre, Denmark). The tooth was then rotated 90° degrees and sectioned again to obtain 1-mm2 sticks. The cross-sectional area of each specimen was measured with a digital caliper (Shinwa, Osaka, Japan) and recorded to calculate the bond strength. The beams were fixed to the jig by the cyanoacrylate glue (Pattex, Henkel, Duesseldorf, Germany) and tested in a universal testing machine (MOD Dental MIC-101, Esetron Smart Robotechnologies, Ankara, Turkey) at a cross-head speed of 0.5 mm/min. The tensile strength was measured in Newtons. The μTBS (microtensile bond strength) values were calculated in megapascals (MPa) by dividing the fracture force by the cross-sectional surface area. The fractured specimens were then examined under a 40X magnification stereomicroscope (SOIF optical instruments, Stereo microscope ST6024-B2, İstanbul, Turkey) to analyze the fracture mode.

For SEM analysis, two teeth in each experimental group were cut in half longitudinally in a buccolingual direction from the center of the restoration with a water-cooled diamond disk (Struers, Diamond cutt-off Wheel MOD15, Rødovre, Denmark). The specimens were dehydrated for 24 h at room temperature and mounted on aluminum stubs, desiccated, sputter-coated with gold/palladium, and examined under a scanning electron microscope (FEI, Quanta 650 FEG, Oregon, USA).

The comparison was made by using the mean of each tooth. The Shapiro–Wilk's test was used to evaluate the normality of the data. The normally distributed data were analyzed by the one-way analysis of variance (ANOVA) and the Tukey HSD (IBM SPSS Statistics V21 Armonk, USA).


   Results Top


The microtensile bond strength results are shown in [Table 1]. Three specimens were excluded due to inadequate remaining dentin thickness (<2 mm) (one in group 1 and one in group 2. Total two beams) or the fracture during the removal of the beams from the cavity (one in group 4). 'Manipulation failures' (human errors) did not include for the mean TBS calculation. No significant difference was found between the mean bond strengths of the groups (P = 0,281).
Table 1: Microtensile bond strength (MPa) for all specimen groups

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Adhesive failure

Greater adhesive failures were observed in all groups. The groups presented similar percentages of fracture patterns [Table 2].
Table 2: Fracture patterns of bonded specimens after the bond strength test (%)

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SEM evaluation

In the samples examined at 5000X magnification, no residual sealer was found in any group [Figure 1]. All of the cleaning protocols were able to completely remove the Endosequence BC Sealer from the dentin surface.
Figure 1: Representative image of the resin-dentin interface (X5,000) in the control group (a), Figure 2: Representative image of the resin-dentin interface (X5,000) in the dry cotton group (b), Figure 3: Representative image of the resin-dentin interface (X5,000) in the wet cotton group (c), Figure 4: Representative image of the resin-dentin interface (X5,000) in the water rinse group (d), and Figure 5: Representative image of the resin-dentin interface (X5,000) in the ultrasonic rinse group (e) (D: Dentin, A: Adhesive, C: Composite resin, RT: Resin tag)

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   Discussion Top


The sealers used during root canal obturation contaminate the floor and walls of the endodontic access cavity. This contamination has to be removed for successful and long-term dentin restoration bonding. In the present study, the removal protocols for contamination caused by calcium silicate-based Endosequence BC Sealer were evaluated. The sealer was removed by all removal methods using water, including dry cotton. Thus, the null hypothesis is not rejected.

Calcium silicate-based bioceramic sealers produce calcium hydroxide by hydration, which affects water sorption and solubility.[26] Therefore, we used water as the solvent to remove the residual calcium silicate sealers in the study. In our study, the highest bond strength was measured in group 4, in which water was activated by ultrasonication. The lowest bond strength was measured on the cavity surfaces cleaned with dry cotton. The ultrasonic activation of the water resulted in higher bond strength compared to the control group, as it allowed proper removal of the residual sealer and even smear layer and debris. The SEM images of the dentin-adhesive interface showed a thin hybridized layer and a few/short resin tags created by the self-etch adhesive. No residual sealer was observed in any of the specimens.

The most commonly used method to characterize the durability of adhesives is the in vitro bond strength test. The microtensile test results are influenced by many physical and chemical factors, i.e., variations in dentin depth, tubule diameter, cavity configuration,[27],[28] and mechanical and thermal stresses.[29]

The microtensile bond strength of the G-Premio BOND in flat dentin without aging is approximately 33.4 ± 1.9 MPa.[30] In the current study, the mean of the microtensile bond strength of the G-Premio BOND was measured to be 11,640 ± 3,05 to 15,034 ± 2,09 MPa. The reason for this decrease may be the aging processes[29] and the use of deep dentin.[27] A high percentage of adhesive failure in all groups may be the result of aging.

The microtensile samples prepared with flat dentin do not imitate the clinical situation. Studies have shown that “flat” versus “cavity” dentin influences the microtensile bond strength due to the differences in the configuration (“C”) factor.[31],[32] In our study, the root canal was reached by opening the box-shaped Class I cavities to the lower molar teeth to mimic the clinical access cavity design.

In our study, the dry cotton group had less bond strength than the water-used groups, but no statistically significant difference was found. The reason for this may be that the polymerization shrinkage due to the C-factor and the stresses created by the mechanical loads exceeded the removal advantage. The cavity configuration factor is the ratio of the bonded surface area to the unbonded surface area. This means that in a box-like Class I cavity, five times more polymerization shrinkage stress is exposed than flat dentin.

Epoxy resin-based sealers adversely interfere with the bond of dentin adhesives,[7] because resin monomers of the sealer and adhesive are chemically different so they do not copolymerize. It is difficult to remove the epoxy resin-based sealers from the access cavity, even if they do not harden. Therefore, several solutions containing ethanol, ethyl acetate, acetone, chloroform, or chlorhexidine digluconate have been recommended for the removal of epoxy resin-based sealer residues from the dentin surface.[7],[8],[9],[11],[12] However, in the current study, the BC sealer was easily removed from the dentin surface before setting. The effective removal of calcium silicate-based cements with all protocols may be seen as an advantage for clinical use.

Oltra et al.[33] retreated the root canal treatment with chloroform after AH Plus and BC sealer completely hardened in the root canal. According to this study, the percentage of residual filling material after root canal obturation, the authors showed that the BC sealer remained significantly more into the dentin tubules than AH Plus. This study also supports the strong chemical bonding of the bioceramic sealers to dentin after setting.[34] Therefore, after the root canal obturation with the bioceramic sealer, the residual sealer in the access cavity should be removed, otherwise, it may jeopardize the coronal restoration.

Studies have reported immediately high in vitro bond strength. To determine the long-term bond strength of the adhesives, the value after exposure to the chewing forces and temperature changes should be measured. Thermal cycling may produce hydrolytic degradation, which changes the stress/strain levels transferred to the interface of the two materials and reducing the bond strength.[35] Also, mastication causes stress in the restored dentin system. Studies have shown that cyclic loading significantly reduces the bond strength of the adhesive.[36]

The bond strength measurements are the appropriate methods to assess the coronal seal. Within the limits of this ex vivo study, it can be concluded that all removal protocols are effective on the resin-dentin bond strengths of the self-etching adhesive. Further clinical trials and research must be performed to evaluate the removal protocols of calcium silicate-based sealers.


   Conclusion Top


According to the results of this study, the calcium silicate sealer was removed from the dentin surface with all the clinical techniques before setting. All removal protocols showed the same results when evaluated with μTBS after the thermal and mechanical cycling tests.

Acknowledgments

The authors would like to acknowledge Prof. Dr. Yuksel Bek, Ondokuz Mayıs University, • Department of Biostatistics and Medical Informatics, Turkey, for him assistance in statistical analysis.

Ethics approval

Non-Invasive Clinical Research Ethics Committee of Cukurova Unversity Faculty of Medicine approval (13-03-20-42) was granted for the use of human subjects.

Financial support and sponsorship

This study was financially supported by Cukurova University Research Board, with project number TSA-2019-12409.

Conflicts of interest

The authors declare that they have no conflict of interest.



 
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