|Year : 2014 | Volume
| Issue : 3 | Page : 130-135
Comparative evaluation of micro-tensile bond strength of one-step self-etching adhesive systems
Mehmet Cebe1, Mehmet Adiguzel2, Fatma Cebe1, Mehmet Tekin3
1 Department of Restorative Dentistry, Faculty of Dentistry, Abant Izzet Baysal University, Bolu, Turkey
2 Department of Endodontic, Faculty of Dentistry, Mustafa Kemal University, Hatay, Turkey
3 Department of Restorative Dentistry, Faculty of Dentistry, Mustafa Kemal University, Hatay, Turkey
|Date of Web Publication||29-Oct-2014|
Department of Restorative Dentistry, Faculty of Dentistry, Abant Izzet Baysal University, Bolu, 14300
Source of Support: None, Conflict of Interest: None
Purpose: The aim of this study was to assess micro-tensile bond strength values to dentin of four different one-step self-etching adhesive systems in vitro in a comparative manner. Materials and Methods: In the present study, 20 caries-free human molar teeth were used. Occlusal surfaces were removed to achieve a uniform dentin surface under water cooling by using a low-speed diamond saw. The dentin surfaces obtained were abraded for one minute by using 600-grit silicon carbide papers. Then, the teeth were randomly assigned into four groups (n = 5). For restoration of teeth prepared, four different one-step self-etching adhesive systems, including Clearfil S 3 Bond Plus, Clearfil S 3 Bond, Xeno V Bond and Adper Easy Bond were used according to manufacturer's instructions. A 4 mm thick of composite resin crown (ClearfilAP-X) was applied to surfaces pre-treated with bonding agent. Samples were stored in distilled water at 37°C for 24 hours until micro-tensile bond strength tests were performed. Statistical analyses were performed by using one-way ANOVA and post-hoc Tukey tests (α =0.05). Fracture surfaces were evaluated using a stereomicroscope. Results: Significant differences were observed in bond strength to dentin among one-step self-etching adhesive systems (P < 0.05). The highest bond strength was achieved by Clearfil S 3 Bond Plus system (P < 0.05). No significant difference was observed in bond strength among other groups (P > 0.05). Conclusion: There were differences between bond strength values of tested one-step self-etch adhesives. Clearfil S 3 Bond Plus exhibited higher values.
Keywords: Bond strength, dentin, micro-tensile, one-step self etch
|How to cite this article:|
Cebe M, Adiguzel M, Cebe F, Tekin M. Comparative evaluation of micro-tensile bond strength of one-step self-etching adhesive systems
. J Res Dent 2014;2:130-5
|How to cite this URL:|
Cebe M, Adiguzel M, Cebe F, Tekin M. Comparative evaluation of micro-tensile bond strength of one-step self-etching adhesive systems
. J Res Dent [serial online] 2014 [cited 2020 Jun 4];2:130-5. Available from: http://www.jresdent.org/text.asp?2014/2/3/130/143596
| Introduction|| |
Adhesive systems are classified based on adhesion strategies used as follows: total-etch, self-etching and glass ionomer-based.  Total-etch adhesive systems involve a three-stage procedure, including etching dental tissue by using 37% phosphoric acid, preparation of surface with primer and bonding. ,, In self-etching systems, acid etching and primer application processes are combined, and washing process is removed. , The intention to spend less time during procedure and tendency to adhesive systems not requiring technical sensibility allow introduction of single-stage self-etching adhesive systems by improving self-etching adhesive systems with various chemical structure and different application patterns. , These systems, also termed as all-in-one adhesive system, combine acid primary and bond in the same solution and become a procedure that can be applied in one step. , Easy and rapid application procedure is the main advantage of one-step systems when compared to their corresponding multi-step procedures. ,
In one-step self-etch adhesive systems, micro-mechanical retention is still considered the principal mechanism, in which minerals removed from dental hard tissues are replaced by resin monomers that upon polymerization become micro-mechanically interlocked in the created porosities.  However, these systems form only submicron-thick hybrid layers, in which hydroxyapatite partially remains around exposed collagen.  Each self-etch adhesive contains its specific functional monomer that, to a large extent, determines its actual adhesive performance.  These monomers are characterized by at least one polymerizable group and a functional group, which can serve different purposes, such as wetting and demineralizing the substrate. , It has been shown that functional groups capable of releasing one or more protons, such as carboxyl, phosphate and phosphonate groups, may also have the potential for chemically binding to calcium in hydroxyapatite.  This model is called 'Adhesion-Decalcification' concept, and it dictates that the functional monomer either decalcifies or bonds to the tooth substrate. 
Today, in market different brands of one-step self-etch adhesive systems are present. The ingredients of these systems vary according to the manufacturer and these differences can affect the performance of adhesive systems.  The in vitro laboratory bond strength testing is used as a screening tool to understand and predict the performance of these products in a short period of time. 
The aim of this study was to assess micro-tensile bond strength values to dentin of four different commercially available one-step self-etching adhesive systems in vitro in a comparative manner and thus to help clinicians to the choice of materials.
The null hypothesis tested was that there are no differences between the bond strength of four different one-step self-etch adhesives.
| Materials and methods|| |
Preparation of samples
Twenty caries-free human molar teeth, which were extracted due to periodontal causes within prior 3 months, were used in this study. Teeth were stored in 10% formalin solution after extraction. Debris on the teeth was removed using scaler and pumice. Occlusal surfaces were removed to achieve a uniform dentin surface under water cooling by using a low-speed diamond saw (Allied, Rancho Dominguez, CA, USA). The dentin surfaces obtained were polished for one minute by using 600-grit silicon carbide (SiC) paper. The teeth were randomly assigned into four groups (n = 5). For restoration of teeth, four different one-step self-etching adhesive systems, including Clearfil S 3 (Kuraray Co., Osaka, Japan), Clearfil S 3 Plus (Kuraray Co., Osaka, Japan), Xeno V Bond (3M, St. Paul, MN, USA) and Adper Easy Bond (Dentsply, DeTrey, Konstanz, Germany) were used according to manufacturer's instructions. A calibrated LED source device (Monitex Blue Light Bt-1200, Monitex Industrial Co., New Taipei City, Taiwan) was used for polymerization. A 4 mm thick composite resin crown (ClearfilAP-X, Kuraray Co., Osaka, Japan) was applied to surfaces treated with bonding agent, which then allowed for polymerization for over 40 seconds. Samples were stored in distilled water at 37°C for 24 hours until micro-tensile bond strength tests. The products used in this study are showed in [Table 1].
Micro-tensile bond strength tests
Roots of the teeth that underwent restoration were removed at a level 2 mm below the enamel-cement junction using a low-speed diamond saw under water cooling. Then, each sample was fixed to acrylic blocks (2 × 4 × 1 cm in size) by using a cyanoacrylate-based adhesive material (Patex, Henkel, Düsseldorf, Germany). These blocks were mounted to precision saw (Isomet 1000; Buehler, Lake Bluff, IL, USA) and square-section test sticks (1.00 ± 0.003 mm 2 in size) containing composite resin and tooth were obtained in the parallel plane to long axis by using low-speed diamond saw. Four test sticks obtained for each test were selected. Thus, overall 20 test sticks were obtained for each group (n = 20).
For micro-tensile bond strength test, test sticks were fixed to micro-tensile test device (Micro-tensile tester, Bisco, Schaumburg, IL, USA) at both ends by using cyanoacrylate-based adhesive material (Patex, Henkel, Düsseldorf, Germany). Test sticks were fractured by using the following parameters: Cross head speed, 1 mm/min and loading force, 100 N. Area of bonding surface was calculated by measuring side length with a digital micrometer (Mitutoyo, Kawasaki, Japan). Results obtained as Newton was transformed to MPa by dividing with surface area.
Stereomicroscopic fracture analysis
Fracture surfaces of each sample underwent micro-tensile strength test and was evaluated under 10× magnification by using a stereomicroscope (Leica Microscope Systems, Wetzlar, Germany).
Failure was considered to be (a) adhesive if it occurred at the dentin/adhesive interface, (b) cohesive if it occurred in the material or in the substrate, and (c) mixed when involving both the interface and the material. The bond failure sites were not statistically analyzed. ,
Scanning electron microscope (SEM) evaluation
The teeth for SEM imaging of dentin-adhesive interfaces were fixed on a glass platform with sticky wax and sectioned vertically into two halves with a slow-speed diamond saw (Isomet, Buehler, Lake Bluff, IL, USA). Specimens were polished with 1200-grit SiC paper under water cooling, etched with 6 mol/L HCl phosphoric acid for 30 seconds, and washed with ultrasonic cleaner for 15 minutes. They were then deproteinized with 5% sodium hypochlorite solution for 5 minutes and washed with ultrasonic cleaner for 15 minutes. Each specimen was next dehydrated in an ascending ethanol series (50%, 70%, 95%, 100%) for 15 minutes each, dried, mounted on metallic stubs prior to gold sputtering (Cressington Sputter Coater 108auto, Cressington, Germany), and observed under SEM (EVO LS10, Zeiss, Oberkochen, Germany) at different magnifications.
The data were entered into a spreadsheet (Excel; version 4.0, Microsoft, Seattle, WA, USA) for the calculation of descriptive statistics. The results of Levene's test (P > 0.05) and Shapiro-Wilk test (P > 0.05) in all of the groups demonstrated variance homogeneity. Therefore, one-way ANOVA and Tukey post-hoc tests were applied to assess the significance of the differences in bond strengths among the experimental groups. Data were analyzed using SPSS 20 for Mac statistical program software. The level of significance was 5% (P < 0.05).
| Results|| |
The mean bonding strength to dentin for four different one-step self-etching adhesive systems are shown in [Table 2]. Significant differences were observed between bond strength to dentin among single-step self-etching adhesive systems (P < 0.05). The highest bond strength was achieved in Clearfil S 3 Bond Plus group (P < 0.05). No significant difference was observed in bond strength between Xeno V Bond Clearfil S 3 Bond and Adper Easy Bond systems (P > 0.05).
|Table 2: Mean micro-tensile bond strength values and standard deviations obtained for the different groups|
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The highest adhesive failure percentage was observed in Xeno V Bond and Adper Easy Bond groups (50%). The highest cohesive failure percentage was observed in Clearfil S 3 Bond and Clearfil S 3 Bond Plus groups (35%). The highest mixed failure percentage was observed in Adper Easy Bond group (30%) [Figure 1].
|Figure 1: Failure modes of specimens after micro-tensile bond strength test|
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SEM photomicrographs are presented in [Figure 2], [Figure 3], [Figure 4], [Figure 5] for resin-dentin interfaces. In [Figure 2], a thin hybrid layer and debonded area were observed. A few short resin tags were also noted.
|Figure 2: SEM photograph illustrating the interfacial morphology after treatment with S3 Bond. Original magnification 2.000×|
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|Figure 3: SEM photograph illustrating the interfacial morphology after treatment with S3 Bond Plus. Original magnification 2.000×|
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|Figure 4: SEM photograph illustrating the interfacial morphology after treatment with Xeno V. Original magnification 2.000×|
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|Figure 5: SEM photograph illustrating the interfacial morphology after treatment with Adper Easy Bond. Original magnification 2.000×|
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In [Figure 3], [Figure 4], [Figure 5], a thin hybrid layer and good contact between composite resin and dentin were observed.
| Discussion|| |
Micro-tensile bond strengths of four different one-step self-etching adhesive systems were investigated in the present study.
Based on our results, the null hypothesis was rejected. There were differences of bond strength values. The highest bond strengths were observed in Clearfil S 3 Bond Plus group, while the lowest bond strengths were observed in Xeno V Bond and Clearfil S 3 Bond groups. Adper Easy Bond group showed bond strength lower than Clearfil S 3 Bond Plus group but higher than other groups.
As long-term clinical follow-up is time-consuming and difficult to perform in a standard manner, in vitro bond strength tests are frequently used to assess dental material and techniques. , For this purpose, shear, micro-shear, tensile and micro-tensile tests have been developed. ,, The advantages of micro-tensile strength test include ability to obtain multiple samples from a single teeth and allowing more adhesive fracture.  We used micro-tensile strength test in the present study considering these advantages.
In this study, it was observed that adhesive failure rates were higher in all groups in general when deficits were assessed. The highest cohesive failure rate was found in Clearfil S 3 Bond and Clearfil S 3 Bond Plus groups, while highest mixed failure rate was observed in Adper Easy Bond group. It is suggested that cohesive failures indicates high bond strength while adhesive failures indicates low bond strength. ,
Developments in adhesive dentistry have led to fundamental transformation in dentistry practice. By these advances, one-step self-etching adhesive systems have been developed instead of three-stage adhesive systems, which eliminate application stages. Time-saving practice, easy applicability and requirement to less technical sensibility make these systems more attractive. 
One-step self-etching systems contain acidic monomers to resolve smear layer and ensure demineralization in dental tissues.  In our study, variation in adhesive bond strength among groups may be due to different acidic monomers. pH value is one of the factors affecting bond strength of adhesive systems.  Van Meerbeek et al. classified self-etching primaries as strong (pH ≤ 1), moderate (pH ≈ 1.5) and weak (pH ≥ 2) according to pH values.  pH values of the systems used in the present study were as follows: Xeno V, pH < 2; Clearfil S 3 Plus, pH = 2.3; Clearfil S 3 , pH = 2.7; Adper Easy Bond, pH = 2.4. In our study, variations in adhesive bond strength may be due to different pH values of adhesive systems. However, it is suggested that pH value isn't the only factor influencing bond strength.  The finding that Xeno V with the lowest values expressed the lowest bond strength in our study supports the above-mentioned suggestion.
According to 'Adhesion-Decalcification' concept, one-step self-etch adhesives chemically binds to the tooth substrate with their functional monomers.  Type of functional monomers can affect the bond strength.  Functional monomers of one-step self-etch adhesives used in present study were different. This situation might have affected the bond strength values.
A water-soluble methacrylate monomer, termed as 2-hydroxyethyl methacrylate (HEMA), is frequently used in dentin adhesives.  It improves the ability to soak adhesive and resin penetration.  It has positive effects on bond strength due to its hydrophilic character and improved ability to mix hydrophilic and hydrophobic components within adhesive. ,, Clearfil S 3 Bond, Clearfil S 3 Bond Plus and Adper Easy Bond used in the present study contain HEMA, while Xeno V did not. Xeno V showed the lowest bond strength value among all the adhesive systems used. This could be due to the lack of HEMA in Xeno V.
Filler content is another factor that affects the bond strength of adhesive systems.  All the adhesives used in the present study contained filler except for Xeno V. Previous studies have shown that compared to unfilled systems, most filled bonding resulted in providing higher bond strength to dentine. , The results of the present study were consistent with the earlier studies.
| Conclusion|| |
Based on 24-hour bond strength values, there were differences between bond strength values of tested one-step self-etch adhesives. Clearfil S 3 Bond Plus exhibited the highest values. However, there is a need for studies on long-term bond strength and clinical success of these systems.
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[Figure 1], [Figure 2], [Figure 3], [Figure 4], [Figure 5]
[Table 1], [Table 2]