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ORIGINAL ARTICLE
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To evaluate and compare the microtensile bond strength of dentine with the use of two-step and one-step adhesives: An ex vivo study


1 Department of Conservative Dentistry and Endodontics, Government Dental College, Ahmedabad, Gujarat, India
2 Department of Conservative Dentistry and Endodontics, College of Dental Sciences and Hospital, Amargadh, Gujarat, India
3 Department of Periodontics and Oral Implantology, College of Dental Sciences and Hospital, Amargadh, Gujarat, India

Date of Submission24-Jan-2022
Date of Acceptance01-Aug-2022
Date of Web Publication23-Sep-2022

Correspondence Address:
Rosaiah Kanaparthy,
Department of Periodontics and Oral Implantology, College of Dental Sciences and Hospital, Amargadh - 364 210, Gujarat
India
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Source of Support: None, Conflict of Interest: None

DOI: 10.4103/aihb.aihb_10_22

  Abstract 


Introduction: In the evolving world of adhesive dentistry, there has always been controversy regarding the adhesive system to be used for superior clinical performance, and clinicians often find themselves in a dilemma with so many products on the market. It, therefore, becomes necessary to know the various properties of different adhesive systems and their comparative analysis. Materials and Methods: Thirty, intact, non-carious and unrestored human mandibular premolars, which were extracted for orthodontic purposes were taken for the study. Teeth were divided into two groups A and B having 15 teeth in each group. The inclusion criteria were that the teeth should be non-carious, unrestored and should have been extracted for orthodontic purposes. Excluded teeth were those with caries, restorations, attrition, cracks and developmental defects. The teeth were embedded in resin, occlusal enamel was removed and the teeth were restored with composite resin using two different approaches for bonding. Teeth of Group A were bonded using single bond and teeth of Group B were bonded using Clearfil S3 Bond and were then sectioned to produce beams with an approximate cross-sectional area of 4 mm × 4 mm. These sections were mounted to a custom acrylic jig and subjected to microtensile bond strength testing using a universal testing machine with a cross head speed of 1 mm/min and stressed to de-bonding of the composite resin from the tooth. Results: Data were subjected to statistical analysis and evaluated using the analysis of variance test and Tukey's test which showed that single bond or two-step adhesive showed higher microtensile bond strength to dentine. Conclusion: The two-step single bond performed better than the one-step Clearfil S3, but the result was statistically non-significant.

Keywords: Dentine, microtensile bond strength, one-step advice



How to cite this URL:
Patel N, Kanaparthy A, Kanaparthy R. To evaluate and compare the microtensile bond strength of dentine with the use of two-step and one-step adhesives: An ex vivo study. Adv Hum Biol [Epub ahead of print] [cited 2022 Sep 27]. Available from: https://www.aihbonline.com/preprintarticle.asp?id=356790




  Introduction Top


The use of adhesive dentistry for restorations has been accepted globally over the past few decades and has become the most acceptable dental restorative procedure for the direct restorations of teeth.[1] Adequate adhesion of resins to enamel and dentine is essential for the success of such restorations. Thus, the success of composite restorations is dependent on adhesion to enamel and dentine not only for resistance and retention but also to prevent microleakage.[2],[3]

The protocol for adhesion started as a three-step adhesive system which was later modified to a two-step etch and rinse approach, and finally, the one-step protocol for simplifying the procedure.[4],[5]

The two-step protocol is technique sensitive, as overdrying or overwetting after etch and rinse step, can interfere with proper bonding.[6] Besides this, it involves more number of clinical steps and a longer application time; therefore, increasing the probability of errors. No-rinse adhesives also called self-etch adhesives were developed to overcome these problems.[7],[8]

The self-etching adhesives act by demineralisation and priming in a single step, with the adhesive resin layer being placed separately (6th generation) or by simultaneous demineralisation, priming and resin infiltration which leads to an adequately infiltrated hybrid layer (one-step seventh generation).[9] Therefore, in the one-step or the seventh-generation bonding agents, the collapse of the collagen network and discrepancies occurring between the depth of etching and resin infiltration are reduced.[10],[11] However, seventh-generation adhesives are too hydrophilic and susceptible to degradation[12] within hybrid layers leading to ineffective enamel and dentine adhesion and leading to decreased bond strength and increased microleakage. The challenges of bonding to dentine are too many when compared to the enamel, as it has more organic content and fluid-filled dentinal tubules.[13]

Bond strength to enamel and dentine is an important indicator of an adhesive system's effectiveness since the bonding must compensate not only the stress due to polymerisation shrinkage but also the stresses due to mastication.[14]

Microtensile bond tests allow a better distribution of stress on the adhesive interface, when compared to the conventional tensile or shear tests; therefore, presenting more reliable results and with less variation.[15] The microtensile also allows a higher number of specimens per tooth, raising the accuracy of the test. According to Griffith's defect theory, when testing uniform materials in tension, the tensile strength of a material decreases with increasing specimen size.[16] This study was carried out to evaluate and compare the microtensile bond strengths of the two-step adhesive system single bond with the one-step adhesive Clearfil S3 Bond systems to dentine.


  Materials and Methods Top


Thirty intact, non-carious and unrestored human premolars extracted for orthodontic purposes were taken for the study. These teeth were scraped off the residue with an ultrasonic scaler and kept in 3% sodium hypochlorite (NaOCl) to remove the residues for 10 min, followed by rinsing under running water and stored in isotonic saline at room temperature for 24 h. Teeth were embedded in acrylic resin, and the occlusal enamel was removed perpendicular to their long axis, to expose a flat, midcoronal dentine surface using a low-speed diamond disc. This surface was polished with silicon carbide paper to produce the smear layer and then rinsed under copious running water and immediately dried with moisture-free air with a chip blower for 5 s.

Teeth were randomly divided into two groups, Group A comprised 15 teeth bonded using a two-step single bond adhesive.

Group B comprised 15 teeth bonded using a one-step bonding agent – Clearfil S3 Bond (Kuraray Medical Inc.)

The teeth assigned to the A group were etched with 37% orthophosphoric acid, and those of the B group were not etched. Bonding agents were applied according to the manufacturer's instructions, and resin composite was built up incrementally to a height of 5 mm. Each increment was light cured for 40 s and finished with Sof-Lex finishing and polishing discs and specimens were stored in distilled water at room temperature for 24 h. Sectioning was done in the mesiodistal direction, and then, the teeth were rotated at 90° and again sectioned in the buccolingual direction to obtain beams with an approximate cross-sectional area of 4 mm × 4 mm. These sections were mounted to a custom acrylic jig and subjected to microtensile bond strength testing using a universal testing machine with a cross head speed of 1 mm/min and stressed to de-bonding of the composite resin from the tooth.

All the measurements were taken in the central part of the specimen, well away from the clamping site so that a uniform stress field is generated and the local tensile stress can be calculated simply from the load divided by the cross-sectional area.

Ethical approval

This study obtained ethical clearance from the Institutional Review Board of mentioned University (CODS/NGU/2021/231).


  Results Top


Data were subjected to the statistical analysis and evaluated using the analysis of variance test and Tukey's test. When bond strength was measured, the following comparisons could be made out. In Group A, the lowest bond strength was 21.51 MPa, whereas the highest bond strength was 288.12 MPa. Whereas in Group B, the lowest bond strength was 51.35 MPa, whereas the highest bond strength was 197.72 MPa [Table 1].
Table 1: Bond strengths of both groups

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A comparison of the mean and standard deviation of bond strength between Groups A and B revealed that mean bond strength was high in Group A (129.652 MPa) as compared to Group B (98.761 MPa). The difference in mean bond strength between Group A and Group B was 30.891 MPa. The difference obtained was found to be statistically non-significant with P = 0.092 [Table 2].
Table 2: Intergroup comparison of bond strengths between Group A and Group B

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  Discussion Top


The fundamental principle of adhesion involves the removal of calcium phosphates, by which microporosities are created in both, enamel and dentine surfaces which is followed by infiltration of resin and subsequent in situ polymerisation.[5] Adhesive systems have constantly evolved in terms of clinical simplicity, reduced application time and minimised procedural errors. The conventional three-step procedures are considered the gold standard in adhesion.[10] However, due to the increased number of steps, the two-step and one-step adhesives were preferred as compared to the three-step adhesives.[3],[17]

Bonding to dentine presents a much greater challenge than bonding to enamel.[18] Enamel is highly mineralised tissue composed of more than 90% (by volume) hydroxyapatite, dentine contains a relatively larger proportion of water and organic material, preliminary type I collagen along with fluid-filled dentinal tubules.[19],[20]

Adhesion can be affected by the remaining dentine thickness.[21] The density of dentinal tubules increases with increasing depth.[22] Hence, different depths in the dentine lead to different quality of adhesion. Therefore, we have removed the superficial dentine so that we can evaluate the bond strength to deeper dentine.

In this study, we had chosen the microtensile bond test, as it is considered the most reliable technique for assessing the 'true' interfacial bond strength between an adhesive material and the substrate of interest. There has been a tremendous rise in the use of this methodology (microtensile bond strength testing [μ TBS]) since its introduction.[23]

Hence, we decided to evaluate and compare the microtensile bond strengths of the fifth and sixth generations of bonding agents. Single bond contains dimethacrylate resins, HEMA, polyalkenanoic acid copolymer filler, ethanol, water and photoinitiator and has a pH of 4.2.

Clearfil S3 Bond contains MDP (10-Methacryloyloxydecyl dihydrogen phosphate), Bis-GMA, HEMA, water and ethanol and has a pH of 2.7. The difference in their monomers and pH also affect their bond strengths to dentine.

In the present study, the sample size comprised 30 intact, non-carious, unrestored human mandibular premolars extracted for orthodontic purposes as the dentine of such teeth would be unaltered. These teeth were scraped of residue and kept in 3% NaOCl to remove the residues for decontamination for 10 min, rinsed under running water and stored in isotonic saline at room temperature for 24 h. Then, the teeth were embedded in acrylic resin, and the occlusal enamel was removed perpendicular to their long axis to expose a flat, midcoronal dentine surface using a low-speed diamond disc. This was done to remove the enamel and superficial dentine, which would otherwise be removed during tooth preparation for composites; the bonding, therefore, takes place with the midcoronal dentine. Furthermore, the number of dentinal tubules would be more as compared to superficial dentine. This surface was polished with silicon carbide paper and then rinsed under copious running water to produce the smear layer and immediately dried with moisture-free air. Adequate air drying time has been suggested to be accurately 5 s, after drying, bonding agents were applied according to the manufacturer's instructions. The resin composite material used was to restore the surfaces.

Sectioning was done by a diamond disc in the mesiodistal direction, then the tooth was rotated at 90° and sectioned in the buccolingual direction to obtain beams with an approximate cross-sectional area of 4 mm × 4 mm, the non-trimming modality producing 4 mm × 4 mm sticks was preferred so that as the trimming would not result in specimens which would be prone to premature failure. These sections were mounted to a custom acrylic jig and subjected to microtensile bond strength testing using a Universal Testing Machine with a cross head speed of 1 mm/min and stressed to debonding of the composite resin from the tooth. All the measurements were taken in the central part of the specimen, well away from the clamping site so that a uniform stress field is generated and the local tensile stress can be calculated simply from the load divided by the cross-sectional area. The results of this study showed the mean and standard deviation values for bond strength for the two groups to be as follows Group A – Single bond, fifth generation two-step 129.652 MPa, and Group B – Clearfil S3 Bond, seventh generation, one-step 98.761 MPa. The result was statistically non-significant.


  Conclusion Top


The microtensile bond strength values obtained from this study using the two-step and one-step adhesives are quite high and more than adequate for overcoming polymerisation shrinkage and stresses due to mastication.

The results of the study showed that the two-step bonding agent single bond exhibited higher bond strength to dentine than the one-step bonding system Clearfil S3 Bond which helps the clinician to choose between the two types of adhesives. However, this study needs further in vivo evaluation as the normal physiological conditions of the oral cavity will have an impact on the results obtained for obvious reasons.

Financial support and sponsorship

Nil.

Conflicts of interest

There are no conflicts of interest.



 
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    Tables

  [Table 1], [Table 2]



 

 
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