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Table of Contents   
ORIGINAL RESEARCH  
Year : 2020  |  Volume : 31  |  Issue : 5  |  Page : 752-757
Comparative evaluation of shear bond strength between fifth, sixth, seventh, and eighth generation bonding agents: An In Vitro study


Department of Conservative Dentistry and Endodontics, Tagore Dental College and Hospital, Near Vandalur, Melakkottaiyur Post, Rathinamangalam, Chennai, Tamil Nadu, India

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Date of Submission13-Aug-2019
Date of Decision21-Aug-2019
Date of Acceptance10-Jan-2020
Date of Web Publication08-Jan-2021
 

   Abstract 


Aim: To evaluate and compare the shear bond strength of composite resin to dentin using eighth generation dental adhesive (G-Premio Bond) with fifth, sixth, and seventh generation dentin adhesives. Materials and Methods: A total of 64 freshly extracted non-carious, intact human premolar teeth were selected. Class V cavity was prepared by using high speed hand piece. The prepared samples were randomly divided into four experimental groups (n = 16). Group I: Adper single Bond 2 [fifth generation] (ASB-5), Group 2: Clearfil SE [sixth generation] (CSE-6), Group 3: Single Bond Universal [seventh generation] (SBU-7), Group 4: G-Premio Bond [eighth generation] (GPB-8). Bonding agents were applied according to the manufacturer's instructions and light cured. Then, the Nano composite Filtek Z350 was placed in a two layer increment using Teflon Jig (2 × 2 × 2 mm) and was light-cured for 40 s. Shear bond strength was tested by a universal testing machine. This study was carried out by using Tukey HSD post-hoc test where P ≤ 0.05 was considered as a statistical significant. Results: The highest value of shear bond strength was obtained from G-Premio Bond (eighth generation) showed statistically significant difference when compared to seventh generation bonding agent. However, there is no statistical significant difference between eighth and fifth, sixth generation. Conclusion: The study concluded the G-Premio Bond (eighth generation) showed effective shear bond strength than other bonding agents. This bonding agent is compatible with self-etch without use of primer which gives highly long lasting esthetic, wear resistant, and it is ideal for hypersensitive tooth.

Keywords: Fifth generation, sixth generation, seventh generation, eighth generation, Adper single bond 2, Clearfil SE, dentin bonding agent, G-Premio bond, shear bond strength, single bond universal

How to cite this article:
Ganesh A S. Comparative evaluation of shear bond strength between fifth, sixth, seventh, and eighth generation bonding agents: An In Vitro study. Indian J Dent Res 2020;31:752-7

How to cite this URL:
Ganesh A S. Comparative evaluation of shear bond strength between fifth, sixth, seventh, and eighth generation bonding agents: An In Vitro study. Indian J Dent Res [serial online] 2020 [cited 2021 Jan 28];31:752-7. Available from: https://www.ijdr.in/text.asp?2020/31/5/752/306456



   Introduction Top


Adhesive bonding to tooth structure has been an integral part of modern restorative dental practice that improves the biomechanical and esthetic quality outcomes of restorations. An effective bonding to tooth structure would durably seal dentinal tubules and restoration margins. This would prevent microleakage and the adverse consequences of post restoration hypersensitivity, marginal discoloration, recurrent caries, and harmful effects on the pulp. Furthermore, it would eliminate the need for extension undercuts, thus conserving tooth structure.

The last two decades have seen a rapid progress in the field of adhesive dentistry. Efforts have been made to improve bond strength and simplify the restorative procedure.

Literature search reveals that the most cited reasons for failure of adhesive restorations are loss of retention and marginal adaptation.[1],[2] Consequently, a viable approach to prolong the clinical life of dental adhesives is to focus on improving the long-term stability of the bond of these biomaterials to tooth hard tissues, especially dentin.

Although many advances have been made in adhesive technology, the bond interface remains the biggest challenge when placing an adhesive restoration.[3] Water sorption is thought to be the main factor destabilizing the adhesive–tooth bond, although the actual interfacial degradation mechanisms are not completely understood.[4],[5] Other factors to consider are all the chemical and mechanical challenges inherent to the oral environment, such as moisture, masticatory stresses, changes in temperature and pH, and dietary and chewing habits.[6]

One of the biggest areas of development has been to simplify the bonding process by use of all-in-one adhesives, but according to the review published by Van Meerbeek and others, ''the conventional three-step etch and rinse adhesives and two-step self-etch adhesives are still the benchmarks for dental adhesion in routine clinical practice''.[7] All-in-one adhesives have certainly improved over the past decade, and the development of functional monomers with strong and stable chemical affinity to hydroxyapatite is a valuable contribution for the improvement of dental adhesion.[8]

Although adhesives have reached an acceptable level of bond strength,[9] attempts have focused on reducing the application steps since the use of multistep agents is difficult and time-consuming.

Simultaneous enamel and dentin etching systems by using two-step fifth generation bonding agents have shown favorable clinical efficacy. A recent revolutionary advancement in dentin bonding agents is the use of acidic adhesives enabling simultaneous application of acid, primer, and bonding agent all together in sixth and seventh generation bonding systems.[8] Aside from the easy steps, the mechanism of action of sixth and seventh generation bonding agents is surface demineralization of dentin and simultaneous penetration of monomers into the resultant porosities.[10] One-step systems simplify and shorten the process of bonding and are beneficial for use.[11]

Development in nanotech dentistry has led to development of nano-composites and nano-adhesives which contains nano-sized fillers. Nano-bonding agents are solutions with nano-fillers which produce better enamel and dentin bond strength, stress absorption, and longer shelf life.[12] It has been observed that filled bonding agents produced higher in vitro bond strength.[13]

Recently, a nano filled eighth generation dentin bonding agent (G-Premio Bond) has been introduced by GC.[14] To date there were no studies comparing the shear bond strength of this newly introduced eighth generation bonding agent (G-Premio Bond) with the fifth, sixth, and seventh generation bonding agents.

Hence, the aim of this study was to evaluate and compare the shear bond strength of eighth generation bonding agent (G-Premio Bond), with the fifth (Adper Single Bond 2), sixth (Clearfil SE), and seventh (Single Bond Universal) generation dentin adhesives.


   Materials and Methods Top


This study was done in the Department of Conservative Dentistry and Endodontics. A total of freshly extracted human premolars with single root were selected. The tooth was examined to be free of cracks, caries, fractures, and should have fully developed apices. They were stored in saline. The specimens utilized for this study were within 3 months of extraction.

Collection, storage, sterilization, and handling of extracted teeth to be used in this study followed the Occupational Safety and Health Administration and Centre for Disease Control and Prevention recommendation guidelines.

  • 0.5% sodium hypochlorite was used in wide mouthed plastic jars for initial collection and storage medium.
  • Handling of teeth was always done using gloves, mask, and protective eyewear.
  • After standing in sodium hypochlorite solution for at least half an hour, the liquid were discarded and the teeth were transferred into separate jars containing physiological saline with 0.1% thymol.
  • The initial collection jars, lids, and gloves employed were discarded into biohazard collection waste receptacles.
  • As the teeth were required, they were removed from the jars with cotton pliers and rinsed in tap water. After soaking in a container of tap water for few minutes, the teeth were rinsed again and used.
  • The teeth were dried and then used for the study purpose.


Coronal to the cement–enamel junction the tooth was sectioned with a diamond disk using a slow speed handpiece under water cooling.

The prepared tooth specimens were embedded in cold cure acrylic resin with the help of custom-made mound of dimensions 2 × 2 cm. Teeth were mounted horizontally, facing the labial surface. The labial surface of each tooth was reduced with a high speed handpiece using #245 carbide bur under constant water spray in order to expose flat surface of dentin. Dentin surfaces were polished with a fine grit sandpaper until a flat area of approximately 5 mm in diameter was established.[14]

They were randomly divided into four groups, with 16 specimens in each group (n = 16).

Group 1: Adper single Bond 2 (3M) pink color acrylic blocks [fifth generation] (ASB-5)

Group 2: Clearfil SE (Kuraray), green color acrylic blocks [sixth generation] (CSE-6)

Group 3: Single Bond Universal (3M) Red color acrylic blocks [seventh generation] (SBU-7)

Group 4: G-Premio Bond (GC, blue color acrylic blocks [eighth generation] (GPB-8)

The adhesive system was used according to manufacturer's instruction for each test group.

Group 1: (ASB-5) Etchant was applied to dentin. Waited for 15 s. Rinse for 10 s [Figure 1]. The excess water was blot dried with using a cotton pellet. After blotting, two to three consecutive coats of adhesive was applied to etched dentin for 15 s with gentle agitation using a fully saturated applicator. Gently air drying was done for 5 s to evaporate solvents. Light curing was done for 10 s.
Figure 1: Application (s) and blow dry of the specimen (b)

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Group 2: (CSE-6) In this group, sixth generation primer (Clearfil SE, Kuraray) was applied to the dentin surface and left for 20 s and dried with mild air flow, then Bonding agent was applied and evenly distributed with mild air flow and light cured for 10 s [Figure 2] and [Figure 5].
Figure 2: Application of primer (a) and bonding agent (c)

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Figure 5: Teflon mould

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Group 3: (SBU-7) In this group, a seventh generation bonding agent (Single Bond Universal, 3M) was applied to dentin surface by scrubbing action for 20 s, air drying of adhesive was done for 5 s, followed by 10 s of light curing [Figure 3] and [Figure 5].
Figure 3: Application (a) and light cure of the specimen (c)

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Group 4: (GPB-8) In this group, an eighth generation bonding agent was applied on tooth structure using a micro brush, was left undisturbed for 10 s after application, followed by thoroughly air drying for 5 s under maximum air pressure and light-curing was done for 10 s [Figure 4] and [Figure 5].
Figure 4: Application (a) and light cure of the specimen (c)

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Filtek Z350 (3M) was then placed in increments, using a Teflon mould measuring 2 mm × 2 mm × 2 mm and cured for 40 s on all the 64 specimens.[15]

The acrylic portion of the samples were color coded for the identification purpose

Group 1 (ASB-5) – pink

Group 2 (CSE-6) – green

Group 3 (SBU-7) – red

Group 4 (GPB-8) – blue

Shear bond testing: The shear bond testing was done at Central Institute for Plastic Engineering and Technology. All acrylic block specimens were transferred to the Instron universal machine [Figure 6] individually and subjected to shear bond strength analysis at crosshead speed of 1.0 mm/min. The load was applied on the junction of the dentin and the composite interface, the values were recorded. The results were then statically analyzed.
Figure 6: Instron universal machine

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The data collected in present study was analyzed using one-way analysis of variance (ANOVA) test. Intergroup analysis of shear bond strength values was carried out using post hoc Tukey HSD test.

In the present study, P ≤ 0.05 was considered as the level of significance.


   Results Top


The shear bond strength values (in MPa) obtained for the four groups tested are given in [Table 1].
Table 1: Shear bond strength

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The Tukey HSD post-hoc test for intergroup comparisons is listed in [Table 2].
Table 2: Tukey HSD post-hoc test for intergroup comparisons

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Mean shear bond strength values was found to be highest for the eighth generation dentin bonding agent (21.56 ± 6.72) followed by sixth generation dentin bonding agent (20.09 ± 7.00), fifth generation dentin bonding agent (17.31 ± 7.44), and seventh generation dentin bonding agent (14.52 ± 6.40), respectively.

Using one-way ANOVA, P ≤ 0.05 was considered as the level of significance.


   Discussion Top


Dental adhesive systems have evolved through several generations with changes in their chemistry, mechanism, and number of steps, application techniques and clinical effectiveness. Currently, etch and rinse adhesives are still considered to be the gold standard among dentin bonding agents and their performance is considered constant and predictable. Hence, they continue to be popular even today. According to Van Meerbeek et al. since etch and rinse adhesives require multiple clinical steps, there are numerous opportunities for errors to occur.[16]

This had led to the development of the two-step self-etch adhesive systems which were introduced in the late 1990's.

The two-step self-etch adhesive systems include the use of a hydrophilic etching primer, which combines acidic monomers that simultaneously etch and prime tooth substrate, and after solvent evaporation, a layer of hydrophobic resin and bonding agent seal the dentin.[17]

The chemical formulation of self-etch adhesive systems, in specific the functional monomers, plays an important role for the adhesive long-term bonding performance.[17]

Among the current generation of self-etch adhesives, the manufacturers have sought to eliminate the etching step or to include it chemically in one of the other steps. A new, simplified adhesive system was introduced, that is the seventh generation adhesive. Just as the fifth-generation bonding agents made the leap from previous multicomponent systems to a rational and easy-to-use single bottle, the seventh generation simplifies the multitude of sixth-generation materials into a single component, single-bottle system.

The seventh generation one bottle dentin bonding agent contains 2-hydroxyethyl methacrylate (HEMA) monomer in order to improve the wettability to dentin surface. HEMA helps in improving binding of the hydrophilic collagen of the dentin to the hydrophobic composite resin material.

The newly introduced eighth generation bonding agents are dual cured, self-etching, nano reinforced agents, and produce comparable bond strengths to both dentin and enamel.[12] They have a mild pH which are assumed to cause less post-operative pain. Eighth generation dentin bonding agent use smear layer as a bonding substrate, leaving residual smear plugs that cause less dentinal fluid flow than etch and rinse adhesives.[18] These mild self-etching adhesives leave hydroxyapatite crystals available for chemical bonding of functional monomers to calcium, which may contribute to interface stability.[18]

Shear bond tests are one of the most widely used laboratory evaluations of adhesive systems. According to Hanan Alzraikat et al. the most commonly used test to assess bond strength is the macro-shear test which has gained popularity as a simple and quick method.[19] Moreover, it is a very popular test that is commonly used to screen new adhesive formulations on their bonding effectiveness.[19] The rationale behind bond strength testing is that, higher the actual bonding capacity of an adhesive, the better it will withstand stresses and longer the restoration will survive in vivo. In the present study, Instron testing machine was used to analyze the shear bond strengths of composite resin to dentin using the fifth, sixth, and seventh and eighth dentin bonding agents. The ISO has recommended that in shear bond strength tests, the load should be applied with cross head speed of within 0.45 mm/min and 1.05 mm/min. Accordingly, the study employed a cross head speed of 1 mm/min.

This study comparatively evaluated the shear bond strength of newly introduced eighth generation dentin bonding adhesive G-premio bond (GBP-8) with Adper single Bond 2 (fifth generation) (ASB-5), Clearfil SE (sixth generation) (CSE-6), and Single Bond Universal (seventh generation) (SBU-7).

There was a statistical significant difference between eighth and seventh generation bonding agent. The following reasons could be attributed for the same:-

  1. 4-Methacryloyloxyethyl trimellitic acid is used as adhesion promoting monomer in G-premio bond. The solvent used in this adhesive is acetone which prevents the esterification of carboxylic acid groups, thereby improving the demineralization and enhancing wetting.[20] Acetone also has a good water chasing capacity.[20]
  2. A previous study by Joseph et al. have shown that the presence of nano sized cross-linking silica fillers may be responsible for increased bond strength in the newly introduced eighth generation bonding agents.[12] Since G-premio bond also has a similar silica fillers, it may have shown the highest bond strength values among all the tested groups.
  3. The seventh generation dentin bonding agent contains HEMA which is absent in the eighth generation G-Premio Bond. These Hydrophilic monomers are added in high concentration in order to facilitate Bis-GMA solubility which would produce a tough, highly cross-linked polymer network. However, after polymerization, HEMA attracts water, causing water sorption, hydrolytic degradation, nano leakage, and resultant decline in bond strength.[21]


Bond strength values of GPB8 were statistically comparable to CSE-6. It has been postulated that the presence of methacryloyloxydecyl dihydrogenphosphate functional monomer in eighth and sixth generation self-etch adhesives results in chemical bonding to dentin substrate as it establishes an ionic bond with hydroxyapatite more readily and intensively.[21]

The lowest bond strength values were obtained by SBU-7. This may be due to the hydrolytic instability of methacrylate monomers used. One-step self-etching adhesives are more hydrophilic than two-step self-etching adhesives, and they attract more water.[13] As it is difficult to evaporate water from these adhesives, water will rapidly diffuse back from the bonded dentin into adhesive resin and subsequently, lower mechanical strength results.[22]

Within the limitations of this study, the newly introduced GPB-8 (eighth generation dentin bonding agent) showed increased bond strength values when compared to the seventh generation bonding agent.


   Conclusion Top


The study concluded the G-Premio Bond (eighth generation) showed effective shear bond strength than fifth, sixth, and seventh generation bonding agents. This bonding agent is compatible with self-etch without use of primer which gives highly long lasting esthetic, wear resistant, and it is ideal for hypersensitive tooth.

However, further studies are needed to investigate the bond strengths of these newer generations of adhesive systems under clinically acceptable conditions.

Financial support and sponsorship

Nil.

Conflicts of interest

There are no conflicts of interest.



 
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Correspondence Address:
Dr. A Sri Ganesh
Department of Endodontics and Conservative Dentistry, Tagore Dental College and Hospital, Near Vandalur, Melakkottaiyur Post, Rathinamangalam, Chennai - 600127, Tamil Nadu
India
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Source of Support: None, Conflict of Interest: None


DOI: 10.4103/ijdr.IJDR_635_19

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    Figures

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