Abstract
Aims and background
In achieving clinical success with adhesive materials, bond strength holds significant importance. The goal of testing the strength of the bond is to establish a value for how strong the binding of an adhesive system is to the dental structures. The aim of this in vitro study is to comparatively evaluate the shear bond strength of fifth, seventh, and eighth-generations of bonding agents.
Materials and methods
Forty-five extracted permanent teeth were allotted into three groups (n = 15), namely, group A: ADPER single bond 2, group B: single bond universal, group C: G-Premio bond. Etchant was applied to the exposed surface, and then adhesive was applied as stated in the manufacturer's instructions, followed by composite (Z350) buildup. The maximum shear force required to debond the specimen was recorded using a universal testing machine. One-way ANOVA test was utilized for statistical comparison at each assessment point, with the significance level set at p < 0.05 using SPSS statistical tool.
Results
The maximum shear bond strength was reported for group C, with the mean shear bond strengths of groups A, B, and C being 13.23, 9.66, and 19.21 MPa, respectively.
Conclusion
The newly introduced eighth-generation adhesive showed superior bond strength values compared to the fifth and seventh-generation bonding agents; this difference was statistically significant.
How to cite this article
Gupta S, Gupta S, Mehra M, et al. Comparative Evaluation of Shear Bond Strength of Fifth, Seventh, and Eighth-generation Bonding Agents in Permanent Teeth: An In Vitro Study. Int J Clin Pediatr Dent 2025;18(3):281–286.
Keywords: Acid etching, Adhesion, Bonding agent, Shear bond strength
Introduction
The emergence of adhesive dentistry has revolutionized the field of esthetic dentistry. Good adhesion between tooth and restorative resins is of primary importance in clinical practice. In the progression of adhesive technology across successive generations, the impetus has been on enhancing bond strength while also simplifying adhesive procedures. In the clinical effectiveness of adhesive materials, bond strength plays a crucial role in analyzing the adhesive effectiveness of any restorative material to the tooth. Hence, the purpose of the study was to assess the shear bond strength of various bonding agent generations on extracted teeth.
Materials and Methods
For the present study, 45 extracted permanent teeth were chosen that are noncarious, not restored, without any dental anomalies, and extracted for orthodontic purposes.
The following formula was used to determine the sample size of 45:
N = (Z a/2)2 2s2/d2
N = sample size.
s = standard deviation derived from the study's references.
d = accuracy of estimate or how close to the true mean.
Z a/2 = normal deviate for two-tailed alternative hypothesis at a level of significance.
Sample Preparation
To get rid of debris stuck to the teeth, the samples were cleaned with an ultrasonic scaler, polished with pumice, and placed in saline to prevent dehydration and stop them from becoming brittle. Every tooth specimen was placed into polyvinyl chloride sleeves (18 mm in length and 20 mm in diameter) using self-polymerizing acrylic resin, maintaining the occlusal surface of the tooth parallel to the ground up to the cemento-enamel junction level. The occlusal tooth surface was reduced using a handpiece at slow speed while being cooled with water and equipped with a diamond disk to obtain a flat dentinoenamel surface that is perpendicular to the tooth's long axis (Fig. 1). The prepared surface of the tooth was polished using pumice for 10 seconds with a rubber prophylactic cup and then cleansed with ethylenediaminetetraacetic acid (EDTA) solution. Pretreatment of the prepared tooth surface was done using an air abrasive unit with 50-µm alumina particles for 5 seconds (as per the manufacturer's instructions). The samples were then randomly distributed into three groups (n = 15) to study the shear bond strength of bonding agents (Table 1).
Fig. 1:
Mounted samples with exposed occlusal surface
Table 1:
Shows grouping of samples according to type of bonding agents used
| Groups | Number of teeth | Dentin bonding agent used |
|---|---|---|
| Group A | 15 | Fifth-generation (ASB-5) ADPER single bond 2 (3M) |
| Group B | 15 | Seventh-generation (SBU-7) Single bond universal (3M) |
| Group C | 15 | Eighth-generation (GPB-8) G-Premio bond (GC) |
Etchant (Scotchbond™ Multi-Purpose)1 was smeared on the exposed enamel and dentin surfaces simultaneously for 15 seconds with a fully saturated micro-applicator with a tip diameter of 1.5 mm, rinsed for 15 seconds, and dried for 5 seconds (Fig. 2). Table 2 displays the materials’ composition. The adhesive application was in compliance with the manufacturer's guidelines (Fig. 3) for each test group, and an LED light-curing unit (Power LED, CRB International) with a light intensity of 1000 mW/cm2 was used for light curing.
Fig. 2:
Etchant application on exposed occlusal surface
Table 2:
Shows composition of materials used
| Materials | Trade name | Manufacture | Composition |
|---|---|---|---|
| Eighth-generation dentin bonding agent | G-Premio bond | GC Corporation Tokyo, Japan | 4-MET (methacryloxyethyl trimellitic acid), 10-MDP (methacryloyloxydecyl dihydrogen phosphate) and 10-MDTP (methacryoyloxydecyl dihydrogen thiophosphate), dimethacrylate, acetone, fillers, photoinitiators, water, silicon dioxide, stabilizer4 |
| Seventh-generation dentin bonding agent | Single bond universal | 3M ESPE, Neuss, Germany | MDP phosphate monomer (10-MDP), dimethacrylate resins, HEMA, Vitrebond™ copolymer (methacrylate functionalized polyalkenoic acid), water, filler, ethanol, initiators, silane3 |
| Fifth-generation dentin bonding agent | ADPERTM single bond 2 | 3M ESPE, Neuss, Germany | BisGMA, HEMA, dimethacylate resins, Vitrebond™ copolymer (methacrylate functionalized polyalkenoic acid), photoinitiators, ethanol, water2 |
| Light cure composite | Filtek™ Z350 XT | 3M ESPE St. Paul, MN, USA | Bis-GMA, UDMA, TEGDMA, Bis-EMA, PEGDMA5 |
| Etchant | ScotchbondTM | 3MTM ESPE St. Paul, MN, USA | 37% phosphoric acid, thickeners, pigments1 |
Fig. 3:
Application of bonding agent followed by light curing
Group A: (ASB-5) This group used a completely saturated micro-applicator to apply a fifth-generation bonding agent (ADPER single bond 2, 3M) to the etched surface for 15 seconds. The solvents were then gently air-dried for 5 seconds, and the surface was light-cured for 10 seconds.2
Group B: (SBU-7) In this group, the etched surface was coated with a seventh-generation bonding agent (single bond universal, 3M) by scrubbing it for 20 seconds, letting the adhesive air-dry for 5 seconds, and then light-curing for 10 seconds.3
Group C: (GPB-8) This group used an eighth-generation bonding agent (G-Premio bond). Application was done on the etched surface with a micro brush and kept for 10 seconds, then air-dried for 5 seconds under maximum air pressure, followed by 10 seconds of light-curing.4
Filtek Z350 (3M)5 composite was placed in increments on all the specimens, using a mold measuring 4 mm in height and 5 mm in diameter (Fig. 4), and curing was done with an LED light-curing unit (Power LED, CRB International) for 40 seconds, with a light intensity of 1000 mW/cm2.
Fig. 4:
Placement of composite restoration followed by light curing
The assessment of the force required for shear bond strength was verified at the Central Institute of Plastics Engineering and Technology, Amritsar, with a Universal Testing Machine (INSTRON). In accordance with ISO recommendations for shear bond strength tests, the load application was set within the range of 0.45–1.05 mm/minute.5 Therefore, a cross-head speed of 1 mm/minute was implemented for the present study. The installed teeth were secured to the Instron's attachment device (universal testing machine) via a modified device (custom-made jig) to apply a shear force using a blade parallel to the adhesive dentin interface (Fig. 5). The analysis technique was carried out for every sample until the composite restoration was debonded. The highest shear force required to debond the sample was noted in newtons.
Figs 5A and B:
(A) Composite buildup; (B) Loading Jig of universal testing machine at bonded interface
Shear bond strength calculated as:
Shear bond strength (in megapascals) = debonding force applied (in Newton)/surface area of mold (in mm2)
Statistical Analysis
The documented data were thus collected and subjected to statistical analysis for evaluating the efficacy of bonding agents. For statistical analysis, the means and standard deviations of the measurements per group were utilized using SPSS (Statistical Package for Social Sciences, 22.00 for Windows; SPSS Inc., Chicago, USA).
Results
The descriptive analysis of different generation bonding agents reveals that the mean shear bond strength of group A (ADPER single bond 2) was 13.23 ± 1.33 MPa with a range of 11.43–15.83 MPa, group B (single bond universal) was 9.66 ± 1.31 MPa with a range of 8.03–12.44 MPa, and group C (G-Premio bond) was 19.21 ± 1.46 MPa with a range of 15.35–20.75 MPa (Table 3 and Fig. 6). The variance in mean shear bond strength between the groups (A, B, and C) when compared by the application of a one-way ANOVA test was found to be statistically significant with p < 0.05 (Table 4 and Fig. 7). The intergroup comparison was analyzed using Tukey's post hoc test, which states that the shear bond strength of group A compared to group B was higher by a mean value of 3.57 MPa (p < 0.01*). The shear bond strength of group A in comparison to group C was lower by a mean value of 5.98 MPa (p < 0.01*). The shear bond strength of group B when compared to group C was lower by a mean value of 9.55 MPa (p < 0.01*).
Table 3:
Shows descriptive analysis of groups A, B, and C in respect to shear bond strength and comparison of shear bond strength (MPa) among groups using ANOVA
| S. no. | Bondin agent | Number of samples | Minimum | Shear bond strength (MPa) | ANOVA test | p-value | ||
|---|---|---|---|---|---|---|---|---|
| Maximum | Mean | SD | ||||||
| 1 | ADPER single bond 2 | 15 | 11.43 | 15.83 | 13.23 | 1.33 | 186.56 | <0.01* |
| 2 | Single bond universal | 15 | 8.03 | 12.44 | 9.66 | 1.31 | ||
| 3 | G-Premio bond | 15 | 15.35 | 20.75 | 19.21 | 1.46 | ||
*Statistically significant
Fig. 6:
Bar graph showing descriptive analysis of fifth-generation (ADPER single bond 2), seventh-generation (single bond universal) and eighth-generation (G-Premio bond) bonding agents
Table 4:
Intergroup comparison of shear bond strength using Tukey HSD post hoc test
| Study variable | Generation of bonding agent compared | Mean difference | 95% confidence interval | p-value | ||
|---|---|---|---|---|---|---|
| Lower bound | Upper bound | |||||
| Shear bond strength (in MPa) | Fifth | Seventh | −3.57 | −4.78 | −2.35 | <0.01* |
| Fifth | Eighth | 5.98 | 4.76 | 7.19 | <0.01* | |
| Seventh | Eighth | 9.55 | 8.33 | 10.76 | <0.01* | |
*Statistically significant
Fig. 7:
Bar graph showing comparison of mean shear bond strength between fifth-generation (ADPER single bond 2), seventh-generation (single bond universal) and eighth-generation (G-Premio bond) bonding agents
Discussion
Two distinct bonding techniques, namely etch-and-rinse approach and self-etch (SE) systems, have been used for dental bonding purposes to date. Etch-and-rinse bonding agents remain a widely used and effective bonding option in dental restorative procedures, offering excellent strength of the bond and reliability when applied correctly. They are technique-sensitive and time-consuming. SE adhesives eliminate the need for a distinct etching step using phosphoric acid and can be used in one or two steps. These adhesives incorporate monomers possessing acidic characteristics that concurrently etch the surface of the tooth and prime it for bonding. Manufacturers continually introduce new adhesive systems, claiming simplified usage, enhanced compositions, and improved bonding capabilities to tooth structure. As biotechnology and materials science progress, nanotechnology is particularly projected to bring significant advancements to dentistry. Nano adhesives, claimed to be universal adhesives by the manufacturer, are one of the chief contributions of nano dentistry, which contain nanosized fillers.6 Incorporation of these fillers into adhesives prevents agglomeration of the adhesive matrix system, thus creating extended shelf life, strong dentin bonds, good stress absorption, and a long-lasting marginal seal.6 Universal adhesives can be used across various etching modes, including SE, selective-etch, and total-etch techniques, depending on the clinician's preference and the clinical situation.
For the clinical effectiveness of adhesive materials, bond strength serves as a broad evaluation tool to determine how well any restorative material adheres to the tooth. Higher bond strength enables the bonding agent to withstand stresses caused by resin contraction and forces applied in the zone between the dental restoration and tooth. Given that the masticatory process primarily involves shearing forces, the shear bond strength represents the adhesive potency of the restorative dental material at the surface amid the tooth and the dental restoration. Therefore, to provide a test result that is both clinically relevant and acceptable, the bond strength must be evaluated in shear mode.7
In this study, we examined the bonding efficacy of the recently familiarized eighth-generation dentin bonding adhesive G-Premio bond GC (GPB-8), a fifth-generation dentin bonding adhesive 3M Adper single bond 2 (ASB-5), and a seventh-generation dentin bonding adhesive 3M single bond universal (SBU-7) after prior acid etching, as assessed through bond-strength testing.
The bonding process, phosphoric acid etching, depends on the adhesive's micromechanical interlocking into the porosities created by enamel demineralization. SE techniques employ weak acid, specifically phosphoric acid ester monomers, as the etching agent. Because of the relatively shallow enamel etching depth compared to phosphoric acid, the resultant bond strength tends to be weaker than what is achieved through the total-etch technique.8 According to Poggio et al., pretreatment of enamel using phosphoric acid significantly enhanced the bond strength values of SE adhesives.9 Another scanning electron microscopy (SEM) analysis conducted on enamel revealed a direct correlation between the penetration depth of etchant and resin infiltrations with bond strength.10 According to Jacker-Guhr al., universal adhesives exhibited increased shear bond strength after additional phosphoric acid etching of enamel and dentin surfaces.11 Therefore, the total-etch process is used for each sample in our study.
On comparative assessment of the shear bond strength in the present study, group C showed superior bond strength with a mean of 19.21 MPa, followed by group A with a mean of 13.23 MPa and group B with a mean of 9.66 MPa. The ANOVA test of statistical analysis shows that the difference in the mean of shear bond strength between groups A, B, and C was statistically significant; p < 0.05 (Table 3).
Eighth-generation bonding agents consist of a distinctive mixture of three functional monomers: 4-META, MDP, and MDTP. According to Van Meerbeek et al., it has been theorized that the inclusion of the MDP functional monomer in eighth-generation adhesives assists chemical bonding to the dentin substrate, establishing a more prompt and robust ionic bond with hydroxyapatite (HAp).12 Yoshida et al. investigated the enhanced bonding capability of 10-methacryloyloxydecyl dihydrogen phosphate (10-MDP) to synthetic HAp, demonstrating superiority over 4-methacryloxyethyl trimellitic (4-MET) and 2-methacryloxyethyl phenyl hydrogen phosphate (Phenyl-P).13 Eighth-generation adhesive has 4-methacryloyloxyethyl trimellitic acid as a bond-promoting monomer. Studies showed that even minute quantities of 2-hydroxyethyl methacrylate (HEMA) can disrupt the chemical attachment of 10-MDP monomers to calcium ions of tooth structure.14 Given that, as per the manufacturer, the eighth-generation universal adhesive does not incorporate HEMA in its formulation, it could be stated that the removal of this substance ensures admirable stability and exceptional strength to adhere to tooth tissue and reduces microleakage.15
The results of this study were reliable with the study led by Chauhan et al., who stated that the maximum mean shear bond strength was exhibited by the eighth-generation bonding agent, followed by the fifth, seventh, and sixth.16 Various studies have stated an increase in shear bond strength through eighth-generation bonding agents compared to previous generations.17,18
Statistical analysis of the comparison using Tukey's post hoc test (Table 4) shows that the shear bond strength of group A, compared to group B, was higher by a mean value of 3.57 MPa. Group B adhesive is more hydrophilic, attracts more water, which can lead to rapid water diffusion back into the bonded dentin, resulting in lower mechanical strength and compromised bonding performance. According to Jang et al., one-step self-etching adhesives demonstrated enhanced bond strength in SE mode rather than total-etch mode due to their hydrophilic nature, and on interaction with underlying dentin, they formed an adhesive layer that was permeable to water, impairing the bonding process.19 According to Francis et al., additional etching of dentin with phosphoric acid causes inferior hybridization with the usage of SE adhesives, thereby reducing its bond strength.20 According to Ikeda et al., decreased bond strength with one-step SE adhesive after prior acid etching is obtained due to resin monomers’ insufficient penetration of the demineralized collagen matrix and the bonding agent's subsequent inadequate dentin adaptation.21
When the shear bond strength of group A is compared with group C, the mean shear bond strength was assessed to be higher in group C. Adhesive systems containing HEMA, such as Adper single bond, may enhance water absorption, leading to hydrogel formation and hydrolytic degradation.22 This hydrolytic degradation could contribute to reduced bond strength in group A. The exclusion of HEMA from the eighth-generation bonding agent may be significant in terms of durability and remarkable bond strengths, extending beyond tooth tissue to encompass various indirect substrates such as composites, precious metals, and non-precious alloys. The results are in concurrence with the study by Sachdeva et al.6
When group B is compared with group C, the mean shear bond strength was significantly assessed to be lower in group B, with a mean value of 9.55 MPa. The difference observed between group B and group C was statistically significant.
Though adhesives are similar, the composition of universal adhesive is different from current SE systems because it contains monomers that can form chemical and micromechanical bonds to dental substrates. This composition is important to take into account because many universal adhesives contain particular carboxylate and/or phosphate monomers that can ionically bond to calcium found in HAp (Ca10[PO4]6[OH]2), thereby influencing bonding effectiveness. One such functional monomer found in certain newer adhesives is MDP, which possesses mild-etching properties. The key monomers facilitating universal adhesive to be applied in any etching modes are MDP. Stable MDP-calcium salts are created during bonding and then deposited in self-assembled nano-layers, which create insoluble Ca2+ salts and enhance strong adherence to the tooth surface. Moreover, universal adhesives may incorporate additional components like biphenyl dimethacrylate (BPDM), dipentaerythritol penta-acrylate phosphoric acid ester (PENTA), and polyalkenoic acid copolymer, further enhancing their ability to adhere to the structure of the tooth. Previous research by Nair et al. suggests that nano-sized cross-linking silica fillers contribute to increased bond strength, and the eighth-generation adhesive, containing similar silica fillers, may exhibit greater bond strength values in comparison to other tested groups.22 The solvent acetone in eighth-generation adhesive improves demineralization and wetness by preventing carboxylic acid groups from becoming esterified. Additionally, acetone has a great ability to chase water.23
Seventh-generation adhesive displayed the lowest bond strength, possibly because of the hydrolytic instability of methacrylate monomers, like HEMA, used to increase wettability on the dentin surface.14 One-step self-etching adhesives, being more hydrophilic, attract more water, which can lead to rapid water diffusion back into the bonded dentin, resulting in lower mechanical strength. Seventh-generation adhesive contains the polyalkenoic acid copolymer (Vitrebond Copolymer), which, when combined with MDP, has shown lower shear bond strength results in the literature.24 There is potential competition between polyalkenoic acid copolymer and the MDP monomer for calcium-binding sites in HAp and hinder monomer alignment during polymerization because of its high molecular weight. The findings are in concurrence with a study by Mishra et al., which stated that the mean shear bond strength was higher for the eighth-generation bonding agent than the seventh-generation bonding agent.25
When compared to the fifth and seventh-generation bonding agents, the recently produced eighth-generation glue demonstrated the maximum shear bond strength values within the parameters of this study.
Footnotes
Source of support: Nil
Conflict of interest: None
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