Abstract
Background:
Bonding agents play a critical role in the longevity and success of restorative dental treatments by minimizing microleakage at the tooth–restoration interface. The evolution from fifth- to eighth-generation bonding systems reflects the ongoing efforts to simplify procedures while improving clinical outcomes.
Materials and Methods:
Sixty extracted human molars were divided into four groups based on the generation of bonding agents used: Fifth (Adper Single Bond 2), sixth (Clearfil SE), seventh (BeautiBond), and eighth (GC Premio Bond). Standardized Class V cavities were prepared and restored. Microleakage was assessed using methylene blue dye under a stereomicroscope.
Results:
Eighth-generation bonding agent demonstrated the least microleakage, while the seventh generation showed the most. Statistical analysis confirmed significant differences among the groups (P < 0.05).
Conclusion:
The eighth-generation bonding agent showed superior performance in reducing microleakage compared to earlier generations, indicating its potential as the most effective adhesive system.
KEYWORDS: Bonding agents, dentin adhesion, microleakage, restorative dentistry, stereomicroscope
INTRODUCTION
Adhesive bonding in dentistry has significantly evolved over the last few decades, revolutionizing restorative practices. The ability to create a strong bond between tooth structure and restorative materials is not only essential for retention but also for preventing postoperative sensitivity, secondary caries, and pulpal damage due to microleakage. Microleakage, defined as the microscopic passage of bacteria, fluids, molecules, or ions between the cavity wall and the restorative material, remains one of the most common causes of restoration failure.[1]
The introduction of acid-etching techniques by Buonocore laid the foundation for adhesive dentistry, which has since progressed through multiple generations of bonding agents. Fifth-generation bonding agents represent a simplified two-step “etch-and-rinse” system, combining primer and adhesive in one bottle. Though effective, they still require a separate etching step, which can lead to technique sensitivity.[2,3]
The sixth-generation bonding agents introduced the concept of “self-etch primers,” reducing clinical steps and eliminating rinsing. This system comprises a separate primer and adhesive, enhancing user-friendliness while maintaining efficacy. Seventh-generation adhesives, or “all-in-one” adhesives, combined etching, priming, and bonding in a single solution to simplify procedures further. However, concerns regarding their lower bond strength and higher microleakage have been reported.[4]
The eighth-generation adhesives, the latest in the series, leverage advancements in nanotechnology to incorporate nanofillers and functional monomers that provide chemical bonding to hydroxyapatite, reduce technique sensitivity, and improve bond durability. They are claimed to be less hydrophilic, thereby minimizing water sorption and improving resistance to degradation.[5]
Despite these advances, the durability of the adhesive interface remains a challenge. Studies indicate that even the latest systems are prone to interfacial degradation primarily due to hydrolytic breakdown. The interaction of adhesives with dentin is more critical than enamel due to the presence of dentinal tubules, fluid, and organic content, which influence the bonding mechanism.[6]
Class V cavities, located at the cervical third of the tooth, present a unique challenge for bonding due to the proximity to gingiva, differences in enamel and dentin composition, and potential for contamination. Therefore, they serve as an ideal model for evaluating the adhesive efficacy of different bonding systems.[7]
This study aims to compare the microleakage characteristics of fifth (Adper Single Bond 2)-, sixth (Clearfil SE Bond)-, seventh (BeautiBond)-, and eighth (GC Premio Bond)-generation bonding agents using methylene blue dye under stereomicroscopy. The null hypothesis assumes that no significant differences in microleakage exist among the four adhesive systems.
MATERIALS AND METHODS
Study design
In vitro experimental study.
Sample size
Sixty freshly extracted human molars (caries-free and without restorations) were selected and randomly divided into four groups (n = 15 per group).
Cavity preparation
Standardized Class V cavities were prepared on both buccal and lingual surfaces at the cementoenamel junction using a carbide bur in a high-speed handpiece. Dimensions: Mesiodistal = 2.5 mm, occluso-gingival = 3 mm, depth = 2 mm.
Bonding protocols
Group 1 (5th Gen – Adper Single Bond 2): Etch for 15s → rinse → blot dry → apply adhesive → air dry (5s) → light cure (10s)
Group 2 (6th Gen – Clearfil SE Bond): Apply primer (20s) → air dry → apply bonding agent → air dry → light cure (10s)
Group 3 (7th Gen – BeautiBond): Apply bonding agent → air dry (5s) → light cure (10s)
Group 4 (8th Gen – GC Premio Bond): Apply bonding agent → wait (10s) → air dry under pressure (5s) → light cure (10s).
Restoration and sectioning
All cavities were restored with resin composite and thermocycled. After 24 h, samples were immersed in 0.5% methylene blue dye for 24 h. The teeth were then longitudinally sectioned in a mesiodistal direction and observed under a stereomicroscope at × 10 magnification.
Scoring system for microleakage
Score 0: No dye penetration
Score 1: Dye penetration up to 1/3 of cavity wall
Score 2: Dye penetration up to 2/3 of cavity wall
Score 3: Dye penetration to the axial wall.
Statistical analysis
Kruskal–Wallis test was used to compare microleakage across groups. Mann–Whitney U-test was used for pairwise comparisons. A P < 0.05 was considered statistically significant.
RESULTS
Eighth-generation bonding agent showed the least mean microleakage score, followed by sixth, fifth, and seventh generation [Table 1].
Table 1.
Distribution of microleakage scores
| Generation | Mean score | SD | Minimum | Maximum | ||||
|---|---|---|---|---|---|---|---|---|
| 5th generation | 1.80 | 0.63 | 1 | 3 | ||||
| 6th generation | 1.47 | 0.64 | 1 | 2 | ||||
| 7th generation | 2.20 | 0.77 | 1 | 3 | ||||
| 8th generation | 0.80 | 0.41 | 0 | 1 |
SD=Standard deviation
Statistically significant differences were observed between the eighth generation and all others, and between the seventh and other groups [Table 2].
Table 2.
Pairwise comparison
| Groups compared | P | |
|---|---|---|
| 5th versus 6th generation | 0.064 | |
| 5th versus 7th generation | 0.031 | |
| 5th versus 8th generation | 0.004 | |
| 6th versus 7th generation | 0.007 | |
| 6th versus 8th generation | 0.013 | |
| 7th versus 8th generation | <0.001 |
DISCUSSION
The findings of this study highlight the continuous improvement in bonding systems from the fifth to the eighth generation, particularly in minimizing microleakage in Class V restorations.
The superior performance of the eighth generation (GC Premio Bond) can be attributed to its advanced formulation containing polyfunctional adhesive monomers and nano-fillers. The acidic monomers enhance demineralization and infiltration of resin into dentin tubules, forming a strong hybrid layer with fewer gaps. Its lower pH (~1.4) allows for better smear layer removal, contributing to a tighter seal.[8]
In contrast, the seventh generation (BeautiBond), despite being an “all-in-one” system, showed the highest microleakage. The absence of HEMA, a hydrophilic monomer, may have compromised the wetting ability of the adhesive and prevented sufficient resin infiltration. According to Pashley et al., HEMA enhances wettability and prevents collapse of collagen fibers, thus maintaining the porosity required for resin tag formation and mechanical interlocking.[9]
The sixth generation (Clearfil SE Bond) fared better than the seventh, likely due to its two-step self-etch system allowing better control and higher monomer penetration. Deliperi and Bardwell also observed similar trends, where Clearfil SE demonstrated lower leakage compared to newer self-etch systems.
The fifth generation (Adper Single Bond 2), despite being a proven system, is more technique sensitive due to its etch-rinse-blot steps. Over-etching or over-drying can collapse the collagen matrix, impeding resin infiltration.
These results are in agreement with previous studies, which showed the efficacy of eighth-generation systems in reducing microleakage. As newer systems integrate functional monomers like 10-MDP and nanotechnology, the long-term stability and ease of use improve.[10]
Limitations of this study include its in vitro nature and small sample size. Clinical performance may be influenced by oral environment, salivary contamination, and operator technique. Further studies with thermocycling, aging, and tensile strength evaluation are needed to confirm long-term performance.
CONCLUSION
This in vitro study demonstrated that all bonding systems exhibited some degree of microleakage in Class V restorations. However, the eighth-generation bonding agent (GC Premio Bond) significantly outperformed the fifth-, sixth-, and seventh-generation adhesives. The findings support the adoption of eighth-generation bonding agents in routine clinical practice for enhanced marginal sealing and restoration longevity.
Conflicts of interest
There are no conflicts of interest.
Funding Statement
Nil.
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