In vitro Comparative Evaluation of Tensile Bond Strength of 6(th), 7(th) and 8(th) Generation Dentin Bonding Agents.

BACKGROUND: Newer dentin bonding agents were developed to improve the quality of composite restoration and to reduce time consumption in its application. The aim of the present study was to evaluate tensile bond strength of 6(th), 7(th) and 8(th) generation bonding agents by in vitro method.
MATERIALS AND METHODS: Selected 60 permanent teeth were assigned into 20 in each group (Group I: 6(th) generation bonding agent-Adper SE plus 3M ESPE, Group II: 7(th) generation bonding agent-G-Bond GC Corp Japan and Group III: 8(th) generation dentin adhesives-FuturaBond, DC, Voco, Germany). With high-speed diamond disc, coronal dentin was exposed, and selected dentin bonding agents were applied, followed by composite restoration. All samples were saved in saline for 24 h and tensile bond strength testing was done using a universal testing machine. The obtained data were tabulated and statistically analyzed using ANOVA test.
RESULTS: The tensile bond strength readings for 6(th) generation bonding agent was 32.2465, for 7(th) generation was 31.6734, and for 8(th)-generation dentine bonding agent was 34.74431. The highest tensile bond strength was seen in 8(th) generation bonding agent compared to 6(th) and 7(th) generation bonding agents.
CONCLUSION: From the present study it can be conclude that 8(th) generation dentine adhesive (Futura DC, Voco, Germany) resulted in highest tensile bond strength compared to 6(th) (Adper SE plus, 3M ESPE) and 7(th) generation (G-Bond) dentin bonding agents.

Introduction

Prognosis of root canal treated teeth depends on the quality of apical and coronal seal and lack of this seal can results in to failure of root canal treatment. Nowadays, amalgam is not usually used as coronal restoration of root canal treated teeth since it lacks proper seal, adhesion, esthetic properties, and there is an environmental and safety issue. Composite core buildup strengthens the coronal tooth structure and increases the resistance to fracture.1 Development in bonding agents has moved from multistep bonding process (etching, washing, drying, primer, adhesive) to simplification i.e. self-etch and single bottle system. Ideal bonding agent should be biocompatible, should have adequate bond strength, and should bond to enamel and dentin. Various dentin bonding agents were developed to improve the quality of adhesives and composite restorations.2,3 The 6th generation bonding agents consists of acidic primer and bonding resin separately, while 7th generation bonding agents are self-etch adhesives with combination of etchant, primer, and bonding agent in one (all-in-one system) component and applied as single step.2 Development in nanotech dentistry has lead to development of nanocomposites and nano-adhesives which contains nanosized fillers. Nano-bonding agents are solutions with nanofillers which produce better enamel and dentin bond strength, stress absorption, and longer shelf life.4 It has been observed that filled bonding agents produced higher in vitro bond strength. Recently the manufacturer of nanofilled dentin adhesives (Futurabond DC, Voco, Germany) has claimed it as 8th generation bonding agent.5 The most frequently applied laboratory parameter to evaluate the effectiveness of adhesives is micro shear and tensile bond strengths.1,3 The aim of this study was to evaluate and compare the tensile bond strength of 6th, 7th and 8th-generation dentin adhesives.

Materials and Methods

For the study, 60 human mandibular permanent molars extracted for periodontal region, free from decay, restorations, and cracks were selected and the teeth were cleaned with scalars and saved in saline. Teeth were divided into 20 in each group (Group I: 6th generation bonding agent-Adper SE plus 3M ESPE, Group II: 7th generation bonding agent-G-Bond GC Corp Japan and Group III: 8th generation dentine adhesive-Futura Bond DC, Voco Germany). With high-speed diamond disc, coronal dentin was exposed. The selected bonding agents were applied on exposed dentine surfaces according to manufacturer’s instructions, followed by composite restoration. Acrylic resin blocks were prepared on each study teeth. All teeth were saved in sterile saline for 24 h and using universal testing machine (KIC-3-050-C, Kalpak Instruments and controls) tensile bond strength was tested. Applied force (N) was divided by the stick cross-sectional area (mm2). The tensile force required to debond the specimen was calculated in MPa. The obtained data were recorded and ANOVA test was used to statistically analyze the data.

Results

For each group the mean tensile bond strength and slandered deviation were calculated. The mean tensile bond strength value for 6th generation bonding agent was 32.2465, for 7th generation was 31.6734, and for 8th generation bonding agent was 34.74431. The highest tensile bond strength was seen in 8th generation bonding agent, followed by 6th generation bonding agent while 7th generation bonding agent showed lowest bond strength (Table 1 and Graph 1).

Table 1

Comparison of tensile bond strength of 6th, 7th and 8th generation bonding agents by ANOVA test.

Graph 1

Comparative evaluation of tensile bond strength of 6th, 7th and 8th generation bonding agents.

Discussion

The main purpose of measuring the bond strength is to assess the bonding strength of a bonding agent to the dental hard structures. Development of newer dentin bonding agents aims to improve the bonding quality and to reduce the time consumption in application. However, polymerization shrinkage is still a major problem in bonding composite to tooth structure. Polymerization contraction occurs during the conversion of monomer molecules into a polymer network. Polymerization shrinkage leads to failure of composite tooth interface and micro-leakage, which ultimately results in postoperative sensitivity, secondary caries, micro-cracking and failure of restoration. 17-21 MPa bond strength has been estimated to withstand this stress of polymerization shrinkage of the composite restoration. Several factors can influence the in vitro bond strength to dentin surface such as; type of tooth, dentine surface, type of bond strength to be tested (shear or tensile), type of bonding agent used, storage media, composite restorative material, and testing procedure.4

All the three tested dentine bonding agents (6th generation - Adper SE plus 3M ESPE, 7th generation - G-Bond GC-Corp Japan and 8th generation - Futura Bond DC, Voco, Germany) used in the present in vitro study were self-etching adhesives. Self-etch adhesives need one step (7th generation) or two-step application (6th generation). They are mild and less aggressive compared to non-self-etch adhesive system. 8th generation an adhesive (Futurabond DC, Voco, Germany) contains nano-sized cross-linking silica particles and can be dual-cured.4

In the present study, the mean tensile bond strength value for 6th generation bonding agent was 32.2465, for 7th generation was 31.6734, and for 8th generation bonding agent was 34.74431. The highest tensile bond strength was seen in 8th generation bonding agent, followed by 6th generation bonding agent and lowest seen with 7th-generation adhesives (Table 1 and Graph 1). Tensile bond strength of 8th generation was more compared to 7th which is statistically significant (P > 0.005). This is similar to study by Joseph et al. 2013.4 Similarly, lower bond strength was observed by several researchers with 7th generation bonding agents compared to 5th or 6th generation1,6 whereas Burrow et al. observed good results with G-Bond.7 Possible reason for lower bond strength observed in 7th generation is due to less cross-linking monomers4 and are more hydrophilic (attract water) than 6th generation bonding agents. This results in to lower mechanical strength of 7th-generation adhesives because the evaporated water from bonded dentin rapidly diffuses back into adhesive.1

Nikhil et al. in 2011 compared three self-etching adhesives for tensile bond strength and found that Adper Easy one was superior to G-Bond and Xeno V system. They concluded that this difference in tensile bond strength was due to hydrophilic nature of Adper Easy one, which enhances adhesion.2 Yaseen and Subba Reddy observed lowest shear bond strength on primary teeth with 6th generation (Contax) bonding agent and highest with 7th generation (Clearfil S3) on permanent teeth3. Similarly, Nair et al. observed higher shear bond strength with 7th generation (Adper Easy one) compared to 6th generation (Adper SE plus) bonding agents.8 Shekhar et al observed highest shear bond strength with Prime and Bond NT (5th generation) compared to Adper SE plus (6th generation) and G-Bond (7th generation) bonding agents.9 Souza-Zaroni et al. observed better tensile bond strength with Clearfil Liner Bond 2V self-etching primer adhesive system compared to Prime and Bond NT.10 Poptani et al. after thermocycling didn’t find any difference between 5th and 7th generation bonding agent.11 Dhawan et al. found higher tensile bond strength with single bond (5th generation) conditioner as compared to scotch bond multipurpose (4th generation) and Prompt-L-Pop (6th generation).12 Chopra et al. observed that multi-bottle bonding agents performed better than single bottle dentin adhesives.13 Elkassas et al. fond that disinfecting the dentine surface prior to application of binding agents decreases the bond quality.14 Borsatto et al. concluded from their study that, application of the two-step self-etch bonding agent (Adper SE Plus) beneath the resin pit- and -fissure sealant placement resulted in a significantly higher bond strength for the Er: YAG laser-irradiated enamel.15

In this study, highest mean tensile bond strength of 34.74431 MPa was observed in 8th generation dentine adhesives (Futurabond DC, Voco, Germany) compared to 6th and 7th generation adhesives, this may be due to its nano-sized cross-linking fillers.

Conclusion

From the present study, it can be conclude that 8th generation dentin adhesives (Futura DC, Voco, Germany) showed better tensile bond strength compared to 6th (Adper SE plus, 3M ESPE) and 7th generation (G-Bond) dentin bonding agents and appears to be more advantageous.