Shear bond strengths of the delayed applications of bonding systems

Objective: The aim of this study was to investigate the dentin shear bond strength of two bonding agents with the different delayed applications.

Methods: Occlusal surfaces of 100 extracted caries-free human premolars were wet ground with 600 and 800-grit silicon carbide abrasive paper. The teeth were divided into 10 groups of 10 teeth each. Two bonding agents of the fifth generation total-etching systems (1. Single Bond 2 (3M ESPE) and 2. Prime & Bond NT (Dentsply)) were applied by using the delayed application time of 0 (immediately), 0.5, 1, 3, 5 minutes. Composite (Z350;3M ESPE) cylinders were polymerized on the treated dentine surfaces and the specimens were stored in distilled water at 37c for 72 hours prior testing. Shear bond strength was tested at a crosshead speed of 0.5 mm/minute. Failure mode was assessed. Data were submitted to analysis of variance and Tukey statistical test.

Results: Statistical analysis revealed a significant effect of the bonding agents and the delayed applications. There were statistically significant differences between the different delayed applications in each bonding system (P<0.001). The longer delayed application time exhibited significantly lower shear bond strength in both bonding systems. Among the bonding systems applied immediately, the Single bond 2 group showed significantly higher shear bond strength than the Prime & Bond NT group. However, no significant differences were found between two bonding systems applied with the delayed duration of 0.5,1,3 and 5 minutes. From the stereomicroscope observations, adhesive failure and mixed failure were more pronounced within each group.

Conclusions: The application time of bonding to etched surfaces is an important factor influencing dentin shear bond strength of bonding agents. The delayed bonding application decreased dentin shear bond strength significantly.

This work was supported by the grant of Faculty of Dentistry, Thammasat University, Thailand.