Relationship between bond strengths and nanoleakage: Evaluation of a new assessment method

Purpose: To test if there was a correlation between resin-dentin bond strengths and nanoleakage of total etch and self-etching primer bonding systems. Materials and Methods: Ten extracted third molars were ground flat with 600 grit SIC paper under running water to expose middle dentin. Clearfil Liner Bond 2V or Single Bond was applied to the dentin surface according to the manufacturers' instructions. A crown was built-up with Clearfil AP-X resin-based composite, and the specimens stored in water for 24 hrs at 37°C. The bonded assemblies were cut mesio-distally perpendicular to the interface into approximately 0.7 mm thick slabs, and trimmed for microtensile bond strength testing. Alternate slices from each tooth were either entirely double-coated with nail varnish leaving a 0.5 mm window around the interface, or left uncoated to be immersed in water for 13 hrs as the control. The varnished (experimental) slabs were immersed in 50% AgNO₃ for 1 hr, and then immersed in a photo developing solution for 12 hrs. All specimens were subjected to microtensile bond test at a crosshead speed of 1 mm/min. After debonding, the specimens were embedded in epoxy resin and observed under a confocal laser scanning microscope for determination of lateral silver penetration within the interface. Silver penetration was further analyzed under the SEM. Data were analyzed with one- and two-way ANOVA, Fisher's PLSD test (P< 0.05), and regression analysis. Results: The bond strengths of Clearfil Liner Bond 2V and Single Bond were not significantly different (P> 0.05); however the bond strengths of the specimens that were soaked in 50% AgNO₃ for 1 hr significantly increased (P< 0.01). No correlation was observed between bond strengths and nanoleakage.