Relationship between nanoleakage and long-term durability of dentin bonds

This study tested the hypothesis that long-term durability of resin bonds to dentin would directly relate to the nanoleakage of dentin bonding systems. Twenty extracted third molars were ground flat with #600 grit SIC paper under running water to expose middle dentin. One-Step or Single Bond was applied to the dentin surface according to the manufacturer's instruction. A crown was built-up with Clearfil AP-X resin composite and the specimens were stored in water for 24 hours at 37 degreesC. The bonded assemblies were cut mesio-distally perpendicular to the interface in approximately 0.7 min thick slabs and trimmed for microtensile bond strength testing. All slabs were immersed in individual bottles containing 37 degreesC water that was changed daily. Specimens were randomly assigned to four groups (one day, three, six and nine months), and at the specified time period, the specimens to be tested were randomly divided into two subgroups for testing: 50% AgNO3 and the control. In the 50% AgNO3 subgroup, the slabs were coated with fingernail varnish except for approximately 0.5 mm around the bonded interface and immersed for one hour in 50% AgNO3, followed by exposure in a photo developing solution for 12 hours just prior to debonding. The specimens in the control subgroup were soaked in water until they were debonded. Then, all specimens were subjected to microtensile bond testing. Micrographs of the fractured surfaces of the debonded specimens in the AgNO3 subgroup were taken using light microscopy. They were then subjected to image analysis by NIH Image PC (Scion, Fredrick, MD, USA), and the area of silver penetration was quantitated. The fractured surface was further analyzed under the SEM. Bond strength data and the silver penetration areas were subjected to two and three-way ANOVA and Fisher's PLSD test at the 95% level of confidence. Regression analysis was used to test the relationship between bond strengths and the silver penetration area at each time period. The tensile bond strength of both materials gradually decreased over time. Specimens bonded with One-Step showed less silver nanoleakage at one day compared to three, six and nine months (p <0.05), but there were no significant differences between the nanoleakage measured at three, six and nine months. In contrast, for specimens bonded with Single Bond, there were no statistically significant differences in the silver nanoleakage among the four time periods tested (p >0.05). No correlation was observed between bond strength and nanoleakage for either bonding system. Nanoleakage occurred in both adhesive systems, and bond strengths gradually decreased over time. However, there was no correlation between bond strength and nanoleakage for either adhesive system in this study.