Durability of resin-dentin bonds

Purpose: The purpose of this study was to determine if the durability of resin-dentin bonds could be evaluated more quickly if the bond specimen was divided into 1x1x8 mm beams incubated at 37°C for a 90day period. Materials and Methods: Extracted human third molars were prepared for bonding by removing the occlusal surface near the dento-enamel junction (superficial dentin group) or near the pulp {deep dentin group). The teeth were bonded either with MacBond, One Step or Clearfil Liner Bond 2, and then builtup to form a flat resin composite crown. After 24 hours in water, each buildup was vertically divided into slabs 1 mm thick, the top half of which was resin, with the bottom half as dentin. Each slab was then vertically sectioned at 1-mm increments to create 1X1X 8-mm beams of resin-bonded dentin. They were incubated for 1 day or 90 days at 37°C, followed by measurement of the tensile bond strengths. The results were analyzed by the Least-Squares Means method at the 95% confidence level. Results: MacBond gave the highest (p < 0.05) 1-day bond strengths to superficial dentin, but significantly lower bond strengths were measured in deep dentin. There were no significant differences in the bond strengths of either One Step or Clearfil Liner Bond 2 to superficial vs deep dentin at 1 day, but at 90 days their bond strengths to deep dentin had fallen significantly (p < 0.05). Prepolymerized cylinders of resin composite bonded together with One Step showed little variation in bond strength over the 90-day experiment. SEM examination of the failed bonds showed increased porosity in intertubular dentin over time. Conclusion: The results indicate that division of large specimens into many small beams accelerated the deterioration of bond strength in deep dentin in all three bonding systems and in both superficial and deep dentin in the MacBond treated specimens. This method seems promising for studying the durability of resin-dentin bonds.