Effect of Adhesives and Thermocycling on the Shear Bond Strength of a Nano-Composite to Coronal and Root Dentin

Objectives: To evaluate the effects of etch & rinse vs self-etch adhesives and thermocycling on the shear bond strength (SBS) of a nano-composite to coronal and root dentin. Materials and Methods: Fifty-six extracted human molars were mounted and ground to expose coronal and root dentin surfaces and were randomly divided into two groups according to adhesive system: SE a two-step self-etch adhesive (Adper SE Plus, 3M ESPE) and ER an etch & rinse adhesive (Adper Single Bond 2, 3M ESPE). The adhesives were applied to the coronal and root dentin of the mounted teeth. A nano-composite (Filtek Supreme XT, 3M ESPE) was applied to both dentin surfaces. The bonded specimens were stored in distilled water at 37 degrees C for 24 hours. Half of the bonded specimens were tested for SBS in a universal testing machine without thermocycling. The remaining specimens were thermocycled (500 cycles between 5 degrees C and 55 degrees C) prior to SBS testing. Two specimens from each group were kept for Scanning Electron Microscope evaluations of the adhesive interfaces. Failure modes were determined under a stereomicroscope. The mean SBS value of each group was calculated, and the results were subjected to ANOVA, Duncan test and Paired samples t-test (p=0.05). Results: Thermocycling did not affect the SBS of coronal dentin for either adhesive. However, it affected the SBS of SE in root dentin (p<0.05). The two different dentin substrates did not exhibit a significant difference except for higher values in root dentin with the SE group without thermocycling. The greatest number of cohesive failures was observed in root dentin with SE adhesive; however, the failure modes were mainly adhesive for the other groups. Conclusion: The SE adhesive exhibited higher SBS values than the ER adhesive in root dentin. Thermocycling did not affect the SBS in coronal dentin for either adhesive but it decreased the SBS of SE in root dentin.