Effect of Adhesives, Thermocycling and Dentin Regions on Bond Strength

Objectives: To evaluate the effects of etch-rinse vs. self-etch adhesive and thermocycling on the shear bond strength (SBS) to coronal and root dentin.

Materials and Methods: Fifty-six human molars were ground flat exposing the coronal and root dentin surfaces and randomly divided into 2 groups according to adhesive systems: SE- A two-step self-etch adhesive (Adper SE Plus /3M); and SB- an etch-rinse adhesive (Adper Single Bond 2 /3M). The adhesives were applied to coronal and root dentin of each mounted tooth. A nanocomposite (Filtek Supreme XT/3M) was applied to both dentin surfaces using a special jig (Ultradent). The bonded specimens were stored in distilled water at 370C for 24 hours. Half of the bonded specimens were tested for SBS in a universal testing machine (1 mm/minute) without thermocycling. The remaining specimens were thermocycled (500 cycles between 5 and 55o C) prior to SBS testing. Two specimens from each group were kept for Scanning Electron Microscope evaluations of adhesive interfaces. Failure modes were determined under a stereomicroscope. The mean SBS values of each group was calculated and the results were subjected to ANOVA, Duncan test and Paired samples t-test (p=0.05).

Results: Thermocycling didn't affect the SBS of coronal dentin for both adhesives however it impaired the SBS of SE in root dentin (p<0.05). The two different dentin substrates didn't exhibit a significant difference except for higher values in root dentin with the SE group without thermocycling. The highest cohesive failure was observed in root dentin with SE; however the failure modes were mainly adhesive for the other groups.

Conclusion: SE exhibited higher SBS values than SB in root dentin. Thermocycling didn't affect the SBS in root dentin for both adhesives whereas it decreased the SBS of SE in coronal dentin.