Method: Roots of thirty-six freshly-extracted premolars were sectioned 5mm below CEJ and pulp tissue was removed. Buccal enamel and cementum were trimmed to obtain standardized flat dentin surface. Specimens were divided into three groups (n=6/group) according to the adhesives utilized; two-step etch-and-rinse adhesive, SB-Adper Single Bond 2, 3MESPE; two-step self-etch adhesive, SE-Clearfil SE Bond, Kuraray Medica Inc. and single-step self-etch adhesive, AE-Adper Easy One, 3MESPE. Adhesives and resin composite were applied while the specimens were subjected to IPPS. After curing, specimens were stored in artificial saliva at 37oC in a specially constructed incubator while the IPPS was maintained for either 24h or 1-year prior to testing. Bonded specimens were sectioned into sticks (n=24/group) with a cross-section of 0.9+/-0.01 mm2and subjected to µTBS testing. Data were statistically analyzed using Multiway ANOVA with repeated measures; one-way ANOVA tests, and Bonferroni post-hoc test (p<0.05). Failure modes were determined for all tested beams using scanning electron microscope at x100 magnification.
Results: ANOVA results revealed statistically significant effect for the adhesive type (P<0.0001), storage period (P<0.0001) as well as their interactions (p=0.024) on the µTBS. However, dentin substrate and its interactions revealed no significant affects. For both dentin substrates, SE revealed statistically significantly higher µTBS than the other two adhesives (SB and AE) after 24 hr and 1-year storage. After 1-year storage, t-test revealed a significant decrease in bond strength values of all tested adhesives with both dentin substrates. Modes of failure were mainly adhesive and mixed.
Conclusion: Bond strengths of tested adhesives were not sensitive to the structural differences between coronal and radicular dentin even after one year storage in artificial saliva and under IPPS.