The aim of this study was to compare the effect of immediate dentin sealing (IDS) on microtensile bond
strength (μTBS) of resin composite restoration using a three-step etch and rinse adhesive under various thermocycling
periods. Sixty-four extracted human third molars were divided into 6 groups (groups 1-3 = controls and groups 4-6
= experimentals) with 10 teeth in each group. The remaining 4 teeth were divided into groups 1 and 4 for scanning
electron microscope (SEM) evaluation. Flat dentin surfaces were prepared, and a 3-step etch and rinse adhesive
was applied as an IDS step after tooth preparation within experimental groups. All specimens were then contaminated
with impressions and provisional restorations. After being stored for 1 week, all samples were restored using a
composite resin under simulated fluid flow. Thermocycling was performed in all groups, and μTBS was measured
at 0, 5,000 and 10,000 cycles, respectively. The specimens were then sectioned to obtain a bonded hourglass of
1.0 ± 0.01 mm2 in area. Microtensile bond strength was tested at a crosshead speed of 1.0 mm/min, and data
analyzed using a Two-way ANOVA, One-way ANOVA and a Tukey’s post hoc test (α = 0.05). Specimens were also
evaluated for modes of fracture using a stereomicroscope at 40X, and data analyzed using a Chi-square test (α = 0.05).
Specimen surfaces and hybrid layers from groups 1 and 4 were also examined before and after restoration using a
SEM analysis. Two-way ANOVA showed significant difference among IDS and thermocycling cycles. An interaction
was not observed. One-way ANOVA showed the mean μTBS of control group was statistically different from those
of experimental group of the same thermocycling cycles. In the same IDS condition, statistically significant decrease
in bond strength was found in 10,000 cycle-thermocycling group, when compared to immediate bond strength (after
24 hours) group. Microscopic evaluation indicated that most failures in all groups were adhesive and mixed failures.
SEM analyses of the dentin surface and hybrid layers showed dentinal tubules obstruction in the experimental groups.