Objectives: To assess the influence of smear-layer interposition on the micro-tensile bond strength (µTBS) of self-adhesive composite cements (SACs) to dentin. Methods: 7 SACs (BisCem, Bisco; exp. SFCem-44, 3M ESPE; G-CEM Automix, GC; seT, SDI; SmartCEM 2, Dentsply; SpeedCEM, Ivoclar Vivadent; Unicem, 3M ESPE) and 1 etch-and-rinse multi-step composite cement (Nexus 3, Kerr) were used to lute feldspathic ceramic blocks (Vita Mark II, Vita) to 80 flat mid-coronal dentin surfaces, which were ground using either a medium-grit (100 µm) diamond bur or 600-grit SiC-paper to produce a thick/compact or thin smear layer, respectively. After 7 days of storage in water (37°C), the specimens were prepared for µTBS testing. Failure patterns were evaluated with a stereomicroscope, and afterwards imaged using Feg-SEM. Two additional specimens per group were processed for TEM.
Except Nexus 3, all cements showed higher bond strength values when bonded to dentin prepared with SiC-paper. No statistically significant difference was found among Nexus 3, G-CEM Automix, SpeedCEM and Unicem when applied on dentin covered by the thinner smear layer (p>0.05). On the other hand, no SACs performed as well as Nexus 3 when applied on bur-cut dentin (p<0.05). SEM and TEM showed numerous micro-bubbles entrapped at the dentin-cement interfaces of SACs. Conclusion: The bonding effectiveness of SACs is adversely affected by the presence of a thick smear layer, although some SACs are able to perform as effective as multi-step composite cements provided that a thinner smear layer is prepared on dentin.