Influence of Dentin Preparation on the Bonding of Self-Adhesive Cements

Objectives: The purpose of this study was to assess the influence of smear layer interference on the micro-tensile bond strength (µTBS) of self-adhesive composite cements (SACs) to central and peripheral dentin.

Methods: Four SACs (exp. GAM100, GC; Unicem, 3M ESPE; seT, SDI; BisCem, Bisco) and one etch-and-rinse system (Nexus 3, Kerr) were used to lute feldspathic ceramic blocks (Vita Mark II, Vita) to 50 flat mid-coronal dentin surfaces, which were previously 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 at 37°C, samples were prepared for µTBS testing. Specimens originating from central and peripheral dentin were tested separately. Failure patterns were initially evaluated with a stereomicroscope, and afterwards imaged using Feg-SEM. Two additional samples per group were processed for TEM.

Results:

All SACs bonded better to the thin than to the thick smear layer, and significantly worse than the multi-step composite cement (control), except for exp. GAM100 and Unicem when bonded to 600-grit SiC-paper prepared dentin. Central and peripheral dentin resulted in a similar bonding effectiveness (Wilcoxon, p>0.05). SEM and TEM showed numerous micro-bubbles entrapped at the dentin-cement interfaces of SACs. The concentration of such voids decreased gradually from central to peripheral dentin.

Conclusions: It is concluded that the bonding effectiveness of SACs is adversely affected by the presence of a thick smear layer. Their performance, however, is not affected by dentin regional variability.