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:
µTBS to dentin (MPa) | |||||
| Nexus 3 | exp. GAM100 | Unicem | seT | BisCem |
Diamond bur | 29.8±5.4A | 12.7±6.1CD | 10.8±4.2D | 2.1±4.1E | 1.0±2.0E |
600# SiC-paper | 27.5±8.5AB | 26.6±7.3AB | 20.2±5.2BC | 3.0±4.3E | 3.6±3.1E |
Same superscripts indicate no significant difference (Kruskal-Wallis, p<0.05)
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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.