Micro-tensile bond strength of adhesives bonded to class-I cavity ...

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1004 J. De Munck et al. Figure 3 Feg-SEM of OptiBond FL. (a) Photomicrograph of the fractured surface of a control specimen (stored as mTBS stick in water for 20 days) at the dentin side. The specimen failed at the interface (I) and within the adhesive resin (Ar). (b) Composite counterpart of (a). (c) Photomicrograph of the fractured surface of a thermo-cycling/cavity specimen at the dentin side. The specimen failed at the interface (I) and within the adhesive resin (Ar). (d) Higher magnification of the composite counterpart of (c). The specimen failed at the top of the hybrid layer (Hy), with the heads of the resin tags still attached to the adhesive resin. (e) Photomicrograph of the fractured surface (dentin side) of a thermo-cycling/stick specimen. The specimen failed at the interface (I) and within the adhesive resin (Ar). (f) Higher magnification of (e) at an area that failed near the interface. The specimen actually failed at the top of the hybrid layer (Hy). Figure 4 Feg-SEM of Clearfil Protect Bond. (a) Photomicrograph of the fractured surface of a control specimen (stored as mTBS stick in water for 20 days) at the dentin side. The specimen failed mainly near the interface (I), apart from a small part that failed within the adhesive resin (Ar). (b) Higher magnification of the composite counterpart of (a). The specimen failed within the hybrid layer (Hy). Some resin flashes (Ar) remained attached to the dentin side of the beam. (c) Photomicrograph of the fractured surface (dentin side) of a thermo-cycling/cavity specimen. The specimen failed at the interface (I) and within the adhesive resin (Ar). (d) Higher magnification of the composite counterpart of (c). The specimen failed within the hybrid layer (Hy). (e) Photomicrograph of the fractured surface (dentin side) of a thermocycling/stick specimen. The specimen failed at the interface (I) and within the adhesive resin (Ar). (f) Higher magnification of (e) at an area that failed near the interface. Again the specimen failed within the hybrid layer (Hy). No morphological differences with the control group could be observed.
Micro-tensile bond strength of adhesives bonded to class-I cavity-bottom dentin after thermo-cycling 1005 Figure 5 Feg-SEM of iBOND. (a) Photomicrograph of the fractured surface of a control specimen (stored mTBS specimen in water for 20 days) at the dentin side. The specimen failed mainly within the adhesive resin (Ar). A small part failed near the interface (I). (b) Photomicrograph of the fractured surface (dentin side) of a thermo-cycling/cavity specimen. The specimen failed entirely within the adhesive resin (Ar). A large part failed, however, very near to the interface (Ar–I) and appeared very porous. (c) Higher magnification of the area marked by the hand-pointer in (b). Many small porosities can be observed in the resin part close to the dentin interface (Ar–I). Also in the adhesive resin itself, some porosities can be observed. (d) Photomicrograph of the fractured surface (dentin side) of a thermo-cycling/mTBS stick specimen. The specimen failed entirely within the adhesive resin (Ar). Again a large part failed near the interface (Ar–I) and appeared porous. (e) Composite counterpart of (d). Part of the adhesive resin chipped off during processing (arrow) and disclosed numerous large voids within the adhesive resin. (f) Higher magnification of (e) at an area that failed near the interface. Many small porosities (0.5–7.5 mm) can be observed. regimen (20 days), one can speculate that the degradation of the interface of the thermo-cycling/ stick group is caused by water exposure rather than by the thermo-cycling itself. To rule out this option, the mTBS sticks of the control group were also stored in water for 20 days at 37 8C, this in contrast to previous studies that had 24-h controls [14,15]. However, degradation caused by 20 days of water storage should have been minimal, as the bonds produced by three-step etch and rinse adhesives and mild two-step self-etch adhesives resisted up to 1-year direct water exposure [16]. This assumption is substantiated by the fact that for OptiBond FL, the highest mTBS was recorded in the thermocycling/cavity group, the only group not directly exposed to water for 20 days. The composite used in this study is known for its high E-modulus (21 GPa) [17]. Applying this composite in a relatively small class-I cavity, must have resulted in high polymerization shrinkage stress [7]. By using a high-efficiency, high-power LED curing device, the polymerization reaction must have been rather fast, so that also the plastic flow of composite, which can reduce the shrinkage stress, must have been limited. As a result, the cavity model used in this study represents a clinical ‘worst case scenario’. In this study, only OptiBond FL and Clearfil Protect Bond were able to withstand the shrinkage stress in this challenging situation, in contrast to iBOND that performed unreliably. From a previous review, it was concluded that 10,000 thermal cycles corresponds to 1 year in vivo degradation [2]. Therefore, the bonds produced by OptiBond FL should be durable for at least 2 years of clinical service. This postulation was supported by many in vitro studies, in which OptiBond FL successfully withstood to up to 4 years of water storage, thermo-cycling and/or mechanical loading [14,–16,18–20]. Only when miniature (0.4–0.6 mm 2 ) mTBS specimens were aged, was a significant decrease in mTBS observed for this three-step etch and rinse adhesive [21,22]. All other types of adhesive did, however, decrease at least to the same extent in a similar study [23]. Also in clinical class-V studies, this three-step etch and rinse adhesive performed very reliably for up to 5 years of clinical service [24,25]. The bond strengths obtained with the mild twostep self-etch adhesive Clearfil Protect Bond were not significantly different from the three-step
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