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Figure 4. Fractographic failure analysis of Optibond DC and Optibond Solo (Kerr). (a). Fe-SEM overview photomicrographs of the fracture surfaces (left = dentin side, right = composite counterpart) of a representative µTBS sample prepared with Optibond Dual Cure that was stored for 4 yrs with the resin-dentin interface indirectly exposed to water (4yr-IE). A small area of 0.11 mm2 or 10% of the total surface area represents an adhesive (A, marked with black line) failure, while the major part (1.0 mm2 or 90% of the total surface area) failed cohesively (C) in resin. (b) TEM photomicrograph (non-demineralized, stained section) of a typical failure of Optibond Dual Cure after 4 yrs of water storage (4yr-DE). A thin layer of a few µm of the particle-filled adhesive resin remained attached to the hybrid layer (H), indicating that the adhesive layer failed cohesively. Although this section was stained by heavy metals (UA/LC), collagen seemed not to have picked up much of the staining solution. E = embedding resin; T = resin tag (T) packed with filler; U = unaffected dentin; arrows = gold coating. (c) TEM photomicrograph (non-demineralized, unstained section) of a sample that was prepared with Optibond solo and stored for 4 yrs with the resin-dentin interface directly exposed to water (4yr-DE). The hybrid layer (H) remained attached to unaffected dentin (U). E = embedding resin; T = resin tag (T). (d) TEM photomicrograph (non-demineralized, unstained section) of the same sample as in (c), but now at a site were the sample failed at the base of the hybrid layer. Small hybrid-layer fragments (arrows) remained attached to unaffected dentin (U). The resin tag (T) was fractured at the same level. E = embedding resin.
