Fig. 5

Representative scanning electron micrographs of the fractured specimens. a and b Scanning electron photomicrographs of the cohesive failure of resin composite. c and d Mixed fractures. c Part of the fracture occurred inside the adhesive layer, probably just under the hybrid layer, because parts of the dentinal tubules are exposed (D-adhesive fracture) and parts are covered by the adhesive layer (A-cohesive fracture) with resin on top of a small adhesive area (R). d A mixed fracture shows deep dentin (DD), a thin adhesive film (AF) on dentin, and the presence of opened dentin tubules (white arrows) and fractured resin tags still attached (black arrows). e and f Adhesive failure: cohesive failure in the bonding resin and/or in the hybrid layer. e The fracture that occurred both between the adhesive layer and resin (AR) and under the hybrid layer (AH)