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Figure 1. Microtensile bond strengths and representive SEM micrographs from the 5 experimental groups. (A) Microtensile bond strengths of the 5 two-step, experimental 4-AET/HEMA self-etching primer solutions: Group 9-0-1 (35.9 ± 7.5 MPa), Group 8-1-1 (43.1 ± 6.1 MPa), Group 7-2-1 (47.6 ± 6.6 MPa), Group 5-4-1 (42.3 ± 7.6 MPa), and Group 3-6-1 (22.6 ± 8.1 MPa). The number inside each bar represents the number of specimens tested for that group. There were no premature failures in any of the groups. Groups with the same upper-case letters are not statistically significant (P > 0.05). (B) SEM micrograph of an adhesive failure from the group with the highest mean bond strength (Group 7-2-1), showing the surface of the fractured hybrid layer that appeared comparatively solid. Hybridized smear plugs (arrows) can be seen within some dentinal tubules. (C) SEM micrograph of an adhesive failure from the group with the lowest mean bond strength (Group 3-6-1). The surface of the hybrid layer was porous (asterisk), and some incompletely infiltrated collagen fibrils (open arrowhead) can be identified along the fractured interface. The condition of the hybrid layer reflects the extensive nanoleakage observed in the TEM (Fig. 4D). D: non-hybridized dentin.
