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Figure 1. Transmission electron micrographs illustrating the application of UniFil Bond to dentin when the adhesive was used (A–B) immediately after being opened and (C–D) at 12 mos after storage at ambient temperature. A, filled adhesive; D, dentin. (A) A stained, demineralized section showing the presence of a 1-µm-thick, electron-dense hybrid layer (H) when the 4-MET-containing self-etching primer was used immediately. Loosely arranged collagen fibrils (arrow) could be identified from the hybrid layer surface. (B) The corresponding undemineralized, silver-impregnated section revealed a 1-µm-thick, partially demineralized zone (between open arrows) that was consistent with the hybrid layer observed in stained, demineralized sections. Little nanoleakage was observed, and appeared as silver deposits (open arrowhead) along the surface of the partially demineralized zone. (C) A stained, demineralized section showing the absence of a stainable hybrid layer when the self-etching primer was used after 12 mos. However, evidence of etching by the primer solution could be identified by the absence of smear layer remnants and the presence of loosely oriented surface collagen fibrils (arrow). (D) The corresponding undemineralized, silver-impregnated section showed the presence of extensive silver deposits (open arrow) within the partially demineralized zone (between open arrows) and beyond (pointers). The depth of these silver deposits (ca. 2 µm) suggested that etching of the dentin was more aggressive, but there was poor resin infiltration or polymerization within the etched dentin.
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