Figure 3. TEM micrographs demonstrating the pathways of water movement through one-step self-etch adhesives. The micrographs were taken from unstained undemineralized sections of adhesive-bonded enamel that were immersed in an ammoniacal silver nitrate tracer solution. Water trees (pointers) can be identified within the adhesives. In addition, isolated silver grains (open arrowheads), probably representing the hydrophilic resin domains, can be observed throughout the adhesive-enamel interfaces. They represent the pathways for water movement within the polymerized adhesives (A). (A) In the more aggressive self-etch adhesive, Prompt L-Pop, the enamel smear layer is completely dissolved, and water trees are seen along the surface of the enamel hybrid layer (R) and above the resin tags (T). (B) In the mild self-etch adhesive iBond, the enamel smear layer (arrow) is incompletely dissolved and separated from the adhesive during specimen preparation. S, empty grid space. (C) A high-magnification view of Fig. 3B, showing the hybridized enamel smear layer (ES) that separated from the adhesive and was probably embedded by the laboratory epoxy resin (XR). The hybridized smear layer consisted of fractured chips of enamel crystallites and can be distinguished from the underlying 300- to 500-nm-thick enamel hybrid layer (between open arrows) that comprised intact apatite crystallites.