Figure 2. Microscopic examination of Exp-Eth/SA, Exp-Eth/UB, Clearfil SE Bond, and iBond. (a) Non-demineralized, non-stained TEM of Exp-Ac/SA. Strong air-blowing before light-curing reduced the number of droplets considerably. Ar = adhesive resin; Hy = hybrid layer; Ud = unaffected dentin. (b) Non-demineralized, non-stained TEM of Exp-Eth/UB. Following a two-step self-etch approach with the HEMA-containing UB bonding agent, the adhesive layer was free of droplets. The hybrid layer resembled that of Exp-Eth. (c) LM of uncured Clearfil SE Bond (Kuraray) primer dispensed on a glass plate. Note the transparency of the drop, some curves representing convection streams caused by solvent evaporation, and the absence of droplets. Original magnification 5x. (d) LM of uncured iBond (Hereaus Kulzer) applied on a glass plate, showing an extensive phase-separation reaction (time after dispensing of adhesive is indicated in sec). Original magnification 5x. (e) Non-demineralized, non-stained TEM of the resin-dentin bond produced by iBond. A partially demineralized hybrid layer and hybridized smear plug (HySp) were formed. Note the presence of small droplets entrapped in the adhesive resin adjacent to the hybrid layer. (f) Feg-SEM of a µTBS failure pattern of iBond (composite side). The bond failed between the adhesive and composite (C) and near the bottom of the adhesive layer, which appeared to be very porous due to the droplets entrapped after the sample was light-cured.