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Figure 3. TEM of undemineralized specimens, showing the variability in bonding of a self-etch and a total-etch adhesive to caries-infected dentin. (A) Stained section of a specimen bonded with the self-etch ABF system. The hybrid layer region (between open arrows) consisted of a superficial layer of carious-infected dentin (CI) that contained bacteria (arrowhead) mixed with some caries-affected dentin (CA). The underlying caries-affected dentin (U) was highly porous. The dentinal tubules (T) were completely obliterated with minerals. (B) Stained section of a specimen bonded with the ABF system, showing a thick layer of caries-infected dentin that contained loose dentin chips (L) and bacteria (B). The extent of the hybrid layer could not be clearly discerned. Caries-infected dentin did not form a hybrid layer in the underlying caries-affected dentin (CA). A gap (asterisk) was present between the unfilled primer component of the adhesive (P) and the surface of the caries-infected dentin. This gap was subsequently filled with the more electron-lucent epoxy resin that was used for laboratory specimen preparation. (C) High magnification of stained section of an ABF specimen showing caries-affected dentin that was about 100 µm beneath the bonded interface. Destruction of the intertubular and peritubular dentin resulted in the confluence of tubules that were filled by micro-organisms. Glycogen-like intracellular polysaccharide granules could be identified within the cytoplasm of the bacteria, some of which were dividing. (D) Stained section of the superficial part of the hybrid layer (H) in a caries-infected dentin specimen bonded with the total-etch, Single Bond adhesive. A loose dentin fragment (pointer) was trapped within the copolymer (P) of the adhesive (A). B, bacteria within dentinal tubules; C, composite.
