In order to produce a superior resin–dentin interface, resin monomers must penetrate into these demineralized dentinal sub-surfaces. However, even though for normal dentin, it has been demonstrated that there are discrepancies between the depths of demineralization and resin

monomer penetration. The wet bonding technique is effective for infiltration of resin GABA assay monomers into deeper acid-etched demineralized layers in caries-affected dentin compared with the dry bonding technique, leading to higher bond strength [4] and [5]. Nevertheless, a deeper demineralized zone is more difficult for resin monomer to penetrate to the bottom of the exposed collagen matrix. In addition, a larger quantity of water in the deeper demineralized zone would compete with penetration of the adhesive resin monomers. Besides the residual water, caries-affected dentin may contain substances that interfere with

free radical generation or propagation, leading to poor polymerization of adhesive monomers. It is reported that the degree of conversion of adhesive agent that penetrated the etched dentin in the caries-affected dentin specimen was lower than in the normal dentin specimens [14]. The mineral deposits in dentinal tubules in the transparent layer are highly acid resistance. Etching with phosphoric acid cannot completely dissolve the deposits that exist in dentinal tubules without dissolution. The presence of mineral deposits inside dentinal tubules would interfere with resin monomer infiltration peripheral to the dentinal tubules as well as resin tag formation, leading to lower bond strength [2] and [5]. The hybrid layer of etch and rinse system Raf inhibitor drugs in caries-affected dentin was thicker but susceptible to the acid and base treatment in scanning electron microscopy (SEM) observation of resin/caries-affected dentin interface [2] Resveratrol (Fig. 4). Transmission electron microscopy (TEM) observation demonstrated a more porous zone along the base of the

hybrid layer in caries-affected dentin created [6]. Micro-Raman spectroscopy investigation suggested that the caries-affected dentin interface was more complicated, whereby the wider demineralized matrix was not protected by the critical Bis-GMA [15]. Light microscopy evaluation with Masson’s trichrome stain indicated wider regions of non-encapsulated collagen in the caries-affected dentin interface [40]. These would be due to reduced penetration of the resin monomers into the etched caries-affected dentin because of the deeper demineralized zone and the presence of the mineral deposits inside the dentinal tubules (Fig. 5). Etching with phosphoric acid might be too aggressive for partially demineralized intertubular caries-affected dentin. However, stronger acids and an extended etching time are suggested for solubilizing acid resistant mineral deposits within the caries-affected tubule lumens, leading to more lateral penetration of the adhesive monomer from the tubule lumens.