In this case, a collagenous band at the base of the hybrid layer will not be impregnated by the resin. Signs of this incomplete resin penetration were observed as a

nanoporous zone present at the base of the hybrid layer [50], which could become a pathway for nanoleakage fluid [51]. This incompletely sealed interface may have facilitated the acid penetration vigorously and given rise to the demineralization of the dentin below the hybrid layer. On the other hand, this study evidently proved that the self-etch adhesive Kinase Inhibitor Library in vivo systems demineralize dentin mildly and partially, leaving hydroxyapatite crystals in the base of the hybrid layer (Fig. 10) [52]. Such residual apatite crystals may serve as a template for additional chemical reaction with the functional monomer, such as MDP in Clearfil SE Bond and Clearfil Protect Bond. It has been reported that MDP adhered to hydroxyapatite readily and intensively [53], forming a less soluble salt, compared to the functional monomers, such as 4-MET (hydrated 4-META) and 2-(methacryloxy) ethylphenyl hydrogenphosphate (Phenyl-P)

[52]. In these self-etch adhesives, the ABRZ was detected in the TEM observations, which were in accordance with the previous SEM studies [10], [11], [33], [34] and [43]. The top area of the ABRZ was exposed Cobimetinib manufacturer to the acid attack for a longer period than the mid and bottom portions, where the electron dense region contained a few haphazardly arranged apatite crystallites with partial dissolution. On the other hand, the bottom area of ABRZ showed densely packed crystallites. These regions with apatite crystallites were continuous with

the dentin, although the dentin below (outer lesion) is demineralized and dissolved. As previously mentioned, Clearfil Protect Bond is a fluoride-ion releasing adhesive system [33]. Fluoride ions are reported to increase the rate of calcium phosphate crystallization and decrease Erlotinib the rate of apatite dissolution [54]. Dentin decalcified by acids is more sensitive to react with fluoride due to the increased porosity [55]. It was assumed in this study that the theory for reduced tendency of the apatite crystal dissolution in the presence of fluoride ions may be applicable for the formation of the thickest ABRZ observed with Clearfil Protect Bond, which has resulted to a better reinforced dentin. Formation of acid resistant fluoroapatite may be another possibility for this finding. But further differentiation among pure hydroxyapatites, carbonated apatites and fluoroapatites should be performed in the future.