Cavity preparation with rotary instruments or others results in the formation of a smear layer on the dentin surface, in which the cutting method affects smear layer characteristics (i.e. thickness, density). The smear layer fills the orifices of dentinal tubules, to form smear plugs, leading to a reduction

in dentin permeability. However, sub-micron porosities in the smear layer still allow for the diffusion of dentinal fluid. The dentin smear layer with smear plugs is composed mostly of submicron particles of mineralized collagen debris [33] and [34], which differs little in composition from the underlying dentin [33], [34] and [35]. Therefore, the smear layer formed on caries-affected dentin would be different in morphological and chemical structures from Trametinib that of normal dentin, because caries-affected dentin is partially demineralized, leading 17-AAG solubility dmso to different mineral/organic contents compared to normal dentin. Indeed, the smear layer of caries-affected dentin is thicker and appears to be enriched with organic components compared with that of normal dentin (Fig. 3) [36] and [37]. Caries-affected dentin produces

lower bond strengths than normal dentin, regardless of the type of adhesive system (etch and rinse system or self-etch system; one-, two- or three-step of bonding procedure) [2], [3], [4], [5], [6], [7], [8], [9], [10], [11], [12], [13], [36], [37], [38] and [39], in which cohesive failure of specimens in dentin increases in resin-bonded caries-affected dentin [6],

[7] and [10]. A reduction in the cohesive strength of caries-affected dentin Tangeritin would be one of the reasons for lower bond strength values to caries-affected dentin compared with normal dentin [6]. On the other hand, Wei et al. [12] demonstrated that when analyzing the effect of dentin type (normal and caries-affected dentin) on bond strength after removing the variance for which hardness accounted as a covariate, it was found that the condition of dentin had a significant effect on bond strength: even if normal and caries-affected dentin had similar intertubular hardness, bond strength to caries-affected dentin would still be significantly lower than to normal dentin. The change in chemical and morphological characteristics of caries-affected dentin would be also reasons for the lower bond strength. The hybrid layers created to caries-affected dentin are thicker than those of normal dentin, because caries-affected dentin is more susceptible to the acid etching due to partially demineralization, resulting in the formation of a deeper demineralized zone [2], [3], [4], [5], [6], [8], [9], [10], [15], [38] and [40].