Although both approaches have shown success in laboratory and clinical studies, their performance Neratinib nmr is highly product-dependent [11]. The fundamental mechanism of bonding to enamel and dentin is based on an exchange process in which minerals removed from the dental hard tissues are replaced by resin monomers

that, upon polymerization, become micromechanically interlocked in the created porosities [12]. The classification of dental adhesives is not straightforward, although a scientifically based classification has been suggested (Fig. 2). Adhesive systems can use either an etch-and-rinse approach or a self-etch approach [13]. Furthermore, the priming and bonding agents can be separate or combined, resulting in two-step or three-step systems for etch-and-rinse adhesives, and one-step or two-step systems for self-etch adhesives, respectively (Fig. 3) [14]. Etch-and-rinse adhesives are characterized by an

initial etching step, followed by a compulsory rinsing procedure that completely removes the smear layer and smear plugs (Fig. 5). Three-step etch-and-rinse systems typically include separate conditioning, priming and adhesive resin-application stages. Two-step etch-and-rinse systems were developed to reduce the number of application steps and to simplify the process by combining the priming and bonding stages. Acid etching promotes dentin demineralization over a depth of 3–5 μm,

thereby CX5461 exposing a scaffold of collagen fibrils lacking hydroxyapatite [15]. The demineralized collagen network must remain loosely organized during adhesive procedures in order to allow adequate resin monomer infiltration. A certain amount of water is crucial to prevent the collagen fibrils within dentin from shrinking. However, it is difficult to determine exactly how moist the dentin should be to ensure complete water removal by an acetone-based primer. Problems resulting from excess water have been reported, PtdIns(3,4)P2 and are known as ‘over-wet’ phenomena [16]. The presence of superfluous water on the dentin surface seems to cause phase separation between the hydrophobic and hydrophilic components of adhesives, resulting in the formation of voids at the resin–dentin interface. Excessive moisture on the adherent surface is also responsible for the improper polymerization of resin monomers, which lowers the mechanical properties of the adhesive layer. Determining how moist the dentin should be remains a major concern, and this factor is difficult to standardize in clinical protocols [17]. Self-etch systems do not require a separate etching step because they contain acidic monomers that simultaneously etch and prime the tooth substrate. The acidic functional monomers in self-etch adhesives dissolve the smear layer and demineralize the underlying tooth substrate (Fig. 4) [18].