This method not only effectively seals the restoration margins in the long term, but also protects the more vulnerable bonds to dentin against degradation EGFR inhibitor [2]. The strength of the

micromechanical attachment of resin to etched enamel has proven adequate for retention in most clinical applications. Enamel is composed mainly of crystalline hydroxyapatite. The inorganic crystals are arranged in an orderly microstructure, which allows selective acid etching to produce a pattern into which the resin can penetrate and interlock [3]. Reliable adhesion to enamel can be achieved, but the bonding performance with dentin has been less consistent. On the other hand, it has been advocated that even with the good sealing of enamel margins with phosphoric acid etching, resin–dentin interface produced by the etch and rinse adhesive showed signs of degradation [4]. So one

should consider that the limitation of enamel sealing in terms of durability of dentin bonding. Dentin has a significant organic content that varies with depth, and lacks the orderly microstructure of enamel. Its structure is characterized by dentinal tubules, the spacing and orientation of which depend on the location and depth of the dentin surface [5]. In vital teeth, these tubules provide direct access to living processes and, ultimately, the pulp (Fig. 1). Opening up the dentin tubules by acid etching significantly increases the dentin permeability [6]. Leakage of pulpal

fluids from the tubules under hydrostatic pressure might disrupt attempts at chemical bonding to the dentin surface. Early attempts to achieve bonding GSK1210151A chemical structure to dentin by extending the enamel acid-etching technique were unsuccessful [7]. As mechanical attachment to etched dentin is not a viable alternative, research has instead focused on forming some type of chemical bond to one or both of the main constituents of dentin (that is, organic collagen and inorganic hydroxyapatite) [8]. It has been proposed that the removal of mineral phase from the dentin by acid etching exposes the dentinal collagen matrix as a bonding substrate, thinking as a practical approach to improve bonding Bay 11-7085 to dentin [9]. The hydrophilic functionality of the adhesion monomer helps facilitate permeation of itself into the exposed collagen fibrils leading to the formation of hybridized layer, whereas the hydrophobic functionality facilitates bonding to the resin composites. The process of hybridization is believed to result from the infiltration of the resin monomer into the collagen fibrils exposed by dentin demineralization, and in situ polymerization. The presence of cutting debris on instrumented dental surfaces in the form of a smear layer and smear plugs that obstruct the dentin tubules is also a significant cofactor [10]. The smear layer should be removed before chemical bonding to the dentin surface is attempted.