Dentin bonding--state of the art 1999

The adhesion of restorative materials to the hard components of tooth structure has been a goal pursued by many researchers ever since Buonocore established the foundation for adhesive and preventive dentistry. Based on the industrial use of phosphoric acid to obtain better adhesion of paints and resin coatings to metal surfaces, Buonocore proposed that phosphoric acid could be used to transform the surface of enamel to "render it more receptive to adhesion." Subsequent research indicated that the formation of taglike resin prolongations into the enamel microporosities was the leading bonding mechanism of resin to phosphoric acid-etched enamel. The enamel bonding agents of the 1960s and 1970s progressively evolved into complex multibottle or universal adhesives in the early 1990s, which were designed to bond to enamel, dentin, composite, amalgam, porcelain, and non-precious metal. Although bonding to enamel has been a dependable technique, bonding to dentin still represents an overwhelming task because dentin is a naturally wet organic tissue penetrated by a tubular maze containing the odontoblastic process, which communicates with the pulp. This intrinsic moisture may actually benefit the chemistry of the newest adhesive systems, which must be applied on moist dentin to be effective. In fact, the collapse of the collagen that occurs on air-drying may prevent the adhesive monomers from penetrating the network of nano-channels formed by the dissolution of hydroxyapatite crystals between collagen fibrils. In view of the complexity of the mechanisms associated with these mechanisms, the objective of this review article is to summarize the most recent concepts in dentin bonding.