Abstract
Since Buonocore (1955) first introduced the acid etching technique to enhance the mechanical retention of resin restoration materials to enamel, the concept of "acid etching for retention" has been widely recommended and practiced. With the development of the adhesive monomers (phosphate ester of methacrylates) the chemical bonding to tooth structure could be realized, in which they reacted either ionically with mineralized dentin or covalently to organic constituents. In 1984, Munksgarrd and Asmussen reported that the use of a chelating agent EDTA instead of phosphoric acid to partially remove the smear layer followed by pretreament of the dentin surface with 35% 2-hydroxy-ethyl-methacrylate (HEMA), and 5% Glutaraldehyde was effective for increasing resin-dentin bonding strength. The mechanism was thought to involve crosslinking or fixation of the exposed collagen fibers by glutaraldehyde resulting from its penetration with HEMA into the matrix of the underlying dentin. Today, most of the dentin bonding systems utilize acidic conditioners to remove the smear layer followed by treatment with primers and bonding agents. In this study, the effects of the primers and bonding agents on the tooth dentin bonding were investigated for various combinations of four different kinds of dentin bonding systems, Clearfil Liner Bond System (CLB), Scotchbond Multi-Purpose (SMP), Prisma Universal Bond 3 (PUB) and Tokuso Light Bond (TLB). The tensile bond tests were performed and their bond strengths were evaluated by ANOVA. The conditioner and/or primer-treated dentin surfaces and the fracture surface after tensile bond test were observed with a scanning electron microscopic. The bonding aspects of the bonding agents were also discussed using synthetic hydroxyapatite (HAp). The results indicate that acidic conditioners are necessary for dentin bonding system and an adhesive-containing bonding agent might contribute to a higher bond strength. The adhesion mechanism might be explained by micromechanical interaction, where adhesive resin would penetrate into the dentinal tubules and the intertubular dentinal process via the intradentinal permeation to gain the mechanical retention, and there have some doubts about the long term durability on chemical bonding to tooth subtrates. Intermixing components of dentin primer and bonding agents between UDMA and Bis-GMA-based resin dentin bonding system should be avoided.
