The effect of priming etched dentin with solvent on the microtensile bond strength of hydrophobic dentin adhesive

Abstract

Deterioration of long-term dentin adhesion durability is thought to occur by hydrolytic degradation within hydrophilic domains of the adhesive and hybrid layers. This study investigated the hypothesis that priming the collagen network with an organic solvent displace water without collapse and thereby obtain good bond strength with an adhesive made of hydrophobic monomers and organic solvents. Three experimental adhesives were prepared by dissolving two hydrophobic monomers, bisphenol-A-glycidylmethacrylate (Bis-GMA) and triethyleneglycol dimethacrylate (TEGDMA), into acetone, ethanol or methanol. After an etching and rinsing procedure, the adhesives were applied onto either wet dentin surfaces (wet bonding) or dentin surfaces primed with the same solvent (solvent-primed bonding). Microtensile bond strength (MTBS) was measured at 48 hrs, 1 month and after 10,000 times of thermocycles. The bonded interfaces were evaluated using a scanning electron microscope (SEM). Regardless of bonding protocols, well-developed hybrid layers were observed at the bonded interface in most specimens. The highest mean MTBS was observed in the adhesive containing ethanol at 48 hrs. With solvent-primed bonding, increased MTBS tendencies were seen with thermocycling in the adhesives containing ethanol or methanol. However, in the case of wet bonding, no increase in MTBS was observed with aging. Ⅰ. IntroductionThe bonding mechanism of dentin adhesives currently available is partly based on the micromechanical retention through formation of a hybrid layer 1) . In order to obtain consistent hybrid layers, the threedimensional structure of a collagen network should be exposed by etchant or acidic monomers. Water is required to obtain the appropriate acidity of etchants or acidic monomers. During infiltration of resin monomers, the interfibrillar space of the collagen network should be maintained by being floated in water. Therefore, as an essential component, hydrophilic monomers are incorporated into adhesives applied on dentin. From the view point of 'long-term durability' , the bonding procedure itself involves several inherent risk factors. These factors include collagen fibers denatured by strong acid, water used to float the collagen network, phase separation between the hydrophilic and hydrophobic monomers, and the resulting exposure of hydrophilic resin monomers and collagens which are weak to hydrolytic attack.During wet bonding, the hydrophobic and hydrophilic monomers dissolved in solvents such as ABSTRACT *Corresponding