Effect of solvent content on resin hybridization in wet dentin bonding

With wet bonding techniques, the channels between the demineralized dentin collagen fibrils are filled with debris, solvent, and water. Commercial adhesives include solvents such as ethanol or acetone to facilitate resin-infiltration into this wet substrate. Under in vivo conditions, the solvent may be diluted because of repeated exposure of the material to the atmosphere, or concentrated because of separation of the bonding liquids into layers within the bottle. The purpose of this study was to investigate the effect of different concentrations of ethanol (10-50%) on infiltration of the adhesive resin and collagen fibril encapsulation in the adhesive/dentin interface using light microscopy, micro-Raman spectroscopy, and scanning electron microscopy. The results indicated that under wet bonding conditions the hybridization process was highly sensitive to the initial solvent concentration in the adhesive system. The staining and scanning electron microscopy results showed that the quality of the interfacial hybrid layer was poor at the lower (10%) or higher (50%) ethanol content. Micro-Raman analysis indicated that there was a distinct difference in the degree of adhesive penetration among adhesives containing different concentrations of ethanol. Adhesives containing 10 or 50% ethanol did not realize effective penetration; the penetration of the adhesive monomers increased dramatically when the initial ethanol content was 30%. The amount of solvents are essential for achieving effective bonding to dentin.