[Study on surface treatment of silica filler. Hydrolytic deterioration of the silane coupling layer]

The mechanism of the hydrolytic deterioration of the silane coupling agent layer on silica filler of composite resin was examined. As a result of the desorption of the absorbed silane molecules, the contact angle between water drop and the silica plate treated with the silane coupling agent decreased when the plate was soaked in hot water and the rate of the decrease in the contact angle leveled off with an increase in the concentration of the silane coupling agent solution. With an increase in the soaking time in hot water, the strength of adhesion of poly (BIS-GMA) to the silica treated with the silane coupling agent decreased and the position of the fracture shifted from the matrix resin (adherend failure) to the silane coupling layer (adhesion failure). The time when the adhesion failure took place depended on the concentration of the silane coupling agent solution and there was the optimum concentration for water-resistant adhesion.