Fracture resistance of dentin-composite interfaces using different adhesive resin layers

The objective of this study was to study the effect of different adhesive layers on the interfacial fracture toughness (K(ICi)) of dentin-resin composite interfaces.

Miniature short-rod fracture toughness specimens containing a chevron-shaped dentin-bonded interface along their midplane were used for testing. Each interface zone contained a thinned (one coat of unfilled adhesive resin, air-thinned), one-layer (one coat of unfilled adhesive resin, brush-thinned), two-layer (two coats of unfilled adhesive resin, brush-thinned), 10% filled or 45% filled adhesive resin layer. After storage in distilled water at 37 degrees C for 24h, the fracture toughness test specimens were loaded in tension at an extension rate of 0.5mm/min until fracture and the K(ICi) were determined. The results were analysed by ANOVA and Fisher's LSD test (p<0.05). Scanning electron microscopy was used to examine representative fracture surfaces.

There were no significant differences in mean K(ICi) among the different unfilled adhesive resin layer groups. SEM examination of these specimens showed that fracture generally occurred between the resin-infiltrated layer and adhesive resin layer during interfacial fracture toughness testing. The mean K(ICi) for the 10% filled groups was not significantly different from the unfilled groups. The 45% filled group, however, demonstrated the highest K(ICi) values, the thickest adhesive resin layer under SEM examination, and a fracture path through the adhesive resin layer.

There were no significant differences in K(ICi) when the unfilled adhesive resin was used despite different application methods. The 45% filled adhesive resin improved the properties of the dentin-composite interface with respect to both interfacial fracture resistance and dentinal seal after fracture.