Fracture toughness ov conventional or photopolymerized glass ionomer/dentin interfaces

Several new light-cured glass-ionomer materials have been developed for restorative use. It is not yet clear, however, whether the ability of the conventional glass ionomers to bond chemically to dentin has been preserved in the new light-cured glass ionomers whose chemical compositions have been modified. The fracture toughness test was recently introduced as an appropriate method of measuring the fracture resistance of an interface. We have applied this test to the glass ionomer/dentin interface for the first time. Ten mini short-rod fracture-toughness specimens were fabricated for each group. Each specimen contained a chevron-shaped glass ionomer/dentin interface along its midplane. After 24 hours in 37 degrees C water, the specimens were tested by loading at 0.5 mm/min. The interfacial Kic results (MPa X m (1/2)) (SD), analyzed by ANOVA and Fisher's LSD test (P<0.05), were: Chem-fil II, 0.17 (0.04); Vitremer, 0.18 (0.15); Fuji II LC, 0.33 (0.16). There were no significant differences in interfacial Kic between the conventional and light-cured glass ionomers. Interfacial Kic's for a light-cured glass ionomer were, however, significantly higher when an intermediary dentin bonding agent was used. SEM examinations of the fractured surfaces indicated that crack propagation generally occurred along the bond interface, and indicated the formation of a resin-infiltrated layer when the dentin bonding agents were used. It was concluded that the fracture-toughness test could be a useful measure of the integrity of the glass ionomer/dentin interface. The clinical effect of an intermediary layer between the glass ionomer and the tooth structure is, however, unknown and requires further investigation.