FRACTURE-TOUGHNESS OF CONVENTIONAL OR PHOTOPOLYMERIZED GLASS IONOMER DENTIN INTERFACES/

Several new light-cured glass-ionomer materials have been developed fo r restorative use. It is not yet clear, however, whether the ability o f the conventional glass ionomers to bond chemically to dentin has bee n preserved in the new light-cured glass ionomers whose chemical compo sitions have been modified. The fracture toughness test was recently i ntroduced as an appropriate method of measuring the fracture resistanc e of an interface. We have applied this test to the glass ionomer/dent in interface for the first time. Ten mini short-rod fracture-toughness specimens were fabricated for each group. Each specimen contained a c hevron-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 K-IC results (MPa . m1/2) (SD), analyze d 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 significant differences in K-IC between the conventional and light-cured glass ionomers. Inte rfacial K-IC's for a light-cured glass ionomer were, however, signific antly higher when an intermediary dentin bonding agent was used. SEM e xamination of the fractured surfaces indicated that crack propagation generally occurred along the bond interface, and indicated the formati on of a resin-infiltrated layer when the dentin bonding agents were us ed. It was concluded that the fracture-toughness test could be a usefu l 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 investi gation.