Depth of cure of resin-modified glass ionomers

The cure of all resin-modified glass ionomer materials depends to some degree on light activation. However, the materials have chemical-cure mechanisms that could increase depth of cure. Thus, this study was conducted to evaluate the depth of cure of five resin-modified glass ionomer restorative materials.

Five specimens of Fuji II LC (GC America), Geristore (Den-Mat), Photac-Fil (ESPE America), VariGlass (Caulk/Dentsply), and Vitremer (3M Dental Products) were fabricated in Teflon molds. Each material was visible light-activated for 40 s. Specimens were 5 mm x 5 mm x 9 mm (depth), but material at depths greater than 5 mm was too soft to measure. Microhardness (KHN) at the surface and at 1 mm increments below the surface of each specimen was measured at 10 min, 1 d, and 7 d after light-curing.

At 10 min post-irradiation, the top layers (0-1 mm) of each material were significantly harder than the deeper layers (4-5 mm). However, at 1 d, Geristore, Photac-Fil, Vitremer and Fuji II LC had uniform hardness, regardless of depth. In contrast, VariGlass hardness decreased significantly with depth, from 43.3 at the surface to 11.7 at 5 mm. At 7 d, Photac-Fil, Vitremer and Fuji II LC had more uniform hardness regardless of depth than either Geristore or VariGlass. Data were analyzed using ANOVA and Duncan's multiple range tests.

Immediately following light activation, the upper layers of each material were harder than the deeper layers, but the degree of cure in the deeper layers improved over time. VariGlass was the only material in which bottom hardness (5mm) and top hardness remained significantly different at 1 d, suggesting that VariGlass has less effective chemical-cure mechanisms than the other materials tested.