Structural and long-term mechanical properties from a resin-modified glass ionomer cement after various delays of light-activation.

This study aimed, after various delays of light-activation, to examine the microstructure of a resin-modified glass ionomer cement (RMGIC) by scanning electron microscopy (SEM) and to test its mechanical properties in short and long term. Five groups of Fuji II LC were investigated with different light-curing protocols. For each, SEM observations were undertaken with etched samples to selectively observe the organic polymer phase. Flexural strength and microhardness were also tested after 24 h and 12 months storage. SEM examination showed different images of the material according to the delay of light-activation. At 24 h, there was a delay with maximal mechanical properties: 5 min for flexural strength, 10 min for microhardness. However, at 12 months, maximal mechanical properties were reached for the shortest delay. The competition between the acid-base and polymerization reactions results in the formation of a structurally and mechanically different material according to the delay of light-activation. This delay should be adapted to the clinical situation.