Long-term mechanical characteristics of resin-modified glass ionomer restorative materials

Objectives. The purpose of this study was to compare the effects of long-term water storage on the mechanical characteristics of four resinmodified glass ionomer restorative materials with those of a conventional glass ionomer cement and a resin composite material. Methods. Cylindrical specimens were prepared and stored in water for 1 h, 24 h, 1 wk, 1 mon, 3 mon and 6 mon prior to determination of diametral tensile strength (DTS) and depth of surface indentation both under 1 N load and after removal of the load. Results. Diametral tensile strength was lowest for the conventional glass ionomer cement and highest for the composite; the resin-modified glass ionomer cements were intermediate between the reference materials. Water storage reduced DTS between 24 h and 1 wk or 1 mon but then remained unaffected until the final measurements after 6 mon. The materials showed a trend toward a slight increase in the depth of indentation both under load and after removal of the load with increasing storage time. These mechanical properties indicate the position of four resin-modified glass ionomer cements on a continuum with convenional glass ionomer cement and resin composite as the end points. Significance The mechanical properties of resin-modified glass ionomers show that this group of materials is weaker than resin composite but stronger than conventional glass ionomer cement. Water storage for 6 mon has little adverse effect on the mechanical properties.