Effect of surface coatings on flexural properties of glass ionomers.

The purpose of this study was to investigate the change in flexural strength and fracture toughness of light-cured glass ionomer cements after long-term immersion in water, and to investigate the effect of surface coatings on their properties. 2 resin-modified and 1 conventional glass ionomer cements were employed. For the flexural strength, a 25 x 2 x 2 mm stainless steel mold was used. For the fracture toughness (KtC), single edge notch specimens with dimensions 25 x 2.5 x 5 mm and a 0.5 mm notch (a/W = 0.5) were prepared in a stainless steel mold. Specimens were subjected to the 3 point bending at 0.5 mm/min after storage in 37 degrees C water for the periods of 1 h, 24 h, 1 wk, 1 month, and 6 months. The glass ionomer cements tended to exhibit an increase in mechanical properties over the 24-h period and then to maintain a constant strength. The surface protection of the resin-modified glass ionomer cement has some effect on the mechanical properties during early setting reactions, and it is desirable that the cement should be protected from direct water contact for at least 1 h after cement mixing.