Water sorption characteristics of resin-modified glass-ionomer cements

When restorative materials take up water, their dimensions and structural integrity may be affected. This study determined, using gravimetric measurements, the water sorption characteristics of four resin-modified glass-ionomer cements (RMGICs) immersed in either distilled water or artificial saliva. The dimensional changes on water storage were also determined. The RMGICs exhibited differing characteristics as they absorbed water. Percentage water uptake and solubility of the liner/base RMGICs were significantly greater than those of the restoratives. Higher rates of water uptake, i.e. higher values of sorption diffusion coefficients, were found in the materials from one manufacturer. The desorption diffusion coefficients of the four cements were not significantly different from one another, but were significantly higher than the sorption coefficients, indicating rapid water loss from the desiccated cements. All the cements expanded on immersion in water and contracted during desorption. Greater weight increase and greater volumetric expansion were observed on long-term storage in artificial saliva than in distilled water.