Changes in surface hardness of conventional restorative glass ionomer cements

The effect of a contact with an aqueous solution on the surface hardness of glass ionomers has been investigated in a few studies and for a limited nu mber of formulations. As there is no information on the long-term changes o f the surface hardness in this respect, the aim of this study was to determ ine these long-term changes in 10 conventionally setting glass ionomer form ulations after storage in water as compared to maturation in a humid atmosp here (85% RH). After setting for 15 min different series of glass ionomer specimens were s tored at 37 degrees C in both experimental media for 1, 7, 28 and 140 days. At the end of the specific maturation times, the mean surface hardness was determined on the basis of Knoop Hardness (KHN). Data were analyzed using ANOVA. In a humid atmosphere the surface hardness generally increases rapidly init ially, followed after 1 day by a more gradual increase. In contact with wat er, the hardness also increases up to one day but not to the same extent. T he surface hardness then remains constant or slightly decreases. Evidence o f a detrimental softening of the surface ascribed previously to the loss of matrix forming ions was not found. A surface erosion is not likely to occu r. (C) 1998 Published by Elsevier Science Ltd. All rights reserved.