MECHANICAL-BEHAVIOR OF GLASS-IONOMER CEMENTS AFFECTED BY LONG-TERM STORAGE IN WATER

Objectives. The early strength of glass ionomer cements was investigat ed previously (Cattani et al., 1993). Using the same set of glass iono mer cements, this study was designed to determine if mechanical proper ty degradation occurred after an extended period of storage in water. Methods. In the present study, the effect of aging in water on the com pressive, tensile and flexural strengths of twelve commercial glass io nomer cements was evaluated at different time intervals after the begi nning of the setting reaction. The aging periods varied from 24 h to 1 2 mon. Results. The results show that the mechanical properties of the tested materials are in some cases affected by long-term aging in wat er. The evolution of strength follows distinct patterns of change. It has been established that the glass ionomer cements are neither charac terized by a continuous increase nor a continuous decrease in strength . Most of the materials tested maintained a constant strength. However , several of them first display an improvement of the mechanical stren gth followed by a reduction. In this case, the 24 h and the 12 mon str engths are usually similar. Significance. The aging mechanisms of glas s ionomers are complex. Strengthening probably results from additional crosslinking and build-up of a silica gel phase, whereas weakening ma y result from erosion and plasticizing effect of water.