Response to thermal stimuli of glass ionomer cements

Objectives This study was designed to determine the dimensional changes of glass ionomers caused by thermal stimuli under both dry and wet conditions. Methods Eight cylindrical specimens (6 mm × 4 mm) were made (using a stainless steel mold) of each of the following materials: a conventional luting glass ionomer, two high viscosity restorative glass ionomers, a resin-modified glass ionomer and a resin composite which was used as a control. The thermal expansion characteristics were determined by a thermal mechanical analyzer (TMA) under wet and dry conditions by heating the samples from 25 to 70 °C at 10 °C min−1. Results All materials showed contraction on heating in dry ambient conditions. In wet conditions, all glass ionomers maintained their original dimensions on heating, but the resin-modified glass ionomer expanded. The resin composite showed expansion in both wet and dry conditions. The results are explained in terms of the opposing effects of thermal expansion and desiccation on heating. Significance Under wet conditions glass ionomers maintain their original dimensions when heated. This kind of behavior may be considered as ‘smart’ behavior.