Impedance as a measure of setting reaction in glass ionomer cements

The setting process for dental glass ionomer cements (GIC) was studied by impedance spectroscopy in a fixed, 10 and 1000 Hz, and wide frequency region, from 0.01 Hz to 1 MHz. For comparison, the setting of the conventional GICs, Fuji IX Fast and Ketac Molar Aplicap, and “resin modified” GIC, Fuji II LC, were investigated. The effect of setting upon electrical conductivity shows a significant decrease and break in conductivity for conventional GICs after the first 15 and 30 minutes, respectively. For light-activated Fuji II LC, only a drop without any evidence of a break in electrical conductivity was observed. Such behavior is the result of the instantaneous photopolymerization and formation of a rather homogeneous cement matrix. The complex impedance plots obtained for the three GICs studied show the presence of features that are attributed to the structural regions in the samples. Evolution of the impedance spectra and changes in the capacitance values reveal gradual transformations related to the development of various constituent regions during the setting process. Thus, impedance spectroscopy could become an essential technique for the separation of the overall electrical properties into their component parts, which could then serve as the foundations for meaningful clinical impedance measurements in vitro and in vivo. The knowledge of the sequences of the setting reactions in dental cements is important as these will affect the handling and the overall physical properties of the cements.