The influence of microstructure on thermal response of glass ionomers
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This study was designed to determine the dimensional changes caused by thermal stimuli of glass ionomers with different glass/matrix ratios. Four cylindrical specimens were made for each of four powder/liquid ratios (3:1, 2.5:1, 2:1 and 1.5:1) for a conventional luting glass ionomer, two high viscosity restorative glass ionomers and a restorative resin-modified glass ionomer. The thermal characteristics were determined using a thermal mechanical analyzer (TMA) by heating the samples from 25 °C to 70 °C at 10 °C per minute. All glass ionomers and the resin-modified glass ionomer lost water on heating. The results of the thermal response of these materials were explained in terms of the opposing effects of thermal expansion and desiccation on heating. The contraction on heating of glass ionomer and related materials was found to relate to the glass/matrix ratio but not directly proportional to it. Materials with lower P/L ratios contracted the most when heated to 70 °C. The water loss from conventional and resin-modified glass ionomer with different glass/matrix ratios compensated for their thermal expansion and led to a minimal dimensional change when heated up to 50 °C. This outcome may be interpreted as an example of smart behaviour of these materials.
KeywordsThermal Response Dimensional Change Restorative Material Luting Cement Luting Material
This paper is based on a thesis submitted to the Graduate School, Faculty of Medical Sciences, University of Newcastle upon Tyne, in partial fulfillment of the requirements for the PhD degree. The authors thank GC Corp, Japan and 3M ESPE, Germany for generous donation of the materials investigated in this study.