Factors contributing to the temperature rise during polymerization of resin-modified glass-ionomer cements

Part of the setting reaction of a resin-modified glass-ionomer cement (RMGIC) is a photoinitiated polymerization. As a result of the polymerization exotherm, the temperature of the cement may rise during setting. This study investigated the temperature rise for two liner/base- and two restorative-type RMGICs. The effects of factors such as specimen thickness, exposure time and environment temperature were investigated. The thermal diffusivity of the cements was also evaluated. Temperatures were measured using a thermocouple embedded in the centre of 6-mm diameter specimen discs of 1, 2 or 3 mm thickness. The exposure times used to cure the specimens varied from 15 to 60 s. The tests were carried out at either 25 or 37°C. The temperature rises attributable to the polymerization reaction ranged from 11 to 26°C for the liner/base cements and from 8 to 17°C for the restorative cements. Increasing the specimen thickness reduced the temperature rise only when inadequate exposure times were used. Raising the environmental temperature resulted in a smaller temperature rise. The thermal diffusivities were determined from cylindrical specimens. These ranged from 1.9 x 10^-3 to 2.5 x 10^-3 cm² s^-1, the lining cements showing lower values than the restorative materials.