Extrinsic energy sources affect hardness through depth during set of a glass-ionomer cement

Abstract

To investigate the effect of various energy sources on the upper and lower surface hardness of a setting glass ionomer with various thicknesses. Cylindrical specimens (4 mm diameter by 1, 2 or 4 mm thickness) of a glass-ionomer cement were prepared with no applied energy source (control), by preheating GIC capsules in a waterbath prior to mixing, application of light with high irradiance or ultrasonic excitation with a scaler tip. The upper and lower surface hardness was measured 0.5 h, 4 h and 1 week following material mixing. The increase in temperature towards the lower surface of each specimen was monitored throughout the first 5 min of setting. No significant differences in hardness between upper and lower surfaces or varying thicknesses were identified for control and preheated samples at any post-mix time (p>0.05). At 0.5 h post-mix, the upper surface hardness of preheated, light and ultrasonic treatments was significantly increased compared with that of the control groups. Following 4 h post-mix, the overall hardness of preheated samples was significantly greater (p<0.001) than other sample groups, which were not statistically different (p=0.684). No significant differences in hardness between test groups were identified following 1 week (p>0.05). Preheating GIC capsules prior to mixing resulted in superior hardness values through depth up to and including 4 h post-mix compared with specimen surfaces treated with light irradiation or with an ultrasonic scaler tip.