Effect of irradiance and exposure duration on temperature and degree of conversion of dual-cure resin cement for ceramic restorations

This study investigated the effects of irradiance and exposure duration on dual-cured resin cements irradiated through ceramic restorative materials. A single light-curing unit was calibrated to three different irradiances (500, 1000, and 1500 mW/cm²) and irradiated to three different attenuating materials (transparent acryl, lithium disilicate, zirconia) with 1-mm thicknesses for 20 or 60 seconds. The changes in irradiance and temperature were measured with a radiometer (or digital thermometer) under the attenuating materials. The degree of conversion (DC) of dual-cure resin cement after irradiation at different irradiances and exposure durations was measured with Fourier transform near infrared spectroscopy. Two-way analysis of variance revealed that irradiance (p,0.001) and exposure duration (p,0.001) significantly affected temperature and DC. All groups showed higher DCs with increased exposure times (p,0.05), but there were no statistically significant differences between the groups irradiated with 1000 mW/cm² and 1500 mW/cm² (p.0.05). Higher-intensity irradiances yielded higher temperatures (p,0.05), but exposure time did not affect temperature when materials were irradiated at 500 mW/cm² (p.0.05).