UV-Vis spectrophotometric analysis and light irradiance through hot-pressed and hot-pressed-veneered glass ceramics.

This study evaluated the irradiance of curing units through core and veneered hot-pressed ceramics as well as the transmittance of these materials. Discs of 0.7, 1.4 and 2 mm in thickness of Empress (EMP) and Empress Esthetic (EST), and 0.8 (n=5) and 1.1 mm (n=5) thickness of Empress 2 (E2) were obtained. For E2, two of the 0.8-mm-thick discs were covered with dentin (1.2- and 1.4-mm-thick) and two with dentin + enamel (1.5-mm-thick). The 1.1-mm-thick specimens were submitted to the same veneering procedures. Specimens were evaluated by UV-Vis transmittance analysis and the percentage of transmittance was recorded. Irradiance through each specimen was evaluated with a quartz-tungsten-halogen (QTH), used in continuous or intermittent exposure modes, or a blue light-emitting diode (LED). Data were analyzed by Dunnett's test, ANOVA and Tukey's test at 5% significance level. Exposure through ceramic decreased the irradiance for all ceramics. Irradiance through EST was significantly higher than through EMP. For E2, reduction in irradiance depended on the core and/or veneer thickness. The QTH intermittent mode showed higher irradiance than the continuous mode, and both showed higher irradiance than LED. The ceramic significantly influenced irradiance and transmittance, which were found to decrease with the increase in thickness.