The Effect of Irradiation Distance on Light Transmittance and Vickers Hardness Ratio of Two Bulk-fill Resin-based Composites

The aims of this study were to assess the light energy transmission and Vickers hardness (VH) ratio of two bulk-fill resin-based composites (RBCs) (Tetric EvoCeram and Filtek) cured at different distances between the light curing unit's (LCU) tip and the surface of the restoration (T-S) using either a Bluephase G2, Bluephase® 'turbo tip' or Bluephase Style LCU. Samples were cured from the top at T-S distances of 2mm, 6mm and 10mm for 20 seconds. A MARC-Resin-Calibrator™ recorded the transmitted irradiance reaching the bottom of the sample, in real time. The VH was measured at the top and bottom after 24h of dark storage. Both the total light energy (TLE) transmitted through the samples and their VH ratios were reduced with increasing T-S distance. At 10mm T-S distance, the VH ratio values of samples cured with Bluephase G2 LCU were significantly greater than the samples cured with the other LCUs while the samples cured with Bluephase® 'turbo tip' showed the lowest values. It can be concluded that TLE transmitted through bulk-fill RBCs and their VH ratio reduces with increasing T-S distance but the rate of decline is LCU dependent. Bluephase G2 was associated with the smallest light attenuation.