The influence of irradiation potential on the degree of conversion and mechanical properties of two bulk-fill flowable RBC base materials

ObjectiveTo assess the depth of cure claims of two bulk-fill flowable RBC bases (SDR and x-tra base) using Fourier transform infrared (FTIR) spectroscopy, biaxial flexure strength (BFS), and Vickers hardness number (VHN) for specimen depths of 8 mm (in 1 mm increments).MethodsThe degree of conversion (DC) was measured by monitoring the peak height (6164 cm−1) of specimens (11.0 ± 0.1 mm diameter, 1.0 ± 0.1 mm thickness) during light irradiation for 20 s using a quartz tungsten halogen light curing unit at 650 ± 26 mW/cm2. DC was measured up to 120 s post irradiation and repeated (n = 3) for irradiation depths up to 8 mm (in 1 mm increments). Further series (n = 20) of eight discs were prepared, stacked, light irradiated and numbered from one to eight (distance from the LCU). The specimens were stored at 37 ± 1 °C for 24 h and BFS tested with the fracture fragments used to determine the VHN for each specimen.ResultsX-tra base can be irradiated to 8 mm without a change in DC, something the SDR material cannot claim. However, the DC results confirm both bulk-fill flowable RBC bases have a depth of cure in excess of 4 mm. One-way ANOVAs of BFS and VHN data showed significant differences between irradiation depths for x-tra base and SDR with increasing irradiation depth (4 mm) resulting in significant reductions in mean BFS and VHN.SignificanceThe claims that the bulk-fill flowable RBC bases have a depth of cure in excess of 4 mm can be confirmed but the differing chemistry of the resin formulations and filler characteristics contribute to significant differences in DC, BFS and VHN data between the two materials tested.