Effects of aging and light-curing unit type on the volume and internal porosity of bulk-fill resin composite restoration

This study explores the effects of aging (thermal cycling and cyclic loading–TC/CL) and different light-curing unit (LCU) types on the volume characteristics and internal porosity of a bulk-fill resin-based composite restoration. Occlusal cavities (4 × 4 × 3 mm) were prepared on extracted human molars (n = 5). Tetric N-Bond Universal was applied, and the cavities were restored using Tetric-N-Ceram Bulk Fill. Photoactivation was performed using a quartz-tungsten halogen (QTH) or a multiple-emission peak light-emitting diode (MLED). Digital images for all restorations were obtained using microcomputed tomography (micro-CT) before (baseline) and after (post-aging) TC/CL (5,000 TC cycles in 5–55 °C baths and a dwell time of 30 s followed by 10,000 sinusoidal CL load cycles in an Instron B3000 at 2 Hz and 10–110 N) and storage (37 °C) for three months. For the micro-CT analysis, three-dimensional images were used to determine the restoration volume and internal porosity. Data were analyzed using a two-way ANOVA and Tukey’s test (p < 0.05). Restorations photoactivated with QTH exhibited a higher object volume than the LED group at baseline and in post-aging conditions without any significant differences in the other evaluated characteristics. All volume/porosity characteristics increased considerably after TC/CL aging, except for the object volume of the QTH group and the closed porosity of the MLED group. The change in all the volume/porosity characteristics between both LCU groups after TC/CL were not significantly different. Thus, the aging process simulated herein increased the volume and porosity characteristics of the bulk-fill restoration, and no significant differences were obtained between the QTH and MLED equipment.