Influence of Tip Diameter and Light Spectrum of Curing Units on the Properties of Bulk-Fill Resin Composites

Objective The aim of this study was to evaluate the influence of different light-curing units (LCUs) with distinct tip diameters and light spectra for activating bulk-fill resins. Materials and Methods The specimens ( n = 10) were made from a conventional composite (Amaris, VOCO) and bulk-fill resins (Aura Bulk Fill, SDI; Filtek One, 3M ESPE; Tetric Bulk Fill, Ivoclar Vivadent) with two diameters, 7 or 10 mm, × 2 mm thickness. Following 24 hours of specimen preparation, the degree of conversion (DC) was evaluated using the Fourier-transform infrared unit. Knoop hardness (KHN) readings were performed on the center and periphery of the specimens. Data were assessed for homoscedasticity and submitted to one-way and three-way analysis of variance followed by the Tukey's and Dunnett's tests, depending on the analysis performed (α = 0.05). Results LCUs and specimen diameter significantly affected the DC. The Tetric Bulk Fill provided increased DC results when light-cured with Valo (54.8 and 53.5%, for 7 and 10 mm, respectively) compared with Radii Xpert (52.1 and 52.9%, for 7 and 10 mm, respectively). No significant differences in KHN results were noted for the conventional resin composite ( Amaris ) compared with LCUs ( p = 0.213) or disc diameters ( p = 0.587), but the center of the specimen exhibited superior KHN ( p ≤ 0.001) than the periphery. Conclusion The light spectrum of the multipeak LCU ( Valo ) significantly increased the DC and KHN of the bulk-fill resin composite with additional initiator to camphorquinone ( Tetric Bulk Fill ) compared with the monowave LCU ( Radii Xpert ). The tip size of the LCUs influenced the performance of some of the resin composites tested.