Fracture Toughness of Resin-Based Composites Photo-Cured Using Laser

Objectives: This study evaluates the fracture toughness (K_IC) of resin-based composites (RBC) photo-cured with new light-curing units (LCU) technologies: one laser (ML, Monet Laser - AMD Lasers), one polywave LED (PC, PowerCure - Ivoclar Vivadent) and one quadwave LED (PW, PinkWave - Apex).
Methods: Four RBCs were used: Evo, Tetric EvoCeram (Ivoclar Vivadent); PF, PowerFill (Ivoclar Vivadent); FS, Filtek Supreme - FS (3M Oral Care); and AF, Admira Fusion x-tra (Voco). Specimens were photo-cured for 1 second with ML; for 60 s on each/both side (only for PF resin) and for 10 s in the High mode, and for 3 s in the 3s Cure mode with PC; and 3 s with PW. Power (mW), irradiance (mW/cm²), energy (J/cm²), and emission spectrum (mW/cm²/nm) were received using an integrating sphere. K_IC was obtained using a bipartite metallic matrix of 8.2 mm in diameter and 2 mm in thickness. After storage for 24 h at 37 °C, the tests were performed in a universal testing machine (Instron) with a displacement rate of 0.5 mm/min until fracture. Data were analyzed according to the experimental design (α = 0.05).
Results: ML presented the highest power and irradiance values but the lowest energy. K_IC values varied between 0.66 and 1.04 MPa*m^1/2. There was no K_IC difference for the LED light sources, but there was between both and the laser. PF obtained higher K_IC values regardless of the source used. LED and laser photoactivation sources significantly influenced K_ICvalues more than the RBC factor.
Conclusions: Despite having higher irradiance values, the laser source has lower energy generated at lower K_IC values.