Influence of photoactivation method on conversion, mechanical properties, degradation in ethanol and contraction stress of resin-based materials

Objectives To investigate the influence of photoactivation method on degree of conversion (DC), flexural strength (FS), flexural modulus (FM) and Knoop hardness (KHN) of a composite and an unfilled resin (Filtek Z250 and Scotchbond multi-purpose plus, 3 M ESPE) after storage in water or ethanol, and on composite contraction stress (CS). Methods Specimens 1×2×10 mm were prepared for FS test, photoactivated by 600 mW/cm2×40 s (A), 200 mW/cm2×120 s (B), or 600 mW/cm2×1 s +3 min delay +600 mW/cm2×39 s (C), and tested after 24 h in water or ethanol. Load and displacement values were used to calculate FM. Specimen fragments were used to measure KHN. DC was determined by FT-Raman spectroscopy. CS was determined by mechanical testing. Data were submitted to ANOVA/Tukeyʹs test (α=0.05). Results Composite DC was not affected by photoactivation (A: 65±1.8%; B: 66±3.4%; C: 65±2.9%). Unfilled resin DC was statistically higher using method A (79±0.3%) than B (74±1.0%) and C (73±0.9%). Photoactivation did not influence composite properties, regardless of the storage medium (p>0.05). After ethanol storage, FS of the unfilled resin was lower for specimens irradiated by method B (p<0.001). Pulse-delay curing (C) significantly reduced CS (7.7±1.3 MPa), compared to A (10.7±1.2 MPa) and B (10.1±1.3 MPa). Significance Photoactivation method did not affect composite properties or susceptibility to ethanol degradation. For the unfilled resin, DC was lower with the use of low intensity and pulse-curing, while FS after ethanol storage was reduced by low intensity curing. Pulse-delay curing significantly reduced CS.