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 unfitted 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 X 2 X 10 mm were prepared for FS test, photoactivated by 600 mW/cm(2) x 40 s (A), 200 mW/cm(2) x 120 s (B), or 600 mW/cm(2) x 1 s + 3 min delay + 600 mW/cm(2) x 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/Tukey's test (alpha=0.05). Results: Composite DC was not affected by photoactivation (A: 65 +/- 1.8%; B: 66 +/- 3.4%; C: 65 +/- 2.9%). Unfitted 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 unfitted resin was lower for specimens irradiated by method B (p<0.001). Pulse-deLay curing (C) significantly reduced CS (7.7 +/- 1.3 Wa), compared to A (10.7 +/- 1.2MPa) and B (10.1 +/- 1.3MPa). Significance: Photoactivation method did not affect composite properties or susceptibility to ethanol degradation. For the unfitted resin, DC was tower with the use of low intensity and pulse-curing, white FS after ethanol storage was reduced by low intensity curing. Pulse-delay curing significantly reduced CS. (c) 2005 Elsevier Ltd. All rights reserved.