title: Influence of photoactivation method on conversion, mechanical properties, degradation in ethanol and contraction stress of resin-based materials.
abstract: OBJECTIVE
  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, 3M ESPE) after storage in water or ethanol, and on composite contraction stress (CS).
  
  
  METHODS
  Specimens 1x2x10 mm were prepared for FS test, photoactivated by 600 mW/cm2 x 40 s (A), 200 mW/cm2 x 120 s (B), or 600 mW/cm2 x1 s +3 min delay +600 mW/cm2 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%). 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).
  
  
  CONCLUSIONS
  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.
authors.affiliation: Department of Dental Materials, School of Dentistry, Av. Prof. Lineu Prestes, 2227, Cidade Universitária, São Paulo, São Paulo, SP, Brazil CEP 05508-000.
authors.forename: Marcelo F
authors.initials: MF
authors.lastname: Witzel
authors.forename: Fernanda C
authors.initials: FC
authors.lastname: Calheiros
authors.forename: Flávia
authors.initials: F
authors.lastname: Gonçalves
authors.forename: Yoshio
authors.initials: Y
authors.lastname: Kawano
authors.forename: Roberto R
authors.initials: RR
authors.lastname: Braga
mesh_terms: D000180:Acrylic Resins / Q000737:chemistry / Q000528:radiation effects*; D003188:Composite Resins / Q000737:chemistry / Q000528:radiation effects*; D004548:Elasticity / Q000528:radiation effects; D000431:Ethanol / Q000494:pharmacology; D006244:Hardness / Q000528:radiation effects; D011140:Polyurethanes / Q000737:chemistry / Q000528:radiation effects*; D012997:Solvents / Q000494:pharmacology
chemical_list: D000180:Acrylic Resins; C029012:Composite Dental Resin; D003188:Composite Resins; D011140:Polyurethanes; D012997:Solvents; D000431:Ethanol