title: Influence of softening test and light-activation protocols on resin composite polymer structure.
abstract: OBJECTIVE
  This study analyzed the influences of the light-activation protocol and softening test on the degree of conversion (DC) and Knoop Hardness (KHN) of a microhybrid resin composite.
  
  
  METHODS
  Filtek Z250 (3M ESPE) was light-activated with a third-generation light-emitting diode (Valo Ultradent) by three protocols - standard, high power, and plasma emulation - or with a quartz-tungsten halogen XL 3000 (3M ESPE) in conventional mode. All modes were set to deliver 19 J/cm(2). The DC (N = 20) was determined by Fourier transform infrared spectrometry on the top (T) and bottom (B) surfaces. For the KHN test, samples were subdivided in four groups (n = 5 each) according to the storage media: absolute ethanol, 75% ethanol, distilled water, and air (control group). The KHN values were evaluated on T and B before and 24 h after immersion in the storage media. Data were analyzed by split-plot analysis of variance (ANOVA; for DC) or repeated-measures split-plot ANOVA (for KHN), followed by Tukey's test (α = 0.05).
  
  
  RESULTS
  For the DC, the light-activation protocol did not influence the results and there was no difference between T and B. For the KHN test, the light-activation protocol did not influence the results and T showed higher microhardness values than B for all experimental conditions. There were significant differences in KHN depending on the storage media. Samples immersed in absolute ethanol generally presented lower KHN values, with no differences compared to samples in 75% ethanol.
  
  
  CONCLUSIONS
  The storage media affected the outcomes of the softening test.
authors: Department of Restorative Dentistry Piracicaba Dental School, University of Campinas, Piracicaba-SP, Brazil.
authors: Maria Cecília Caldas
authors: MCC
authors: Giorgi
authors: Department of Restorative Dentistry Piracicaba Dental School, University of Campinas, Piracicaba-SP, Brazil.
authors: Débora Alves Nunes Leite
authors: DANL
authors: Lima
authors: Department of Restorative Dentistry Piracicaba Dental School, University of Campinas, Piracicaba-SP, Brazil.
authors: Giselle Maria
authors: GM
authors: Marchi
authors: Department of Social Dentistry, Piracicaba Dental School, University of Campinas, Piracicaba-SP, Brazil.
authors: Gláucia Maria
authors: GM
authors: Ambrosano
authors: Department of Restorative Dentistry Piracicaba Dental School, University of Campinas, Piracicaba-SP, Brazil.
authors: Flávio Henrique Baggio
authors: FHB
authors: Aguiar
keywords: Dental light-curing; ethanol; hardness; polymerization