title: Cross-link density evaluation through softening tests: effect of ethanol concentration.
abstract: OBJECTIVE
  The aim of this study was to investigate whether the ethanol concentration used would influence the outcomes obtained through softening tests when comparing light-activation modes.
  
  
  METHODS
  Disc specimens (n=20) of Filtek Z250 and Filtek Z100 (3M ESPE) were light activated by standard (S) and pulse-delay (PD) modes. Initial Knoop hardness (KHN) measurements were performed 24h after dry storage at 37 degrees C. Half of the specimens (n=10) of each resin-composite were stored in absolute ethanol (100%) and the other half in 75% ethanol solution, for 24h at room temperature, and KHN was determined anew. Initial hardness data were submitted to Student's t-test (p=0.05). Percentages of hardness decrease were analyzed by two-way ANOVA followed by pairwise Tukey's test (p=0.05). The statistical analyses were performed separately for each resin-composite.
  
  
  RESULTS
  No statistically significant differences were observed between standard and pulse-delay modes for initial Knoop hardness values. After storage in 75% ethanol solution, KHN was decreased in all cases but no significant differences were detected between light-activation modes (Filtek Z250: PD=12.6%, S=13.5%; Filtek Z100: PD=13.5%, S=11.8%) regardless of the resin-composite tested. After absolute ethanol storage, higher decrease in KHN were observed. Samples light-activated by the PD mode (Filtek Z250=20.4% and Filtek Z100=16.9%) exhibited significantly higher percentage decrease of KHN than specimens light-activated by the standard mode (Filtek Z250=14.1% and Filtek Z100=8.8%), regardless of the resin-composite tested.
  
  
  CONCLUSIONS
  The ethanol concentration affected the outcomes of the softening test.
authors.affiliation: Dental Materials Area, University of Campinas, School of Dentistry, Piracicaba, Brazil. schneider@fop.unicamp.br
authors.forename: Luis Felipe J
authors.initials: LF
authors.lastname: Schneider
authors.forename: Rafael R
authors.initials: RR
authors.lastname: Moraes
authors.forename: Larissa M
authors.initials: LM
authors.lastname: Cavalcante
authors.forename: Mário A C
authors.initials: MA
authors.lastname: Sinhoreti
authors.forename: Lourenço
authors.initials: L
authors.lastname: Correr-Sobrinho
authors.forename: Simonides
authors.initials: S
authors.lastname: Consani
mesh_terms: D003188:Composite Resins / Q000737:chemistry* / Q000528:radiation effects; D003432:Cross-Linking Reagents / Q000737:chemistry; D000431:Ethanol / Q000008:administration & dosage / Q000737:chemistry*; D006244:Hardness; D006801:Humans; D008027:Light; D008422:Materials Testing; D011108:Polymers / Q000737:chemistry / Q000528:radiation effects; D011829:Radiation Dosage; D012822:Silicon Dioxide / Q000737:chemistry / Q000528:radiation effects; D012997:Solvents / Q000008:administration & dosage / Q000737:chemistry*; D013696:Temperature; D013997:Time Factors; D015040:Zirconium / Q000737:chemistry / Q000528:radiation effects
chemical_list: D003188:Composite Resins; D003432:Cross-Linking Reagents; C444701:Filtek Z250; D011108:Polymers; D012997:Solvents; C083568:Z100 composite resin; D000431:Ethanol; D012822:Silicon Dioxide; D015040:Zirconium