title: Evaluation of the surface hardness of composite resins before and after polishing at different times.
abstract: OBJECTIVE
  The aim of this study was to evaluate the surface hardness of six composite resins: Revolution, Natural Flow, Fill Magic Flow, Flow-it! (flowables), Silux Plus (microfilled) and Z100 (minifilled) before and after polishing at different times.
  
  
  METHODS
  For this purpose, 240 specimens (5mm diameter, 1.4mm high) were prepared. Vickers hardness was determined before and after polishing at different times: immediately, 24h, 7 and 21 days after preparation of the samples. Statistical analysis was performed by ANOVA and Tukey test.
  
  
  RESULTS
  There was no difference in the hardness of flowable resins, which had lower hardness than the minifilled resin. The minifilled resin showed the highest surface hardness as compared to the other materials (p<0.01). All materials exhibited higher hardness after polishing, being more evident after 7 days.
  
  
  CONCLUSIONS
  It may be concluded that, regardless of the composite resin, surface hardness was considerably increased when polishing was delayed and performed 1 week after preparation of the samples.
authors.affiliation: Department of Restorative Dentistry, Ribeirão Preto Dental School, University of São Paulo, Ribeirão Preto - SP, Brazil. michinelatti@gmail.com
authors.forename: Michelle Alexandra
authors.initials: MA
authors.lastname: Chinelatti
authors.forename: Daniela Thomazatti
authors.initials: DT
authors.lastname: Chimello
authors.forename: Renata Pereira
authors.initials: RP
authors.lastname: Ramos
authors.forename: Regina Guenka
authors.initials: RG
authors.lastname: Palma-Dibb