title: Effect of curing lights and bleaching agents on physical properties of a hybrid composite resin.
abstract: The aim of this in vitro study was to evaluate the microhardness (MH) and diametral tensile strength (DTS) of a minifill hybrid composite (Filtek Z250, 3M ESPE), polymerized with halogen lamp or second generation light-emitting diode (LED), submitted to different bleaching agents. Composite resin specimens were randomly polymerized according to experimental groups (halogen, 550 mW/cm(2)/20 seconds; LED, 550 mW/cm(2)/25 seconds) and subdivided into three subgroups (N=8): A, without bleaching (control); H, 35% hydrogen peroxide; and C, 16% carbamide peroxide. After that, the MH test and DTS test were performed. Two-way analysis of variance (whitening x light) and Tukey's tests (alpha=5%) were performed. For DTS, there were no statistical differences among the bleaching agents and the control group; however, the halogen group presented statistically lower DTS (p<0.05) than the LED group. For the MH test, the carbamide peroxide group presented statistically lower MH means (p<0.05) than the control groups, and there were no statistical differences among the light-curing units. Sixteen percent carbamide peroxide reduced the MH of the hybrid composite tested. The second generation LED presented a performance similar to or better than the halogen lamp for hardness and DTS, respectively.
  
  
  CONCLUSIONS
  Repolishing of minifill hybrid composite is suggested, as the alteration caused after the contact with 16% carbamide peroxide was limited to the material surface. The second generation light-emitting diode is a good option for a curing light device when the polymerization initiator of composite resin is camphorquinone.
authors.affiliation: Department of Restorative Dentistry, Piracicaba School of Dentistry-Campinas State University, SP, Brazil.
authors.forename: Débora Alves Nunes Leite
authors.initials: DA
authors.lastname: Lima
authors.forename: Rodrigo Sversut
authors.initials: RS
authors.lastname: De Alexandre
authors.forename: Ana Cláudia Moraes
authors.initials: AC
authors.lastname: Martins
authors.forename: Flávio Henrique Baggio
authors.initials: FH
authors.lastname: Aguiar
authors.forename: Gláucia Maria Bovi
authors.initials: GM
authors.lastname: Ambrosano
authors.forename: José Roberto
authors.initials: JR
authors.lastname: Lovadino