title: Influence of curing light attenuation caused by aesthetic indirect restorative materials on resin cement polymerization.
abstract: OBJECTIVE
  To verify the effect of interposing different indirect restorative materials on degree of conversion (DC), hardness, and flexural strength of a dual-cure resin cement.
  
  
  METHODS
  Discs (2 mm-thick, n=5) of four indirect restorative materials were manufactured: a layered glass-ceramic (GC); a heat-pressed lithium disilicate-based glass-ceramic veneered with the layered glass-ceramic (LD); a micro-hybrid (MH); and a micro-filled (MF) indirect composite resin. The light transmittance of these materials was determined using a double-beam spectrophotometer with an integrating sphere. Bar-shaped specimens of a dual-cure resin cement (Nexus 2/SDS Kerr), with (dual-cure mode) and without the catalyst paste (light-cure mode), were photoactivated through the discs using either a quartz-tungsten-halogen (QTH) or a light-emitting diode (LED) unit. As a control, specimens were photoactivated without the interposed discs. Specimens were stored at 37 masculineC for 24h before being submitted to FT-Raman spectrometry (n=3), Knoop microhardness (n=6) and three-point bending (n=6) tests. Data were analyzed by ANOVA/Tukey's test (alpha=0.05).
  
  
  RESULTS
  MH presented the highest transmittance. The DC was lower in light-cure mode than in dual-cure mode. All restorative materials reduced the cement microhardness in light-cure mode. GC and LD with QTH and GC with LED decreased the strength of the cement for both activation modes compared to the controls. Curing units did not affect DC or microhardness, except when the dual-cure cement was photoactivated through LD (LED>QTH). Flexural strength was higher with QTH compared to LED.
  
  
  CONCLUSIONS
  Differences in transmittance among the restorative materials significantly influenced cement DC and flexural strength, regardless of the activation mode, as well as the microhardness of the resin cement tested in light-cure mode. Microhardness was not impaired by the interposed materials when the resin cement was used in dual-cure mode.
authors.affiliation: Department of Dental Materials, University of São Paulo, Brazil.
authors.forename: Bárbara
authors.initials: B
authors.lastname: Pick
authors.forename: Carla Castiglia
authors.initials: CC
authors.lastname: Gonzaga
authors.forename: Washington Steagall
authors.initials: WS
authors.lastname: Junior
authors.forename: Yoshio
authors.initials: Y
authors.lastname: Kawano
authors.forename: Roberto Ruggiero
authors.initials: RR
authors.lastname: Braga
authors.forename: Paulo Eduardo Capel
authors.initials: PE
authors.lastname: Cardoso