title: A critical analysis of the degree of conversion of resin-based luting cements.
abstract: OBJECTIVE
  This study analyzed the degree of conversion (DC%) of four resin-based cements (All Ceram, Enforce, Rely X ARC and Variolink II) activated by two modes (chemical and dual), and evaluated the decrease of DC% in the dual mode promoted by the interposition of a 2.0-mm-thick IPS Empress 2 disc.
  
  
  METHODS
  In the chemical activation, the resin-based cements were prepared by mixing equal amounts of base and catalyst pastes. In the dual activation, after mixing, the cements were light-activated at 650 mW/cm² for 40 s. In a third group, the cements were light-activated through a 2.0-mm-thick IPS Empress 2 disc. The DC% was evaluated in a FT-IR spectrometer equipped with an attenuated total reflectance crystal (ATR). The data were analyzed by two-way ANOVA and Tukey's HSD test.
  
  
  RESULTS
  For all resin-based cements, the DC% was significantly higher with dual activation, followed by dual activation through IPS Empress 2, and chemical activation (p<0.05). Irrespective of the activation mode, Rely X presented the highest DC% (p<0.05). Chemically activated Variolink and All Ceram showed the worst results (p<0.05). The DC% decreased significantly when activation was performed through a 2.0-mm-thick IPS Empress 2 disc (p<0.05).
  
  
  CONCLUSIONS
  The results of the present study suggest that resin-based cements could present low DC% when the materials are dually activated through 2.0 mm of reinforced ceramic materials with translucency equal to or less than that of IPS-Empress 2.
authors.affiliation: Department of Restorative Dentistry, School of Dentistry, Federal Fluminense University, Niterói, RJ, Brazil.
authors.forename: Jaime Dutra
authors.initials: JD
authors.lastname: Noronha Filho
authors.forename: Natasha Lamego
authors.initials: NL
authors.lastname: Brandão
authors.forename: Laiza Tatiana
authors.initials: LT
authors.lastname: Poskus
authors.forename: José Guilherme Antunes
authors.initials: JG
authors.lastname: Guimarães
authors.forename: Eduardo Moreira da
authors.initials: EM
authors.lastname: Silva
mesh_terms: D017438:Bisphenol A-Glycidyl Methacrylate / Q000737:chemistry / Q000528:radiation effects; D002516:Ceramics / Q000737:chemistry; D055117:Curing Lights, Dental; D006244:Hardness; D008422:Materials Testing; D008689:Methacrylates / Q000737:chemistry / Q000528:radiation effects; D011092:Polyethylene Glycols / Q000737:chemistry / Q000528:radiation effects; D058105:Polymerization / Q000528:radiation effects*; D011109:Polymethacrylic Acids / Q000737:chemistry / Q000528:radiation effects; D019279:Resin Cements / Q000737:chemistry* / Q000528:radiation effects; D017550:Spectroscopy, Fourier Transform Infrared; D013499:Surface Properties; D013997:Time Factors
chemical_list: D008689:Methacrylates; D011109:Polymethacrylic Acids; D019279:Resin Cements; C020946:triethylene glycol dimethacrylate; C041979:2,2-bis-(4-(2-methacryloxyethoxy)phenyl)propane; D011092:Polyethylene Glycols; D017438:Bisphenol A-Glycidyl Methacrylate