title: Effect of immediate or delayed light activation on curing kinetics and shrinkage stress of dual-cure resin cements.
abstract: OBJECTIVE
  This study evaluated the effect of light activation (absence, immediate, or delayed) on conversion kinetics and polymerization stress of three commercial dual-cured resin cements (Enforce, RelyX ARC, and Panavia F).
  
  
  METHODS
  Degree of conversion (DC) was monitored for 30 minutes using real-time near–Fourier transform infrared spectroscopy. The cement was mixed, placed on the spectrometer sample holder, and light activated either immediately or after five minutes (delayed light activation). When no light activation was performed, the materials were protected from light exposure (control). DC was evaluated at five and 30 minutes postmixture. Maximum rates of polymerization (Rp(max)) were obtained from the first derivative of the DC vs time curve. Polymerization stress was monitored for 30 minutes in 1-mm-thick specimens inserted between two cylinders attached to a universal testing machine. Data were submitted to analysis of variance/Tukey tests (α=0.05).
  
  
  RESULTS
  Immediate light activation promoted the highest DC at five minutes. At 30 minutes, only RelyX ARC did not present a significant difference in DC between activation modes. Enforce and Panavia F presented higher Rp(max) for immediate and delayed light-activation, respectively. RelyX ARC showed similar Rp(max) for all activation modes. The absence of light activation resulted in the lowest stress followed by delayed light activation, while immediate light activation led to the highest values. RelyX ARC showed higher stress than Enforce, while the stress of Panavia F was similar to that of the others.
  
  
  CONCLUSIONS
  Delayed light activation reduced the polymerization stress of the resin cements tested without jeopardizing DC.
authors.affiliation: Department of Dentistry, Federal University of Sergipe, Aracaju, SE, Brazil. faria_silva@ufs.br
authors.forename: Andre
authors.initials: A
authors.lastname: Faria-e-Silva
authors.forename: Leticia
authors.initials: L
authors.lastname: Boaro
authors.forename: Roberto
authors.initials: R
authors.lastname: Braga
authors.forename: Evandro
authors.initials: E
authors.lastname: Piva
authors.forename: Vanessa
authors.initials: V
authors.lastname: Arias
authors.forename: Luis
authors.initials: L
authors.lastname: Martins
mesh_terms: D017438:Bisphenol A-Glycidyl Methacrylate / Q000737:chemistry / Q000528:radiation effects; D003799:Dental Stress Analysis / Q000295:instrumentation; D006801:Humans; D007700:Kinetics; D008027:Light; D055115:Light-Curing of Dental Adhesives; D008422:Materials Testing; D055668:Photochemical Processes; 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*; D055116:Self-Curing of Dental Resins; D017550:Spectroscopy, Fourier Transform Infrared; D013314:Stress, Mechanical; D013997:Time Factors
chemical_list: C103503:EnForce-Sure Cure; C438843:Panavia-Fluoro; D011109:Polymethacrylic Acids; C462240:RelyX ARC; D019279:Resin Cements; D011092:Polyethylene Glycols; D017438:Bisphenol A-Glycidyl Methacrylate