title: Assessment of the polymerization contraction stress of composites photoactivated by halogen light and light-emitting diode.
abstract: OBJECTIVE
  The aim of this study was to compare the polymerization contraction stress of composites photoactivated by two light sources: quartz tungsten halogen light (QTH) and light emitting diode (LED).
  
  
  METHODS
  Glass rods were fabricated (5.0 mm X 5.0 cm) and one of the surfaces was air abraded with aluminum oxide. An adhesive was applied to this surface and photoactivated by LED. The glass rods were assembled to a Universal Testing machine (Instron - 5565) and the composite were applied to the lower rod using a manual instrument. The upper rod was placed closer, at 2 mm, and an extensometer was attached to the rods. The twenty composites were polymerized by either by QTH (N.=10) or LED (N.=10). Polymerization was carried out using two apparatuses positioned in opposite sides, which were simultaneously activated for 30 seconds. Contraction stress was analyzed twice: shortly after polymerization (t30s) and 30 minutes later (t30min).
  
  
  RESULTS
  The contraction stress for all composites was higher at t30min than at t30s, regardless of the activation source. Z100 showed lower contraction stress values (P<0.05) compared to the other composites. Regarding to Charisma and TPH, the photoactivation source had no influence on contraction stress, except for Z100 at t30min.
  
  
  CONCLUSIONS
  It was concluded that composite composition is the factor that most influence the polymerization contraction stress.
authors.affiliation: Department of Restorative Dentistry, Dental Materials Area, Piracicaba School of Dentistry, Campinas State UniversityPiracicaba, São Paulo, Brazil. lucasgarcia@fop.unicamp.br
authors.forename: L
authors.initials: L
authors.lastname: da Fonseca Roberti Garcia
authors.forename: L
authors.initials: L
authors.lastname: Zago Naves
authors.forename: L
authors.initials: L
authors.lastname: Correr-Sobrinho
authors.forename: S
authors.initials: S
authors.lastname: Consani
mesh_terms: D003188:Composite Resins / Q000528:radiation effects*; D055117:Curing Lights, Dental; D066298:In Vitro Techniques; D008027:Light; D055115:Light-Curing of Dental Adhesives / Q000379:methods*; D008422:Materials Testing; D055668:Photochemical Processes; D019279:Resin Cements / Q000528:radiation effects*; D012822:Silicon Dioxide / Q000528:radiation effects*; D013314:Stress, Mechanical; D015040:Zirconium / Q000528:radiation effects*
chemical_list: C084111:Charisma composite resin; D003188:Composite Resins; D019279:Resin Cements; C113300:TPH hybrid; C083568:Z100 composite resin; D012822:Silicon Dioxide; C041330:Scotchbond; D015040:Zirconium