title: Effect of exposure intensity and post-cure temperature storage on hardness of contemporary photo-activated composites.
abstract: OBJECTIVE
  The effect of variation in post-exposure storage temperature (18 vs. 37 degrees C) and light intensity (200 vs. 500mW/cm(2)) on micro-hardness of seven light-activated resin composite materials, cured with a Prismetics Mk II (Dentsply) light activation unit, were studied.
  
  
  METHODS
  Hardness values at the upper and lower surfaces of 2mm thick disc shaped specimens of seven light-cured resin composite materials (Herculite XRV and Prodigy/Kerr, Z100 and Silux Plus/3M, TPH/Dentsply, Pertac-Hybrid/Espe, and Charisma/Kulzer), which had been stored dry, were determined 24h after irradiation with a Prismetics Mk II (Dentsply) light activation unit.
  
  
  RESULTS
  Hardness values varied with product, surface, storage temperature, and curing light intensity. In no case did the hardness at the lower surface equal that of the upper surface, and the combination of 500mW/cm(2) intensity and 37 degrees C storage produced the best hardness results at the lower surface.
  
  
  CONCLUSIONS
  Material composition had a significant influence on surface hardness. Only one of the seven products (TPH) produced a mean hardness values at the lower surface >80% of the maximum mean upper surface hardness obtained for the corresponding product at 500mW/cm(2) intensity/37 degrees C storage temperature when subjected to all four test regimes. Despite optimum post-cure storage conditions, 200mW/cm(2) intensity curing for 40s will not produce acceptable hardness at the lower surface of 2mm increments of the majority of products tested.
authors.affiliation: The University of Birmingham, The Dental School, St. Chad's Queensway, B4 6NN, Birmingham, UK.
authors.forename: S C
authors.initials: SC
authors.lastname: Quance
authors.forename: A C
authors.initials: AC
authors.lastname: Shortall
authors.forename: E
authors.initials: E
authors.lastname: Harrington
authors.forename: P J
authors.initials: PJ
authors.lastname: Lumley
mesh_terms: D000704:Analysis of Variance; D017438:Bisphenol A-Glycidyl Methacrylate / Q000737:chemistry; D003188:Composite Resins / Q000737:chemistry* / Q000528:radiation effects; D004356:Drug Storage; D006244:Hardness; D006801:Humans; D008027:Light; D008029:Lighting / Q000295:instrumentation; D008422:Materials Testing; D019279:Resin Cements / Q000737:chemistry; D012822:Silicon Dioxide; D013223:Statistics as Topic; D013499:Surface Properties; D013696:Temperature; D015040:Zirconium
chemical_list: C084111:Charisma composite resin; D003188:Composite Resins; C079764:Pertac hybrid; C099128:Prodigy; D019279:Resin Cements; C113300:TPH hybrid; C083568:Z100 composite resin; C065770:Herculite XR; C074741:Silux Plus; D017438:Bisphenol A-Glycidyl Methacrylate; D012822:Silicon Dioxide; D015040:Zirconium