title: The effect of light intensity on double bond conversion and flexural strength of a model, unfilled dental resin.
abstract: OBJECTIVE
  Two visible light sources (tungsten-quartz-halogen and xenon-arc plasma) with vastly different intensities (200 and 1800 mW/cm(2)) but similar spectral outputs, were used to examine the effects of light intensity on conversion and flexural strength of a model dental resin formulation (75/25wt% bis-GMA/TEGDMA).
  
  
  METHODS
  The exact same polymer samples were used to correlate double bond conversion (measured with near-IR spectroscopy) to flexural strength, both immediately after light exposure and after storage.
  
  
  RESULTS
  In general, polymers which were irradiated with the high light intensity source exhibited greater double bond conversion. However, increasing the light intensity also increased the maximum temperature reached during polymerization. Therefore, the greater double bond conversion was caused by a combination of both photo and thermal effects. Regardless of the light intensity, a single linear relationship existed between conversion and final flexural strength (measured 4 days after cure) over the conversion range analyzed (50-80%). However, deviations from linearity were noted in several samples that were tested immediately after exposure.
  
  
  CONCLUSIONS
  These findings illustrate that light intensity does not affect the final flexural strength of a dental resin as long as the final conversions are similar.
authors.affiliation: Department of Chemical Engineering, Engineering Center, University of Colorado at Boulder, ROOM ECCH 111, Campus Box 424, Boulder, CO 80309-0424, USA.
authors.forename: Lale G
authors.initials: LG
authors.lastname: Lovell
authors.forename: Sheldon M
authors.initials: SM
authors.lastname: Newman
authors.forename: Matthew M
authors.initials: MM
authors.lastname: Donaldson
authors.forename: Christopher N
authors.initials: CN
authors.lastname: Bowman
mesh_terms: D000704:Analysis of Variance; D017438:Bisphenol A-Glycidyl Methacrylate / Q000737:chemistry / Q000528:radiation effects; D003188:Composite Resins / Q000737:chemistry* / Q000528:radiation effects*; D006219:Halogens; D008027:Light; D008422:Materials Testing; D015394:Molecular Structure; D018583:Pliability / Q000528:radiation effects; D011092:Polyethylene Glycols / Q000737:chemistry / Q000528:radiation effects; D011108:Polymers / Q000737:chemistry; D011109:Polymethacrylic Acids / Q000737:chemistry / Q000528:radiation effects; D012044:Regression Analysis; D013696:Temperature; D014978:Xenon
chemical_list: D003188:Composite Resins; D006219:Halogens; D011108:Polymers; D011109:Polymethacrylic Acids; C020946:triethylene glycol dimethacrylate; D014978:Xenon; D011092:Polyethylene Glycols; D017438:Bisphenol A-Glycidyl Methacrylate