title: The reciprocity law concerning light dose relationships applied to BisGMA/TEGDMA photopolymers: theoretical analysis and experimental characterization.
abstract: OBJECTIVE
  A model BisGMA/TEGDMA unfilled resin was utilized to investigate the effect of varied irradiation intensity on the photopolymerization kinetics and shrinkage stress evolution, as a means for evaluation of the reciprocity relationship.
  
  
  METHODS
  Functional group conversion was determined by FTIR spectroscopy and polymerization shrinkage stress was obtained by a tensometer. Samples were polymerized with UV light from an EXFO Acticure with 0.1wt% photoinitiator. A one-dimensional kinetic model was utilized to predict the conversion-dose relationship.
  
  
  RESULTS
  As irradiation intensity increased, conversion decreased at a constant irradiation dose and the overall dose required to achieve full conversion increased. Methacrylate conversion ranged from 64±2% at 3mW/cm(2) to 78±1% at 24mW/cm(2) while the final shrinkage stress varied from 2.4±0.1MPa to 3.0±0.1MPa. The ultimate conversion and shrinkage stress levels achieved were dependent not only upon dose but also the irradiation intensity, in contrast to an idealized reciprocity relationship. A kinetic model was utilized to analyze this behavior and provide theoretical conversion profiles versus irradiation time and dose.
  
  
  CONCLUSIONS
  Analysis of the experimental and modeling results demonstrated that the polymerization kinetics do not and should not be expected to follow the reciprocity law behavior. As irradiation intensity is increased, the overall dose required to achieve full conversion also increased. Further, the ultimate conversion and shrinkage stress that are achieved are not dependent only upon dose but rather upon the irradiation intensity and corresponding polymerization rate.
authors.affiliation: Department of Chemical & Biological Engineering, University of Colorado, Boulder, CO, United States.
authors.forename: James W
authors.initials: JW
authors.lastname: Wydra
authors.affiliation: Department of Chemical & Biological Engineering, University of Colorado, Boulder, CO, United States.
authors.forename: Neil B
authors.initials: NB
authors.lastname: Cramer
authors.affiliation: Department of Craniofacial Biology, University of Colorado School of Dental Medicine, Aurora, CO, United States.
authors.forename: Jeffrey W
authors.initials: JW
authors.lastname: Stansbury
authors.affiliation: Department of Chemical & Biological Engineering, University of Colorado, Boulder, CO, United States; Department of Craniofacial Biology, University of Colorado School of Dental Medicine, Aurora, CO, United States; University of Colorado, Boulder, CO, United States. Electronic address: christopher.bowman@colorado.edu.
authors.forename: Christopher N
authors.initials: CN
authors.lastname: Bowman
mesh_terms: D004307:Dose-Response Relationship, Radiation; D008027:Light; D008956:Models, Chemical; D011092:Polyethylene Glycols / Q000737:chemistry*; D058105:Polymerization; D011109:Polymethacrylic Acids / Q000737:chemistry*; D017550:Spectroscopy, Fourier Transform Infrared
chemical_list: D011109:Polymethacrylic Acids; C020946:triethylene glycol dimethacrylate; D011092:Polyethylene Glycols
keywords: Dental restorative materials; Photopolymerization; Reciprocity law