title: Photobleaching of camphorquinone during polymerization of dimethacrylate-based resins.
abstract: OBJECTIVE
  The aim of this study was to compare the photobleaching rate of CQ in different dental resins.
  
  
  METHODS
  The photodecomposition rate of CQ/amine system in bis-GMA/TEGDMA, bis-EMA and UDMA polymerizing monomers was evaluated at different light intensities. The photobleaching of the CQ was studied by monitoring the decrease in light absorption as a function of continuous irradiation time. The absorption changes were assessed by recording the transmitted light that passed through samples of monomers containing CQ/amine.
  
  
  RESULTS
  Complete photobleaching of CQ was observed in all the monomer tested and the rate constant for the photobleaching was proportional to the radiation intensity. Hydrogen abstraction from amines by the excited CQ state via electron transfer and direct hydrogen abstraction from monomer structures were involved in the CQ photoreduction. CQ was photobleached in the absence of coinitiator in a dimethacrylate monomer containing a carbamate functional group (UDMA). This behavior was attributed to the presence of labile hydrogen atoms in the UDMA monomer. The CQ photobleaching rate constant in UDMA containing CQ/amine was similar to that in UDMA in the absence of amine. Moreover, the efficiency of CQ to photoinitiate the polymerization of UDMA in the absence of amine demonstrated that the radicals derived from the UDMA monomer via hydrogen abstraction are highly reactive toward double bonds.
  
  
  CONCLUSIONS
  CQ photoinitiates the polymerization of the UDMA monomer in the absence of amine and the efficiency of this process is comparable to that of traditional bis-GMA and bis-EMA monomers activated with CQ/amine.
authors.affiliation: Instituto de Investigación en Ciencia y Tecnología de Materiales, Mar del Plata University - National Research Council (CONICET), Av. Juan B. Justo 4302, 7600 Mar del Plata, Argentina.
authors.forename: Silvana
authors.initials: S
authors.lastname: Asmusen
authors.forename: Gustavo
authors.initials: G
authors.lastname: Arenas
authors.forename: Wayne D
authors.initials: WD
authors.lastname: Cook
authors.forename: Claudia
authors.initials: C
authors.lastname: Vallo
mesh_terms: D010129:4-Aminobenzoic Acid / Q000737:chemistry / Q000528:radiation effects; D000042:Absorption; D000465:Algorithms; D017438:Bisphenol A-Glycidyl Methacrylate / Q000737:chemistry / Q000528:radiation effects; D003188:Composite Resins / Q000737:chemistry* / Q000528:radiation effects; D003764:Dental Materials / Q000737:chemistry* / Q000528:radiation effects; D004735:Energy Transfer; D006801:Humans; D006859:Hydrogen / Q000737:chemistry / Q000528:radiation effects; D008027:Light; D008422:Materials Testing; D008689:Methacrylates / Q000737:chemistry* / Q000528:radiation effects; D011092:Polyethylene Glycols / Q000737:chemistry / Q000528:radiation effects; D011108:Polymers / Q000737:chemistry / Q000528:radiation effects; D011109:Polymethacrylic Acids / Q000737:chemistry / Q000528:radiation effects; D011140:Polyurethanes / Q000737:chemistry / Q000528:radiation effects; D011829:Radiation Dosage; D019163:Reducing Agents / Q000737:chemistry / Q000528:radiation effects; D013729:Terpenes / Q000737:chemistry / Q000528:radiation effects*; D013997:Time Factors; D062366:para-Aminobenzoates
chemical_list: D003188:Composite Resins; D003764:Dental Materials; D008689:Methacrylates; D011108:Polymers; D011109:Polymethacrylic Acids; D011140:Polyurethanes; D019163:Reducing Agents; D013729:Terpenes; C523330:ethyl 4-N,N-dimethylaminobenzoate; D062366:para-Aminobenzoates; C029824:urethane dimethacrylate luting resin; C020946:triethylene glycol dimethacrylate; C041979:2,2-bis-(4-(2-methacryloxyethoxy)phenyl)propane; D011092:Polyethylene Glycols; D017438:Bisphenol A-Glycidyl Methacrylate; C048339:camphoroquinone; D006859:Hydrogen; C049840:2-(dimethylamino)ethyl methacrylate; D010129:4-Aminobenzoic Acid