title: Photoinitiation chemistry affects light transmission and degree of conversion of curing experimental dental resin composites.
abstract: BACKGROUND
  The effect of photoinitiator and co-initiator chemistry on the setting reaction and degree of conversion of dental resin-based composites (RBCs) has rarely been determined explicitly. This work examines the effect of type and concentration of photoinitiator and co-initiator on the rate of change of light transmission throughout polymerisation and degree of conversion of model RBC formulations.
  
  
  METHODS
  Bisphenol-A diglycidyl ether dimethacrylate (bis-GMA) and triethylene glycol dimethacrylate (TEGDMA) (6:4 molar ratio) resins filled with silanized glass filler (74wt.%) and containing various photoinitiators (camphorquinone; CQ, 1-phenyl-1,2-propanedione; PPD, benzil; BZ), co-initiator types (N,N-dimethyl-p-amino benzoic acid ethyl ester; DABE, N,N-cyanoethyl methylaniline; CEMA, N,N-diethanol-p-toluidine; DEPT) and concentration (0.0-0.3% DABE) were polymerised using a halogen or LED light curing-unit (LCU) for 10, 20 and 40s. The setting reaction was monitored in real-time by measuring the light transmittance through the curing specimen and bulk degree of conversion (DC) evaluated using Fourier transform infra-red spectroscopy.
  
  
  RESULTS
  Specimens containing CQ and PPD cured with the halogen LCU did not have a significant effect on DC or changes in light transmission, although a significant increase in DC was observed for CQ compared with PPD specimens cured with the LED LCU. DABE and CEMA were more effective co-initiators than DEPT. Although DC was not limited by co-initiator concentration, the absence of a co-initiator resulted in marked differences in light transmission and decreased DC throughout 40s irradiation with each LCU type.
  
  
  CONCLUSIONS
  The spectral range emitted from different types of LCU and absorption characteristics of the photoinitiator chemistry of light-activated resin-based composites play a critical role in the efficiency of polymerisation.
authors.affiliation: 8th Floor, Biomaterials Unit, School of Dentistry, University of Birmingham, St Chad's Queensway, Birmingham B4 6NN, UK.
authors.forename: A
authors.initials: A
authors.lastname: Ogunyinka
authors.forename: W M
authors.initials: WM
authors.lastname: Palin
authors.forename: A C
authors.initials: AC
authors.lastname: Shortall
authors.forename: P M
authors.initials: PM
authors.lastname: Marquis
mesh_terms: D000704:Analysis of Variance; D017438:Bisphenol A-Glycidyl Methacrylate; D047188:Chalcones / Q000737:chemistry; D003188:Composite Resins / Q000737:chemistry* / Q000528:radiation effects*; D006244:Hardness; D008027:Light; D044367:Phase Transition; D010658:Phenylglyoxal / Q000031:analogs & derivatives / Q000737:chemistry; D010777:Photochemistry; D011092:Polyethylene Glycols; D011109:Polymethacrylic Acids; D017550:Spectroscopy, Fourier Transform Infrared; D013729:Terpenes / Q000737:chemistry
chemical_list: D047188:Chalcones; D003188:Composite Resins; D011109:Polymethacrylic Acids; D013729:Terpenes; C020946:triethylene glycol dimethacrylate; D011092:Polyethylene Glycols; D017438:Bisphenol A-Glycidyl Methacrylate; C048339:camphoroquinone; D010658:Phenylglyoxal; C006697:benzil; C100349:1-phenyl-1,2-propanedione