title: Photopolymerization of highly filled dimethacrylate-based composites using Type I or Type II photoinitiators and varying co-monomer ratios.
abstract: OBJECTIVE
  The use of a Type I photoinitiator (monoacylphosphine oxide, MAPO) was described as advantageous in a model formulation, as compared to the conventional Type II photoinitiator (Camphorquinone, CQ). The aim of the present work was to study the kinetics of polymerization of various composite mixtures (20-40-60-80 mol%) of bisphenol A glycidyl dimethacrylate/triethylene glycol dimethacrylate (BisGMA/TegDMA) containing either CQ or MAPO, based on real-time measurements and on the characterization of various post-cure characteristics.
  
  
  METHODS
  Polymerization kinetics were monitored by Fourier-transform near-infrared spectroscopy (FT-NIRS) and dielectric analysis (DEA). A range of postcure properties was also investigated.
  
  
  RESULTS
  FT-NIRS and DEA proved complementary to follow the fast kinetics observed with both systems. Autodecceleration occurred after ≈1 s irradiation for MAPO-composites and ≈5-10 s for CQ-composites. Conversion decreased with increasing initial viscosity for both photoinitiating systems. However despite shorter light exposure (3s for MAPO vs 20s for CQ-composites), MAPO-composites yielded higher conversions for all co-monomer mixtures, except at 20 mol% BisGMA, the less viscous material. MAPO systems were associated with increased amounts of trapped free radicals, improved flexural strength and modulus, and reduced free monomer release for all co-monomer ratios, except at 20 mol% BisGMA.
  
  
  CONCLUSIONS
  This work confirms the major influence of the initiation system both on the conversion and network cross-linking of highly-filled composites, and further highlights the advantages of using MAPO photoinitiating systems in highly-filled dimethacrylate-based composites provided that sufficient BisGMA content (>40 mol%) and adapted light spectrum are used.
authors.affiliation: ADDB, Louvain Drug Research Institute, Université catholique de Louvain, Brussels, Belgium; Institute of Condensed Matter and Nanosciences, Bio- and Soft- Matter, Université catholique de Louvain, Louvain-la-Neuve, Belgium; CRIBIO (Center for Research and Engineering on Biomaterials), Brussels, Belgium. Electronic address: luc.randolph@uclouvain.be.
authors.forename: Luc D
authors.initials: LD
authors.lastname: Randolph
authors.affiliation: Bonn-Rhein-Sieg University of Applied Sciences, Department of Natural Sciences, von Liebig Str. 20, D-53359 Rheinbach, Germany.
authors.forename: Johannes
authors.initials: J
authors.lastname: Steinhaus
authors.affiliation: Bonn-Rhein-Sieg University of Applied Sciences, Department of Natural Sciences, von Liebig Str. 20, D-53359 Rheinbach, Germany.
authors.forename: Bernhard
authors.initials: B
authors.lastname: Möginger
authors.affiliation: REMA, Louvain Drug Research Institute, Université catholique de Louvain, Brussels, Belgium.
authors.forename: Bernard
authors.initials: B
authors.lastname: Gallez
authors.affiliation: Department of Chemical and Biological Engineering, University of Colorado, Boulder, CO 80309, USA.
authors.forename: Jeffrey
authors.initials: J
authors.lastname: Stansbury
authors.affiliation: Biomaterials Unit, University of Birmingham, College of Medical and Dental Sciences, School of Dentistry, St Chad's Queensway, Birmingham B4 6NN, UK.
authors.forename: William M
authors.initials: WM
authors.lastname: Palin
authors.affiliation: ADDB, Louvain Drug Research Institute, Université catholique de Louvain, Brussels, Belgium; Institute of Condensed Matter and Nanosciences, Bio- and Soft- Matter, Université catholique de Louvain, Louvain-la-Neuve, Belgium; CRIBIO (Center for Research and Engineering on Biomaterials), Brussels, Belgium; School of Dentistry and Stomatology, Université catholique de Louvain, Brussels, Belgium.
authors.forename: Gaëtane
authors.initials: G
authors.lastname: Leloup
authors.affiliation: ADDB, Louvain Drug Research Institute, Université catholique de Louvain, Brussels, Belgium; Institute of Condensed Matter and Nanosciences, Bio- and Soft- Matter, Université catholique de Louvain, Louvain-la-Neuve, Belgium; CRIBIO (Center for Research and Engineering on Biomaterials), Brussels, Belgium; School of Dentistry and Stomatology, Université catholique de Louvain, Brussels, Belgium.
authors.forename: Julian G
authors.initials: JG
authors.lastname: Leprince
mesh_terms: D017438:Bisphenol A-Glycidyl Methacrylate / Q000737:chemistry*; D002164:Camphor / Q000031:analogs & derivatives* / Q000737:chemistry; D003188:Composite Resins / Q000737:chemistry*; D055117:Curing Lights, Dental; D055119:Elastic Modulus; D006244:Hardness; D008422:Materials Testing; D008689:Methacrylates / Q000737:chemistry; D010087:Oxides / Q000737:chemistry*; D010720:Phosphines / Q000737:chemistry*; D011092:Polyethylene Glycols / Q000737:chemistry*; D058105:Polymerization; D011109:Polymethacrylic Acids / Q000737:chemistry*; D017550:Spectroscopy, Fourier Transform Infrared; D014783:Viscosity
chemical_list: D003188:Composite Resins; D008689:Methacrylates; D010087:Oxides; D010720:Phosphines; D011109:Polymethacrylic Acids; C020946:triethylene glycol dimethacrylate; D011092:Polyethylene Glycols; D017438:Bisphenol A-Glycidyl Methacrylate; D002164:Camphor; C049840:2-(dimethylamino)ethyl methacrylate; C553149:camphorquinone
keywords: Camphorquinone; Dielectric analysis; Dimethacrylate; Elution; Kinetics; MAPO; Photoinitiator; Photopolymerization; Resin composite; Trapped radicals