title: Ultra-fast light-curing resin composite with increased conversion and reduced monomer elution.
abstract: OBJECTIVE
  To test the null hypotheses that photoactive resin composites containing a Type I photoinitiator would exhibit reduced DC or increased monomer elution at substantially short curing times compared with materials based on a Type 2 ketone/amine system.
  
  
  METHODS
  Two experimental resin composites were prepared, using either Lucirin-TPO or camphorquinone/DMAEMA. Specimens were light-cured using appropriate spectral emission that coincided with the absorption properties of each initiator using different irradiation protocols (0.5, 1, 3, 9s at 500, 1000 and 2000mW/cm(2) for Lucirin-TPO based composites and 20 or 40s at 1000mW/cm(2) for Lucirin-TPO and camphorquinone-based composites). Degree of conversion (DC) was measured by Raman spectroscopy, propagating radical concentrations were collected by means of electron paramagnetic resonance (EPR) and monomer leaching was characterized using high-performance liquid chromatography (HPLC).
  
  
  RESULTS
  The null hypotheses were rejected, except for a single irradiation protocol (0.5s @ 500mW/cm(2)). Lucirin-TPO-based composites could cure 20 times faster and release at least 4 times less monomers in comparison to camphorquinone-based composites. At 1000mW/cm(2), and 1s irradiation time for curing times of 1s, Lucirin-TPO based composites displayed 10% higher DC. The difference in polymerization efficiency of Lucirin-TPO compared with camphorquinone-based resin composites were explained using EPR; the former showing a significantly greater yield of radicals which varied logarithmically with radiant exposure.
  
  
  CONCLUSIONS
  Lucirin-TPO is substantially more efficient at absorbing and converting photon energy when using a curing-light with an appropriate spectral emission and otherwise a limitation noted in several previous publications. At concentrations of 0.0134mol/L, Lucirin-TPO-based composites require a minimum light intensity of 1000mW/cm(2) and an exposure time of 1s to provide significantly improved DC and minimal elution compared with a conventional photoinitiator system. The use of a wide range of curing protocols in the current experiment has realized the significant potential of Lucirin-TPO and its impact for clinical applications, in replacement to materials using camphorquinone.
authors.affiliation: 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: lucrandolph@gmail.com.
authors.forename: Luc D
authors.initials: LD
authors.lastname: Randolph
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: 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.
authors.forename: Sabine
authors.initials: S
authors.lastname: Bebelman
authors.affiliation: 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.
authors.forename: Jacques
authors.initials: J
authors.lastname: Devaux
authors.affiliation: Louvain Drug Research Institute, Université catholique de Louvain, Brussels, Belgium; CRIBIO (Center for Research and Engineering on Biomaterials), Brussels, Belgium.
authors.forename: Bernard
authors.initials: B
authors.lastname: Gallez
authors.affiliation: 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: Gaetane
authors.initials: G
authors.lastname: Leloup
authors.affiliation: 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: D003188:Composite Resins / Q000737:chemistry*; D055117:Curing Lights, Dental
chemical_list: D003188:Composite Resins
keywords: Conversion; Elution; Irradiation protocols; Kinetics; Polymerization efficiency