title: Polymerization kinetics and impact of post polymerization on the Degree of Conversion of bulk-fill resin-composite at clinically relevant depth.
abstract: OBJECTIVE
  Since bulk-fill (BF) resin composites should cure efficiently to a depth up to 4mm, the aim of the study was to determine the time-dependence of degree of conversion (DC) at that depth during 24h post-irradiation.
  
  
  METHODS
  Eight representative BF resin composites were studied [x-tra base (XTB), Venus Bulk Fill (VBF), Tetric EvoCeram Bulk Fill (TECBF), Sonic Fill (SF), Filtek Bulk Fill (FBF), everX Posterior (eXP), Beautifil-Bulk Flowable (BBF), Beautifil-Bulk Restorative (BBR)]. Specimens were fabricated in white Delrin moulds of 4mm height and 5mm internal diameter directly on an attenuated total reflectance (ATR) accessory attachment of an (FTIR) spectrometer (Nicolet iS50, Thermo Fisher, Madison, USA). Upper specimen surfaces were irradiated in situ for 20 s with an LED curing unit (Elipar S10 with average tip irradiance of 1200 mW/cm(2)). Spectra from the lower surface were recorded continuously in real-time for 5 min and then at 30 and 60 min and 24h post irradiation.
  
  
  RESULTS
  Mean ranges of DC4mm (%) of the materials at 4mm depth were 39-67; 48-75; 45-74; and 50-72 at 5, 30 and 60 min and 24h respectively. DCs for XTB, VBF, TECBF, FBF, BBR increased significantly 30 min after irradiation (p<0.05) and were not affected by subsequent time up to 24h (p>0.05). DC for SF was not affected by subsequent time after 5 min (p>0.05). For eXP and BBF, DC increased 24h after irradiation (p<0.05). The data were described by the superposition of two exponential functions characterising the gel phase (described by parameters a, b) and the glass phase (described by parameters c and d).
  
  
  CONCLUSIONS
  Post polymerization impact of bulk-fill composites is material dependent. Five materials exhibited their maximum DC4mm already 30 min after starting the irradiation while DC4mm for two materials optimized after 24h. BF materials were found to exhibit after 24h a DC between 50 and 72% at 4mm depth under the stated irradiation conditions.
authors: Biomaterials Science Research Group, School of Dentistry, University of Manchester, UK; College of Dentistry, King Saud University, Riyadh, Saudi Arabia.
authors: Khold
authors: K
authors: Al-Ahdal
authors: Ludwig-Maximilians-University of Munich, Germany. Electronic address: nilie@dent-med.uni-muenchen.de.
authors: Nicoleta
authors: N
authors: Ilie
authors: Biomaterials Science Research Group, School of Dentistry, University of Manchester, UK.
authors: Nick
authors: N
authors: Silikas
authors: Biomaterials Science Research Group, School of Dentistry, University of Manchester, UK; Photon Science Institute, University of Manchester, UK.
authors: David C
authors: DC
authors: Watts
mesh_terms: D003188:Composite Resins / Q000737:chemistry* / Q000528:radiation effects; D003764:Dental Materials / Q000737:chemistry* / Q000528:radiation effects; D055119:Elastic Modulus; D006244:Hardness; D007700:Kinetics; D008422:Materials Testing; D044367:Phase Transition; D058105:Polymerization; D017550:Spectroscopy, Fourier Transform Infrared; D013314:Stress, Mechanical; D013696:Temperature; D013997:Time Factors
chemical_list: D003188:Composite Resins; D003764:Dental Materials
keywords: Bulk-fill; Degree of conversion; Depth of cure; Polymerization kinetics; Resin-composite