title: Comparison of two methods for measuring the polymerization characteristics of flowable resin composites.
abstract: OBJECTIVE
  The purpose of this study was to compare two methods for assessing the polymerization characteristics of flowable resin composites.
  
  
  METHODS
  Two different flowable resin composites and a hybrid resin composite control were investigated. In order to measure the volumetric shrinkage (DeltaV), each material was placed into a mould and extruded into a water-filled dilatometer. The specimens were then light irradiated for 30s using a curing unit with the power density adjusted to either 100 or 600mW/cm(2). For the speckle contrast measurement, each resin composite was condensed into a glass tube and irradiated. The laser-speckle field was recorded in a digital frame. The calculated values were obtained for each pair of adjacent patterns and the changes in speckle contrast as a function of time were obtained.
  
  
  RESULTS
  The average DeltaV values of the resins after 180s ranged from approximately 3.3 to 4.4% for the flowable composites and from approximately 1.8 to 2.3% for the hybrid composite control. The overall magnitude of the speckle contrasts decreased soon after the initial light exposure commenced and gradually increased thereafter. The speckle contrast measurements revealed changes in the pastes due to the polymerization of the flowable resins that were greater than those obtained with the water-filled dilatometer.
  
  
  CONCLUSIONS
  These data suggest that the polymerization characteristics of flowable resins can be measured successfully using two different methods. Moreover, our findings are of clinical relevance, as the data obtained under laboratory conditions might give an indication of the suitability of flowable resin composites for specific clinical applications.
authors.affiliation: Department of Operative Dentistry, Nihon University School of Dentistry, 1-8-13 Kanda-Surugadai, Chiyoda-ku, Tokyo 101-8310, Japan.
authors.forename: Akira
authors.initials: A
authors.lastname: Yamamoto
authors.forename: Masashi
authors.initials: M
authors.lastname: Miyazaki
authors.forename: Akitomo
authors.initials: A
authors.lastname: Rikuta
authors.forename: Hiroyasu
authors.initials: H
authors.lastname: Kurokawa
authors.forename: Toshiki
authors.initials: T
authors.lastname: Takamizawa
mesh_terms: D000704:Analysis of Variance; D017438:Bisphenol A-Glycidyl Methacrylate / Q000737:chemistry / Q000528:radiation effects; D003188:Composite Resins / Q000737:chemistry / Q000528:radiation effects*; D003793:Dental Restoration, Permanent; D003799:Dental Stress Analysis / Q000379:methods; D006244:Hardness; D008027:Light; D008422:Materials Testing; D044367:Phase Transition; D012212:Rheology; D012542:Scattering, Radiation; D014783:Viscosity
chemical_list: C470433:Beautifil composite resin; D003188:Composite Resins; C083468:Lite-fil CR; D017438:Bisphenol A-Glycidyl Methacrylate