title: Examining exposure reciprocity in a resin based composite using high irradiance levels and real-time degree of conversion values.
abstract: OBJECTIVE
  Exposure reciprocity suggests that, as long as the same radiant exposure is delivered, different combinations of irradiance and exposure time will achieve the same degree of resin polymerization. This study examined the validity of exposure reciprocity using real time degree of conversion results from one commercial flowable dental resin. Additionally a new fitting function to describe the polymerization kinetics is proposed.
  
  
  METHODS
  A Plasma Arc Light Curing Unit (LCU) was used to deliver 0.75, 1.2, 1.5, 3.7 or 7.5 W/cm(2) to 2mm thick samples of Tetric EvoFlow (Ivoclar Vivadent). The irradiances and radiant exposures received by the resin were determined using an integrating sphere connected to a fiber-optic spectrometer. The degree of conversion (DC) was recorded at a rate of 8.5 measurements a second at the bottom of the resin using attenuated total reflectance Fourier Transform mid-infrared spectroscopy (FT-MIR). Five specimens were exposed at each irradiance level. The DC reached after 170s and after 5, 10 and 15 J/cm(2) had been delivered was compared using analysis of variance and Fisher's PLSD post hoc multiple comparison tests (alpha=0.05).
  
  
  RESULTS
  The same DC values were not reached after the same radiant exposures of 5, 10 and 15 J/cm(2) had been delivered at an irradiance of 3.7 and 7.5 W/cm(2). Thus exposure reciprocity was not supported for Tetric EvoFlow (p<0.05).
  
  
  CONCLUSIONS
  For Tetric EvoFlow, there was no significant difference in the DC when 5, 10 and 15J/cm(2) were delivered at irradiance levels of 0.75, 1.2 and 1.5 W/cm(2). The optimum combination of irradiance and exposure time for this commercial dental resin may be close to 1.5 W/cm(2) for 12s.
authors: Dalhousie University, Department of Dental Clinical Sciences, Faculty of Dentistry, Halifax, Canada; Bonn-Rhein-Sieg University of Applied Sciences, Department of Natural Sciences, Rheinbach, Germany; FH Aachen University of Applied Sciences, Department of Natural Sciences, Jülich, Germany.
authors: Daniela
authors: D
authors: Selig
authors: Dalhousie University, Department of Dental Clinical Sciences, Faculty of Dentistry, Halifax, Canada; Bonn-Rhein-Sieg University of Applied Sciences, Department of Natural Sciences, Rheinbach, Germany; Tomas Bata University in Zlin, Faculty of Technology, Department of Production Engineering, Zlin, Czech Republic; Tomas Bata University in Zlin, University Institute, Centre of Polymer Systems, Zlin, Czech Republic.
authors: Thomas
authors: T
authors: Haenel
authors: Tomas Bata University in Zlin, Faculty of Technology, Department of Production Engineering, Zlin, Czech Republic; Tomas Bata University in Zlin, University Institute, Centre of Polymer Systems, Zlin, Czech Republic.
authors: Berenika
authors: B
authors: Hausnerová
authors: Bonn-Rhein-Sieg University of Applied Sciences, Department of Natural Sciences, Rheinbach, Germany.
authors: Bernhard
authors: B
authors: Moeginger
authors: Dalhousie University, Department of Physics and Atmospheric Sciences, Halifax, Canada.
authors: Daniel
authors: D
authors: Labrie
authors: Dalhousie University, Department of Dental Clinical Sciences, Faculty of Dentistry, Halifax, Canada.
authors: Braden
authors: B
authors: Sullivan
authors: Dalhousie University, Department of Dental Clinical Sciences, Faculty of Dentistry, Halifax, Canada. Electronic address: rbprice@dal.ca.
authors: Richard B T
authors: RB
authors: Price
mesh_terms: D003188:Composite Resins / Q000737:chemistry* / Q000528:radiation effects*; D055117:Curing Lights, Dental; D055115:Light-Curing of Dental Adhesives; D008422:Materials Testing; D058105:Polymerization; D017550:Spectroscopy, Fourier Transform Infrared
chemical_list: D003188:Composite Resins; C452226:tetric flow composite resin
keywords: Degree of conversion; Dental curing light; Exposure reciprocity; Flowable composite; Irradiance; Mid FTIR; Polymerization kinetics; Radiant exposure