title: Degree of conversion and mechanical properties of a BisGMA:TEGDMA composite as a function of the applied radiant exposure.
abstract: OBJECTIVE
  Verify the influence of radiant exposure (H) on composite degree of conversion (DC) and mechanical properties.
  
  
  METHODS
  Composite was photoactivated with 3, 6, 12, 24, or 48 J/cm(2). Properties were measured after 48-h dry storage at room temperature. DC was determined on the flat surfaces of 6 mm x 2 mm disk-shaped specimens using FTIR. Flexural strength (FS) and modulus (FM) were accessed by three-point bending. Knoop microhardness number (KHN) was measured on fragments of FS specimens. Data were analyzed by one-way ANOVA/Tukey test, Student's t-test, and regression analysis.
  
  
  RESULTS
  DC/top between 6 and 12 J/cm(2) and between 24 and 48 J/cm(2) were not statistically different. No differences between DC/top and bottom were detected. DC/bottom, FM, and KHN/top showed significant differences among all H levels. FS did not vary between 12 and 24 J/cm(2) and between 24 and 48 J/cm(2). KHN/bottom at 3 and 6 J/cm(2) was similar. KHN between top and bottom was different up to 12 J/cm(2). Regression analyses having H as independent variable showed a plateau region above 24 J/cm(2). KHN increased exponentially (top) or linearly (bottom) with DC. FS and FM increased almost linearly with DC/bottom up to 55% conversion.
  
  
  CONCLUSIONS
  DC and mechanical properties increased with radiant exposure. Variables leveled off at high H levels.
authors.affiliation: Department of Biomaterials and Oral Biochemistry, School of Dentistry, University of São Paulo, São Paulo, Brazil.
authors.forename: Fernanda C
authors.initials: FC
authors.lastname: Calheiros
authors.forename: Márcia
authors.initials: M
authors.lastname: Daronch
authors.forename: Frederick A
authors.initials: FA
authors.lastname: Rueggeberg
authors.forename: Roberto R
authors.initials: RR
authors.lastname: Braga
mesh_terms: D017438:Bisphenol A-Glycidyl Methacrylate / Q000737:chemistry; D003188:Composite Resins / Q000737:chemistry; D004307:Dose-Response Relationship, Radiation; D006244:Hardness; D008027:Light; D010777:Photochemistry; D011092:Polyethylene Glycols / Q000737:chemistry; D011109:Polymethacrylic Acids / Q000737:chemistry
chemical_list: D003188:Composite Resins; D011109:Polymethacrylic Acids; C020946:triethylene glycol dimethacrylate; D011092:Polyethylene Glycols; D017438:Bisphenol A-Glycidyl Methacrylate