title: Influence of matrix composition on polymerization stress development of experimental composites.
abstract: OBJECTIVE
  Stress development at the tooth/restoration interface is one of the most important reasons for failure of adhesive restorations. The aim of this study was to evaluate the influence of BisGMA/TEGDMA (B/T) and UDMA/TEGDMA (U/T) ratios on polymerization stress (PS) and on the variables related to its development: degree of conversion (DC), polymerization maximum rate (Rp(max)), volumetric shrinkage (VS), elastic modulus (E), stress relaxation (SR) and viscosity of experimental composites.
  
  
  METHODS
  Composites were formulated containing B/T or U/T in mol% ratios of 2:8, 3:7, 4:6, 5:5, 6:4, 7:3 and 8:2, and 15 wt% of fumed silica. PS was determined with a universal testing machine. VS was measured with a linometer. E and SR were obtained in three-point bending. DC and Rp(max) were determined by real time NIR spectroscopy and viscosity was measured in viscometer. Data were submitted to one-way ANOVA, Tukey test (alpha=0.05%) and regression analyses.
  
  
  RESULTS
  PS, VS, E and DC decreased and viscosity and Rp(max) increased with base monomer content in both series. PS showed strong correlation with VS, DC and viscosity. PS, VS and DC were higher and viscosity was lower for UDMA-based materials.
  
  
  CONCLUSIONS
  Reduced viscosity, kinetics parameters and molecular characteristics led UDMA-based composites to elevated conversion and relatively lower PS at lower TEGDMA contents, compared to B/T composites.
authors.affiliation: Department of Dental Materials, University of São Paulo, Av. Prof. Lineu Prestes, 2227, São Paulo, SP 05508-900, Brazil. fgoncalves@usp.br
authors.forename: Flávia
authors.initials: F
authors.lastname: Gonçalves
authors.forename: Carmem C S
authors.initials: CC
authors.lastname: Pfeifer
authors.forename: Jeffrey W
authors.initials: JW
authors.lastname: Stansbury
authors.forename: Sheldon M
authors.initials: SM
authors.lastname: Newman
authors.forename: Roberto R
authors.initials: RR
authors.lastname: Braga
mesh_terms: D000704:Analysis of Variance; D017438:Bisphenol A-Glycidyl Methacrylate; D003188:Composite Resins / Q000737:chemistry*; D018772:Dental Marginal Adaptation; D003799:Dental Stress Analysis; D055119:Elastic Modulus; D007700:Kinetics; D055115:Light-Curing of Dental Adhesives; D008422:Materials Testing; D008689:Methacrylates; D044367:Phase Transition; D011092:Polyethylene Glycols; D011109:Polymethacrylic Acids; D011140:Polyurethanes; D012044:Regression Analysis; D014783:Viscosity
chemical_list: D003188:Composite Resins; D008689:Methacrylates; D011109:Polymethacrylic Acids; D011140:Polyurethanes; C029824:urethane dimethacrylate luting resin; C020946:triethylene glycol dimethacrylate; D011092:Polyethylene Glycols; D017438:Bisphenol A-Glycidyl Methacrylate