title: Contraction stress related to composite inorganic content.
abstract: OBJECTIVE
  The role of inorganic content on physical properties of resin composites is well known. However, its influence on polymerization stress development has not been established. The aim of this investigation was to evaluate the influence of inorganic fraction on polymerization stress and its determinants, namely, volumetric shrinkage, elastic modulus and degree of conversion.
  
  
  METHODS
  Eight experimental composites containing 1:1 BisGMA (bisphenylglycidyl dimethacrylate):TEGDMA (triethylene glycol dimethacrylate) (in mol) and barium glass at increasing concentrations from 25 to 60 vol.% (5% increments) were tested. Stress was determined in a universal test machine using acrylic as bonding substrate. Nominal polymerization stress was obtained diving the maximum load by the cross-surface area. Shrinkage was measured using a water picnometer. Elastic modulus was obtained by three-point flexural test. Degree of conversion was determined by FT-Raman spectroscopy.
  
  
  RESULTS
  Polymerization stress and shrinkage showed inverse relationships with filler content (R(2)=0.965 and R(2)=0.966, respectively). Elastic modulus presented a direct correlation with inorganic content (R(2)=0.984). Degree of conversion did not vary significantly. Polymerization stress showed a strong direct correlation with shrinkage (R(2)=0.982) and inverse with elastic modulus (R(2)=0.966).
  
  
  CONCLUSIONS
  High inorganic contents were associated with low polymerization stress values, which can be explained by the reduced volumetric shrinkage presented by heavily filled composites.
authors.affiliation: Department of Dental Materials, School of Dentistry, University of São Paulo, São Paulo, SP, Brazil. fgoncalves@usp.br
authors.forename: F
authors.initials: F
authors.lastname: Gonçalves
authors.forename: Y
authors.initials: Y
authors.lastname: Kawano
authors.forename: R R
authors.initials: RR
authors.lastname: Braga
mesh_terms: D000704:Analysis of Variance; D017609:Barium Compounds; D017438:Bisphenol A-Glycidyl Methacrylate; D003188:Composite Resins / Q000737:chemistry* / Q000528:radiation effects; D018772:Dental Marginal Adaptation; D003799:Dental Stress Analysis; D055119:Elastic Modulus; D006244:Hardness; D007287:Inorganic Chemicals; D055115:Light-Curing of Dental Adhesives; D008422:Materials Testing; D010316:Particle Size; D044367:Phase Transition; D018583:Pliability; D011092:Polyethylene Glycols; D011109:Polymethacrylic Acids; D012044:Regression Analysis; D012822:Silicon Dioxide; D017550:Spectroscopy, Fourier Transform Infrared
chemical_list: D017609:Barium Compounds; D003188:Composite Resins; D007287:Inorganic Chemicals; D011109:Polymethacrylic Acids; C102738:barium glass filler; C020946:triethylene glycol dimethacrylate; D011092:Polyethylene Glycols; D017438:Bisphenol A-Glycidyl Methacrylate; D012822:Silicon Dioxide