title: The effect of resin matrix composition on the polymerization shrinkage and rheological properties of experimental dental composites.
abstract: OBJECTIVE
  This study was undertaken to evaluate the effect of the resin matrix composition of experimental composites on their polymerization shrinkage and rheological properties.
  
  
  METHODS
  Six experimental composites consisting of varying ratios of Bis-GMA, TEGDMA, and UDMA were made. All composites had the same amount of filler (barium-aluminum-silicate glass, 76.5 wt.%) and initiator concentrations (camphorquinone, 1.7 wt.%). To investigate the effects of different resin matrices on the polymerization shrinkage, a newly developed measurement method was used. Using a rotational rheometer, a dynamic oscillatory shear test was undertaken to evaluate the rheological properties, including the storage shear modulus (G'), loss shear modulus (G''), loss tangent (tandelta), phase angle (delta), and complex viscosity (eta*) of the experimental composites as a function of frequency (0.1-10Hz).
  
  
  RESULTS
  The polymerization shrinkage and complex viscosity of the experimental composites ranged from 2.61 to 3.88 vol.% and from 3.8 to 181.4Pas, respectively. The experimental composite composed of 17.5% Bis-GMA and 4.4% TEGDMA showed the lowest shrinkage and highest viscosity. The composite composed of 8.7% Bis-GMA and 13.1% TEGDMA showed the highest shrinkage and lowest viscosity. With increasing TEGDMA content, the polymerization shrinkage increased but the viscosity decreased. The substitution of UDMA for TEGDMA reduced the shrinkage level but increased viscosity. There was an inverse relationship between the polymerization shrinkage and complex viscosity. All experimental composites exhibited pseudoplasticity.
  
  
  CONCLUSIONS
  Within the limitations of this study, resin matrix composition significantly affected the volumetric shrinkage and rheological properties of the experimental composites.
authors.affiliation: Restorative Dentistry, Biomaterials Unit, College of Dentistry, King Faisal University, Dammam, Saudi Arabia.
authors.forename: Ayman
authors.initials: A
authors.lastname: Ellakwa
authors.forename: Nakyeon
authors.initials: N
authors.lastname: Cho
authors.forename: In Bog
authors.initials: IB
authors.lastname: Lee
mesh_terms: D000180:Acrylic Resins / Q000737:chemistry*; D017438:Bisphenol A-Glycidyl Methacrylate / Q000737:chemistry; D003188:Composite Resins / Q000737:chemistry*; D011092:Polyethylene Glycols / Q000737:chemistry; D011108:Polymers; D011109:Polymethacrylic Acids / Q000737:chemistry; D011140:Polyurethanes / Q000737:chemistry*; D012212:Rheology; D033081:Shear Strength; D014783:Viscosity
chemical_list: D000180:Acrylic Resins; C029012:Composite Dental Resin; D003188:Composite Resins; D011108:Polymers; D011109:Polymethacrylic Acids; D011140:Polyurethanes; C020946:triethylene glycol dimethacrylate; D011092:Polyethylene Glycols; D017438:Bisphenol A-Glycidyl Methacrylate