title: Network structure of Bis-GMA- and UDMA-based resin systems.
abstract: OBJECTIVE
  The commonly used dental base monomers 2,2-bis[p-(2'-hydroxy-3'-methacryloxypropoxy)phenylene]propane (Bis-GMA) and 1,6-bis(methacryloxy-2-ethoxycarbonylamino)-2,4,4-trimethylhexane (UDMA) require the use of a diluent monomer, such as triethylene glycol dimethacrylate (TEGDMA). The aim of this study was to measure double bond conversion of UDMA/TEGDMA and Bis-GMA/TEGDMA polymeric systems, determine the leachable portion, and analyze network formation by evaluating crosslinking and pendant double bonds.
  
  
  METHODS
  UDMA or Bis-GMA was combined with TEGDMA in systematic increments and irradiated to form light cured polymers. Fourier transform infrared spectroscopy in the near-infrared region was used to measure double bond conversion. The leachable sol fraction was analyzed by 1H NMR. Resin composites were formulated. Flexural strength was measured by three-point bending and volumetric shrinkage was determined with a mercury dilatometer.
  
  
  RESULTS
  The amount of base monomer greatly influenced double bond conversion, sol fraction, and crosslinking. Increasing base monomer concentration decreased double bond conversion, increased the leachable fraction, and decreased crosslinking and network formation. At mole fractions higher than 0.125, the UDMA polymers had significantly higher conversion than the Bis-GMA polymers. Bis-GMA polymers had higher leachable amounts of unreacted monomer, while UDMA mixtures had more crosslinking than the Bis-GMA mixtures. In regards to the physical properties of resin composites, increasing the base monomer improved flexural strength and decreased volumetric shrinkage.
  
  
  CONCLUSIONS
  This systematic study for the evaluation of conversion, leachability, crosslinking, and network structure along with physical properties, like volumetric shrinkage and flexural strength, are required for the optimization of competing desirable properties for the development of durable materials.
authors.affiliation: American Dental Association Foundation, Paffenbarger Research Center, National Institute of Standards and Technology, Gaithersburg, MD 20899-8546, USA.
authors.forename: Cynthia J E
authors.initials: CJ
authors.lastname: Floyd
authors.forename: Sabine H
authors.initials: SH
authors.lastname: Dickens
mesh_terms: D017438:Bisphenol A-Glycidyl Methacrylate / Q000737:chemistry; D003188:Composite Resins / Q000737:chemistry*; D003799:Dental Stress Analysis; D016014:Linear Models; D008689:Methacrylates / Q000737:chemistry; D015394:Molecular Structure; D044367:Phase Transition; D018583:Pliability; D011092:Polyethylene Glycols / Q000737:chemistry; D011109:Polymethacrylic Acids / Q000737:chemistry; D011140:Polyurethanes / Q000737:chemistry; D017550:Spectroscopy, Fourier Transform Infrared
chemical_list: D003188:Composite Resins; D008689:Methacrylates; D011109:Polymethacrylic Acids; D011140:Polyurethanes; C029824:urethane dimethacrylate luting resin; C080508:poly(triethylene glycol dimethacrylate-1,6-bis(methacryloxy-2-ethoxycarbonylamino)-2,4,4-trimethylhexane) copolymer; D011092:Polyethylene Glycols; D017438:Bisphenol A-Glycidyl Methacrylate