title: Properties of methacrylate-thiol-ene formulations as dental restorative materials.
abstract: OBJECTIVE
  The objective of this study was to evaluate ternary methacrylate-thiol-ene systems, with varying thiol-ene content and thiol:ene stoichiometry, as dental restorative resin materials. It was hypothesized that an off-stoichiometric thiol-ene component would enhance interactions between the methacrylate and thiol-ene processes to reduce shrinkage stress while maintaining equivalent mechanical properties.
  
  
  METHODS
  Polymerization kinetics and functional group conversions were determined by Fourier transform infrared spectroscopy (FTIR). Cured resin mechanical properties were evaluated using a three-point flexural test, carried out with a hydraulic universal test system. Polymerization shrinkage stress was measured with a tensometer coupled with simultaneous real-time conversion monitoring.
  
  
  RESULTS
  The incorporation of thiol-ene mixtures as reactive diluents into conventional dimethacrylate resins previously was shown to combine synergistically advantageous methacrylate mechanical properties with the improved polymerization kinetics and reduced shrinkage stress of thiol-ene systems. In these systems, due to thiol consumption resultant from both the thiol-ene reaction and chain transfer involving the methacrylate polymerization, the optimum thiol:ene stoichiometry deviates from the traditional 1:1 ratio. Increasing the thiol:ene stoichiometry up to 3:1 results in systems with equivalent flexural modulus, 6-20% reduced flexural strength, and 5-33% reduced shrinkage stress relative to 1:1 stoichiometric thiol:ene systems.
  
  
  CONCLUSIONS
  Due to their improved overall functional group conversion, and shrinkage stress reduction while maintaining equivalent flexural modulus, methacrylate-thiol-ene resins, particularly those with excess thiol, beyond the conventional 1:1 thiol:ene molar ratio, yield superior dental restorative materials compared with purely dimethacrylate resins.
authors.affiliation: Department of Chemical & Biological Engineering, University of Colorado, Boulder, CO 80309, United States. neil.cramer@colorado.edu
authors.forename: Neil B
authors.initials: NB
authors.lastname: Cramer
authors.forename: Charles L
authors.initials: CL
authors.lastname: Couch
authors.forename: Kathleen M
authors.initials: KM
authors.lastname: Schreck
authors.forename: Jordan E
authors.initials: JE
authors.lastname: Boulden
authors.forename: Robert
authors.initials: R
authors.lastname: Wydra
authors.forename: Jeffrey W
authors.initials: JW
authors.lastname: Stansbury
authors.forename: Christopher N
authors.initials: CN
authors.lastname: Bowman
mesh_terms: D000498:Allyl Compounds / Q000737:chemistry*; D000704:Analysis of Variance; D003188:Composite Resins / Q000737:chemistry*; D018772:Dental Marginal Adaptation; D003793:Dental Restoration, Permanent; D003799:Dental Stress Analysis; D007700:Kinetics; D055115:Light-Curing of Dental Adhesives; D008422:Materials Testing; D008689:Methacrylates / Q000737:chemistry; D009636:Norbornanes / Q000737:chemistry*; D044367:Phase Transition; D018583:Pliability; D017550:Spectroscopy, Fourier Transform Infrared; D018709:Statistics, Nonparametric; D014227:Triazines / Q000737:chemistry*
chemical_list: D000498:Allyl Compounds; D003188:Composite Resins; D008689:Methacrylates; D009636:Norbornanes; D014227:Triazines; C507611:triallyl-1,3,5-triazine-2,4,6-trione