title: Ester-free thiol-ene dental restoratives--Part A: Resin development.
abstract: OBJECTIVE
  To detail the development of ester-free thiol-ene dental resins with enhanced mechanical performance, limited potential for water uptake/leachables/degradation and low polymerization shrinkage stress.
  
  
  METHODS
  Thiol-terminated oligomers were prepared via a thiol-Michael reaction and a bulky tetra-allyl monomer containing urethane linkages was synthesized. The experimental oligomers and/or monomers were photopolymerized using visible light activation. Several thiol-ene formulations were investigated and their performance ranked by comparisons of the thermo-mechanical properties, polymerization shrinkage stress, water sorption/solubility, and reactivity with respect to a control comprising a conventional BisGMA/TEGDMA dental resin.
  
  
  RESULTS
  The ester-free thiol-ene formulations had significantly lower viscosities, water sorption and solubility than the BisGMA/TEGDMA control. Depending on the resin, the limiting functional conversions were equivalent to or greater than that of BisGMA/TEGDMA. At comparable conversions, lower shrinkage stress values were achieved by the thiol-ene systems. The polymerization shrinkage stress was dramatically reduced when the tetra-allyl monomer was used as the ene in ester-free thiol-ene mixtures. Although exhibiting lower Young's modulus, flexural strength, and glass transition temperatures, the toughness values associated with thiol-ene resins were greater than that of the BisGMA/TEGDMA control. In addition, the thiol-ene polymerization resulted in highly uniform polymer networks as indicated by the narrow tan delta peak widths.
  
  
  CONCLUSIONS
  Employing the developed thiol-ene resins in dental composites will reduce shrinkage stress and moisture absorption and form tougher materials. Furthermore, their low viscosities are expected to enable higher loadings of functionalized micro/nano-scale filler particles relevant for practical dental systems.
authors.affiliation: Department of Chemical and Biological Engineering, University of Colorado, 3415 Colorado Ave, JSC Biotech Building, Boulder, CO 80309, USA; Department of Polymer Chemistry, Faculty of Chemistry, MCS University, Gliniana St. 33, 20-614 Lublin, Poland.
authors.forename: Maciej
authors.initials: M
authors.lastname: Podgórski
authors.affiliation: Department of Chemical and Biological Engineering, University of Colorado, 3415 Colorado Ave, JSC Biotech Building, Boulder, CO 80309, USA.
authors.forename: Eftalda
authors.initials: E
authors.lastname: Becka
authors.affiliation: Department of Chemical and Biological Engineering, University of Colorado, 3415 Colorado Ave, JSC Biotech Building, Boulder, CO 80309, USA.
authors.forename: Mauro
authors.initials: M
authors.lastname: Claudino
authors.affiliation: Department of Chemical and Biological Engineering, University of Colorado, 3415 Colorado Ave, JSC Biotech Building, Boulder, CO 80309, USA.
authors.forename: Alexander
authors.initials: A
authors.lastname: Flores
authors.affiliation: Department of Chemical and Biological Engineering, University of Colorado, 3415 Colorado Ave, JSC Biotech Building, Boulder, CO 80309, USA.
authors.forename: Parag K
authors.initials: PK
authors.lastname: Shah
authors.affiliation: Department of Chemical and Biological Engineering, University of Colorado, 3415 Colorado Ave, JSC Biotech Building, Boulder, CO 80309, USA; Department of Craniofacial Biology, School of Dental Medicine, University of Colorado, Anschutz Medical Campus, Mail Stop 8310, 12800E. 19th Avenue, Aurora, CO 80045, USA.
authors.forename: Jeffrey W
authors.initials: JW
authors.lastname: Stansbury
authors.affiliation: Department of Chemical and Biological Engineering, University of Colorado, 3415 Colorado Ave, JSC Biotech Building, Boulder, CO 80309, USA. Electronic address: christopher.bowman@colorado.edu.
authors.forename: Christopher N
authors.initials: CN
authors.lastname: Bowman
mesh_terms: D017438:Bisphenol A-Glycidyl Methacrylate; D003188:Composite Resins; D008422:Materials Testing; D008689:Methacrylates; D018583:Pliability; D011092:Polyethylene Glycols; D011109:Polymethacrylic Acids; D013314:Stress, Mechanical; D013438:Sulfhydryl Compounds
chemical_list: D003188:Composite Resins; D008689:Methacrylates; D011109:Polymethacrylic Acids; D013438:Sulfhydryl Compounds; D011092:Polyethylene Glycols; D017438:Bisphenol A-Glycidyl Methacrylate
keywords: Dental resin; Photopolymerization; Shrinkage stress; Thiol–ene