title: Investigations of step-growth thiol-ene polymerizations for novel dental restoratives.
abstract: OBJECTIVE
  The goal of this work was to investigate the feasibility of formulating novel dental restorative materials that utilize a step-growth thiol-ene photopolymerization. Particularly, we are aiming to significantly reduce the polymerization shrinkage and shrinkage stress while retaining adequate physical properties as compared to current dimethacrylatre-based systems.
  
  
  METHODS
  The thiol-ene system is composed of a 4:3 molar mixture of triallyl-1,3,5-triazine-2,4,6-trione (TATATO) and pentaerythritol tetramercaptopropionate (PETMP). The simultaneous measurement of shrinkage stress and functional group conversion was performed. Solvent extraction of unreacted monomers and dynamic mechanical analysis on the polymer networks that were formed were also studied. Flexural strength was measured for both filled and unfilled PETMP/TATATO and Bis-GMA/TEGDMA systems.
  
  
  RESULTS
  Photopolymerization of PETMP/TATATO occurs at a much higher rate, with the maximum polymerization rate six times faster, than Bis-GMA/TEGDMA cured under the identical conditions. The results from the simultaneous measurement of shrinkage stress and conversion showed that the onset of shrinkage stress coincides with the delayed gel point conversion, which is predicted to be 41% for the 3:4 stoichiometric PETMP/TATATO resin composition. The maximum shrinkage stress developed for PETMP/TATATO was about 0.4 MPa, which was only approximately 14% of the maximum shrinkage stress of the Bis-GMA/TEGDMA system. Adequate flexural strength and flexural modulus values were obtained for both filled and unfilled PETMP/TATATO systems.
  
  
  CONCLUSIONS
  The dramatically reduced shrinkage stress, increased polymerization rate, significance increased functional group conversion, and decreased leachable species are all benefits for the use-of thiol-ene systems as potential dental restorative materials.
authors.affiliation: Department of Chemical and Biological Engineering, Engineering Center, ECCH 111, University of Colorado at Boulder, 80309-0424, USA.
authors.forename: Hui
authors.initials: H
authors.lastname: Lu
authors.forename: Jacquelyn A
authors.initials: JA
authors.lastname: Carioscia
authors.forename: Jeffery W
authors.initials: JW
authors.lastname: Stansbury
authors.forename: Christopher N
authors.initials: CN
authors.lastname: Bowman
mesh_terms: D015097:3-Mercaptopropionic Acid / Q000031:analogs & derivatives* / Q000737:chemistry; D000498:Allyl Compounds / Q000737:chemistry*; D017438:Bisphenol A-Glycidyl Methacrylate / Q000737:chemistry; D055598:Chemical Phenomena; D002627:Chemistry, Physical; D003188:Composite Resins / Q000737:chemistry; D003764:Dental Materials / Q000737:chemistry*; D004548:Elasticity; D004987:Ethers / Q000737:chemistry; D005026:Ethylene Glycols / Q000737:chemistry; D005240:Feasibility Studies; D006801:Humans; D008422:Materials Testing; D018583:Pliability; D011092:Polyethylene Glycols / Q000737:chemistry; D011108:Polymers / Q000737:chemistry; D011109:Polymethacrylic Acids / Q000737:chemistry; D011409:Propylene Glycols / Q000737:chemistry*; D013314:Stress, Mechanical; D013438:Sulfhydryl Compounds / Q000737:chemistry; D013499:Surface Properties; D013997:Time Factors; D014227:Triazines / Q000737:chemistry*; D014753:Vinyl Compounds / Q000737:chemistry
chemical_list: D000498:Allyl Compounds; D003188:Composite Resins; D003764:Dental Materials; D004987:Ethers; D005026:Ethylene Glycols; D011108:Polymers; D011109:Polymethacrylic Acids; D011409:Propylene Glycols; D013438:Sulfhydryl Compounds; D014227:Triazines; D014753:Vinyl Compounds; C501435:pentaerythritol tetra(3-mercaptopropionate); C507611:triallyl-1,3,5-triazine-2,4,6-trione; C501434:triethyleneglycol divinylether; C020946:triethylene glycol dimethacrylate; C100195:vinyl ether; D011092:Polyethylene Glycols; D017438:Bisphenol A-Glycidyl Methacrylate; D015097:3-Mercaptopropionic Acid; C501433:1,6-hexanedithiol