title: Stress relaxation of trithiocarbonate-dimethacrylate-based dental composites.
abstract: OBJECTIVE
  To reduce polymerization-induced shrinkage stress while maintaining mechanical properties, reversible addition-fragmentation chain transfer (RAFT)-capable functional groups were incorporated into a photopolymerizable dimethacrylate-based dental composite. We hypothesize that the incorporation of trithiocarbonate-based RAFT functional groups into conventional dimethacrylate dental resins will reduce polymerization stress.
  
  
  METHODS
  A trithiocarbonate dimethacrylate (TTCDMA) monomer, capable of undergoing radical-mediated RAFT, is mixed with 70 wt% BisGMA (bisphenylglycidyl dimethacrylate) and compared to a conventional dental resin comprised of TEGDMA (triethylene glycol dimethacrylate) and 70 wt% BisGMA. The shrinkage stress and methacrylate conversion were simultaneously measured during polymerization. The fracture toughness and elastic modulus were measured to evaluate the effect of the TTCDMA monomer on the mechanical properties. All the materials used herein were evaluated as a composite, including 75 wt% silica fillers. ANOVA (CI 95%) was conducted to assess the differences between the means.
  
  
  RESULTS
  The TTCDMA composite exhibited a 65% stress reduction compared with TEGDMA-BisGMA though the reaction rate was slower than the conventional dental composite, owing to the additional RAFT reaction. The fracture toughness and elastic modulus of the TTCDMA-based composite were not significantly different than in the TEGDMA-based composite, while the T(g) was decreased by 30 °C to 155 ± 2 °C.
  
  
  CONCLUSIONS
  Despite only replacing the reactive-diluent, significant and dramatic stress reduction was observed while maintaining the elastic modulus and fracture toughness. This new RAFT-capable monomer shows great promise to replace the reactive diluent in BisGMA-based dental materials. Formulation optimization and further exploration of other RAFT-capable functional groups will provide further stress reduction in dental materials.
authors.affiliation: Department of Chemical and Biological Engineering, Engineering Center, CB 424, University of Colorado, Boulder, CO 80309, USA.
authors.forename: Hee Young
authors.initials: HY
authors.lastname: Park
authors.forename: Christopher J
authors.initials: CJ
authors.lastname: Kloxin
authors.forename: Mark F
authors.initials: MF
authors.lastname: Fordney
authors.forename: Christopher N
authors.initials: CN
authors.lastname: Bowman
mesh_terms: D017438:Bisphenol A-Glycidyl Methacrylate; D003188:Composite Resins / Q000737:chemistry*; D003799:Dental Stress Analysis; D055119:Elastic Modulus; D006244:Hardness; D055115:Light-Curing of Dental Adhesives; D008689:Methacrylates / Q000737:chemistry*; D015394:Molecular Structure; D011092:Polyethylene Glycols; D058105:Polymerization; D011109:Polymethacrylic Acids; D013871:Thiones
chemical_list: D003188:Composite Resins; D008689:Methacrylates; D011109:Polymethacrylic Acids; D013871:Thiones; C020946:triethylene glycol dimethacrylate; D011092:Polyethylene Glycols; D017438:Bisphenol A-Glycidyl Methacrylate; C013321:trithiocarbonic acid