title: Evaluation of fracture toughness and mechanical properties of ternary thiol-ene-methacrylate systems as resin matrix for dental restorative composites.
abstract: OBJECTIVE
  Study and evaluation of fracture toughness, flexural and dynamic mechanical properties, and crosslink density of ternary thiol-ene-methacrylate systems and comparison with corresponding conventional methacrylate system were considered in the present study.
  
  
  METHODS
  Urethane tetra allyl ether monomer (UTAE) was synthesized as ene monomer. Different formulations were prepared based on combination of UTAE, BisGMA/TEGDMA and a tetrathiol monomer (PETMP). The photocuring reaction was conducted under visible light using BD/CQ combination as photoinitiator system. Mechanical properties were evaluated via measuring flexural strength, flexural modulus and fracture toughness. Scanning electron microscopy (SEM) was utilized to study the morphology of the fractured specimen's cross section. Viscoelastic properties of the samples were also determined by dynamic mechanical thermal analysis (DMTA). The same study was performed on a conventional methacrylate system. The data were analyzed and compared by ANOVA and Tukey HSD tests (significance level=0.05).
  
  
  RESULTS
  The results showed improvement in fracture toughness of the specimens containing thiol-ene moieties. DMTA revealed a lower glass transition temperature and more homogenous structure for thiol-ene containing specimens in comparison to the system containing merely methacrylate monomer. The flexural modulus and flexural strength of the specimens with higher thiol-ene content were lower than the neat methacrylate system. The SEM micrographs of the fractured surface of specimens with higher methacrylate content were smooth and mirror-like (shiny) which represent brittle fracture.
  
  
  CONCLUSIONS
  The thiol-ene-methacrylate system can be used as resin matrix of dental composites with enhanced fracture toughness in comparison to the methacrylate analogous.
authors.affiliation: Iran Polymer and Petrochemical Institute IPPI, P.O. Box 14965/115, Tehran, Iran.
authors.forename: Saeed
authors.initials: S
authors.lastname: Beigi
authors.forename: Hamid
authors.initials: H
authors.lastname: Yeganeh
authors.forename: Mohammad
authors.initials: M
authors.lastname: Atai
mesh_terms: D003188:Composite Resins / Q000737:chemistry*; D003432:Cross-Linking Reagents; D003793:Dental Restoration, Permanent; D003799:Dental Stress Analysis; D004548:Elasticity; D055115:Light-Curing of Dental Adhesives; D008422:Materials Testing; D055595:Mechanical Phenomena; D008689:Methacrylates / Q000737:chemistry*; D018583:Pliability; D058105:Polymerization; D011140:Polyurethanes / Q000737:chemistry; D013438:Sulfhydryl Compounds / Q000737:chemistry*; D013499:Surface Properties; D014783:Viscosity
chemical_list: D003188:Composite Resins; D003432:Cross-Linking Reagents; D008689:Methacrylates; D011140:Polyurethanes; D013438:Sulfhydryl Compounds; C404582:urethane tetramethacrylate; C091839:urethanetrimethacrylate