title: Investigation of mechanical properties of experimental Bis-GMA/TEGDMA dental composite resins containing various mass fractions of silica nanoparticles.
abstract: OBJECTIVE
  Mechanical properties of dental composite resins need to be improved in order to enhance their performance for applications in direct restorations. Application of nanoparticles in this field is a recent development. The aim of this study was to investigate the mechanical properties of experimental composites containing various mass fractions of silica nanoparticles.
  
  
  METHODS
  Experimental composites were composed of a visible-light-curing monomer mixture (70 wt% Bis-GMA and 30 wt% TEGDMA) and silica nanoparticles of a size ranging from 20 nm to 50 nm modified with gamma-methacryloxy propyl trimethoxy silane (gamma-MPS) as reinforcing filler. The composites were classified into four groups according to their filler mass fractions ranging from 20% to 50%. Following the same preparation procedure, a conventional composite was also fabricated consisting of a mass percentage of 60% silica fillers having particle sizes ranging from 10 microm to 40 microm in the same organic matrix, which served as control. Ten specimens were prepared of each experimental group and also of the control. Fracture toughness was measured using single-edge notched bend (SENB) specimens. Specimen fracture surfaces were mounted on aluminum stubs with carbon cement, sputter-coated with gold and examined under scanning electron microscopy (SEM). Flexural strength was evaluated through a standard three-point bending test and Vickers microhardness test was performed to investigate the hardness of the samples.
  
  
  RESULTS
  Filler mass fraction had a significant effect on composite properties. Fracture toughness, flexural strength, and hardness of composites at filler mass fraction of 40% of silica nanoparticles were (mean +/- SD) 1.43 +/- 0.08 MPa.m(1/2), 149.74 +/- 8.14 MPa, and 62.12 +/- 3.07 VHN, respectively; relevant values for composites at 50% mass fraction of silica nanoparticles were 1.38 +/- 0.07 MPa.m(1/2), 122.83 +/- 6.13 MPa, and 70.69 +/- 3.67 VHN, respectively, all of which were significantly higher than 1.07 +/- 0.06 MPa.m(1/2), 104.61 +/- 8.73 MPa, and 52.14 +/- 4.02 VHN of the control, respectively (Tukey's multiple comparison test; family confidence coefficient = 0.95). Measured values for composites at 20% mass fraction of silica nanoparticles were 0.94 +/- 0.06 MPa.m(1/2), 103.41 +/- 7.62 MPa, and 42.87 +/- 2.61 VHN, respectively; relevant values for composites at 30% mass fraction of silica nanoparticles were 1.16 +/- 0.07 MPa.m(1/2), 127.91 +/- 7.05 MPa, and 51.78 +/- 3.41 VHN, respectively.
  
  
  CONCLUSIONS
  Reinforcement of dental composite resins with silica nanoparticles resulted in a significant increase in the evaluated mechanical properties in comparison with the conventional composite. The filler mass fraction played a critical role in determining the composite's mechanical properties.
authors.affiliation: Department of Metallurgy & Materials Engineering, Iran University of Science and Technology, Tehran 16844, Iran.
authors.forename: Mohammad
authors.initials: M
authors.lastname: Hosseinalipour
authors.forename: Jafar
authors.initials: J
authors.lastname: Javadpour
authors.forename: Hamidreza
authors.initials: H
authors.lastname: Rezaie
authors.forename: Taimaz
authors.initials: T
authors.lastname: Dadras
authors.forename: Amir Nemati
authors.initials: AN
authors.lastname: Hayati
mesh_terms: D000704:Analysis of Variance; D017438:Bisphenol A-Glycidyl Methacrylate; D003188:Composite Resins / Q000737:chemistry*; D003799:Dental Stress Analysis; D006244:Hardness; D008422:Materials Testing; D008689:Methacrylates; D053758:Nanoparticles; D010316:Particle Size; D018583:Pliability; D011092:Polyethylene Glycols; D011109:Polymethacrylic Acids; D012821:Silanes; D012822:Silicon Dioxide
chemical_list: D003188:Composite Resins; D008689:Methacrylates; D011109:Polymethacrylic Acids; D012821:Silanes; C020946:triethylene glycol dimethacrylate; C017492:methacryloxypropyltrimethoxysilane; D011092:Polyethylene Glycols; D017438:Bisphenol A-Glycidyl Methacrylate; D012822:Silicon Dioxide