title: Effect of cross-sectional design on the modulus of elasticity and toughness of fiber-reinforced composite materials.
abstract: BACKGROUND
  Many current fabrication protocols for dental fiber-reinforced composites use hand lay-up techniques and technician design input. Little information exists regarding how the manipulation of the cross-sectional design of a prosthesis might affect the modulus of elasticity and toughness.
  
  
  OBJECTIVE
  The aim of this study was to determine the effect of simple and complex cross-sectional designs on the modulus of elasticity and toughness of fiber-reinforced composite used for dental prostheses.
  
  
  METHODS
  Two particulate composites (BelleGlass HP and Targis) were reinforced with ultra-high-molecular-weight polyethylene fiber ribbon (Connect), woven E-glass fibers (Vectris Frame), or unidirectional R-glass fibers (Vectris Pontic). A range of fiber positions, orientations, or geometries were incorporated into the rhombic specimens (2 x 2 x 25 mm(3)) to achieve simple and complex experimental cross-sectional designs. The control specimen did not contain fiber reinforcement. Specimens (n=6) were stored 1 week in distilled water at 37 degrees C prior to 3-point load testing to determine the modulus of elasticity (GPa) and toughness (MPa). The data within each main fiber group were subjected to 1-way analysis of variance and a Tukey post hoc test (alpha=.05). Cross-sections of randomly selected test specimens (n=2) were made for scanning electron microscope (SEM) analysis of the fiber distribution.
  
  
  RESULTS
  The mean modulus of elasticity varied from 8.7 +/- 2.0 GPa (Targis control) to 21.6 +/- 1.4 GPa (2 unidirectional glass fiber reinforcements, 1 each at the tension side and the compression side). Mean toughness varied from 0.07 +/- 0.02 MPa (unidirectional glass fiber positioned at the compression side) as the lowest mean, to 4.53 +/- 0.89 MPa (unidirectional glass fiber positioned at the tension side) as the highest. Significant differences were identified between specimen groups in each main category (all groups P<.001, except modulus of elasticity of the woven E-glass groups, where P=.003). SEM micrographs showed fiber distribution in the cross section of test specimens to correspond with the intended fiber geometry.
  
  
  CONCLUSIONS
  The modulus of elasticity of the composite specimens increased when 1 or more glass fiber groups were located at the compression side of the specimen. Toughness was most effectively increased when 1 or more fiber groups were located at the tension side of the specimen.
authors.affiliation: Department of Restorative Dentistry, Division of Biomaterials and Biomechanics, Oregon Health and Science University, 611 SW Campus Drive, Portland, OR 97239, USA. dyers@ohsu.edu
authors.forename: Scott R
authors.initials: SR
authors.lastname: Dyer
authors.forename: Lippo V J
authors.initials: LV
authors.lastname: Lassila
authors.forename: Mikko
authors.initials: M
authors.lastname: Jokinen
authors.forename: Pekka K
authors.initials: PK
authors.lastname: Vallittu
mesh_terms: D000704:Analysis of Variance; D003188:Composite Resins / Q000737:chemistry*; D019245:Compressive Strength; D003799:Dental Stress Analysis; D004548:Elasticity; D005898:Glass; D005899:Glass Ionomer Cements; D008422:Materials Testing; D008689:Methacrylates; D008855:Microscopy, Electron, Scanning; D011095:Polyethylenes; D012823:Silicate Cement; D013718:Tensile Strength
chemical_list: D003188:Composite Resins; C495566:Connect resin; D005899:Glass Ionomer Cements; D008689:Methacrylates; D011095:Polyethylenes; C110370:belleGlass; C111282:dental polyglass; C009753:fiberglass; C111601:ultra-high molecular weight polyethylene; D012823:Silicate Cement