title: Effects of adding silver nanoparticles on the toughening of dental porcelain.
abstract: BACKGROUND
  Dental porcelains currently used for ceramic restorations are brittle, and it is sometimes necessary to replace fractured or chipped restorations. Porcelain is fragile and exhibits elastic deformation rather than plastic deformation, leading to fracture or chipping of restorations.
  
  
  OBJECTIVE
  The purpose of this study was to investigate the toughening of porcelain through the addition of silver nanoparticles.
  
  
  METHODS
  Noritake Super (NS) Porcelain AAA modified with the addition of silver nanoparticles was used. The concentration of silver in the solution was adjusted to 100, 200, 500, and 1000 ppm (Ag100, Ag200, Ag500, and Ag1000). The Vickers hardness (Hv) and median crack length extending from the corner of each indent were measured. The fracture toughness (KIC) was calculated by the indentation method. Optical reflectance spectra were recorded by using a spectrometer in the wavelength range of 200 to 700 nm. X-ray diffraction spectroscopy, color measurement, Fourier transform infrared spectroscopy, and electron probe microanalysis were also performed. The observed values of Hv, 2a, E, and KIC were compared and evaluated with a 1-way ANOVA, followed by the Bonferroni method (α=.05).
  
  
  RESULTS
  The addition of silver nanoparticles significantly increased the Hv of all specimens with the exception of Ag100. The median crack length was significantly smaller in Ag500 (104.5 μm, SD: 11.9) and Ag1000 (100.0 µm, SD: 5.5). Significantly higher toughness values were observed for Ag500 (1.54 MPa·m(1/2), SD: 0.05) and Ag1000 (1.51 MPa·m(1/2), SD: 0.08) than for the control (1.36 MPa·m(1/2), SD: 0.03). In terms of color difference, Ag500 (5.08, SD:1.32) and Ag1000 (5.47, SD:1.05) had values significantly greater than ΔE*=2.69.
  
  
  CONCLUSIONS
  The addition of silver nanoparticles significantly increased the fracture toughness and Vickers hardness of the NS porcelain. A residual compressive stress was generated due to the ion exchange reaction and differential thermal expansion of the silver metal nanoparticles. However, the addition of Ag500 and Ag1000 nanoparticles led to a color change.
authors.affiliation: Department of Prosthodontics, Division of Oral Functional Science and Rehabilitation, Asahi University School of Dentistry, Gifu 501-0296, Japan. uno@dent.asahi-u.ac.jp
authors.forename: Mitsunori
authors.initials: M
authors.lastname: Uno
authors.forename: Masakazu
authors.initials: M
authors.lastname: Kurachi
authors.forename: Nobukazu
authors.initials: N
authors.lastname: Wakamatsu
authors.forename: Yutaka
authors.initials: Y
authors.lastname: Doi
mesh_terms: D000535:Aluminum / Q000737:chemistry; D003116:Color; D003776:Dental Porcelain / Q000737:chemistry*; D055119:Elastic Modulus; D004548:Elasticity; D004577:Electron Probe Microanalysis; D006244:Hardness; D006358:Hot Temperature; D006801:Humans; D007474:Ion Exchange; D008422:Materials Testing; D055595:Mechanical Phenomena; D053758:Nanoparticles / Q000737:chemistry*; D010100:Oxygen / Q000737:chemistry; D010316:Particle Size; D012825:Silicon / Q000737:chemistry; D012834:Silver / Q000737:chemistry*; D013055:Spectrophotometry, Infrared; D013056:Spectrophotometry, Ultraviolet; D017550:Spectroscopy, Fourier Transform Infrared; D013314:Stress, Mechanical; D013499:Surface Properties; D013816:Thermodynamics; D014961:X-Ray Diffraction
chemical_list: D003776:Dental Porcelain; D012834:Silver; D000535:Aluminum; D010100:Oxygen; D012825:Silicon