title: Effect of fiber addition on slow crack growth of a dental porcelain.
abstract: OBJECTIVE
  To evaluate the effect of the processing method (conventional sintering, S, and heat-pressing, HP) and addition of potassium titanate fibers, PTF, on the microstructure, mechanical properties (flexural strength, σf, and Weibull parameters, m and σ5%), slow crack growth parameters n (stress corrosion susceptibility coefficient), and optical properties (translucency parameter, TP, and opalescence index, OI) of a feldsphatic dental porcelain.
  
  
  METHODS
  Disks (n = 240, Ø12 × 1 mm) of porcelain (Vintage-Halo, Shofu) were produced using S and HP methods with and without addition of 10 wt% (conventional sintering) or 5 wt% (heat-pressing) of PTF. For the S method, porcelain was sintered in a conventional furnace. In the HP technique, refractory molds were produced by lost wax technique. The porcelain slurry was dry-pressed (3t/30s) to form a cylinder with 12 mm (diameter) and 20mm (height), which was heat-pressed for 5 min/3.5 bar into the mold. Specimens were tested for biaxial flexural strength in artificial saliva at 37°C. Weibull analysis was used to determine m and σ5%. Slow crack growth (SCG) parameters were determined by the dynamic fatigue test, and specimens were tested in biaxial flexure at five stress rates: 10(-2), 10(-1), 10(0), 10(1) and 10(2)MPa/s (n=10), immersed in artificial saliva at 37°C. Parameter n was calculated and statistically analyzed according to ASTM F394-78. Optical properties were determined in a spectrophotometer in the diffuse reflectance mode.
  
  
  RESULTS
  The highest n value was obtained by the combination of heat-pressing with fiber addition (37.1) and this value was significantly higher than those obtained by both sintered groups (26.2 for control group and 27.7 for sintered with fiber). Although heat-pressing alone also resulted in higher n values compared to the sintered groups, there were no significant differences among them. Fiber addition had no effect on mechanical strength, but it resulted in decreased TP values and increased OI values for both processing methods. Heat-pressing alone was able to reduce the porosity level of the porcelain.
  
  
  CONCLUSIONS
  Addition of PTF combined with heat-pressing can reduce strength degradation of a dental porcelain compared to sintered materials with or without fibers. Heat-pressing (HP) alone should be considered as a good alternative for clinical cases where high translucency is required.
authors.affiliation: Departamento de Biomateriais e Biologia Oral, Faculdade de Odontologia, Universidade de São Paulo, São Paulo, SP, Brazil. Electronic address: maicodda@gmail.com.
authors.forename: Maico Dutra
authors.initials: MD
authors.lastname: de Araújo
authors.affiliation: Departamento de Biomateriais e Biologia Oral, Faculdade de Odontologia, Universidade de São Paulo, São Paulo, SP, Brazil.
authors.forename: Ranulfo Benedito de Paula
authors.initials: RB
authors.lastname: Miranda
authors.affiliation: Instituto de Pesquisas Tecnológicas, São Paulo, SP, Brazil.
authors.forename: Catia
authors.initials: C
authors.lastname: Fredericci
authors.affiliation: Centro de Engenharia, Modelagem e Ciências Sociais Aplicadas, Universidade Federal do ABC, Santo André, SP, Brazil.
authors.forename: Humberto Naoyuki
authors.initials: HN
authors.lastname: Yoshimura
authors.affiliation: Departamento de Biomateriais e Biologia Oral, Faculdade de Odontologia, Universidade de São Paulo, São Paulo, SP, Brazil.
authors.forename: Paulo Francisco
authors.initials: PF
authors.lastname: Cesar
mesh_terms: D003343:Corrosion; D003776:Dental Porcelain / Q000737:chemistry*; D019232:Dental Restoration Failure; D004548:Elasticity; D006358:Hot Temperature; D008422:Materials Testing; D055595:Mechanical Phenomena; D055620:Optical Phenomena; D013314:Stress, Mechanical; D014025:Titanium / Q000737:chemistry
chemical_list: D003776:Dental Porcelain; C009934:potassium titanate; D014025:Titanium
keywords: Dental ceramic; Fibers; Sintering process