title: Effect of the layering technique on bond strength and cohesive resistance of a porcelain-zirconia system.
abstract: OBJECTIVE
  To evaluate the influence of the number of porcelain layers on its cohesive strength and on bonding to zirconia.
  
  
  METHODS
  Y-TZP blocks were cut into 1 cm3 specimens (n = 30). The feldspathic porcelain (V9) was applied to the zirconia in different numbers of layers up to 1 cm total thickness (n = 10): ZP1 - one layer; ZP2 - two layers; ZP3 - three layers. Ten specimens with V9 were prepared following the same protocols of groups 1 (P1) and 3 (P3). All study specimens were sintered three times. The specimens were cut into 1 mm2 microbars and tested under tension in a universal testing machine (0.5 mm/min). We calculated strength (σ, in MPa) by dividing the fracture load (N) by the fractured area (mm2). The failure mode was classified as cohesive (used to calculate the cohesive strength, σc) or adhesive (bond strength, σa). The data were analyzed by Kruskal-Wallis and Dunn's tests (α = 0.05) or ANOVA and Tukey's test (α = 0.05), according to their distribution parameters.
  
  
  RESULTS
  The ZP1 group presented the highest values for σa data, compared with other groups, which were statistically similar. The predominant failure mode for the bonded specimens was cohesive. With regard to the cohesive strength (σc), ZP1 presented the highest values.
  
  
  CONCLUSIONS
  It can be concluded that the presence of more than one porcelain layer decreases its cohesive strength and its bonding strength to zirconia.
authors.forename: Vanessa Cruz
authors.initials: VC
authors.lastname: Macedo
authors.forename: Lilian Costa
authors.initials: LC
authors.lastname: Anami
authors.forename: Renata Marques
authors.initials: RM
authors.lastname: de Melo
authors.forename: Marco Antonio
authors.initials: MA
authors.lastname: Bottino
authors.forename: Luiz Felipe
authors.initials: LF
authors.lastname: Valandro
mesh_terms: D000268:Adhesiveness; D000538:Aluminum Silicates / Q000737:chemistry; D001840:Dental Bonding; D003764:Dental Materials / Q000737:chemistry*; D003776:Dental Porcelain / Q000737:chemistry*; D003799:Dental Stress Analysis / Q000295:instrumentation; D006358:Hot Temperature; D006801:Humans; D008422:Materials Testing; D017680:Potassium Compounds / Q000737:chemistry; D013314:Stress, Mechanical; D013499:Surface Properties; D013718:Tensile Strength; D015019:Yttrium / Q000737:chemistry*; D015040:Zirconium / Q000737:chemistry*
chemical_list: D000538:Aluminum Silicates; D003764:Dental Materials; C485633:In-Ceram Zirconia; D017680:Potassium Compounds; C499362:yttria stabilized tetragonal zirconia; D003776:Dental Porcelain; C016447:feldspar; D015019:Yttrium; D015040:Zirconium