title: Effect of multiple firing and silica deposition on the zirconia-porcelain interfacial bond strength.
abstract: OBJECTIVE
  To test the hypothesis that multiple firing and silica deposition on the zirconia surface influence the bond strength to porcelain.
  
  
  METHODS
  Specimens were cut from yttria-stabilized zirconia blocks and sintered. Half of the specimens (group S) were silica coated (physical vapor deposition (PVD)) via reactive magnetron sputtering before porcelain veneering. The remaining specimens (group N) had no treatment before veneering. The contact angle before and after silica deposition was measured. Porcelain was applied on all specimens and submitted to two (N2 and S2) or three firing cycles (N3 and S3). The resulting porcelain-zirconia blocks were sectioned to obtain bar-shaped specimens with 1mm(2) of cross-sectional area. Specimens were attached to a universal testing machine and tested in tension until fracture. Fractured surfaces were examined using optical microscopy. Data were statistically analyzed using two-way ANOVA, Tukey's test (α=0.05) and Weibull analysis.
  
  
  RESULTS
  Specimens submitted to three firing cycles (N3 and S3) showed higher mean bond strength values than specimens fired twice (N2 and S2). Mean contact angle was lower for specimens with silica layer, but it had no effect on bond strength. Most fractures initiated at porcelain-zirconia interface and propagated through the porcelain.
  
  
  CONCLUSIONS
  The molecular deposition of silica on the zirconia surface had no influence on bond strength to porcelain, while the number of porcelain firing cycles significantly affected the bond strength of the ceramic system, partially accepting the study hypothesis. Yet, the Weibull modulus values of S groups were significantly greater than the m values of N groups.
authors.affiliation: São Paulo State University, Department of Dental Materials and Prosthodontics, São José dos Campos, São Paulo, Brazil.
authors.forename: José Renato Cavalcanti
authors.initials: JR
authors.lastname: Queiroz
authors.forename: Paula
authors.initials: P
authors.lastname: Benetti
authors.forename: Marcos
authors.initials: M
authors.lastname: Massi
authors.forename: Lafayette Nogueira
authors.initials: LN
authors.lastname: Junior
authors.forename: Alvaro
authors.initials: A
authors.lastname: Della Bona
mesh_terms: D000704:Analysis of Variance; D001840:Dental Bonding / Q000379:methods*; D003764:Dental Materials / Q000737:chemistry*; D003776:Dental Porcelain / Q000737:chemistry*; D003799:Dental Stress Analysis; D006358:Hot Temperature; D008422:Materials Testing; D012822:Silicon Dioxide / Q000737:chemistry*; D013499:Surface Properties; D013718:Tensile Strength; D015040:Zirconium / Q000737:chemistry*
chemical_list: D003764:Dental Materials; D003776:Dental Porcelain; D012822:Silicon Dioxide; D015040:Zirconium; C028541:zirconium oxide