title: Opaque layer firing temperature and aging effect on the flexural strength of ceramic fused to cobalt-chromium alloy.
abstract: OBJECTIVE
  To evaluate the effect of the opaque layer firing temperature and mechanical and thermal cycling on the flexural strength of a ceramic fused to commercial cobalt-chromium alloy (Co-Cr). The hypotheses were that higher opaque layer temperatures increase the metal/ceramic bond strength and that aging reduces the bond strength.
  
  
  METHODS
  Metallic frameworks (25 x 3 x 0.5 mm(3); ISO 9693) (N = 60) were cast in Co-Cr and airborne-particle abraded (Al(2)O(3): 150 mum) at the central area of the frameworks (8 x 3 mm(2)) and divided into three groups (N = 20), according to the opaque layer firing temperature: Gr1 (control)-900 degrees C; Gr2-950 degrees C; Gr3-1000 degrees C. The opaque ceramic (Opaque, Vita Zahnfabrick, Bad Säckingen, Germany) was applied, and the glass ceramic (Vita Omega 900, Vita Zahnfabrick) was fired onto it (thickness: 1 mm). While half the specimens from each group were randomly tested without aging (water storage: 37 degrees C/24 hours), the other half were mechanically loaded (20,000 cycles; 50 N load; distilled water at 37 degrees C) and thermocycled (3000 cycles; 5 degrees C to 55 degrees C, dwell time: 30 seconds). After the flexural strength test, failure types were noted. The data were analyzed using 2-way ANOVA and Tukey's test (alpha= 0.05).
  
  
  RESULTS
  Gr2 (19.41 +/- 5.5 N) and Gr3 (20.6 +/- 5 N) presented higher values than Gr1 (13.3 +/- 1.6 N) (p= 0.001). Mechanical and thermal cycling did not significantly influence the mean flexural strength values (p > 0.05). Increasing the opaque layer firing temperature improved the flexural bond strength values (p < 0.05). The hypotheses were partially accepted.
  
  
  CONCLUSIONS
  Increasing of the opaque layer firing temperature improved the flexural bond strength between ceramic fused to Co-Cr alloy.
authors.affiliation: Department of Dental Materials and Prosthodontics, State University of São Paulo, São José dos Campos, Brazil. lgovasconcellos11@terra.com.br
authors.forename: Luis Gustavo Oliveira
authors.initials: LG
authors.lastname: de Vasconcellos
authors.forename: Leonardo
authors.initials: L
authors.lastname: Buso
authors.forename: Geraldo H L
authors.initials: GH
authors.lastname: Lombardo
authors.forename: Rodrigo O A
authors.initials: RO
authors.lastname: Souza
authors.forename: Lafayette
authors.initials: L
authors.lastname: Nogueira
authors.forename: Marco Antonio
authors.initials: MA
authors.lastname: Bottino
authors.forename: Mutlu
authors.initials: M
authors.lastname: Ozcan
mesh_terms: D000537:Aluminum Oxide / Q000737:chemistry; D002516:Ceramics / Q000737:chemistry; D002858:Chromium Alloys / Q000737:chemistry*; D001840:Dental Bonding; D045662:Dental Etching; D003776:Dental Porcelain / Q000737:chemistry*; D006358:Hot Temperature; D006801:Humans; D008422:Materials Testing; D016876:Metal Ceramic Alloys / Q000737:chemistry*; D018583:Pliability; D013314:Stress, Mechanical; D013499:Surface Properties; D013696:Temperature; D013997:Time Factors; D014867:Water / Q000737:chemistry
chemical_list: D002858:Chromium Alloys; D016876:Metal Ceramic Alloys; C110711:vita omega; D014867:Water; D003776:Dental Porcelain; C023506:Glass ceramics; D000537:Aluminum Oxide