title: Effect of surface and heat treatments on the biaxial flexural strength and phase transformation of a Y-TZP ceramic.
abstract: OBJECTIVE
  To evaluate the effect of grinding and airborne-particle abrasion on the biaxial flexural strength (BFS) and phase transformation of a Y-TZP ceramic, and examine whether sintering the veneering porcelain renders the previous heat treatment recommended by the manufacturer unnecessary.
  
  
  METHODS
  Lava zirconia specimens (N = 108) were obtained with the following dimensions: 14.0 mm diameter × 1.3 mm thickness (n = 36) and 14.0 mm × 1.6 mm (n = 72). The thicker specimens were ground with diamond burs under irrigation and received (heat-treated groups) or not (non-heat-treated groups) a heat treatment (1000°C for 30 min) prior to the four firing cycles applied to simulate the sintering of the veneering porcelain. All specimens were air abraded as follows (n = 12): 1) 30-μm silica-modified Al₂O₃particles (Rocatec Soft); 2) 110-μm silica-modified Al₂O₃particles (Rocatec Plus); and 3) 120-μm Al₂O₃particles, followed by Rocatec Plus. Three specimens of each group were analyzed by x-ray diffraction (XRD) to assess the monoclinic phase content (%). The BFS test was performed in a mechanical testing machine (Instron 8874). Data (MPa) were analyzed by two-way ANOVA (grinding × airborne-particle abrasion and heat treatment × airborne-particle abrasion) and Tukey's post-hoc test (α = 0.05). The strength reliability was analyzed using the Weibull distribution.
  
  
  RESULTS
  Grinding significantly decreased the BFS of the non-heat-treated groups (p < 0.01). Within the ground groups, the previous heat treatment did not influence the BFS (p > 0.05). Air abrasion only influenced the BFS of the ground/heat-treated groups (p < 0.01). For the non-heat-treated groups, the grinding did not decrease the Weibull modulus (m), but it did decrease the characteristic strength (σ0). For Rocatec Soft and 120-μm Al₂O₃particles + Rocatec Plus, the heat-treated groups presented lower m and higher σ0 than the ground/non-heat-treated groups. The independent variables did not seem to influence phase transformation. Air-abraded surfaces presented higher monoclinic zirconia content than the as-sintered and ground surfaces, which exhibited similar content.
  
  
  CONCLUSIONS
  Even under irrigation, grinding compromised the Y-TZP ceramic strength. The sintering of the veneering porcelain rendered the previous heat treatment recommended by the manufacturer unnecessary. Airborneparticle abrasion influenced the strength of heat-treated zirconia.
authors.forename: Renata Garcia
authors.initials: RG
authors.lastname: Fonseca
authors.forename: Filipe de Oliveira
authors.initials: Fde O
authors.lastname: Abi-Rached
authors.forename: Filipe Samuel Correia Pereira
authors.initials: FS
authors.lastname: da Silva
authors.forename: Bruno Alexandre Pacheco de
authors.initials: BA
authors.lastname: Henriques
authors.forename: Ligia Antunes Pereira
authors.initials: LA
authors.lastname: Pinelli
mesh_terms: D000537:Aluminum Oxide / Q000737:chemistry; D003461:Crystallography; D045662:Dental Etching / Q000379:methods; D003776:Dental Porcelain / Q000737:chemistry*; D003799:Dental Stress Analysis / Q000295:instrumentation; D003801:Dental Veneers; D018130:Diamond / Q000737:chemistry; D055119:Elastic Modulus; D006358:Hot Temperature; D008422:Materials Testing; D018583:Pliability; D012822:Silicon Dioxide / Q000737:chemistry; D013314:Stress, Mechanical; D013499:Surface Properties; D014867:Water / Q000737:chemistry; D014961:X-Ray Diffraction / Q000379:methods; D015019:Yttrium / Q000737:chemistry*; D015040:Zirconium / Q000737:chemistry*
chemical_list: C499362:yttria stabilized tetragonal zirconia; D014867:Water; D003776:Dental Porcelain; D015019:Yttrium; D012822:Silicon Dioxide; D018130:Diamond; D015040:Zirconium; D000537:Aluminum Oxide; C028541:zirconium oxide