Impact of different pretreatments and aging procedures on the flexural strength and phase structure of zirconia ceramics

OBJECTIVE To test the impact of zirconia pretreatment and aging on flexural strength and phase structure. METHODS For flexural strength measurements, 180 3Y-TZP$_{0.25}$ specimens were fabricated and pretreated: (i) air-abraded (105-μm alumina, 0.25MPa), (ii) air-abraded (50-μm alumina, 0.25MPa), (iii) air-abraded (30-μm silica-coated alumina, 0.28MPa) (iv) non-pretreated. Each pretreated group (n=15) was aged: (a) hydrothermal (134°C, 0.23MPa, 2h) (b) in a mastication simulator (1,200,000×, 5/55°C) and (c) not aged. The fractured specimens were stored dry for 5 years (23°C) for analysis of phase transformation. Additionally, specimens were fabricated from 3Y-TZP$_{0.25}$ (n=12) and 3Y-TZP$_{0.05}$ (n=8), pretreated (i, ii, iii, iv), and hydrothermally aged. Each air-abrasion method was alternated using 0.05, 0.25 and 0.4MPa pressure. The phase transformation was examined by Raman spectroscopy and surface topography by scanning electron microscope. Data were analyzed using univariate ANOVA with the Scheffé post hoc test and partial-eta-squared (ƞ$_{p}$²) (α=0.05). RESULTS The highest impact on flexural strength was exerted by the pretreatment (η$_{P}$²=0.261, p