Mechanical strength, lifetime, failure mode and bond strength of zirconia structures to a resin cement: effect of the surface treatment

Abstract

The objectives of this study will be: 1) To evaluate and compare the surface roughness and phase transformation of Y-TZP structures after the following surface treatments (STr): (a) Control (without STr, just final sintering); (b) Silica-coating using 30µm aluminum oxide particles modified by silica (CoJet®-Sand) after final sintering; and (c) Silica-coating in advance, and then final sintering; 2) To evaluate the effect of STr (a-c) and (d) application of a glass layer (Glaze Spray VITA AKZENT) on the 4-point flexural strength (Ã4P) and Weibull modulus (m) of Y-TZP structures; 3) To correlate Ã4P and surface roughness data; 4) To determine the fatigue resistance and subcritical crack growth (n) of Y-TZP bars after STr; 5) To determine the fatigue lifetime of treated Y-TZP crowns via chewing simulation; 6) To determine the failure mode by fractography; and 7) to evaluate the shear bond strength between the treated Y-TZP and a resin cement after 24 hours and thermocycling (TC). Y-TZP specimens in the shape of bars (1.2 mm x 4 mm x 20 mm), crowns and cylinders (ø: 3.4 mm x h: 4 mm) will be produced and subjected to STr. Surface roughness, phase composition, 4-point flexural strength and cyclic fatigue will be examined in the ceramic bars. Weibull analyses and fatigue testing will be used to determine m and n values, respectively. The crowns of each STr condition will be cemented onto dies and submitted to thermo-mechanical fatigue in the dual-axis chewing simulator at 200N/1Hz until failure. After the mechanical tests, the specimens will be inspected under polarized light stereomicroscopy and SEM. Y-TZP cylinders will be cemented to resin composite blocks and submitted to the shear bond strength test at 0.5 mm/min. Half of the specimens from each condition will be tested after 6.000 thermal cycles (5º to 55º C), and the remaining half after 24-h storage. Data will be statistically analyzed using ANOVA and Tukey's posthoc tests (pd0.05). (AU)