To obtain greater longevity of indirect restorations, it is important to have a strong and durable bonding at the cement/restoration interface. This objective may be achieved by means of surface treatments in order to get appropriate surface characteristics of zirconia to allow an intimate contact of the cement with the substrate. For this purpose, the zirconia surface is airborne-particle abraded to promote micromechanical retention at that interface. The airborne-particle abrasion is usually performed after the manufacture of the restoration by the prosthetic technician. However, there is not a conscious choice about the particle size used in this procedure, which is an important factor to be considered. Moreover, the effect of the air-abrasion moment on the bonding quality is unknown. Therefore, the aim of this study is to investigate the influence of the particle size and the air-abrasion moment on the composition, morphology, wettability, roughness and bond strength at the cement/zirconia interface. Thus, zirconia discs with specific dimensions for each analysis will be airborne-particle abraded with 1) 50 µm Al2O3 particles; 2) 120 µm Al2O3 particles; 3) 30 µm silica-modified Al2O3 particles (Rocatec Soft - 3M ESPE); and 4) 110 µm silica-modified Al2O3 particles (Rocatec Plus - 3M ESPE) at the following moments: 1) after zirconia sintering (control group); 2) before sintering; and 3) before and after sintering. To evaluate the information previously mentioned, EDS and SEM analyses, contact angle and roughness will be respectively performed. For the shear bond strength test, the air-abraded zirconia discs will be treated with silane (RelyX - 3M ESPE) and cemented to a composite resin disc with resin cement (RelyX ARC - 3M ESPE). The specimens will be thermocycled (10,000 cycles - 5 and 55 °C and dwell time of 30 s) and submitted to the shear bond strength test in a mechanical testing machine (EMIC). After the test, the failure mode of specimens will be examined under a stereomicroscope (x20). The surface roughness (Sa), surface wettability (°) and shear bond strength (MPa) data will be statistically analyzed according to the results of normality and homocedasticity tests (±=0.05) with particle and air-abrasion moment as factors of variation. The surface morphology and chemical composition analyses will be only descriptive.
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