Comportamento mecânico sob fadiga de zircônia policristalina: efeito do desgaste por brocas para usinagem em CAD/CAM e tratamentos de superfície

Abstract

Three studies compose the present study. The first one evaluated the effect of different intaglio surface treatments on fatigue behavior (biaxial flexural fatigue strength) and surface characteristics (topography and roughness) of a 5 mol% partially stabilized zirconia ceramic (5YSZ). For that, ceramic discs (ISO 6872-2015) were allocated considering: Ctrl: no-treatment; GLZ: low-fusing porcelain glaze; SNF: SiO2 nanofilm deposition (5nm); AlOx: air-abrasion with aluminum oxide; SiC: air-abrasion with silica-coated AlOx; 7%Si: air-abrasion with 7% silica-coated AlOx. The biaxial flexural fatigue strength tests were performed (piston-on-three-balls assembly), besides topographic, surface roughness, fractographic and phase analysis. According to the results, low-fusing porcelain glaze enhances the fatigue performance of 5YSZ, while the deposition of silica nanofilms does not affect its mechanical properties. Among air-abrasions, the AlOx decreased the fatigue behavior of ceramic. The second study evaluated the distinct conditioning effect of the intaglio surface of bonded 5 mol% stabilized zirconia simplified restorations on the mechanical fatigue behavior of the set, prior to and after aging. Ceramic discs (Ø= 10mm; thick= 1mm) were allocated considering “surface treatments” (Ctrl: no-treatment; PM: primer; GLZ: glaze; SNF: SiO2 nanofilm deposition (5 nm); AlOx: air-abrasion with AlOx; SiC: air-abrasion with silica-coated AlOx; 7%Si: air-abrasion with 7% silica-coated AlOx; and “aging” (baseline: 24h (37°C); aged: 90 days (37°C) + 12,000 thermal cycles). The discs were treated, luted with resin cement onto the dentin analogue, subjected to aging or not, and subsequently tested under a step-stress fatigue test. Fractography, topography, surface roughness, contact angle, and atomic force microscopy were performed. In conclusion, conditioning the intaglio surface of zirconia is mandatory for fatigue behavior stability after aging of the set, while non-treatment induces unstable results. The third study evaluated the effect of in-lab simulation of CAD/CAM grinding and intaglio surface treatments on the surface characteristics (topography and roughness) and fatigue behavior of adhesively luted 4 mol% yttria-stabilized zirconia (4YSZ) simplified restorations. Ceramic discs (Ø= 10mm; thick= 1mm) were allocated considering “In-lab simulation of CAD/CAM grinding” (ground; polished) and “surface treatments” (Ctrl: no treatment; AlOx: air abrasion with AlOx; GLZ: glaze), and posteriorly luted with resin cement onto a dentin analogue material and tested under a step-stress fatigue test. Complementary analysis was performed to verify the ability of GLZ infiltration in surface defects to increase the flexural strength (FS) of 4YSZ. For that, specimens in bars were confeccioned considering the groups N-ID: non-indented; ID: indented; ID-GLZ: indented + GLZ, and tested in the FS test. In conclusion, in-lab simulation of CAD/CAM grinding promoted deleterious fatigue behavior of 4YSZ and GLZ induced a better performance compared to air abrasion. In addition, GLZ increased the flexural strength of the bars after indentation. Furthermore, there is an inverse relationship between roughness and fatigue failure load of 4YSZ, the higher the surface roughness, the lower the fatigue behavior of the set.