Nanostructures for the development of high-performance dental Y-TZP ceramics

Abstract

Yttria-stabilized polycrystalline tetragonal zirconia (Y-TZP) is a material with great potential for application in dentistry due to its mechanical properties, especially its fracture toughness. However, this material presents hydrothermal instability at low temperatures due to the phase transformation of the metastable tetragonal into the monoclinic structure, which leads to Low-Temperature Degradation (LTD) and compromises mechanical properties. This project proposes the synthesis, structural and microstructural characterization, and survival probability analyses, before and after artificial aging, of materials based on Y-TZP with nanometric grains and toughening mechanisms based on non-uniform yttria distributions and/or nanotube reinforcements, to improve resistance to LTD while preserving the mechanical properties. 3 experimental groups of samples will be developed (n=106/group), consisting of pure Y-TZP samples with nanometric grains, and samples of Y-TZP with nanometric grains with additions of pure zirconia powder (ZrO2) and/or ZrO2 nanotubes. The samples will be formed into discs by dry and wet processes, to optimize all stages of ceramic processing, and sintered by the two-step method. After sintered and polished, some of the samples from each group will be aged in an autoclave (134ºC, 2.2 bar, 20 hours) to simulate the LTD process. The crystalline phases will be determined by X-Ray Diffraction (XRD) and the possible changes on the surface and the microstructure after aging will be characterized by Scanning Electron Microscopy. The hardness and fracture toughness will be assessed by Vickers microhardness and by nanoindentation, and the biaxial flexural strength (ISO 6872: 2015) will be used to determine the probability of survival, Weibull modulus, and characteristic strength. Accelerated life tests will be performed followed by fractographic analysis to assess fatigue survival. Optical properties, such as translucency, of the nanometric samples, will be evaluated by UV/visible spectroscopy. (AU)