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Fatigue is one of the most important properties to be considered in ceramic dental implants due to cyclic mechanical stresses arising from the chewing process. In this work, the fatigue behaviour of hydrothermally degraded ZrO2-based ceramics stabilized with 3mol% Y2O3 (3Y-TZP) was studied in 4-point bending tests. Samples of 3Y-TZP were compacted (100MPa), sintered at 1475 °C for 2 h, polished and hydrothermally degraded in an autoclave as described in the ISO-13356 standard. The samples were characterized by their relative density, crystalline phase composition, microstructure and surface roughness. The highly dense (>99.6%TD) sintered 3Y-TZP ceramics has only tetragonal t-ZrO2 phase, even after hydrothermal ageing. Furthermore, the ceramic materials presented a Vickers hardness of 12.7±0.2GPa, a fracture toughness of 7.1±0.3MPa•m1/2 and a 4-point bending strength of 940.1±67MPa. Based on the bending test results 5 different stress levels for the fatigue tests were selected and conducted by cyclic 4-point bending obtaining the S-N curve. Weibull statistics was used for the statistical analysis. The fatigue tests indicate that the limit of fatigue resistance of this 3Y-TZP ceramics is around 550MPa, i.e. higher than the limits established in the ISO-13356 standard for the use of Y-TZP ceramics for the manufacture of implants. The fatigue behaviour of the investigated 3Y-TZP ceramics was related to the toughening mechanisms acting in Y-TZP ceramics, such as transformation toughening related to t→m phase transformation and microcracking.

Adenosine Triphosphate is a molecule with the function of generating energy, where high levels are directly related to cellular and muscular health. Oral supplementation appears as a possibility to guarantee such levels, and is normally consumed in capsules, which can be acute or chronic. To verify the influence of a dose of ATP on muscular performance in adults. This is an acute, crossover, randomized, double-blind, placebo-controlled intervention study. 18 trained men were recruited, with an average age of 27.95 years. Two visits were made to the laboratory, where each of the protocols consisted of randomized supplementation of 400 mg of Peak ATP® or placebo, and 30 min later, five series were performed, where the first consisted of five repetitions and the following four of ten repetitions at 60° per second in knee extension and flexion on a Biodex® 4.0 isokinetic dynamometer, where the volunteers' muscle strength and resistance to fatigue were measured. For data analysis, data normality was assessed using Shapiro Wilk, the ANOVA repeated measures test with Bonferroni post hoc. To identify the size of the effect, the Cohen test was performed, and the statistical package used was SPSS 25 with an applied significance of p < 0.05. Acute supplementation was unable to achieve significant improvements in muscle strength indicators. The supplement delays drops in strength as the exercise progresses in knee extension compared to the placebo. An acute dose of 400 mg of ATP did not improve the volunteers' muscle strength indicators, but it was able to reduce fatigue levels as the exercise progressed, enabling greater performance for longer. [ABSTRACT FROM AUTHOR]

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Vickers indentation (IF) and single‐edge‐V‐notched beam (SEVNB), to measure the fracture toughness (KIC) of zirconia‐based dental ceramics and mathematical models were proposed to establish a correlation between both. Zirconia (ZrO2) stabilized with 3 mol. % of Y2O3 (3Y‐TZP) and 5 mol% of Y2O3 (5Y‐PSZ) were compacted (n = 42) and sintered for 2 h at different temperatures (1475°C, 1500°C, 1550°C, or 1600°C). After sintering, they were characterized by relative density using the ASTM C373‐88 standard, X‐ray diffraction (XRD) and scanning electron microscopy (SEM). The average grain size was measured according to the ASTM E1382‐97 standard. The fracture toughness (KIC) was determined using two methods: Vickers indentation fracture toughness (KIC‐IF): method based on mathematical modeling that considers the parameters used for the Vickers hardness test and Fracture toughness by the single‐edge‐V‐notch‐beam (KIC‐SEVNB): method proposed by ISO 23146:08. The main phases of the 3Y‐TZP and 5Y‐PSZ ceramics were ZrO2‐tetragonal and ZrO2‐cubic, respectively. The 3Y‐TZP specimens showed equiaxed grains with average grain sizes ranging from 0.55 to 0.79 μm. The grain sizes of 5Y‐PSZ of specimens sintered at 1475°C and 1600°C were 0.62 and 2.32 μm, respectively. For all ceramics the crack size ratio was c/a < 2.5, suggesting a Palmqvist‐type crack system. The fracture toughness measured by the Vickers indentation method (KIC‐IF) and by the SEVNB method (KIC‐SEVNB) was the same when the experimental data were fit to a mathematical model. [ABSTRACT FROM AUTHOR]

Phase stability in the Al2O3-Nb2O5-Y2O3 ceramic system at 1300 °C was experimentally investigated. Disks samples fabricated from homogenized powders were uniaxially pressed at room temperature and heat treated at 1300 °C for 222 hours under laboratory atmosphere to achieve thermodynamic equilibrium. As results, the microstructures of the heat-treated samples did not exhibit pseudo-ternary phases and the phase relations confirmed nine three-phase fields in the proposed isothermal section at 1300 °C. [ABSTRACT FROM AUTHOR]

The main goal of this work was to obtain dense Al2O3–Y3Al5O12 ceramic composites by reactive sintering of three-dimensional samples, built by direct ink writing from a paste containing a mixture of Al2O3 and Y2O3 powders. To obtain a ceramic ink with proper rheological properties for extrusion-based printing, highly pure Al2O3 and Y2O3 powders in a percentage–weight ratio of 64:36 was mixed with 0.2 wt% MgO in a total solid loading of 42 vol% in aqueous media, adding carboxymethyl cellulose and polyethyleneimine solution as additives. The dried printed samples were sintered at final temperatures in the range of 1550 °C and 1650 °C; thus, relative densities of 83.7 ± 0.8%, 95.4 ± 0.4%, and 96.5 ± 0.5% were obtained for 1550 °C, 1600 °C, and 1650 °C, respectively. Rietveld refinement performed on the X-ray diffraction patterns indicated the presence of Al2O3 (42 to 47%) and Y3Al15O12 (58 to 61%) as crystalline phases, while micrographs showed the presence of equiaxial micrometric grains with average sizes of 1.8 ± 0.6 μm, for both phases and all sintering conditions. Samples sintered at 1600 °C and 1650 °C presented similar average Vickers hardness values of 14.2 ± 0.27 GPa and 14.5 ± 0.25 GPa, respectively. A slight increase in fracture toughness as sintering temperature increases was also stated, consistent with the densification. [ABSTRACT FROM AUTHOR]