Search Results (78)

MnO₂-doped 9 mol% CaO-stabilized zirconia (CSZ) was investigated in terms of phase stability, microstructure, and mechanical properties before and after thermal cycling. As the MnO₂ content increased from 2 to 4 mol%, the monoclinic phase fraction decreased significantly (from 32.6% to 2.5%), while the tetragonal phase fraction increased (from 58.2% to 90.3%), indicating an enhanced phase stability comparable to fully stabilized ZrO₂. The cubic phase fraction decreased from 9.2% to 3.4% with 2–3 mol% MnO₂, but increased to 7.2% at 4 mol%. The 9 mol% CSZ showed a mixture of grains around 2 μm and 10 μm, while the MnO₂-doped CSZ exhibited only grains larger than 30 μm, suggesting that MnO₂ acted as a sintering aid. After thermal cycling, increasing the MnO₂ content from 2 to 4 mol% led to an increase in the monoclinic phase fraction (from 7.8% to 17.2%) and a decrease in the tetragonal phase fraction (from 53.6% to 21.8%). The Vickers hardness and wear resistance of MnO₂-doped CSZ were superior to those of undoped 9-CSZ, and improved as the MnO₂ doping level increased. These mechanical properties were maximized in the CSZ doped with 3 mol% MnO₂, and this trend persisted after thermal cycling. These results demonstrate that MnO₂ doping effectively enhances the phase stability and mechanical performance of CaO-partially stabilized zirconia under thermal stress cycling conditions. Full article

In this study, the structural, electronic, and elastic properties of cubic zirconium dioxide (c-ZrO₂) were investigated using the Density Functional Theory (DFT) approach. Lattice parameter optimization revealed that the lattice constant is 5.107 Å, the Zr–O bond length is 2.21 Å, and the unit cell density is 6.075 g/cm³ for the B3LYP functional. The bandgap width was determined to be 5.1722 eV. The investigation of the elastic properties of the cubic ZrO₂ crystal determined the Young’s modulus, bulk modulus, Poisson’s ratio, and hardness, which were found to be 315.91 GPa, 241 GPa, 0.282, and 13 (Hv), respectively, under zero external pressure. These results confirm the mechanical stability of ZrO₂. Full article

Background/Objectives: High-translucency zirconia is a dental ceramic offering excellent aesthetic results but with mechanical limitations restricting its applications. This study aimed to simulate the mechanical behavior of anatomical dental prostheses made from high-translucency zirconia using the finite element method (FEM) to assess the material’s reliability. Methods: Samples of high-translucency zirconia were compacted, sintered, and characterized for relative density. Structural and microstructural analyses were performed using X-ray diffraction (XRD) and scanning electron microscopy (SEM). Its mechanical properties, including hardness, fracture toughness, and flexural strength, were measured. Additionally, elastic parameters such as Young’s modulus and Poisson’s ratio were determined using the impulse excitation technique and subsequently employed in numerical simulations under various masticatory loads (50 to 500 N). These simulations modeled an anatomical molar (tooth 26) using the HyperMesh and ABAQUS codes, applying loads from three directions: vertical, angular (45°), and horizontal, at different points on the prosthesis. Results: The sintered zirconia ceramics exhibited excellent densification and a microstructure composed of cubic and tetragonal grains (c-ZrO₂ and t-ZrO₂). The measured properties included a hardness of 1315 ± 48 HV, fracture toughness of 3.7 ± 0.2 MPam^1/2, and flexural strength of 434 ± 67 MPa. Elastic parameters were determined as a Young’s modulus of 192.2 ± 4.8 GPa and a Poisson’s ratio of 0.31. Numerical simulations demonstrated that vertically applied loads of 500 N resulted in a maximum stress of approximately 299.2 MPa, horizontal stress reached 320.8 MPa at a 200 N load, and angular stress peaked at 447.3 MPa under a 350 N load. These findings indicate that the material can safely withstand these conditions without failure. Conclusions: Within the limits of this investigation, the methodology proved to be an effective tool for predicting the mechanical behavior of new dental ceramics. For high-translucency zirconia, the material demonstrated high reliability under masticatory vertical loads up to 500 N, angular loads up to 350 N, and horizontal loads up to 200 N. Full article

Isotropic shrinkage is critical for producing dimensionally accurate prostheses using zirconia. However, the anisotropic shrinkage of 3D-printed zirconia limits its utility in clinical applications. We aimed to evaluate the impact of specimen axis alterations on the shrinkage of digital light processing (DLP)-printed zirconia. Cubes measuring 10 × 10 × 10 mm³ (similar in size to molar crowns) and cuboids measuring 10 × 10 × 20 mm (similar in size to a three-unit bridge) were manufactured using a DLP 3D printer. Zirconia specimens were pre-sintered at 1300 °C and 1400 °C. The Z-axis of some specimens was switched to the X-axis before the final sintering procedure. The X-axis, Y-axis, and Z-axis lengths of the green body, pre-sintered block, and fully sintered block were measured using digital calipers. The 3D-printed specimens showed lower shrinkage and higher deviation than the milled specimens, whose shrinkage rate was 26%. The shrinkage rates of the 3D-printed cubic specimens were 19.9% (length), 20.0% (width), and 21.99% (height), while those of the cuboidal specimens were 20.26%, 19.72%, and 21.81%, respectively. For the 3D-printed specimens, which shrink anisotropically during sintering, the axis change step had no significant impact on the shrinkage rate. In all groups, the shrinkage rate along the building direction during printing significantly exceeded that along the gravity direction during sintering. Full article

Zirconia restorations are widely used in dentistry due to their high esthetic expectations and physical durability. However, zirconia’s opaque white color can compromise esthetics. Therefore, zirconia is often veneered with porcelain, but fractures may occur in the veneer layer. Monolithic zirconia restorations, which do not require porcelain veneering and offer higher translucency, have been developed to address this issue. Zirconia exists in three main crystal phases: monoclinic, tetragonal, and cubic. Metal oxides such as yttrium are added to stabilize the tetragonal phase at room temperature. 3Y-TZP contains 3 mol% yttrium and provides high mechanical strength but has poor optical properties. Recently, 4Y-PSZ and 5Y-PSZ ceramics, which offer better optical properties but lower mechanical strength, have been introduced. This review examines the factors affecting the color change in monolithic zirconia ceramics. These factors are categorized into six main groups: cement type and color, restoration thickness, substrate color, sintering, aging, and zirconia type. Cement type and color are crucial in determining the final shade, especially in thin restorations. Increased restoration thickness reduces the influence of the substrate color while the sintering temperature and process improve optical properties. These findings emphasize the importance of material selection and application processes in ensuring esthetic harmony in zirconia restorations. This review aims to bridge gaps in the literature by providing valuable insights that guide clinicians in selecting and applying zirconia materials to meet both esthetic and functional requirements in restorative dentistry. Full article

X-ray diffraction analysis of the pseudo-binary SrFe_1−xV_xO_3−δ system showed that the solid solution formation limit at atmospheric oxygen pressure corresponds to x ≈ 0.1. SrFe_0.9V_0.1O_3−δ has a cubic perovskite-type structure with the Pm$\overline{3}$m space group. The oxygen nonstoichiometry variations in SrFe_0.9V_0.1O_3−δ, measured by coulometric titration in the oxygen partial pressure range of 10⁻²¹ to 0.5 atm at 1023–1223 K, can be adequately described using an ideal solution approximation with V⁵⁺ as the main oxidation state of vanadium cations. This approach was additionally validated by statistical thermodynamic modeling. The incorporation of vanadium decreases both oxygen deficiency and the average iron oxidation state with respect to undoped SrFeO_3−δ. As a result, the electrical conductivity, thermal expansion and chemical expansivity associated with the oxygen vacancy formation all become lower compared to strontium ferrite. At 923 K, the conductivity of SrFe_0.9V_0.1O_3−δ is 14% lower than that of SrFeO_3−δ but 21% higher compared to SrFe_0.9Ta_0.1O_3−δ. The area-specific polarization resistance of the porous SrFe_0.9V_0.1O_3−δ electrode deposited onto 10 mol.% scandia- and 1 mol.% yttria-co-stabilized zirconia solid electrolyte with a protective Ce_0.9Gd_0.1O_2−δ interlayer, was 0.34 Ohm×cm² under open-circuit conditions at 1173 K in air. Full article

Highly translucent zirconia (TZ) is frequently used in dentistry. The properties of several highly translucent zirconia materials available in the market require an in-depth understanding. In this study, we assessed the translucency, crystalline phase, mechanical properties, and microstructures of three newly developed highly translucent zirconia materials (Zpex 4. m, 4 mol% yttria-stabilized zirconia: 4YSZ; Zpex Smile.m, 5YSZ; ZR Lucent ULTRA, 6YSZ). The translucency parameter (TP) was analyzed using the CIELAB system. X-ray diffraction was conducted for the crystalline phase analysis, followed by Rietveld refinement. A biaxial flexural strength test using the Weibull analysis was performed to evaluate the mechanical properties. Scanning electron microscopy, grain size distribution, and average grain size were used to analyze the microstructures. The TP content of the ZR Lucent ULTRA was the highest among the samples investigated. The Rietveld analysis revealed that the cubic zirconia phase content of the ZR Lucent ULTRA was the highest. The biaxial flexural strength of the ZR Lucent ULTRA was the lowest (622.9 MPa). The average grain size and proportion of large grains (1.0 µm < x) were the highest in ZR Lucent ULTRA. Therefore, extra-high translucent zirconia has the potential for use in anterior monolithic restorations owing to its esthetics and strength. Full article

In this study, 12 mol% ceria-stabilized tetragonal zirconia polycrystal ceramics with xNd₂O₃ (where x equals 0, 0.1, 0.2, 0.3, 0.4, 0.5, and 0.7) were synthesized via the solid-state method, and the effects of Nd₂O₃ doping amounts on the mechanical properties and microstructure were studied. The results show that with an increase in the Nd₂O₃ doping amount, the grain size of the ceramics was reduced from 2.93 μm to 0.69 μm. The hardness and strength of the ceramics increased significantly, while the fracture toughness decreased. The reduction in fracture toughness was attributed to the reduction in tetragonal grain size, which suppressed the tetragonal–monoclinic phase transformation caused by stress. Additionally, as the content of Nd₂O₃ increased, the formation of cubic zirconia accelerated, but no second phase was observed. Most importantly, when the doping amount of Nd₂O₃ reached 0.3 mol%, the comprehensive mechanical characteristics of the ceramics were optimal. This provides a research basis for the preparation of nanoscale 12 mol% ceria-stabilized tetragonal zirconia polycrystal ceramics. Full article

The aim of this paper was to investigate the structure and thermal properties of zirconia ceramics co-doped with rare earth (RE) elements in equimolar concentrations. We prepared (1 − x)ZrO₂ − x(yLa₂O₃ + yNd₂O₃ + ySm₂O₃ + yGd₂O₃ + yYb₂O₃) (x = 0.2; y = 0.2) powders by a hydrothermal method in mild conditions (200 °C, 2 h, 60–100 atm.) The powder was analyzed by XRD, SEM-EDAX, BET, and FT-IR after synthesis and heat treatments at 1200 °C and 1500 °C. The samples exhibit good thermal stability, with a single cubic phase presented after heat treatment at 1500 °C. The compound exhibits a low thermal conductivity (0.61 W·m⁻¹·K⁻¹), a low heat capacity (0.42 J·g⁻¹K⁻¹), and a low thermal diffusivity (0.34 mm²·s⁻¹). The values are lower than reported for conventional RE-doped zirconia. Full article

Improvements in phase stability and dielectric characteristics can broaden the applications of zirconia in ceramics. Herein, a series of Y₂O₃-stabilized zirconia (YSZ) ceramics are synthesized using solid-state sintering, followed by an investigation into their phase evolution, grain size, dielectric constant, and breaking field. As the Y₂O₃ content increases from 0 wt% to 4 wt%, the as-grown YSZ ceramics undergo a distinct phase transformation, transitioning from monoclinic to monoclinic + tetragonal and further to monoclinic + tetragonal + cubic, before finally returning to monoclinic + cubic. Significant changes occur in the internal microstructure and grain size of the ceramics as the phase composition alters, resulting in a reduction in grain size from 3.17 μm to 0.27 μm. Moreover, their dielectric constants exhibit an increasing trend as the Y₂O₃ content increases, rising from 3.92 to 13.2. Importantly, the dielectric breakdown field of these YSZ ceramics shows a similar variation to the phase evolution, ranging from 0.11 to 0.15 MV/cm. This study sheds light on the phase evolution and dielectric properties of YSZ ceramics, offering an efficient strategy for enhancing their dielectric performances. Full article

The main objectives of the present prospective clinical study were to evaluate the survival and success rates of implant-supported zirconia single crowns fabricated with a full digital workflow for the rehabilitation of mono- and bilateral agenesis of maxillary lateral incisors after 2 years of clinical function; biological and technical parameters affecting the prosthetic restorations were recorded, as well as the patient-satisfaction score. Twenty-two patients showing mono- or bilateral agenesis of the maxillary lateral incisors were included in this study, and a total of 30 narrow-diameter implants were inserted. Thirty screw-retained monolithic cubic zirconia single crowns with internal connections were fabricated. Objective outcome evaluations were performed by means of the Functional Implant Prosthodontic Score, whereas the patient-satisfaction score was evaluated using Visual Analog Scales. Descriptive statistics were performed and the Kaplan–Meier analysis was run to analyze time-to-event data. After 2 years of clinical function, the overall FIPS found in the present study was 9.2, whereas the average patient-satisfaction score was 8.7. The Kaplan–Meier analysis at the 2-year follow-up reported a cumulative survival rate of 100% and a cumulative success rate of 93.3%. The implant-prosthetic rehabilitation with a full digital workflow proved to be an effective and reliable procedure for the functional and aesthetic treatment of the agenesis of maxillary lateral incisors in the short-term. Clinical investigations with wider sample populations and longer observational follow-ups could be useful to validate, in the long-term, the clinical outcomes of the present prospective clinical study. Full article

The local binding and migration behavior of the proton defect in cubic yttria-stabilized zirconia (YSZ) is studied by first-principles calculations and muon-spin spectroscopy (μSR) measurements. The calculations are based on density-functional theory (DFT) supplemented with a hybrid-functional approach with the proton defect embedded in quasi-random supercells of 10.3 mol% yttria content, where the yttrium–zirconium substitutional defects are charge compensated by oxygen vacancies. Representative migration pathways for the proton comprising both transfer and bond reorientation modes are analysed and linked to the underlying microstructure of the YSZ lattice. The μSR data show the evolution of the diamagnetic fraction corresponding to the muon-isotope analogue with an activation energy of diffusion equal to 0.17 eV. Comparisons between the calculations and the experiment allow an assessment of the character of the short-range migration of the proton particle in cubic YSZ. Full article

This paper presents the results of the experimental research on diamond-reinforced composites with WC–Co matrices enhanced with a ZrO₂ additive. The samples were prepared using a modified spark plasma sintering method with a directly applied alternating current. The structure and performance of the basic composite 94 wt.%WC–6 wt.%Co was compared with the ones with ZrO₂ added in proportions up to 10 wt.%. It was demonstrated that an increase in zirconia content contributed to the intense refinement of the phase components. The composite 25 wt.%C_diamond–70.5 wt.%WC–4.5 wt.%Co consisted of a hexagonal WC phase with lattice parameters a = 0.2906 nm and c = 0.2837 nm, a cubic phase (a = 1.1112 nm), hexagonal graphite phase (a = 0.2464 nm, c = 0.6711 nm), as well as diamond grits. After the addition of zirconia nanopowder, the sintered composite contained structural WC and Co₃W₃C phases, amorphous carbon, tetragonal phase t-ZrO₂ (a = 0.36019 nm, c = 0.5174 nm), and diamond grits—these structural changes, after an addition of 6 wt.% ZrO₂ contributed to an increase in the fracture toughness by more than 20%, up to K_Ic = 16.9 ± 0.76 MPa·m^0.5, with a negligible decrease in the hardness. Moreover, the composite exhibited an alteration of the destruction mechanism after the addition of zirconia, as well as enhanced forces holding the diamond grits in the matrix. Full article

The cubic zirconia (ZrO₂) is attractive for a broad range of applications. However, at room temperature, the cubic phase needs to be stabilized. The most studied stabilization method is the addition of the oxides of trivalent metals, such as Sc₂O₃. Another method is the stabilization of the cubic phase in nanostructures—nanopowders or nanocrystallites of pure zirconia. We studied the relationship between the size factor and the dopant concentration range for the formation and stabilization of the cubic phase in scandium-stabilized zirconia (ScSZ) films. The thin films of (ZrO₂)_1−x(Sc₂O₃)_x, with x from 0 to 0.2, were deposited on room-temperature substrates by reactive direct current magnetron co-sputtering. The crystal structure of films with an average crystallite size of 85 Å was cubic at Sc₂O₃ content from 6.5 to 17.5 mol%, which is much broader than the range of 8–12 mol.% of the conventional deposition methods. The sputtering of ScSZ films on hot substrates resulted in a doubling of crystallite size and a decrease in the cubic phase range to 7.4–11 mol% of Sc₂O₃ content. This confirmed that the size of crystallites is one of the determining factors for expanding the concentration range for forming and stabilizing the cubic phase of ScSZ films. Full article

Multifunctional nanocomposites from an equimolar As₄S₄/Fe₃O₄ cut section have been successfully fabricated from coarse-grained bulky counterparts, employing two-step mechanochemical processing in a high-energy mill operational in dry- and wet-milling modes (in an aqueous solution of Poloxamer 407 acting as a surfactant). As was inferred from the X-ray diffraction analysis, these surfactant-free and surfactant-capped nanocomposites are β-As₄S₄-bearing nanocrystalline–amorphous substances supplemented by an iso-compositional amorphous phase (a-AsS), both principal constituents (monoclinic β-As₄S₄ and cubic Fe₃O₄) being core–shell structured and enriched after wet milling by contamination products (such as nanocrystalline–amorphous zirconia), suppressing their nanocrystalline behavior. The fluorescence and magnetic properties of these nanocomposites are intricate, being tuned by the sizes of the nanoparticles and their interfaces, dependent on storage after nanocomposite fabrication. A specific core–shell arrangement consisted of inner and outer shell interfaces around quantum-confined nm-sized β-As₄S₄ crystallites hosting a-AsS, and the capping agent is responsible for the blue-cyan fluorescence in as-fabricated Poloxamer capped nanocomposites peaking at ~417 nm and ~442 nm, while fluorescence quenching in one-year-aged nanocomposites is explained in terms of their destroyed core–shell architectures. The magnetic co-functionalization of these nanocomposites is defined by size-extended heterogeneous shells around homogeneous nanocrystalline Fe₃O₄ cores, composed by an admixture of amorphous phase (a-AsS), nanocrystalline–amorphous zirconia as products of contamination in the wet-milling mode, and surfactant. Full article