Search Results (165)

Background: This study investigated a new multi-acid-etching formulation for zirconia ceramics, containing hydrochloric, hydrofluoric, nitric, orthophosphoric, and sulfuric acids. The solution was tested on polycrystalline (5Y-TZP zirconia), lithium disilicate, hybrid ceramic, and feldspathic porcelain to assess compatibility, etching selectivity, and surface conditioning. Methods: Two-hundred-and-forty CAD/CAM specimens were etched for 20 s, 60 s, 30 min, or 1 h, and their surface roughness and etching patterns ware evaluated using 3D optical profilometry and scanning electron microscopy (SEM). Results: A positive correlation was observed between etching time and surface roughness (Ra values). The most pronounced changes were observed in lithium disilicate and feldspathic porcelain, with Ra values increasing from 0.733 ± 0.082 µm (Group 5) to 1.295 ± 0.123 µm (Group 8), and from 0.902 ± 0.102 µm (Group 13) to 1.480 ± 0.096 µm (Group 16), respectively. Zirconia increased from 0.181 ± 0.043 µm (Group 1) to 0.371 ± 0.074 µm (Group 4), and the hybrid ceramic from 0.053 ± 0.008 µm (Group 9) to 0.099 ± 0.016 µm (Group 12). Two-way ANOVA revealed significant effects of material and etching time, as well as a significant interaction between the two factors (p < 0.001). SEM observation revealed non-selective etching pattern for the lithium disilicate groups, indicating a risk of over-etching. Conclusions: The tested etching solution increased surface roughness, especially for the lithium disilicate and feldspathic porcelain specimens. In zirconia, one-hour etching improved surface characteristics with minimal observable damage. However, additional studies are necessary to validate the mechanical stability and bond effectives of this approach. Full article

This article deals with the effect of Kr¹⁵⁺ ion irradiation on the structure and properties of partially stabilized zirconium dioxide (ZrO₂ + 3 mol. % Y₂O₃) ceramics. Ion irradiation is used to simulate radiation damage typical of operating conditions in nuclear reactors and space technology. It is shown that with an increase in the irradiation fluence, point defects are formed, dislocations accumulate, and the crystal lattice parameters change. At high fluences (>10¹³ ions/cm²), a phase transition of the monoclinic (m-ZrO₂) phase to the tetragonal (t-ZrO₂) and cubic (c-ZrO₂) modifications is observed, which is accompanied by a decrease in the crystallite size and an increase in internal stresses. Changes in the mechanical properties of the material were also observed: at moderate irradiation fluences, strengthening is observed due to the formation of dislocation structures, whereas at high fluences (>10¹⁴ ions/cm²), a decrease in strength and a potential amorphization of the structure begins. The change in the phase composition was confirmed by X-ray phase analysis and Raman spectroscopy. The results obtained allow a deeper understanding of the mechanisms of radiation-induced phase transformations in stabilized ZrO₂ and can be used in the development of ceramic materials with increased radiation resistance. Full article

The aim of translucency-enhancing liquids (TEL) is to locally influence the phase composition of zirconia in order to increase its translucency. This study aimed to determine the influence of TEL on 3Y- and 4Y-TZP zirconia concerning roughness, hardness, wear, flexural strength, dynamic stability and fracture force of fixed dental prostheses after thermal cycling and mechanical loading. Two zirconia materials (4Y-TZP; 3Y-TZP-LA, n = 8 per material and test) were investigated with and without prior application of TEL. Two-body wear tests were performed in a pneumatic pin-on-block design (50 N, 120,000 cycles, 1.6 Hz) with steatite balls (r = 1.5 mm) as antagonists. Mean and maximum vertical loss as well as roughness (Ra, Rz) were measured with a 3D laser-scanning microscope (KJ 3D, Keyence, J). Antagonist wear was determined as percent area of the projected antagonist area. Martens hardness (HM; ISO 14577-1) and biaxial flexural strength (BFS; ISO 6872) were investigated. The flexural fatigue limit BFSdyn was determined under cyclic loading in a staircase approach with a piston-on-three-ball-test. Thermal cycling and mechanical loading (TCML: 2 × 3000 × 5 °C/55 °C, 2 min/cycle, H₂O dist., 1.2 × 10⁶ force á 50 N) was performed on four-unit fixed dental prostheses (FDPs) (n = 8 per group) and the fracture force after TCML was determined. Statistics: ANOVA, Bonferroni test, Kaplan–Meier survival, Pearson correlation; α = 0.05. TEL application significantly influences roughness, hardness, biaxial flexural strength, dynamic performance, as well as fracture force after TCML in 3Y-TZP. For 4Y-TZP, a distinct influence of TEL was only identified for BFS. The application of TEL on 3Y- or 4Y-TZP did not affect wear. TEL application has a strong effect on the mechanical properties of 3Y-TZP and minor effects on 4Y-TZP. All effects of the TEL application are of a magnitude that is unlikely to restrict clinical application. Full article

This study examined the relationship between microhardness, morphology, and phase composition of dental yttria-stabilized tetragonal zirconia polycrystals (Y-TZP), which directly impact their long-term clinical performance and durability. The primary objective was to investigate the effects of yttria content and polishing on the surface properties and hardness of these materials. Samples from ZirCAD Prime, Cercon ht ML, ZIRCONIA YML, and ZirCAD LT were analyzed using Vickers hardness testing, Powder X-ray Diffraction (PXRD), and Scanning Electron Microscopy (SEM). SEM analysis revealed a gradual increase in grain size and porosity with higher yttria content in unpolished samples. Polishing resulted in a relatively uniform surface morphology with observable striations across all samples, subsequently leading to similar Vickers hardness values for all polished samples. PXRD and SEM analyses identified that these similar hardness values were likely due to the predominant monoclinic phase on the surface, induced by polishing. These findings underscore the significant influence of yttria content and polishing on Y-TZP microstructure and surface hardness, highlighting their critical role in the long-term success and clinical applicability of dental restorations. Full article

The stability of yttria-stabilized zirconia (YSZ) as a dental implant material is highly dependent on its resistance to low-temperature degradation (LTD) and surface dissolution, particularly in acidic oral environments. This study investigates the effects of yttrium ion (Y³⁺) release on the phase stability of zirconia during constant immersion and pH cycling tests, simulating oral conditions. Zirconia disks were immersed in acidic (pH 2), neutral (pH 7), and basic (pH 10) solutions over a 27-day period. Inductively coupled plasma (ICP) analysis revealed significant yttrium ion release during acidic phases, while zirconium ion (Zr⁴⁺) release remained minimal. X-ray photoelectron spectroscopy (XPS) showed a shift in zirconium 3d binding energies, indicating a transformation from the tetragonal to the monoclinic phase, driven by yttrium leaching. X-ray diffraction (XRD) confirmed this phase change, with the appearance of the monoclinic (111) peak after exposure to acidic conditions. This study concludes that yttrium ion depletion under acidic conditions destabilizes the tetragonal phase, promoting LTD and compromising the material’s long-term performance as a dental implant or restorative material. Full article

This work systematically investigates the influence of two spark plasma sintering (SPS) temperatures (1400 °C and 1600 °C) on the mechanical and tribological properties of two yttria-stabilized zirconia ceramics: 3 mol.% Y₂O₃ (3Y-TZP) and 1.5 mol.% Y₂O₃ (1.5Y-TZP). The ceramics’ microhardness, nanohardness, Young’s modulus, fracture toughness, and tribological performance were evaluated. The results show that 3Y-TZP maintains high hardness (Vickers hardness HV ~1300; nanohardness ~17.1 GPa) and stable fracture toughness (~4.2 MPa·m½), nearly independently of sintering temperature. In contrast, 1.5Y-TZP exhibits a critical trade-off: sintering at 1400 °C yields exceptional fracture toughness (~6.2 MPa·m½), but increasing the temperature to 1600 °C causes a sharp drop to ~4.5 MPa·m½. Tribologically, the highest wear resistance under a 5 N load was observed for the 3Y-TZP sample sintered at 1600 °C. These findings suggest that for low-yttria compositions, higher SPS temperatures can trigger detrimental microstructural changes that degrade toughness. The results provide crucial insights for tailoring SPS parameters and Y-TZP compositions for specific high-performance applications, balancing the competing requirements of hardness and fracture toughness. Full article

The existing scientific literature lacks comprehensive information regarding the influence of zirconia crown height on debonding and fracture of the ceramic restorations on titanium base abutments. Additionally, there is a lack of comparative studies evaluating different types of zirconia as restorative options for screw-retained restorations. Purpose: The purpose of this study was to assess the fracture strength and the failure modes of the zirconia crown/titanium abutment complex by investigating the impact of increasing the height of zirconia crown and comparing different types of zirconia (3 mol% yttria-stabilized zirconia and translucent 5 mol% yttria-stabilized zirconia). Materials and Methods: Six groups of 10 specimens in each group were fabricated. Three groups of specimens (groups # 1, 2, and 3) were fabricated from 3Y zirconia in corresponding heights of 8, 10, and 12 mm. Three more groups (groups # 4, 5, and 6) were fabricated from 5Y zirconia in the same heights (8, 10 and 12 mm). All copings were bonded to 4 mm high titanium base abutments using dual-polymerization resin cement. The specimens underwent load cycling of 100,000 cycles with a force of 100 N. Subsequently, the specimens were loaded to compression until fracture and the failure mode was visually evaluated. Results: Statistically significant differences in fracture strength were noted among all tested groups. Conclusions: 3Y zirconia showed increased strength compared to 5Y in all heights. Ceramic copings with lower height showed increased strength compared to higher copings in both tested zirconia materials. Full article

This study provides an investigation into the influence of surface roughness, porosity, and chemistry on the wettability and infiltration behavior of calcia-magnesia-alumino-silicates (CMASs) in thermal and environmental barrier coatings (T/EBCs) used in high-temperature gas turbine engines. High-temperature contact angle measurements were performed at 1260 °C on 7 wt.% yttria-stabilized zirconia (7YSZ) and yttrium ytterbium disilicate (YYbDS, (Y_1/2Yb_1/2)₂Si₂O₇) to evaluate the interaction of CMASs with different surface finishes and coating microstructures. The findings demonstrate that porosity plays a dominant role in determining CMAS infiltration dynamics. In YYbDS, increasing porosity from 6.3% to 22.7% facilitated the formation of an apatite layer that limited CMAS penetration to approximately 2 µm. Surface roughness exhibited a subtler influence in that reducing Sa from 0.61 µm to 0.05 µm increased the change in the contact angle by ~2°, although its impact was found to be less significant compared to porosity and reactive chemistry. These results indicate that an integrated approach that optimizes porosity, chemistry, and surface morphology can significantly enhance CMAS resistance. The study emphasizes that leveraging both microstructural and chemical properties is critical to developing coatings capable of withstanding the harsh conditions encountered in aerospace environments. Full article

Aging of yttria-stabilized tetragonal zirconia polycrystal (Y-TZP) under wet conditions is known as low-temperature degradation (LTD), which is associated with phase change and decreasing mechanical strength. Herein, we studied the effects of different surface treatments on the LTD of three different commercial Y-TZP blocks utilizing CAD/CAM technology, namely, Cercon^®, e.max^® ZirCAD, and Vita In-ceram^® YZ. The blocks were immersed in 4% acetic acid at 80 °C for 0, 7, 14, and 28 days. The effects of surface treatments such as sandblasting and polishing were also examined. The results showed that the monoclinic phase increased with immersion time in all three brands. In Cercon^® blocks, a minimal amount of phase transformation was observed, with the smallest amount of degradation after immersion. Sandblasting and polishing both suppressed phase transformation. After immersion, the mechanical strength exhibited a small decrease with time. Accelerating the evaluation of the LTD of zirconia may effectively help with clinical applications. Full article

Our planet is currently facing dual challenges of global warming and energy crisis. The heavy reliance of the energy sector on fossil fuels significantly contributes to the accumulation of greenhouse gases, such as CH₄ and CO₂, in the environment atmosphere, exacerbating global warming. Stabilized zirconia-based material offer a promising solutions to address both challenges. As a catalytic support material, active sites incorporated stabilized-zirconia can facilitate the conversions of greenhouse gases like CH₄ and CO₂ into syngas (H₂ and CO). This reaction is popularly known as dry reforming of methane (DRM). Additionally, stabilized zirconia-based materials act as solid-state electrolyte in fuel cells enabling the electrochemical conversion of H₂ and O₂ to generate electricity. Both processes require high-temperature stability and oxide ionic conductivity, making “Ca, Mg, Sc, Y-stabilized zirconia” an optimal choice. In DRM, the key factors influencing catalytic efficiency include metal–support interaction, reducibility, and basicity. Meanwhile, for solid oxide fuel cells, performance is governed by factors such as size-fit, charge imbalance, dopant miscibility, ion conducting phases, densification, electrolyte thickness, and grain boundary volume. This compressive review explores the dual functionality of “Ca, Mg, Sc, Y-stabilized zirconia” as a catalyst’support for DRM and as an solid electrolyte for fuel cells. The most promising research outcomes are highlighted, and future research directions are outlined. By bringing together the catalytic and fuel cell research communities, this study aims to advance sustainable energy technologies and contribute to mitigating environmental and energy crisis through the development of stabilized zirconia-based materials. Full article

In this work, the impact resistance of three zirconia ceramics was investigated: two yttria-stabilized zirconia (3Y-TZP and 1.5Y-TZP) and a ceria-stabilized-zirconia (Ce-TZP) composite. The impact resistance was evaluated through drop-ball impact tests on disk-shaped samples. The results are discussed in terms of the materials’ transformability, which was correlated to the size of tetragonal-to-monoclinic (t-m) transformation zones observed after the impact tests and to the volume fraction of the monoclinic content on fractured surfaces. The findings show that impact resistance increases with the ability of the material to undergo t-m transformation. The Ce-TZP composite exhibited the highest transformability and consequently the highest impact resistance, followed by 1.5Y-TZP, and then 3Y-TZP. 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

This study evaluated the impact of glazing and multiple firing on the flexural strength, translucency, and color stability of three types of zirconia: 3 mol% yttria-stabilized tetragonal zirconia polycrystals (3Y-TZP), 4 mol% yttria partially stabilized zirconia (4Y-PSZ), and 5 mol% yttria partially stabilized zirconia (5Y-PSZ). A total of 120 samples were categorized into four groups: polishing only (P), polishing + glazing (PG), polishing + glazing + one glaze firing (PGF), and polishing + glazing + two glaze firings (PGFF). A three-point bending test was used for assessing flexural strength and a spectrophotometer analysis for assessing color difference (ΔE*_ab) and translucency parameter (TP). Statistical analysis included one-way ANOVA and Kruskal–Wallis tests, with significance set at α = 0.05. The type 3Y-TZP showed the highest flexural strength (918.46 MPa) and lowest translucency (TP = 4.32), while 5Y-PSZ exhibited the lowest strength (401.58 MPa, p < 0.001) and highest translucency (TP = 6.26, p ≤ 0.012). Heat treatment resulted in a significant reduction in the flexural strength of 5Y-PSZ (p = 0.002), followed by 3Y-TZP (p = 0.04). The type 5Y-PSZ exhibited significant change in translucency (p = 0.003) and unacceptable variations in color (ΔE*_ab: 1.49–9.6). The type 4Y-PSZ exhibited the highest stability in flexural strength, translucency, and color under multiple treatments. In conclusion, while glazing and firing significantly compromised 5Y-PSZ’s flexural strength and altered its color and translucency, 4Y-PSZ demonstrated the highest stability. Full article

This study compares the mechanical properties of 5-mol% yttria partially stabilized zirconia (5Y-PSZ) materials, designed for 3D printing or milling. Three 5Y-PSZ materials were investigated: printed zirconia (PZ) and two milled zirconia materials, VITA-YZ-XT (MZ-1) and Cercon xt (MZ-2). PZ samples were made from a novel ceramic suspension via digital light processing and divided into three subgroups: PZ-HN-ZD (horizontal nesting, printed with Zipro-D Dental), PZ-VN-Z (vertical nesting, printed with Zipro-D Dental) and PZ-VN-Z (vertical nesting, printed with Zipro Dental). Key outcomes included biaxial flexural strength (ISO 6872) and Vickers hardness (n ≥ 23 samples/subgroup). Microstructure and grain size were analyzed using light and scanning electron microscopy. Printed specimens exhibited biaxial flexural strengths of 1059 ± 178 MPa (PZ-HN-ZD), 797 ± 135 MPa (PZ-VN-ZD), and 793 ± 75 MPa (PZ-VN-Z). Milled samples showed strengths of 745 ± 96 MPa (MZ-1) and 928 ± 87 MPa (MZ-2). Significant differences (α = 0.05) were observed, except between vertically printed groups and MZ-1. Vickers hardness was highest for PZ-VN-Z (HV0.5 = 1590 ± 24), followed by MZ-1 (HV0.5 = 1577 ± 9) and MZ-2 (HV0.5 = 1524 ± 4), with significant differences, except between PZ and MZ-1. PZ samples had the smallest grain size (0.744 ± 0.024 µm) compared to MZ-1 (0.820 ± 0.042 µm) and MZ-2 (1.023 ± 0.081 µm). All materials met ISO 6872 standards for crowns and three-unit prostheses in posterior regions. Full article

The high yttria content of a stabilized zirconia (YSZ) (38 wt% Y₂O₃) coating was deposited by atmospheric plasma spraying (APS) from Metco 207 powders on an Inconel 718 (Ni-based superalloy) substrate. As a metal coating connection, a layer of cermet powder (Ni-20% Al—410NS) was used before the ceramic layer deposition. The electro-chemical corrosion resistance of these materials was tested using Inconel cylinders with a diameter of 10 mm and a thickness of 1 mm, with and without the ceramic layer. Linear and cyclic measurements were obtained in H₂SO₄ electrolyte media at pH = 2. Electro-impedance spectroscopy (EIS) experiments were performed on the sample covered with the ceramic layer to evaluate the interface behavior. Scanning electron microscopy (SEM), along with equipment to determine chemical composition, and an energy dispersive spectrometry (EDS) detector were used to characterize the material surface before and after corrosion tests. It was observed that the corrosion resistance of Inconel was influenced by the bonding layer and the ceramic coating. Full article