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We evaluated the mechanical properties of zirconia restorations produced via additive manufacturing (AM) and the crown accuracy of zirconia crowns. Zirconia disks, bars, and crowns were manufactured via subtractive (CNC group) and additive manufacturing (AM group) techniques. Disk-shaped specimens in each group were autoclaved at 134 °C and 216 kPa for 5, 10, and 24 h. The phases of the specimens were analyzed using an X-ray diffractometer. The flexural strengths were measured via biaxial flexural tests. The morphologies were examined using a scanning electron microscope. The correlation between the m-phase fraction and biaxial flexural strength by autoclave time in each group was analyzed via linear mixed model and Pearson's correlation analysis. For each group, crown specimens were used to assess the marginal and internal gaps using the replica technique. Buccolingual and mesiodistal cross-sections were measured, and a repeated measures one-way ANOVA was performed. Linear mixed model analysis indicated that for both groups, with an increase in the autoclave time, the flexural strength decreased, whereas the m-phase fraction increased. Pearson's correlation analysis revealed no correlation between the m-phase fraction and flexural strength for either group. A repeated measures one-way ANOVA was conducted on instrumented sections (buccal, lingual, mesial, and distal), revealing that the marginal and internal gaps of AM-produced zirconia crowns were less accurate than those of CNC-produced zirconia crowns. These findings suggest that additively produced zirconia restorations have mechanical properties comparable to those of conventionally produced ceramics and may be suitable for clinical applications. [Display omitted] • Mechanical properties of additively manufactured zirconia restorations were evaluated. • Crown accuracy of zirconia dental crowns was assessed. • Additively produced zirconia restorations may be suitable for clinical applications. [ABSTRACT FROM AUTHOR]

Nanostructured Y‐TZP samples with Non‐Homogeneous Yttria Distribution (NNHYD) were prepared by mixing co‐precipitated 3Y‐TZP powder (Tosoh TZ‐3Y) with yttria‐free monoclinic powder (Tosoh TZ‐0), yielding an overall yttria content of 2 mol%. The cyclic fatigue behavior of NNHYD was evaluated by Step‐Stress Accelerated Life Testing (SSALT) and mechanical cycling in a biaxial flexural strength test (BFST) setup and compared to Conventional Submicrometric 3Y‐TZP (CS). Physical, structural, microstructural, and mechanical characterizations of all groups were also evaluated and compared before and after artificial aging in autoclave. NNHYD presented a higher capacity for damage accumulation and maintenance of phase transformation potential than CS, associated with elevated resistance to the propagation of Low‐Temperature Degradation (LTD). A nanostructured 3Y‐TZP surface layer introduced in NNHYD by dip coating (DC‐NNHYD) improved resistance to LTD at the cost of reduced reliability under cyclic fatigue by increasing the stability of the tetragonal phase. This surface alteration highlights the impact of surface properties on mechanical performance. The results of this study present practical possibilities to help achieve the ideal balance between strength, toughness, and LTD resistance to improve the lifetime of zirconia‐based biomaterials. [ABSTRACT FROM AUTHOR]

The low fracture toughness and sensitivity to low-temperature degradation (LTD) are the primary reasons for the suboptimal long-term performance of dental zirconia. Composite ceramics of zirconia have gained popularity due to their ability to combine the benefits of various reinforcements. In this study, Al2O3–SrAl12O19–3Y/4Y/5Y–ZrO2 composite ceramics were fabricated using the Pechini method, and the optimal sintering temperature and time were investigated. The relative density, microstructure, grain size, mechanical properties, and LTD resistance of the samples were characterized. The results indicated that the composite achieved optimal performance when sintered at 1500 °C for 3 h. Al2O3 and SrAl12O19 primarily influence the properties of the zirconia composite ceramics by modulating their density and grain size. With an increase in the content of Al2O3 and SrAl12O19, the relative density first increases and then decreases, while the grain size exhibits an inverse trend, resulting in an initial increase followed by a decrease in fracture toughness. Additionally, the rate of increase in the m-phase fraction of the zirconia composite slowed down, but it reached a similar level after 64 h of LTD. The incorporation of 8 vol% Al2O3 and 8 vol% SrAl12O19 into 3Y–ZrO2 resulted in a ceramic composite with the highest fracture toughness values and acceptable LTD sensitivity, measured at 5.23 ± 0.25 MPa m1/2 and 48.35 ± 5.70% m-phase (LTD 64 h), respectively. This composite also exhibited high bending strength (990.09 MPa) and hardness (16.52 GPa), making it a promising alternative to conventional 3Y-TZP ceramics commonly used in dentistry.

Employed ubiquitously in oral restorations, zirconia-based bioceramics face challenges with low-temperature degradation (LTD) in the tetragonal phase (t-ZrO 2) within oral environments. In order to improve the resistance of ZrO 2 ceramics to LTD, this study utilized vat photopolymerization technology to prepare 7Ce3Y–ZrO 2 (7 mol% CeO 2 and 3 mol% Y 2 O 3). By adjusting the dispersant content and photosensitive resin ratio enabled the attainment of a 63.5 μm curing depth with a 400 mJ/cm2 exposure, meeting the requirements for vat photopolymerization printing. After sintering at 1550 °C, these ceramics shown a relative density of 97.84 % and an impressive flexural strength of 503.1 MPa. Accelerated LTD tests were conducted to assess LTD-resistance, revealing no degradation in mechanical properties or evidence of tetragonal to monoclinic phase transitions. This stability is credited to the cerium ions' efficacy in hindering oxygen vacancy formation and subsequent aging within the ZrO 2. This study affirms that CeO 2 –Y 2 O 3 co-stabilized ZrO 2 ceramics prepared using vat photopolymerization technology exhibit outstanding properties and resistance to LTD, showcasing significant potential in the field of oral restoration. [ABSTRACT FROM AUTHOR]

Copyright of West China Journal of Stomatology is the property of Sichuan University, West China College of Stomatology and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

Copyright of West China Journal of Stomatology is the property of Sichuan University, West China College of Stomatology and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

The aim of this study was to investigate the low-temperature degradation (LTD) kinetics of tetragonal zirconia with 3 mol% yttria (3Y-TZP) dental ceramic using two degradation methods: hydrothermal degradation and immersed degradation. To study transformation kinetics, we prepared 3Y-TZP powders. We pressed these powders uniaxially into a stainless mold at 100 MPa. We then sintered the compacted bodies at intervals of 50 °C between 1300 °C and 1550 °C and immersed the specimens at various temperatures from 60 °C to 80 °C in 4% acetic acid or from 110 °C to 140 °C for the hydrothermal method. We used a scanning electron microscope (SEM) to confirm crystalline grain size and used X-ray diffraction to analyze the zirconia phase. As the sintering temperature increased, the calculated crystalline grain size also increased. We confirmed this change with the SEM image. The higher sintering temperatures were associated with more phase transformation. According to the Mehl–Avrami–Johnson equation, the activation energies achieved using the hydrothermal method were 101 kJ/mol, 95 kJ/mol, and 86 kJ/mol at sintering temperatures of 1450 °C, 1500 °C, and 1550 °C, respectively. In addition, the activation energies of the specimens immersed in 4% acetic acid were 60 kJ/mol, 55 kJ/mol, 48 kJ/mol, and 35 kJ/mol, with sintered temperatures of 1400 °C, 1450 °C, 1500 °C, and 1550 °C, respectively. The results showed that a lower sintering temperature would restrain the phase transformation of zirconia because of the smaller crystalline grain size. As a result, the rate of LTD decreased. [ABSTRACT FROM AUTHOR]

This study aims to investigate the diffusion stabilization process of nano-Co2O3 during the non-precursor transformation of 3Y-TZP. 3Y-TZP was set as the control group, and the experimental groups were 0.1–0.3 mol% nano-Co2O3-doped 3Y-TZP. The samples were prepared by the ball milling process, isostatic cool pressing, and sintering. All samples were hydrothermally treated at 134°C and 2 bar for different time periods. The resistance to low-temperature degradation of nano-Co2O3-doped 3Y-TZP was analyzed by X-ray diffraction. The microstructure of zirconia ceramic samples was determined by scanning electron microscopy, transmission electron microscopy, atomic force microscopy, and electron paramagnetic resonance studies. The addition of nano-Co2O3 into 3Y-TZP resulted in higher hydrothermal aging resistance than 3Y-TZP. The addition of 0.2 mol% nano-Co2O3 dopants resulted in the highest hydrothermal aging resistance among nano-Co2O3-doped 3Y-TZP ceramics. The grain sizes of 3Y-0.2Co are smaller than those in the control group. With the increase of cobaltous oxide doping contents, the segregation of Co3+ ions at the crystal boundary increased. The content of oxygen vacancies on the surface of the sample increased with the increase of the Co2O3 doping content. The oxygen vacancy concentrations of 3Y-0.2Co increased obviously after aging. 3Y-0.1Co, 3Y-0.3Co, and the control showed decreased oxygen vacancy concentrations after aging. Trivalent element doping of 3Y-TZP effectively improved the aging resistance of 3Y-TZP. The addition of 0.2 mol% nano-Co2O3 resulted in the highest hydrothermal aging resistance. Improved aging resistance is attributed to the nano-Co2O3 doping resulting in the 3Y-TZP grain size inhibition, grain boundary segregation of cobalt ions, and oxygen vacancy maintenance. This work is expected to provide an effective reference for the development and application of budget dental materials by regulating grain boundary engineering.

While the in situ return of corn straw can improve soil fertility and farmland ecology, additional bacterial agents are required in low-temperature areas of northern China to accelerate straw degradation. Moisture is an important factor affecting microbial activity; however, owing to a lack of bacterial agents adapted to low-temperature complex soil environments, the effects of soil moisture on the interaction between exogenous bacterial agents and indigenous soil microorganisms remain unclear. To this end, we explored the effect of the compound bacterial agent CFF constructed using Pseudomonas putida and Acinetobacter lwoffii, developed to degrade corn straw in low-temperature soils (15 °C), on indigenous bacterial and fungal communities under dry (10% moisture content), slightly wet (20%), and wet (30%) soil-moisture conditions. The results showed that CFF application significantly affected the α-diversity of bacterial communities and changed both bacterial and fungal community structures, enhancing the correlation between microbial communities and soil-moisture content. CFF application also changed the network structure and the species of key microbial taxa, promoting more linkages among microbial genera. Notably, with an increase in soil moisture, CFF enhanced the rate of corn straw degradation by inducing positive interactions between bacterial and fungal genera and enriching straw degradation-related microbial taxa. Overall, our study demonstrates the alteration of indigenous microbial communities using bacterial agents (CFF) to overcome the limitations of indigenous microorganisms for in situ straw-return agriculture in low-temperature areas. Key points: • Low-temperature and variable moisture conditions (10–30%) were compared • Soil microbial network structure and linkages between genera were altered • CFF improves straw degradation via positive interactions between soil microbes [ABSTRACT FROM AUTHOR]

ABSTRACTIn the humid oral environment, 3Y-TZP ceramics always suffer from low-temperature degradation (LTD) for a long time, which results in the degradation of mechanical properties and catastrophic failure. The low-temperature degradation (LTD) and mechanical properties of low-cost tetravalent (Ge4+, Ti4+) element-doped 3Y-TZP were investigated by analysing grain boundary segregation in samples with deferent contents. The results show that GeO2 is superior to TiO2 in limiting LTD but results in lower flexural strength and fracture toughness when the content is ≥1.5 mol%. This dilemma can be improved by adding only 0.1%-0.5 wt% Al2O3, and the flexural strength and fracture toughness of 0.25 wt% Al2O3 zirconia are then increased to 898 MPa and 4.68 MPa·m1/2 compared with 1Ge-3Y, respectively. This work is expected to provide an effective reference for the development and application of budget dental materials.

Dense and homogeneous nanostructured Y-TZP ceramics were prepared by colloidal processing and 2-step sintering using commercial powders. The influence of non-homogeneous yttria distributions on mechanical properties and Low-Temperature Degradation (LTD) resistance were assessed. Physical, structural, microstructural, and mechanical characterizations of all groups were evaluated and compared before and after artificial aging. Nanostructured Y-TZP samples with non-homogeneous yttria distributions presented the highest fracture toughness and elevated fracture strength. These samples were susceptible to LTD, but with the transformed monoclinic phase fraction restricted to the near-surface region. The characterization data of nanostructured samples were compared to those of conventional 3Y-TZP. The results of this work indicate that it may be possible to prepare Y-TZP ceramics with improved mechanical properties and resistance to LTD by careful and systematic design and engineering of nanostructures. [Display omitted] [ABSTRACT FROM AUTHOR]

In the humid oral environment, 3Y-TZP ceramics always suffer from low-temperature degradation (LTD) for a long time, which results in the degradation of mechanical properties and catastrophic failure. The low-temperature degradation (LTD) and mechanical properties of low-cost tetravalent (Ge4+, Ti4+) element-doped 3Y-TZP were investigated by analysing grain boundary segregation in samples with deferent contents. The results show that GeO2 is superior to TiO2 in limiting LTD but results in lower flexural strength and fracture toughness when the content is ≥1.5 mol%. This dilemma can be improved by adding only 0.1%-0.5 wt% Al2O3, and the flexural strength and fracture toughness of 0.25 wt% Al2O3 zirconia are then increased to 898 MPa and 4.68 MPa·m1/2 compared with 1Ge-3Y, respectively. This work is expected to provide an effective reference for the development and application of budget dental materials. [ABSTRACT FROM AUTHOR]

The "Window to the Brain" is a transparent cranial implant under development, based on nanocrystalline yttria-stabilized zirconia (nc-YSZ) transparent ceramic material. Previous work has demonstrated the feasibility of this material to facilitate brain imaging over time, but the long-term stability of the material over decades in the body is unknown. In this study, the low-temperature degradation (LTD) of nc-YSZ of 3, 6, and 8 mol % yttria is compared before and after accelerated ageing treatments following ISO standards for assessing the ageing resistance of zirconia ceramics. After 100 hr of accelerated ageing (equivalent to many decades of ageing in the body), the samples do not show any signs of phase transformation to monoclinic by X-ray diffraction and micro-Raman spectroscopy. Moreover, the mechanical hardness of the samples did not decrease, and changes in optical transmittance from 500 to 1000 nm due to ageing treatments was minimal (below 3% for all samples), and unlikely to be due to phase transformation of surface crystals to monoclinic. These results indicate the nc-YSZ has excellent ageing resistance and can withstand long-term implantation conditions without exhibiting LTD.

Low-temperature degradation (LTD) is a progressive degradation following tetragonal-to-monoclinic transformation in a water environment, and it represents a problem for the long-term integrity of zirconia implants. However, there is little documentation on the low-temperature degradation characteristics of zirconia with surface treatment. We investigated the LTD properties of such systems to assess the influence of surface treatment using nanosecond (thermal) and picosecond (less thermal) pulsed lasers, as well as an additional annealing process. The nanosecond and picosecond pulsed lasers generated periodic structures on the surfaces of tetragonal zirconia polycrystals stabilized with 3 mol% yttria (Y-TZP). Cross-sectional observations using scanning electron microscopy (SEM) and scanning transmission electron microscopy (STEM) revealed the characteristics of the microstructure and the heat effects. Both laser treatments resulted in heat-damaged layers. Moreover, the nanosecond laser induced grain growth on the outermost surface. However, annealing after nanosecond laser treatment resulted in a porous structure below the surface. X-ray diffraction analysis detected monoclinic crystals on the surfaces treated with the nanosecond and picosecond pulsed lasers after the LTD acceleration test. Cross-sectional observations revealed the propagation of the monoclinic-transformed layer. We concluded that the thermal shock from the lasers deteriorates the LTD resistance of the materials, and the use of additional annealing hinders LTD propagation. Stress relaxation and the microstructures produced by annealing may contribute to maintaining toward LTD resistance. • The low-temperature deterioration of Y-TZP treated with laser and annealing techniques was investigated. • More monoclinic transformation was found on the surface treated with nanosecond laser. • Additional annealing after nanosecond-laser treatment hampered the low-temperature degradation. [ABSTRACT FROM AUTHOR]

Copyright of Bulletin of the Chinese Ceramic Society is the property of Bulletin of the Chinese Ceramic Society Editorial Office and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

The aim of this study was to investigate the low-temperature degradation (LTD) kinetics of tetragonal zirconia with 3 mol% yttria (3Y-TZP) dental ceramic using two degradation methods: hydrothermal degradation and immersed degradation. To study transformation kinetics, we prepared 3Y-TZP powders. We pressed these powders uniaxially into a stainless mold at 100 MPa. We then sintered the compacted bodies at intervals of 50 °C between 1300 °C and 1550 °C and immersed the specimens at various temperatures from 60 °C to 80 °C in 4% acetic acid or from 110 °C to 140 °C for the hydrothermal method. We used a scanning electron microscope (SEM) to confirm crystalline grain size and used X-ray diffraction to analyze the zirconia phase. As the sintering temperature increased, the calculated crystalline grain size also increased. We confirmed this change with the SEM image. The higher sintering temperatures were associated with more phase transformation. According to the Mehl–Avrami–Johnson equation, the activation energies achieved using the hydrothermal method were 101 kJ/mol, 95 kJ/mol, and 86 kJ/mol at sintering temperatures of 1450 °C, 1500 °C, and 1550 °C, respectively. In addition, the activation energies of the specimens immersed in 4% acetic acid were 60 kJ/mol, 55 kJ/mol, 48 kJ/mol, and 35 kJ/mol, with sintered temperatures of 1400 °C, 1450 °C, 1500 °C, and 1550 °C, respectively. The results showed that a lower sintering temperature would restrain the phase transformation of zirconia because of the smaller crystalline grain size. As a result, the rate of LTD decreased.

Aim: The aim of the study is to systematically assess the impact of low-temperature degradation (LTD) simulation in an autoclave on mechanical and microstructural properties of infiltrated monolithic zirconia compared to the noninfiltrated zirconia. Settings and Design: Systematic review following Preferred Reporting Items for Systematic Reviews and Meta-Analysis 2020 guidelines. Materials and Methods: An electronic search was done within these databases: PubMed, Scopus, and Web of Science, Science Direct, Embase, Wiley, Google Scholar for articles published between 2000 and March 2021. Search results that met eligibility criteria were categorized into two groups based on properties assessed of infiltrated monolithic zirconia exposed to LTD (also called aging simulation) – (a) mechanical (flexural strength and fracture toughness) and (b) microstructural properties (phase transformation rate and m content). Statistical Analysis Used: Qualitative analysis. Results: The search identified 272 preliminary results. After discarding duplicates, and screening of titles, abstracts, and full texts, 10 articles finally met inclusion criteria. Data were collected on author's details and their countries, journal and year of publication, type and percentage of infiltration, aging protocol (duration and temperature), mechanical, and microstructural properties. All the included studies invariably revealed better aging resistance without a change in mechanical properties for infiltrated monolithic zirconia as compared to noninfiltrated species. Conclusion: Infiltration within monolithic zirconia can reduce degradation and simultaneously maintain their mechanical properties by preventing water entry into grain contours. The final m content was less for infiltrated Zirconium, indicating a lesser phase transformation and better aging resistance. Other Information: Systematic review protocol registered at PROSPERO CRD42021248153.

Y2O3‐stabilized ZrO2 (YSZ) ceramics have been used for various engineering applications because of their excellent mechanical properties or oxide‐ion conductivity applicable to solid‐electrolyte. The performance of YSZ depends on the sintered texture that is directly determined by sinterability of raw powders. A new kinetic analysis method of diffusion mechanism based on an initial sintering theory (grain‐boundary or volume diffusion) is theoretically derived, the initial sintering mechanism of hydrolytic YSZ powder is experimentally determined, and the effects of powder characteristics on sinterability are discussed. Furthermore, the additive‐enhanced sintering is proposed. A small amount of Al2O3 significantly enhances the densification. Using the additive effect, the low‐temperature degradation that is the fault of zirconia ceramics can be improved by decreasing the sintering temperature. [ABSTRACT FROM AUTHOR]

This study examined the impact of interfacial interactions on bilayer yttria-stabilized zirconia (YSZ) used in dental restorations. In-house bilayer structures of 3YSZ and 5YSZ composition underwent hydrothermal degradation to compare the properties of control and low-temperature degradation (LTD) treated groups. Biaxial flexural strength via piston-on-three-balls, staircase fatigue strength over 10 6 cycles at 15 Hz, phase characterization and quantification through XRD and Rietveld refinement, and fractography were conducted. Weibull analysis was employed to determine the Weibull modulus and characteristic strength. Results demonstrated an enhancement in the mechanical performance of 3YSZ composition after LTD treatment, whereas the mechanical properties of 5YSZ remained largely unaffected post-degradation. Fractographic analysis revealed that failure originated at the surface tensile location across all specimen groups. These findings offer insights into the mechanical behavior of bilayer zirconia structures and reinforce the significance of hydrothermal treatment in enhancing their performance, particularly in the case of 3Y compositions., Competing Interests: Declaration of competing interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2024 Elsevier Ltd. All rights reserved.)

In this study, 3 mol%-Y2O3-stabilized–tetragonal zirconia composite ceramics (3Y-TZP) with 0 wt%–1 wt% nano MgO content were prepared using an atmospheric pressure sintering method at 1,400 °C–1,600 °C. The microstructure, surface phase, and grain size were subsequently investigated using X-ray diffraction and scanning electron microscopy. The mechanical and wear resistance properties were determined using a Vickers microhardness tester, a microcomputer-controlled electronic universal testing machine, and a material surface multifunctional tester. Low-temperature degradation (LTD) was performed in an autoclave at 134 °C/0.2 MPa to evaluate the antidegradation properties. The results indicated that the sintered specimens were all t-ZrO2 at 1,500 °C, with the surface morphology exhibiting a high degree of denseness without the presence of cracks. The average grain size of the sintered specimens at 1,500 °C was 0.28–0.54 μm, whereas the best mechanical properties were obtained for the sample with a nano MgO content of 0.4 wt. %, with a relative density of 96%, a flexural strength of 660.13 MPa, and a Vickers hardness of 1,656.3 HV. The coefficient of friction was 0.15 and the mass wear rate was as low as 0.08 mg/Nm. No significant monoclinic phase was generated after 10 h of LTD, with the monoclinic phase content decreasing from 64.8% to 15.3% after 60 h. [ABSTRACT FROM AUTHOR]

This paper presents a study of Al2O3–ZrO2 (ZTA) nanocomposites with different contents of reduced graphene oxide (rGO). The influence of the rGO content on the physico-mechanical properties of the oxide composite was revealed. Graphene oxide was obtained using a modified Hummers method. Well-dispersed ZTA-GO nanopowders were produced using the colloidal processing method. Using spark plasma sintering technology (SPS), theoretically dense composites were obtained, which also reduced GO during SPS. The microstructure, phase composition, and physico-mechanical properties of the sintered composites were studied. The sintered ZTA composite with an in situ reduced graphene content of 0.28 wt.% after the characterization showed improved mechanical properties: bending strength was 876 ± 43 MPa, fracture toughness—6.8 ± 0.3 MPa·m1/2 and hardness—17.6 ± 0.3 GPa. Microstructure studies showed a uniform zirconia distribution in the ZTA ceramics. The study of the electrical conductivity of reduced graphene oxide-containing composites showed electrical conductivity above the percolation threshold with a small content of graphene oxide (0.28 wt.%). This electrical conductivity makes it possible to produce sintered ceramics by electrical discharge machining (EDM), which significantly reduces the cost of manufacturing complex-shaped products. Besides improved mechanical properties and EDM machinability, 0.28 wt.% rGO composites demonstrated high resistance to hydrothermal degradation. [ABSTRACT FROM AUTHOR]

Aim: The aim of the study is to systematically assess the impact of low-temperature degradation (LTD) simulation in an autoclave on mechanical and microstructural properties of infiltrated monolithic zirconia compared to the noninfiltrated zirconia. Settings and Design: Systematic review following Preferred Reporting Items for Systematic Reviews and Meta-Analysis 2020 guidelines. Materials and Methods: An electronic search was done within these databases: PubMed, Scopus, and Web of Science, Science Direct, Embase, Wiley, Google Scholar for articles published between 2000 and March 2021. Search results that met eligibility criteria were categorized into two groups based on properties assessed of infiltrated monolithic zirconia exposed to LTD (also called aging simulation) - (a) mechanical (flexural strength and fracture toughness) and (b) microstructural properties (phase transformation rate and m content). Statistical Analysis Used: Qualitative analysis. Results: The search identified 272 preliminary results. After discarding duplicates, and screening of titles, abstracts, and full texts, 10 articles finally met inclusion criteria. Data were collected on author's details and their countries, journal and year of publication, type and percentage of infiltration, aging protocol (duration and temperature), mechanical, and microstructural properties. All the included studies invariably revealed better aging resistance without a change in mechanical properties for infiltrated monolithic zirconia as compared to noninfiltrated species. Conclusion: Infiltration within monolithic zirconia can reduce degradation and simultaneously maintain their mechanical properties by preventing water entry into grain contours. The final m content was less for infiltrated Zirconium, indicating a lesser phase transformation and better aging resistance. [ABSTRACT FROM AUTHOR]

The purpose of this study was to fully realize the clinical plausibility of a newly introduced yttria gradient monolithic multilayer dental zirconia and the current indication range for dental zirconia; hence, an investigation leading to a comprehensive understanding of the effect of yttria content on the properties of zirconia was undertaken. Each layer from a yttria gradient monolithic multilayer zirconia system with two types (esthetic and functional types, Meiying Zirconia, UPCERA, China) was selected for investigation of its chemical composition by X-ray fluorescence. Layers with yttria content interval of about 0.4 mol%-0.5 mol% were chosen for subsequent testing. Their phase fractions, grain sizes, low-temperature degradation (LTD) resistance, coefficient of thermal expansion (CTE), and mechanical properties were characterized. The yttria content from the occlusal to the gingival region was from 5 mol% to 4.1 mol% and 4.7 mol% to 3.2 mol% for esthetic type and functional type, respectively. Ultimately, we investigated the selected five yttria content layers, 5Y, 4.5Y, 4Y, 3.6Y, and 3.2Y. With increased yttria content, increasing cubic phase fractions (from 25.86 wt% to 58.53 wt%) and mean grain sizes (from 0.31 μm to 0.72 μm) were detected; monoclinic content after LTD decreased; and there was a decreasing tendency for CTE, although no statistically significant difference was found (F = 2.43, p = 0.117). In addition, yttria dopant showed no effect on elastic modulus (F = 2.43, p = 0.464) but slightly increased hardness (F = 4.10, p = 0.014). However, there were notable decreases in fracture toughness (F = 227.58, p < 0.001), biaxial flexural (F = 52.31, p < 0.001), and fatigue strength (F = 56.52, p < 0.001). The percentages of strength degradation from monotonic to fatigue tests were about 33%–40%, independent of yttria doping (F = 1.82, p = 0.136). [ABSTRACT FROM AUTHOR]

ZrO2‐based ceramics are widely used in biomedical applications due to its color, biocompatibility, and excellent mechanical properties. However, low‐temperature degradation (LTD) introduces a potential risk for long‐term reliability of these materials. The development of innovative nondestructive techniques, which can explore LTD in zirconia‐derived compounds, is strongly required. Yttria stabilized zirconia, 3Y‐TZP, is one of the well‐developed ZrO2‐based ceramics with improved resistance to LTD for dental crown and implant applications. Here, 3Y‐TZP ceramic powders were pressed and sintered to study the LTD phenomenon by phase transition behavior. The LTD‐driven tetragonal‐to‐monoclinic phase transition was confirmed by XRD. XPS analysis demonstrated that induced LTD reduced the oxygen vacancies which supports these findings. It is proved that after the degradation, the 3Y‐TZP ceramics show the decreased dielectric permittivity at terahertz frequencies due to the crystallographic phase transformation. Terahertz nondestructive probe is a promising method to investigate LTD in zirconia ceramics. [ABSTRACT FROM AUTHOR]

Objectives: This work aimed to evaluate the effect of artificial aging on the translucency and color difference (ΔE) of ultra-translucent zirconia and provide a reference for clinical application., Methods: The discs of ultra-translucent zirconia from six brands (Wieland, 3M ESPE, Amann Girrbach, Kuraray Noritake, Upcera, and Besmile) were cut and sintered according to each manufacturer's product instructions; the experimental groups were named ZNT, LVP, AG, KAT, UPC, and BSM, respectively. IPS e.max Press was used as the control group (PLT). The specimens ( n =6) were prepared with a diameter of 14 mm and a thickness of 1 mm. The specimens were subjected to artificial aging treatment according to the following conditions: in an autoclave at 134 ℃ at 0.2 MPa for 4, 8, and 12 h. According to the CIE1976Lab system, the CIE L*, a*, and b* values of the specimens before and after aging were measured by a co-lorimeter. The translucency parameter (TP) and ΔE were calculated., Results: The mean TP values of each group before aging inorder were PLT>KAT>AG>ZNT>BSM>UPC>LVP. We found no significant difference in translucency in all experimental groups after aging for 4 and 8 h compared with those before aging. After 12 h of aging, the TP values of the KAT and ZNT groups were not significantly different from those before aging, but the TP values of the AG, BSM, LVP, and UPC groups were significantly lower than those before aging ( P <0.05). The TP value of the control group was significantly higher than that of the other experimental groups at different stages ( P <0.05). ΔE=3.3 was considered the visible color difference, and ΔE was less than 3.3 in all groups after 4 h of aging. After aging for 8 h, ΔE of the UPC group was slightly higher than 3.3. ΔE of the BSM and UPC groups was greater than 3.3 after 12 h of aging., Conclusions: The TP and ΔE of different brands of ultra-translucent zirconia may change after various aging times. The translucency of some zirconia showed a decreasing trend and the color difference showed an increasing trend with the aging time.

Long-term, reliable operation of Solid Oxide fuel and electrolysis Cell (SOCs) necessitates cells with high strength and resistance to mechanical degradation. In this work, strength, Young's modulus and Low-Temperature Degradation (LTD) of several zirconia-based SOCs supports are studied. The study shows that replacing 3YSZ with a tetragonal zirconia compound having lower stabilizer contents can improve the strength of porous supports. An enhancement up to 30 % over the-state-of-the-art support (NiO‒3YSZ) can be achieved for example with using NiO‒2.5YSZ. It is further evidenced that tetragonal zirconia-based SOC components (both Y-doped and Ce-Y co-doped) are susceptible to LTD in the studied range of grain sizes (i.e. ≈ 200−300 nm). Addition of small amount of alumina (0.5 wt%) is observed to increase the LTD resistance of porous supports. The susceptibility to LTD must be considered in designing materials for SOCs, also during materials processing, storage, handling and operation where a dry atmosphere is recommended. [ABSTRACT FROM AUTHOR]

Nanocrystalline ceramic samples of the ZrO2–3 mol % Y2O3 composition with varying degrees of tetragonality c/a (1.4337 and 1.0425) are obtained. The process of the low-temperature degradation of ceramics is studied by the methods of X-ray phase analysis and electron microscopy. It is found that samples with a high degree of tetragonality are more resistant to the action of a humid environment, while the phase composition in the bulk of the samples remains practically unchanged and the transformation t-ZrO2 → m-ZrO2 occurs mainly in the surface layers without significantly affecting the mechanical properties of the ceramics. [ABSTRACT FROM AUTHOR]

• In vivo aging kinetics was assessed for biomedical grade 3Y-TZP ceramics. • 2-year exposure showed ∼3-times faster aging kinetics compared to in vitro extrapolation. • Airborne-particle abrasion significantly suppresses in vivo aging. • Surface degradation after 2-year in vivo was within clinically acceptable range. In vivo aging of biomedical grade 3Y-TZP ceramics in the oral environment was assessed and compared to artificially accelerated in vitro hydrothermal aging extrapolations at 37 °C. 88 discs were pressed and sintered (1450–1500 °C) from two commercial 3Y-TZP compositions containing 0.25% Al 2 O 3 to generate finer- and coarser-grained specimens. As-sintered (AS) and airborne-particle abraded (APA; 50 μm Al 2 O 3) surfaces were investigated. In vivo aging was performed by incorporating specimens in lingual flanges of complete dentures of 12 edentulous volunteers who wore them continuously for up to 24 months. For comparison, in vitro hydrothermal aging at 134 °C was also performed and analysed by XRD and (FIB)-SEM. Data was statistically analysed with linear regression models. Finer and coarser-grained specimens exhibited statistically insignificant differences in aging in vivo. The monoclinic fraction (X m) on AS surfaces abruptly increased to ∼8% after 6 months. The aging process then proceeded with slower linear kinetics (∼0.24%/month). After 24 months, X m reached ∼12%. The calculated maximum transformed layer was 0.385 μm representing one layer of transformed grains. APA surfaces were highly aging resistant. The initial X m of ∼4.0% linearly increased by 0.03%/month in vivo. In vitro aging exhibited an initial induction period, followed by linear aging kinetics. Coarser-grained AS surfaces aged significantly faster than fine-grained (2.41%/h compared to 2.16%/h). APA discs aged at a rate of 0.3%/h in vitro. Microcracking within a single grain and pull-out of grain clusters were observed on aged AS surfaces. Biomedical grade 3Y-TZP was susceptible to in vivo aging. After 2 years in vivo , the aging kinetics were almost 3-times faster than the generally accepted in vitro-in vivo extrapolation. [ABSTRACT FROM AUTHOR]

Niobia (1 mol. %) doped Ceria Stabilized Zirconia (NbCSZ) powders were synthesized using a co-precipitation method. The synthesized powders were uniaxially compacted and sintered in air. The two-step sintering method was adopted to sinter the samples, and the sintering schedule was optimized based on density, grain size, the phase present, and the hardness of the sintered sample. It was observed that the two-step sintering method effectively suppressed the grain growth of NbCSZ samples and helped in achieving a finer grain size of 1.57 μm along with the hardness of 1195 HV10 and optimum fracture toughness value 6.20 MPa m1/2. The Low-Temperature Degradation (LTD) behavior of the sintered samples was estimated through an accelerated hydrothermal aging test, which revealed that the samples are highly resistant to LTD and shown no phase change even after 150 h of study. Moreover, the cytocompatibility of the NbCSZ was tested by culturing MG63 cells on the samples for 7 days. The NbCSZ was found to be highly biocompatible as evident from cell viability and metabolic activity assay. [ABSTRACT FROM AUTHOR]

Objectives: Fatigue and low-temperature degradation (LTD) are the main factors contributing to zirconia restoration failure. This study evaluated the effect of LTD on the fatigue performance of the novel "strength & shade-gradient" multilayered zirconia restorations., Methods: Discs (15 mm × 1.2 mm) of each yttria content layer from a newly developed strength-gradient multilayered zirconia were fabricated and under accelerated aging in an autoclave at 134℃ for 0 h, 32 h, and 64 h. Then, the phase transformation, microstructure, and mechanical properties after LTD were assessed. In addition, the crown samples, including the multi-Zir, 3Y-Zir, and 5Y-Zir were fabricated, and their monotonic and fatigue load before and after LTD, percentage of fatigue degradation (S d ) and the fracture morphology were investigated. Statistical analyses were performed using paired samples t-test (α' = α/3 = 0.017), one-way ANOVA and Weibull analysis., Results: After LTD, the phase transformation, surface roughness, depth of transformed zone, and residual stress were increased and inversely associated with the yttria content. The indentation elastic modulus and hardness after LTD decreased; however, there was no significant difference between the different yttria content layers. The monotonic and fatigue load of multi-Zir restorations decreased, but their Weibull modulus increased, and S d decreased, similar to 3Y-Zir. The crack origin was associated with the cervical region., Conclusion: These results show that although LTD reduces the absolute fatigue strength of strength-gradient multilayered zirconia restorations, it also reduces the effect of cyclic fatigue itself on the strength of zirconia (relative to monotonic strength), which might be due to the increase of residual stress., Clinical Significance: The novel "strength & shade-gradient" multilayered zirconia restorations show a promising performance during in vitro LTD and fatigue test and their reliability to some extent is comparable to 3Y-Zir. Yet, further in vivo longitudinal studies are warranted to confirm their precise performance., Competing Interests: Declaration of competing interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2024 Elsevier Ltd. All rights reserved.)

Objectives: This work aimed to evaluate the effect of speed sintering and low-temperature degradation on the translucency of high-translucent zirconia., Methods: The ST and TT specimens were randomly divided into two groups depending on the sintering process: conventional sintering and speed sintering. The sintered specimens were divided into three subgroups according to the aging time: aged for 0, 5, and 20 h. Chromatic parameters (L*, a*, and b* values) were measured by Shade Eye NCC computer colorimeter in a dark environment under black and white background, and the translucency parameter (TP) was used to evaluate the translucency of zirconia., Results: Speed sintering may decrease the TP of ST and increase the TP of TT. As for the effect of low-temperature degradation on the translucency of zirconia, the TP of ST decreased with the extension of aging time, and no significant difference was found in rapid sintering ST. Although the TP of TT decreased, no statistical difference was observed., Conclusions: Speed sintering may decrease the translucency of high-strength zirconia and increase the translucency of high-translucent zirconia. Low-temperature degradation had no effect on the translucency of high-translucent zirconia. Speed sintering can be recommended for high-translucent zirconia in terms of translucency.

Abstract In this research, results of the investigation of the sliding friction and wear of yttria-stabilized tetragonal zirconia polycrystalline (Y-TZP) and Y-TZP-Al2O3 samples preliminarily subjected to low-temperature degradation are reported. The investigation was carried out using a pin-on-disk tribometer with simultaneous recording of acoustic emission (AE) and vibration acceleration. The sliding wear process was found to be determined by dynamic direct and inverse Y-TZP transformations detected by monoclinic and tetragonal X-ray diffraction peak ratios. The AE signals generated under direct and inverse transformations can be used to characterize wear and friction mechanisms as well as direct and inversed sliding-induced phase transformations. The AE signal energy grows with the friction coefficient and the inverse transformation degree. Reduction of the AE signal energy indicates establishing the mild wear stage caused by effective stress-induced direct martensitic transformation. The AE signal median frequency increases in the case of lower friction. Numerical studies of wear subsurface fracture under conditions of stress-induced martensitic transformation were used to elucidate the role played by the phase transformation in Y-TZP and Y-TZP-Al2O3. Martensitic transformation in Y-TZP was described with use of the non-associated dilatant plasticity model. Simulation results particularly show that increase in the value of dilatancy coefficient from 0 to 0.2 is accompanied by 25%−30% reduce in characteristic length and penetration depth of sliding-induced subsurface cracks. As shown the AE may be an effective tool for in-situ monitoring the subsurface wear of materials experiencing both direct and inverse transformations.

This study aimed to evaluate the effects of low-temperature degradation (LTD) on the translucency, flexural strength, and surface hardness of ultra-transparent 5Y-TZP ceramics. Three commercial zirconia materials were investigated, including 5Y-TZP and two 3Y-TZP samples. The LTD process was mimicked by hydrothermal aging at 134 °C for 20 h. The translucency parameters (TPs) corresponding to different thicknesses were analyzed. The surface volume fraction of the monoclinic phase was determined by X-ray diffraction (XRD). The three-point flexural strength was measured, and the surface hardness was measured by the indentation method. The translucency of all three ceramics showed a significant decrease with increasing thickness. A translucency gradient was present within a ceramic block of 5Y-TZP, whose translucency was higher than that of both 3Y-TZP products. Aging at 134 °C for 20 h did not reduce the TPs of the three ceramics. The XRD analysis showed a high monoclinic phase content in both 3Y-TZP surfaces after aging, while no monoclinic phase was detected in 5Y-TZP. Hydrothermal aging had no significant effect on the flexural strength; however, the flexural strength of 5Y-TZP was significantly lower than that of 3Y-TZP. No statistical difference in surface hardness was observed among the three products. In summary, 5Y-TZP presented higher LTD resistance than 3Y-TZP. [ABSTRACT FROM AUTHOR]

The low-temperature degradation and mechanical properties of 3Y-TZP- x YF 3 ceramics synthesized by a conventional solid-state reaction were investigated. The addition of YF 3 has a significant effect on the aging and mechanical properties of 3Y-TZP ceramics. The results show that the mechanical properties and aging resistance of 3Y-TZP- x YF 3 ceramics with slow grain growth are greatly improved when the content of YF 3 is maintained in a reasonable biphasic region (RBR) due to the dominant role of T-M (tetragonal to monoclinic). When the content of YF 3 exceeds 0.15 mol%, the mechanical properties and aging properties of ceramics in a saturated biphasic region (SBR) decrease due to the influence of T-C (tetragonal to cubic). More importantly, 3Y-TZP-0.15YF 3 ceramics have good aging resistance and mechanical properties, and YF 3 doping makes the application of 3Y-TZP in dental ceramics more meaningful. [ABSTRACT FROM AUTHOR]

This study compared the physical properties of conventional and monolithic yttria-zirconia (Yz) materials after low-temperature degradation (LTD). Bar-shaped specimens (2.0 mm thick × 4.0 mm wide × 16.0 mm in length) were produced. Autoclave aging was executed at 134°C under 2 bar pressure for 5 h. The surface characteristics were assessed using a confocal laser microscope, microstructural phase alterations via an X-ray diffractometer (XRD), 3-point flexural strength using a universal testing machine, Vickers microhardness via a digital microhardness tester, and toughness using a durometer. Fractured specimens and indented surfaces was observed via a scanning electron microscope for fractography characterization. All of the data underwent specific statistical tests considering their distribution and homogeneity. Regarding topography, different Yz materials were very similar after LTD. Conventional Yz materials were smoother. The XRD data support that both materials were mainly composed of tetragonal crystals, whereas slight monoclinic peaks were detected. Monolithic Yz showed higher flexural strength than conventional Yz. All of the fractures started on surface defects at the side where tensile stress was concentrated (opposite to load application) and propagated to the opposite side. Vickers microhardness and toughness analysis found that conventional Yz had higher performance than monolithic Yz. This study has found that there are slight differences in strength, hardness, and toughness between conventional and monolithic yttria-stabilized zirconia ceramics, although both materials demonstrate adequate performance for clinical use. [ABSTRACT FROM AUTHOR]

This study aimed to assess the effect of low-temperature degradation (LTD) and surface treatment on the flexural strength of additive-manufactured (AM) zirconia by comparison to subtractive-manufactured (SM) zirconia. Disc-shaped zirconia specimens were fabricated using AM and SM technology, and each group was assigned to 3 subgroups according to the type of surface treatment: control, sandblasting (SB), and 9% hydrofluoric acid etching (HF). The groups were then further divided into 2 subgroups: unaged and aged. Biaxial flexural strength, crystal phase, surface topography, and surface roughness were measured to evaluate the mechanical properties. Statistical analyses were performed with 3-way ANOVA, followed by the comparison of means with Bonferroni post hoc analyses. The means and standard deviations of the biaxial flexural strength and Weibull parameters were calculated with descriptive statistics. All SM groups showed significantly greater flexural strength than the AM groups (p <.05), and LTD did not affect flexural strength except for the SMHF group (p <.05). After LTD, monoclinic phases (m-phase) were found in all groups, and SEM images showed grain pullout due to zirconia volume expansion in both control groups. Sandblasting significantly affected flexural strength (p <.05), whereas the HF group did not affect flexural strength except in the SMHF group after LTD (p <.05). No significant difference was observed in the surface roughness of AM compared to SM groups conditioned with the same surface treatment regardless of LTD. AM zirconia has comparable mechanical properties to SM zirconia, regardless of low-temperature degradation and surface treatment, which indicates the potential of the AM technique for clinical applications. [ABSTRACT FROM AUTHOR]

Abstract The aim of this investigation was to discuss the mechanical properties and aging-resistance of 3Y-TZP (3 mol% yttria-tetragonal zirconia with 0–0.25 wt% alumina added 3Y-TZP) by comparing the effect of high-energy ball milling zirconia powders (HP) and commercially available zirconia powders (CP). The results showed that a hardness of 12.93 GPa, combined with an excellent high-fracture toughness of 9.17 MPa m1/2, could be attained for HP-doped (0–0.25 wt% (Al 2 O 3)) ceramics, as well as an increase in hydrothermal stability with the increase in Al 2 O 3 content. The HP + 0.15 wt% (Al 2 O 3) ceramics exhibited better antiaging performance and mechanical properties. These 3Y-TZP ceramics, with high-fracture toughness and better aging-resistance, which were prepared by a high-energy ball milling method, could meet the different demands of practical dental ceramics. [ABSTRACT FROM AUTHOR]

Abstract A comprehensive study on the influence of typical additives on zirconia (ZrO 2) crystallization was presented. Zirconium nitrate pentahydrate (Zr(NO 3) 4 ·5H 2 O) and cerium(III) nitrate hexahydrate (Ce(NO 3) 3 ·6H 2 O) were employed as reagents, ethylenediaminetetraacetic acid disodium salt (EDTA-2Na) or glycerol were adopted as additives, and ammonia water was adopted as pH regulator. The ZrO 2 powders were prepared by hydrothermal method. The crystal phase purity, grain size and micro morphology of the ZrO 2 powders were characterized by X-ray diffraction (XRD), scanning electron microscope (SEM) equipped with energy dispersive spectrometer (EDS) to investigate the influence of EDTA-2Na, glycerol and Ce4+ content on the purity of tetragonal phase and the grain size of ceria-stabilized tetragonal zirconia polycrystals (Ce-TZP). It was found that EDTA-2Na could decrease the purity of tetragonal phase and alter the grain size of Ce-TZP nonlinearly, while glycerol could not decrease the purity of tetragonal phase and the grain size of Ce-TZP, and the grain size was not linear with the amount of glycerol; Doping Ce4+ could increase the purity of tetragonal phase of zirconia but could not decrease the grain size, and the grain size was not linear with the Ce4+ content; In addition, it was indicated that EDTA-2Na and glycerol could not improve the distribution uniformity of Ce4+. This study is expected to have provided a novel path to achieve tailored ZrO 2 crystals with reduced low-temperature degradation. [ABSTRACT FROM AUTHOR]

Purpose: To evaluate the influence of specimen thickness and low‐temperature degradation (LTD) on yttrium‐stabilized tetragonal zirconia polycrystals (Y‐TZP). Materials and Methods: Thin discs of Y‐TZP from four manufacturers were sintered according to each manufacturer's recommendations, cut into 23 mm (length) × 4 mm (width) × 0.8 mm/1.5 mm (thickness) specimens, artificially aged under standard autoclave sterilization conditions (34°C at 0.2 MPa for 10 and 20 hours), and finally ground and polished. Tetragonal to monoclinic transformation was confirmed by X‐ray diffraction (XRD) analysis. Flexural strength was measured by 3‐point bending tests and Vickers hardness measurements. Fracture surfaces were examined by scanning electron microscopy (SEM). Results: SEM investigation revealed that with increasing aging time, the surface defects and grain size increased, particularly in the 20‐hour group. Compared with the 1.5 mm group, the 0.8 mm group showed more significant defects, irrespective of aging time. The flexural strengths of Y‐TZP materials decreased with a decrease in the thickness. Moreover, LTD of Y‐TZP can cause significant tetragonal to monoclinic transformation, which also results in a statistically significant decrease in the flexural strength. Conclusion: A thinner Y‐TZP specimen was likely to present surface defects and microcracks after aging. In addition, the flexural strengths decreased with a decrease in the thickness, a notable fact for further studies. [ABSTRACT FROM AUTHOR]

Abstract The state of understanding on the devastating effects of hydrothermal ageing on the properties of yttria-tetragonal zirconia polycrystal (Y-TZP) when exposed to humid environment are reviewed. The prime factors governing the ageing-induced tetragonal to monoclinic phase transformation include the tetragonal grain size, sintering techniques particularly two-step sintering, microwave sintering and electric field assisted sintering, and yttria content are discussed. In addition, the beneficial effects of sintering additives or dopants in promoting sintering as well as suppressing the ageing-induced monoclinic formation are also deliberated. Selective dopants and co-dopants such as copper oxide, alumina, iron oxide and magnesium oxide were found to be beneficial in suppressing hydrothermal ageing in zirconia. Other important boundary conditions to be considered when evaluating the ageing behaviour of Y-TZP includes the ageing environment i.e. temperature, medium and applied pressure which were discovered to have an impact on the rate of phase transformation. Furthermore, the effects of ageing-induced monoclinic formation on the surface topography and mechanical properties of Y-TZP are reviewed. This review indicated that the ageing of Y-TZP can be rather intricate as there are many combinatory factors that needs to be tailored in order to develop an ageing-resistant zirconia without compromising on the transformation toughening effect and other properties. [ABSTRACT FROM AUTHOR]

The degradation of tetragonal zirconia polycrystalline (3Y-TZP) ceramics prepared by a novel film growth technique, and by sintering at 1400 °C, was evaluated for one year using two processes: (i) degradation under oral conditions in artificial saliva (37 °C and pH 6.8) and (ii) accelerated degradation by autoclaving at 134 °C at 0.2 MPa of pressure. X-ray diffraction analysis of 3Y-TZP ceramics sintered at 1400 °C showed a phase transformation (tetragonal to monoclinic) in 3Y-TZP ceramics after the fifth month in artificial saliva. After 12 months in artificial saliva, there was ∼11% of monoclinic phase present in 3Y-TZP ceramics, but only ∼2% of monoclinic phase in samples that were subjected to accelerated degradation for 5 h. No correlation was found between the level of ageing during accelerated degradation and degradation in artificial saliva. There was no degradation of 3Y-TZP ceramics prepared by a novel film growth technique, independently of the degradation method used, which suggests that this material could be used for dental prosthetics.

Abstract This study aimed to characterize and compare the effect of different aging regimens on surface characteristic (topography and roughness), structural stability (phase transformation) and mechanical performance (Weibull analysis) of a Y-TZP ceramic. Discs (15 × 1.2 mm; VITA In-Ceram YZ) were prepared according to ISO 6872-2015 for biaxial flexural strength testing and randomly assigned into five groups (n = 30): as-sintered, no aging treatment (CTRL); 20 h in autoclave at 134°C, 2 bar pressure (AUT); intermittent mechanical loading at 20 Hz/106 load pulses (MechLoad); AUT followed by MechLoad (AUT+MechLoad); and storage in distilled water at 37°C, for 1 year (STO). The following analyses were performed: roughness (n = 30), surface topography (n = 2), phase transformation (n = 2) and biaxial flexure strength (n = 30). Phase transformation (increase of m-phase content) was shown to be a spontaneous, unavoidable and time-dependent process, occurring even under ambient conditions (dry storage after 1 year = 6.0% increase), and is considerably accelerated in the presence of moisture (STO = 17.6%; AUT= 63.1%; and AUT+MechLoad = 59.9%). For roughness parameters, only Ra was affected by aging, and the highest values were observed for AUT+MechLoad (0.25 ± 0.07 µm). For Weibull analysis, structural reliability (Weibull moduli) and characteristic strength were not impaired after aging, and some aging conditions led to increased values (highest weibull moduli in AUT, and highest characteristic strength in STO). Phase transformation proves to be a time-dependent spontaneous mechanism that is accelerated in the presence of different stimuli. However, none of the aging regimens had a negative effect on the characteristic strength and structural reliability of Y-TZP ceramic.

In this research, results of the investigation of the sliding friction and wear of yttria-stabilized tetragonal zirconia polycrystalline (Y-TZP) and Y-TZP-Al2O3 samples preliminarily subjected to low-temperature degradation are reported. The investigation was carried out using a pin-on-disk tribometer with simultaneous recording of acoustic emission (AE) and vibration acceleration. The sliding wear process was found to be determined by dynamic direct and inverse Y-TZP transformations detected by monoclinic and tetragonal X-ray diffraction peak ratios. The AE signals generated under direct and inverse transformations can be used to characterize wear and friction mechanisms as well as direct and inversed sliding-induced phase transformations. The AE signal energy grows with the friction coefficient and the inverse transformation degree. Reduction of the AE signal energy indicates establishing the mild wear stage caused by effective stress-induced direct martensitic transformation. The AE signal median frequency increases in the case of lower friction. Numerical studies of wear subsurface fracture under conditions of stress-induced martensitic transformation were used to elucidate the role played by the phase transformation in Y-TZP and Y-TZP-Al2O3. Martensitic transformation in Y-TZP was described with use of the non-associated dilatant plasticity model. Simulation results particularly show that increase in the value of dilatancy coefficient from 0 to 0.2 is accompanied by 25%−30% reduce in characteristic length and penetration depth of sliding-induced subsurface cracks. As shown the AE may be an effective tool for in-situ monitoring the subsurface wear of materials experiencing both direct and inverse transformations. [ABSTRACT FROM AUTHOR]

The aim of this study was to determine the effect of aging on the biaxial flexural strength (BFS) of Ce-TZP/Al 2 O 3 and Y-TZP after occlusal adjustment. NanoZr block (Ce-TZP/Al 2 O 3 nanocomposite) and Katana zirconia block (Y-TZP) were prepared by milling with the aid of CAD/CAM into disk-shaped specimens. For each type of zirconia, 16 specimens were prepared without grinding for the control group (diameter of 16 mm and thickness of 1.20±0.05 mm, mean±SD), while 48 specimens were prepared for 3 experimental groups ( n =16 each; 16 mm in diameter and 1.50±0.05 mm thick) with different types of surface grinding: superfine diamond bur (group I), zirconia stone bur (group II), and zirconia stone and fine polishing bur (group III). These specimens underwent an aging process in a steam autoclave for 5 h at 0.2 MPa and 134 °C, and then X-ray diffractometry was applied along with measurements of surface roughness and BFS. After occlusal adjustment, the monoclinic phase percentage increased in 3 experimental groups. Overall the increase was greater for Ce-TZP/Al 2 O 3 than for Y-TZP. The Ra value showed similar changes for both types of zirconia. Following the aging process, Y-TZP showed a greater increase in the monoclinic phase percentage, but the change was not statistically significant. The Ra value showed similar changes in both types of zirconia, with no significant differences between before and after the aging process. The results of the BFS test showed that applying the aging process after grinding significantly increased the strength of both types of zirconia, with Ce-TZP/Al 2 O 3 being significantly stronger than Y-TZP. The specimens treated by a superfine diamond bur exhibited the highest BFS in the four tested groups. Ce-TZP/Al 2 O 3 had a higher BFS and greater resistance to low-temperature degradation than did Y-TZP. [ABSTRACT FROM AUTHOR]

Objective The combined effects of alumina airborne-particle abrasion and prolonged in vitro ageing on the flexural strength of 3Y-TZP ceramic have been studied. The aim was to identify the different effects on the surface and subsurface regions that govern the performance of this popular bioceramic known for its susceptibility to low-temperature degradation (LTD). Methods As-sintered or airborne-particle abraded 3Y-TZP discs were subjected to ageing at 134 °C for up to 480 h. Biaxial flexural strength was measured and the relative amount of monoclinic phase determined using X-ray diffraction. The transformed zone depth (TZD) was observed on cross-sections with scanning electron microscopy coupled with a focused ion beam. Segmented linear regression was used to analyze the flexural strength and TZD as functions of the ageing time. Results A two-step linear ageing kinetics was detected in airborne-particle abraded specimens, reflecting the different microstructures through which the LTD proceeds into the bulk. A 10 μm thick altered zone under the abraded surface was involved in both the surface strengthening and the increased ageing resistance. When the zone was annihilated by the LTD, the strength of the ceramic specimens and the speed of LTD returned to the values measured before abrasion. Even at prolonged ageing times, the strength of abraded groups was not lower than that of as-sintered groups. Significance Both the ageing kinetics and the flexural strength were prominently affected by airborne-particle abrasion, which altered the subsurface microstructure and phase composition. Airborne-particle abrasion was not harmful to the 3Y-TZP ceramics’ stability. [ABSTRACT FROM AUTHOR]

Purpose The purpose of this study was to determine if the optical properties of zirconia and glass–ceramic (e.max) were affected by low-temperature degradation (aging). Methods Experiment samples were fabricated with seven zirconia brands (n = 10): Zenostar, Zirlux, Katana, Bruxzir, DD-BioZX 2 , DD-cubeX 2 , NexxZr; and e.max were used as a control. This resulted in a total of 80 samples in the experiment. The L*, a* and b* were measured for each sample, and then the optical properties including translucency parameter (TP), contrast ratio (CR), and opalescence parameter (OP) were calculated. The samples were aged (20, 40, 60, 80, 100 h), and the optical properties were calculated after each interval. Results Most zirconia brands had lower L*, higher a*, higher b* with increased aging, which visually corresponds to darker, redder, and more yellow. Aging also increased CR, lowered TP, and lowered OP. e.max was also affected by aging but still had the highest TP (23.9 ± 2.8), L* (81.7 ± 3.4), and lowest CR (0.41 ± 0.05) compared to any zirconia. The Zenostar had the closest TP (24.1 ± 0.4), and L* (90.2 ± 0.5) values to e.max before aging. However, after 100 h of aging, the DD-cubeX 2 was least effected and had the highest TP (22.2 ± 0.6) and lowest CR (0.43 ± 0.01) compared with other zirconia samples and highest OP (11.3 ± 0.2) of all ceramic samples. Conclusions The optical properties of zirconia and e.max materials were affected by aging with the effects increasing with time. The magnitude of change was affected by seven brands of dental zirconia. [ABSTRACT FROM AUTHOR]

This study aimed to characterize and compare the effect of different aging regimens on surface characteristic (topography and roughness), structural stability (phase transformation) and mechanical performance (Weibull analysis) of a Y-TZP ceramic. Discs (15 ~ 1.2 mm; VITA In-Ceram YZ) were prepared according to ISO 6872-2015 for biaxial flexural strength testing and randomly assigned into five groups (n = 30): as-sintered, no aging treatment (CTRL); 20 h in autoclave at 134°C, 2 bar pressure (AUT); intermittent mechanical loading at 20 Hz/106 load pulses (MechLoad); AUT followed by MechLoad (AUT+MechLoad); and storage in distilled water at 37°C, for 1 year (STO). The following analyses were performed: roughness (n = 30), surface topography (n = 2), phase transformation (n = 2) and biaxial flexure strength (n = 30). Phase transformation (increase of m-phase content) was shown to be a spontaneous, unavoidable and time-dependent process, occurring even under ambient conditions (dry storage after 1 year = 6.0% increase), and is considerably accelerated in the presence of moisture (STO = 17.6%; AUT= 63.1%; and AUT+MechLoad = 59.9%). For roughness parameters, only Ra was affected by aging, and the highest values were observed for AUT+MechLoad (0.25 ± 0.07 ƒÊm). For Weibull analysis, structural reliability (Weibull moduli) and characteristic strength were not impaired after aging, and some aging conditions led to increased values (highest weibull moduli in AUT, and highest characteristic strength in STO). Phase transformation proves to be a time-dependent spontaneous mechanism that is accelerated in the presence of different stimuli. However, none of the aging regimens had a negative effect on the characteristic strength and structural reliability of Y-TZP ceramic. [ABSTRACT FROM AUTHOR]