Y-TZP Ceramics Research Articles

Effect of grain size on mechanical properties and aging of yttria-stabilized tetragonal zirconia polycrystal fabricated by stereolithography-based additive manufacturing

The objective of this investigation was to comprehensively assess the impact of grain size on the mechanical properties and low-temperature degradation (LTD) of yttria-stabilized tetragonal zirconia polycrystal (3Y-TZP) fabricated by stereolithography-based additive manufacturing at the submicron scale. Four 3Y-TZP ceramics with high relative density (>98%), ranging in grain size from 0.2 μm to 1 μm, were successfully prepared and validated for studying mechanical properties (including Vickers hardness, fracture toughness, and flexural strength) as well as LTD progression. This study elucidates the mechanical behavior of zirconia ceramics at the submicron scale, focusing on fracture micromechanisms and the grain size dependence of transformation toughening. Additionally, it examines the influence of grain size on the hydrothermal aging behavior of zirconia ceramics at the submicron scale using Raman spectroscopy.

Effect of surface textures fabricated by two-dimensional ultrasonic vibration-assisted milling on the key surface properties of dental ceramics

The exceptionally high hardness and active plaque adhesion ability of 3Y-TZP ceramics often cause lots of oral diseases. This work intends to enhance the service performance of such ceramic dentures in human oral cavity by surface texturing technique. Efforts have been made to tackle the surface texture formation mechanism under 2D-UVAM process and establish the connection between the key surface properties and texture morphologies. The impacts of cutting parameters, vibration parameters, and tool geometry parameters on texture morphologies were rigorously studied. The coupling effect of wettability, antibacterial activity, and frictional performance of textured ceramic surfaces was also investigated. The acquired results indicate that the fish-scale texture with high density helps to enhance the hydrophobicity of the zirconia ceramics, while the wavy texture with low density promotes the ceramic material towards a hydrophilic direction. The antibacterial activity is highly related to wettability. The larger contact angle generally means the more pronounced inhibition effect on plaque adhesion. The wear of natural teeth decreases significantly after introducing textures on the ceramic surfaces, but the wear amount is not sensitive to wettability. Therefore, the hydrophobic surface can simultaneously improve the antibacterial characteristics of 3Y-TZP ceramics and its tribological compatibility with the natural teeth.

The impact of aging and thickness on flexural strength of various zirconia ceramics

BackgroundEffects of the aging process on the flexural strength of Y-TZP and different Y-PSZ ceramics of different thicknesses were investigated.Methods300 disc-shaped samples (12 mm diameter, 0.8 and 1.5 mm thicknesses) were made from 5 different zirconia materials 3Y-TZP LA, 4Y-PSZ, 5Y-PSZ, 3 + 5Y-PSZ and 4 + 5Y-PSZ. Experimental groups were artificially aged in an autoclave at 134 °C, 2 bar pressure for 1 and 5 h; control groups were not subjected to any treatment. Microstructural analysis was conducted using Scanning Electron Microscopy, and X-Ray Diffraction analysis determined the crystalline phase content. The impact of aging on flexural strength was investigated with the use of the biaxial flexural strength test. Data were analyzed using three-way ANOVA tests with a significance level of p < 0.05, applying Bonferroni correction for multiple comparisons.ResultsStatistically significant differences in flexural strength were observed among the materials and the material thicknesses (p < 0.05), while there were no significant differences among the aging times (p > 0.05). The highest mean flexural strength values were recorded in the case of the 3 Y-TZP-1.5 mm–5 h group (744.1 ± 61.2 MPa), which was attributed to phase-transformation toughening. The lowest values were observed in the case of the 5 Y-PSZ-1.5 mm–5 h (338.3 ± 34.8 MPa) group.ConclusionsBoth material type and thickness significantly affect the flexural strength of zirconia ceramics, whereas aging time does not; thus, material selection and thickness are crucial considerations for clinicians.

Effects of external staining on mechanical, optical, and biocompatibility properties of additively manufactured 3Y-TZP ceramic for dental applications

Three mole percent yttria-stabilized tetragonal zirconia polycrystal (3Y-TZP) ceramics are exemplary materials for dental restoration due to their high mechanical strength, fracture toughness, chemical endurance, and biocompatibility. Nevertheless, 3Y-TZP ceramics are opaque and their CAD/CAM manufacturing process may cause micro-cracks in conventional clinical practice. In this study, 3Y-TZP ceramic samples were prepared using vat photopolymerization, pre-sintering, external staining, and final high-temperature sintering. The microstructures, mechanical properties, optical properties, and cytotoxicity of the 3Y-TZP ceramic samples were investigated. The results indicate that with increasing Fe3+ concentration of staining solution from 0.1 mol/L to 0.3 mol/L and increasing staining time from 5 s to 30 min, the 3Y-TZP ceramic samples showed a tetragonal crystal structure of zirconia with densely packed grains and a slight increase in grain size. The flexural strength, Vickers hardness, and fracture toughness of 3Y-TZP ceramic samples stained in 0.1–0.3 mol/L Fe3+ solution for 5 s to 3 min were all greater than 665 MPa, 11.9 GPa, and 5 MPa m1/2, respectively, meeting the mechanical requirements for clinical application. Colorimetric analysis revealed a decrease in L* (black-white index) from 90.4 to 81.3, an increase in a* (green-red index) from −1.5 to 3.2, and an increase in b* (blue-yellow index) from 11.6 to 20.3, approximating the commercial VITA 3D-Master Shade Guide chromaticity. Furthermore, the 3Y-TZP ceramic samples exhibited a cell viability of 90% or higher toward L929 cells.

Novel zirconia ceramics for dental implant materials

Ceria-stabilized tetragonal zirconia (Ce-TZP) has become an interesting alternative for the widely used yttria-stabilized zirconia (Y-TZP), whereas efforts are needed to control its microstructure in order to improve the strength of Ce-TZP ceramics. In this work, CaO was used to co-dope Ce-TZP ceramics. More specifically, 0.2–2.0 mol% Ca(NO3)3·4H2O precursor-based CaO was used to dope 10 mol% ceria-stabilized zirconia. Sintering was performed at 1300, 1350, or 1400 °C, which is lower than the temperatures commonly applied for zirconia ceramics. The microstructure and mechanical properties were investigated and correlated, revealing that 0.2 mol% CaO-doped CeO2-stabilised zirconia sintered at 1350 °C exhibited a fully dense fine-grained tetragonal ZrO2 microstructure with high toughness (10.4 MPa m1/2) and biaxial bending strength (1210 ± 43 MPa), and a narrow strength distribution (weibull modulus of 32.5). 1.5 and 2.0 mol% CaO-doping resulted in excellent biaxial bending strength but wider strength distribution and lower fracture resistance. The homogeneously distributed Ca(NO3)3·4H2O precursor prevented cubic zirconia-phase formation for CaO-doping up to 2.0 mol%. CaO-doped (≥ 0.2 mol%) 10Ce-TZP sintered at 1350 °C also highly resisted hydrothermal degradation. Furthermore, CaO-doping enabled to make Ce-TZP ceramics as translucent as different commercially available 3Y-TZP ceramics, opening possibilities to use Ce-TZP for dental restorations.

Dielectric probing of low-temperature degradation resistance of commercial zirconia bio-ceramics

ObjectivesTo investigate the effect of the stability of oxygen vacancies on the low-temperature degradation (LTD) resistance of two kinds of commercial zirconia-based materials (3Y-TZP ceramics and Ce-TZP/Al2O3 composites) via the dielectric probing methods. MethodsThe commercial 3Y-TZP ceramics and Ce-TZP/Al2O3 composites were prepared via conventional solid-state methods. Density, phase content, microstructure, strain, and biaxial flexural strength (BFS) of two materials were investigated using Archimedes method, XRD, SEM, strain-electric field (S-E) loops and ball-on-ring methods, respectively. The concentration of oxygen vacancies before and after LTD of two materials were evaluated using dielectric probing and XPS methods. ResultsThe XRD analysis revealed that compared to the 3Y-TZP ceramics, the Ce-TZP/Al2O3 composites showed better LTD resistance, without clear LTD. The greater LTD resistance for Ce-TZP/Al2O3 composites was associated with their stability of oxygen vacancies, by higher activation energy based on the dielectric measurements and XPS results. For the 3Y-TZP ceramics that underwent the tetragonal to the monoclinic phase transition during the LTD treatment, the concentration of their oxygen vacancies decreased after LTD. In addition, the Ce-TZP/Al2O3 composites exhibited higher flexural strength and potential fracture toughness based on the BFS testing and strain vs electric field measurement results, indicating a great potential for use in fixed restorative dental applications. SignificanceThis work suggested the stability of oxygen vacancies played a key role in the resistance to LTD. Optimizing the stability of the oxygen vacancies is key to the development of more reliable zirconia- based dental biomaterials with greater resistance to LTD.

Development and characterization of Al2O3/SrAl12O19 reinforced zirconia with high fracture toughness and low-temperature degradation-resistant for dental applications

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.

Influence of mechanical properties on material deformation behavior of different ceramics in scratching

To understand the differences in material removal behavior during grinding for different ceramics, scratching of Al2O3, AlN, Si3N4 and ZrO2 (3Y-TZP) ceramics by a cube-corner diamond indenter was investigated in this paper. Scratching characteristics, including material deformation, scratching force, coefficient of friction (COF) and scratching damage of different ceramics were compared and analyzed. Elastic recovery rate model and stress field model were built to analyze the mechanism of material deformation and scratching damage during scratching on different ceramics. The results demonstrated that material deformation behaviors vary significantly, and depend on mechanical properties of the ceramics. Ceramics with higher hardness exhibit shallower penetration depth of scratching, while higher fracture toughness results in shorter maximum surface damage distance. Elastic recovery rate model can predict the extent of material deformation. The ceramic with the highest elastic recovery rate is Al2O3, followed by Si3N4, ZrO2, and finally AlN. Elastic recovery rate decreases with increase in force. In stress field model, AlN exhibits the highest maximum principal stress, followed by Al2O3 and Si3N4, with ZrO2 displaying the lowest stress. These distribution patterns are consistent with the results of scratching damage pattern.

Temperature field simulation and optimization of processing parameters for laser-assisted machining of 3Y-TZP ceramics

To obtain low surface roughness in the laser-assisted machining of 3Y-TZP ceramics, a laser-assisted heating model of 3Y-TZP ceramics was established. The temperature field in the cutting zone was simulated using ABAQUS software to analyze the effects of laser power, rotational speed, and warm-up time on softening layer depth (distance between the workpiece surface and lower boundary of softening layer) and thickness (distance between the upper and lower boundaries of softening layer). Furthermore, the accuracy of the simulation results was verified through experiments. The Plackett-Burman design, Steepest ascent experiment, and Box-Behnken design method were used sequentially to optimize process parameters, and the surface quality, chip morphology, and tool wear of 3Y-TZP ceramic with laser-assisted cutting and traditional cutting were compared under the best process parameters. The results show that the rotational speed and laser power are the main factors influencing the softening layer depth and thickness, and the suitable warm-up time is 15 s; the most influential factor on the surface roughness is the cutting depth, and the optimized process parameter combinations for the best surface roughness are as follows: laser power of 90.3 W, rotational speed of 400 r/min, cutting depth of 0.21 mm, and feed speed of 4.4 mm/min; with laser-assisted, the surface roughness value of the workpiece is reduced by 54.12 %, the amount of tool wear is reduced by 56.5 %, the chip morphology is transformed from powder to strip with a length of more than 50 μm, and the primary material removal mode is changed from brittle removal to plastic removal.

Effect of grain boundary segregation and oxygen vacancy annihilation on aging resistance of cobalt oxide-doped 3Y-TZP ceramics for biomedical applications

Abstract 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.

Evaluation of zirconia surfaces and shear bond strength after acid–etching with ultrasonic vibration

To evaluate the effect of surface reaction process after hydrofluoric (HF) acid etching using ultrasound and the shear bond strength (SBS) of resin cement to zirconia polycrystal (Y-TZP) ceramic. Y-TZP ceramic sheets were divided into rinsing group (Group P), ultrasonic cleaning group (Group C), and ultrasonic reaction + rinsing group (Group CP), and all the groups were treated for 5, 10, 20, 30, 40, 50, and 60 min, respectively. The surface morphology, elements distribution, roughness, and wettability of the ceramic sheets in each group were observed. The SBS of ceramic-resin bonding specimens was tested after immersion and after cooling-heating cycles, respectively. Octahedral and spiculate products were observed on the surface of Y-TZP that was etched with HF acid in Group P. The amount of these products increased over time. In contrast, only a few octahedral products remained on the surface of Y-TZP in Groups C and CP. Within the same reaction time, the surface reaction of the CP group was stronger than that of the other two groups, accompanied by a more uniform morphology. The shear force in Group C was the lowest, and the shear force reduction in Group CP was the least after cooling-heating cycling, with statistically significant differences (P< 0.05). After the reaction time exceeded 30 min, the shear force in each group decreased instead of increasing. Octahedral and spiculate acid etching products on the surface of HF acid-etched Y-TZP can enhance the bonding force of zirconia. Ultrasonic cleaning would drive the exfoliation of acid etching products from the sample surface, leading to the decrease of the bonding force. The acid etching with ultrasonic vibration can accelerate the HF acid etching process of Y-TZP ceramics, which is conducive to improving the bond strength to resin and durability.

Abnormal grain growth inhibition of extrusion-based 3D-Printed 3Y-TZP ceramics sintered by flash sintering

This study investigated the combination of Direct Ink Writing (DIW) and Flash Sintering of zirconia stabilized with 3 mol. % Y2O3 (3Y-TZP). The samples were printed in two stacking configurations, and flash sintering was performed without current ramp control (FS) and using current ramp (CRFS) for comparison purposes. In both conditions, an electric field of 80 V cm−1 and a current density of 150 mA mm−2 were applied. The physical, microstructural, and mechanical properties of the printed samples were evaluated. The stacking configuration influenced both the grain size gradients and mechanical properties. Furthermore, controlling the current density ramp resulted in a slight homogenization of the grains’ size across different regions of the sample (core, edge, and flat surfaces). The presence of zirconia polymorphs, such as ZrO2-t and ZrO2-c, as well as a distorted form of the tetragonal phase (ZrO2-t'), was observed in the samples. These phases were affected by both the printing strategy and the current ramp control during the flash sintering step. In addition, the samples demonstrated typical values of Vickers hardness for 3Y-TZP (ranging from 10.5 to 11.8 GPa) and fracture toughness (ranging from 3.6 to 4.7 MPa m1/2), with a minor current density ramp control influence. Therefore, both FS and CRFS techniques represent viable pathways for producing dense 3D printed ceramic materials.

Dental zirconia microwave-sintering followed by rapid cooling protocol

ObjectivesThis study aimed to evaluate the effect of microwave sintering temperature and cooling rate (MS) on 3Y-TZP ceramics and its influence on the ceramic microstructure and mechanical properties. Specifically, to optimize the sintering process, reducing the total sintering time compared to conventional sintering. Materials and methodsEighty-four pre-sintered Y-TZP discs (Vipi block Zirconn, VIPI) (ISO 6872) were divided into seven groups (n = 12) according to the sintering conditions: conventional sintering (CS) at 1530 °C for 120 min and microwave sintering at 1400 °C (MS1400) and 1450 °C (MS1450) for 15 min followed by different cooling conditions: rapid cooling (RC), cooling at 400 °C (C400) and 25 °C (C25). The specimens were submitted to apparent density measurements, X-ray diffraction analysis (XRD), scanning electron microscopy, and biaxial flexural strength test. Data was statistically analyzed through two-way ANOVA, Tukey, Sidak, Dunnett and Weibull (α = 0.05). ResultsAll MS1400 groups presented lower density values than the CS and MS1450 groups. Two-way ANOVA revealed that the MS temperature and cooling rate affected the biaxial flexural strength of the Y-TZP (p < 0.01). Group MS1400RC presented lower biaxial flexural strength values (681.9 MPa) than MS1450RC (824.7 MPa). The cooling rate did not statistically decrease the biaxial strength among the groups submitted to microwave sintering at 1450 °C. XRD analysis showed that the sintering and cooling temperature did not induce tetragonal to monoclinic phase transformation. ConclusionsMicrowave sintering at 1450 °C for 15 min followed by rapid cooling can be a viable fast alternative protocol for Y-TZP sintering, compared with the conventional sintering, reducing the total sintering time by 75% and reducing the energy used for the sintering process without affecting the Y-TZP biaxial flexural strength and relative density compared to the conventional sintering. Moreover, the microwave technique promoted smaller grains and did not induce monoclinic phase formation.

2Y-TZP ceramics with high strength and toughness by optimizing the microstructure

Low-yttria doped zirconia polycrystals (Y-TZP) have recently emerged as new fine-grained zirconia ceramics exhibiting a promising combination of high fracture toughness and strength. In this investigation, we optimized the strength and fracture toughness of 2Y-TZP ceramics prepared by gelcasting and pressureless sintering. The 2Y-TZP ceramics with optimized processing reached a mean biaxial strength of 1070MPa, similar to the strength obtained for the standard 3Y-TZP ceramics. However, a higher transformability of tetragonal grains in 2Y-TZP ceramics resulted in a stronger transformation toughening effect compared with 3Y-TZP ceramics. The fracture toughness obtained for 2Y-TZP exceeded that of 3Y-TZP (7.7 vs. 5.2MPa m0.5). The differences in the microstructure and toughening mechanism between 2Y-TZP and 3Y-TZP were described, and the potential benefits of the 2Y-TZP were discussed.

Mechanical, low temperature degradation, and biocompatibility of Al-doped dental 3Y-TZP ceramic

3Y-TZP ceramics are widely used in dental restoration materials due to their excellent biocompatibility, mechanical properties, and aesthetics. However, the low temperature aging characteristics seriously affect the service life of 3Y-TZP. This study aimed to investigate the mechanical properties, low temperature degradation properties and biocompatibility of a certain amount of alumina doped dental 3Y-TZP ceramics. The 3Y-TZP powder was produced by co-precipitation and then combined in a predetermined ratio with alumina powder. The fitting results of the Johnson-Mehl-Avramorow-Kolmogorow (JMAK) equation shows that the doping of alumina is beneficial to improve the low temperature degradation resistance of 3Y-TZP. The doped 3Y-TZP exhibited favorable biocompatibility, indicating its potential suitability as a dental restorative material.

Load-bearing capacity under fatigue of bonded-yttria tetragonal zirconia polycrystals and -yttria-stabilized zirconia: Effects of the viscosity of a dual-cured resin cement

This study aimed to evaluate the effect of low and high viscosities of dual-cured resin cement on the mechanical fatigue behavior of yttria tetragonal zirconia polycrystals (3Y-TZP) and yttria-stabilized zirconia (4YSZ) adhesively luted to a dentin analogue (glass fiber-reinforced epoxy resin). Ceramic discs were randomly divided into four groups (n = 20) based on the following study factors: dual-cured resin cement viscosities (low and high) and zirconia microstructure (3Y-TZP and 4YSZ). The discs were treated by air abrasion with aluminum oxide particles (50 μm), followed by the application of primer, and then luted with high or low viscosity resin cement to the dentin analogue. Subsequently, the luted sets underwent a step-stress fatigue test, which involved an initial load of 200 N, step increments of 100 N, 10,000 cycles per step, and a frequency of 20 Hz. Data on fatigue failure load (FFL) and the number of cycles for failure (CFF) were collected and analyzed using survival tests, including Kaplan-Meier and Mantel-Cox analyses, as well as Weibull analysis. Additionally, topography analysis, fractographic features, bonding interface analysis, and Raman spectroscopy were performed. The results revealed that 3Y-TZP exhibited superior fatigue behavior compared to 4YSZ, regardless of the viscosity of the resin cement used for luting. Among all groups, 3Y-Low exhibited the best fatigue performance, while 4YSZ luted with low or high viscosity resin cements yielded the lowest fatigue behavior (FFL). There were no significant differences in Weibull modulus among the groups. After air abrasion, both ceramics showed similar topography. Raman analysis indicated that the surface of 3Y-TZP ceramics prior to sintering had a monoclinic phase, which transitioned predominantly to tetragonal phase peaks after sintering. A similar transition was observed in 4YSZ ceramics. In summary, 3Y-TZP exhibited superior mechanical fatigue behavior compared to 4YSZ. The influence of resin cement viscosity on fatigue behavior was more pronounced in 3Y-TZP, with low-viscosity resin cement enhancing its performance. However, the mechanical fatigue behavior of 4YSZ was less affected by the viscosity of the dual-cured resin cement, showing similar results with both low and high viscosities. In conclusion, 3Y-TZP demonstrated superior mechanical fatigue behavior compared to 4YSZ. The impact of resin cement viscosity on fatigue behavior was more pronounced in 3Y-TZP, with low-viscosity resin cement enhancing its performance. Conversely, the mechanical fatigue behavior of 4YSZ was less sensitive to the viscosity of the dual-cured resin cement, resulting in similar outcomes with both low and high viscosities.

Effect of airborne particle abrasion and regeneration firing on the strength of 3D-printed 3Y and 5Y zirconia ceramics

ObjectivesThis study aimed to assess the effect of airborne particle abrasion (APA) and regeneration firing (RF) on the subsurface damage and strength distribution of 3D-printed 3Y-TZP and 5Y-PSZ zirconia parts for dental applications. MethodsDisc-shaped specimens were prepared using vat photopolymerization (VPP) technology from 3Y and 5Y zirconia ceramics, followed by thermal debinding and sintering. APA treatment with 50 µm Al2O3 particles and RF at 1000 °C for 15 min were applied. Microstructural analysis was conducted using FIB-SEM, and XRD analysis determined crystalline phase content. Biaxial flexural strength was measured using the ball on three balls method and analyzed with Weibull statistics. ANOVA and Tukey HSD test were employed to compare strength differences between groups. ResultsAPA treatment increased the flexural strength of the 3Y specimens but decreased it for the 5Y specimens. RF treatment reversed the effect, restoring the strength to as-sintered levels for both materials. APA-treated 3Y specimens exhibited characteristic strength values above 1400 MPa, attributed to phase-transformation toughening. As sintered 5Y specimens showed strength values above 600 MPa. APA treatment increased the Weibull modulus of the 5Y specimens, indicating a narrower defect size distribution. SignificanceThe study demonstrates that the impact of APA and RF treatments on the mechanical properties and reliability of VPP-fabricated 3Y-TZP and 5Y-PSZ ceramics is comparable to conventionally prepared zirconia. VPP technology for 3D printing provides a viable approach for future manufacturing of dental restorations with potential clinical applications.

Enhanced flexural strength of pre-densified ZrO2 ceramics by a facile method of flash treatment

Traditional methods for strengthening ceramics rely on reasonable strategies implemented in material preparation and/or sintering process, but few of them can improve the strength of a pre-densified ceramic. In this paper, a facile method of flash treatment was proposed to strengthen the pre-densified zirconia ceramics. After flash treatment, the flexural strength of 3Y-TZP ceramics was improved to 859 MPa, which was 13 % higher than that of the original 3Y-TZP ceramics (759 MPa). The flash treatment could increase the intergranular fracture proportion of ceramics and affect the fracture behavior. Meanwhile, we proposed that the comprehensive effects of flash treatment would strengthen grains by introducing residual compressive stresses and dislocations, and relatively weaken grain boundaries by introducing tensile stresses and defects (vacancies and pores).

Investigation of mechanical properties and low-temperature degradation of dental 3Y-TZP ceramics fabricated by stereolithography in combination with microwave sintering

The purpose of this study was to obtain dental ceramic materials with excellent mechanical properties and high resistance to low temperature degradation (LTD) via stereolithography (SLA) in combination with microwave sintering (MWS). The results have shown that the unaged MWS-1425 °C 3Y-TZP ceramics with uniform microstructure have high density up to 99.04% and excellent mechanical properties (Vickers hardness 14.07 GPa, fracture toughness 4.32 MPa m1/2, flexural strength 947.87 MPa). After 50 h of LTD, the m-phase content of MWS 3Y-TZP ceramics accounts for only 10.3%. In addition, the surface roughness increases by only 1.3 nm, the degraded depth is less than 5 μm, and the flexural strength exceeds 900 MPa. This exhibits the high resistance to LTD and excellent mechanical properties of dental 3Y-TZP ceramics can be obtained.

Impact of 13-93 bio-glass inclusion on the machinability, in-vitro degradation, and biological behavior of Y-TZP-based bioceramic composite

Nowadays, bio-ceramic composite material is demanded in the biomedical industry due to its remarkable biological and mechanical properties. But, the shaping of such material challenges the manufacturer. In this work, bioceramic composite materials, having general weight composition [(100-x) (3Y-TZP) – x (13-93 BG)] where x = 0 to 25 wt%, has been prepared, and their machinability in terms of MRR (material removal rate) and SR (surface roughness) is studied as a function of BG composition and machining temperature. It is found that MRR decreases with increasing the concentration of bioactive glass (BG) while it increases with increasing the machining temperature. The SR is found in the opposite trend. The MRR, SR, and material removal mechanics (MRM) are also confirmed by the HR-SEM and AFM (atomic force microscopy) analysis. The effect of BG addition on the physical, mechanical, in-vitro degradation, and cell culture behaviour of the composite materials are also evaluated. The relative density and mechanical properties, such as flexural and compressive strength, are found to increase up to 10 wt% of BG content; afterward, it decreases. The hardness is increased with BG addition in 3Y-TZP ceramics. The in-vitro degradation indicates the dissolution and apatite layer formation after 35 days of immersion in simulated body fluid (SBF) solution. The cell proliferation is examined by MTT assay over MG-63 cell lines. The cell proliferation ability of the composite is increased with increasing the BG concentration and found a maximum of up to 25 wt% of BG. Overall, the best findings were obtained with 10 wt% BG contained 3Y-TZP ceramic composite sintered at 1250 °C. The relative density, flexural strength, and compressive strength are about 98.34%, 397.9 MPa, and 488.7 MPa, respectively. Based on the obtained results, it may be recommended that 10 wt% BG concentration in 3Y-TZP bioceramic composite is the most suitable and potential material for biomedical application.