Mechanical Properties Of Zirconia Research Articles

Comparative effects of glazing versus polishing on mechanical, optical, and surface properties of zirconia ceramics with different translucencies.

This study compared the effects of glazing versus polishing on mechanical, optical, and surface properties of zirconia ceramics with different translucencies. In this in vitro study, 120 bar-shaped specimens (25 × 4 × 1.2 mm) were fabricated from three different types of zirconia with different translucencies (n = 40, DD Bio ZW, ZX2, and Cube X2). After sintering, each zirconia group was randomly divided into five subgroups of control (glazing), glazing + bur abrasion, glazing + bur abrasion + polishing with EVE Diacera® kit, glazing + bur abrasion + reglazing, and glazing + bur abrasion + polishing with EVE Diacera® kit + reglazing. The specimens underwent surface roughness, hardness, flexural strength, and translucency tests, as well as X-ray diffraction (XRD) and scanning electron microscopy (SEM) for assessment of surface topography. Data were analyzed by one-way analysis of variance, Tukey test, and Pearson test (α = .05). Flexural strength, surface hardness, and translucency were significantly correlated with zirconia type. ZW zirconia had significantly higher flexural strength and surface hardness and significantly lower translucency than Cube X2 and ZX2 (p < .001). Surface roughness had no significant correlation with zirconia type (p = .274). Polishing created the smoothest, and bur abrasion created the roughest surface (p < .001). Flexural strength and hardness in most experimental groups were significantly lower than in the control group (p < .001). Translucency was not significantly different in bur abrasion and polishing groups, compared with the control group; however, reglazing significantly increased the translucency (p < .001). SEM micrographs confirmed the surface roughness results. XRD showed monoclinic phase only in reglazed groups. Of different surface treatments, polishing improved the surface properties and caused the smallest change in mechanical properties of zirconia with different translucencies.

Analysis of zirconia mechanical properties after application of a protocol to simulate clinical aging

In order to test the effects of hydrothermal and clinically related aging on zirconia, monolithic disc-shaped samples were milled, sintered and polished from two high translucency zirconia , 3 mol % (HT) and 5 mol % (XT). Samples were divided into three groups: non-aged: control (CT); hydrothermal aging (HA - autoclave aging for 12.5 h at 134 °C, 2 bar); in vitro clinically-related aging (CRA - chewing simulation for 1.2 million cycles followed by 50,000 thermocycles and acidic exposure in HCl, pH 1.2, for 15 h). Mechanical properties (flexural strength, fatigue, hardness and elastic modulus) were analyzed and compared using the analysis of variance (at a level of 5% significance). In vitro clinically-related aging significantly decreased fatigue strength of XT zirconia with no effects on HT zirconia. Surface hardness and elastic modulus were not affected (p = 0.591 and 0.392 respectively). Hydrothermal aging increased fatigue strength for both materials and decreased the surface hardness and modulus of HT zirconia (p ≤ 0.001). Hydrothermal aging and in vitro clinically-related aging have different effects on the mechanical properties of zirconia , when used to simulate five years of clinical service.

The Influence of Polishing on the Mechanical Properties of Zirconia—A Systematic Review

Purpose: To systematically review studies that investigated the consequences of various polishing protocols on the mechanical properties of zirconia. The effects on the roughness and crystalline phase transformation were also evaluated. Materials and methods: The Preferred Reporting Items for Systematic Reviews and Meta-Analysis (PRISMA) was followed. The electronic searches were conducted via OVID MEDLINE (R) and Scopus for publications between 1996 and August 2022. The search strategy was limited to full texts in the English language and in vitro studies. The influences on flexural strength, hardness, fracture strength, fracture toughness, wear resistance, roughness and phase transformation were collected. Various methodologies to measure these properties were also outlined and compared. The risk of bias for included studies was evaluated according to a modified Consolidated Standards of Reporting Trials (CONSORT) checklist. Results: After removing duplicates, the systematic search identified a total of 419 studies. Nineteen studies satisfied the inclusion criteria and were selected for final analysis. Fifteen of the included studies observed the changes in surface roughness along with the mechanical properties and ten studies detected the tetragonal (T) to monoclinic (M) phase transformation. Eight studies also investigated the change in properties after polishing the ground surface. Testing parameters were not consistent among studies due to the varying methods. Conclusions: To a certain extent, polishing influences the strength, hardness, toughness and wear resistance. The damage in some mechanical properties, as well as the roughened surface, from grinding can be restored via an appropriate polishing treatment. The polishing process itself barely induces the transition from the tetragonal to monoclinic phase of zirconia, while this commonly occurs after grinding. If the subsequent polishing is adequate, the transformed monoclinic phase can be eliminated with the removal of the outermost surface layer. In dentistry, polishing is an imperative step to maintain the superior functions and service life of zirconia for patients.

Effect of sintering condition and low-temperature degradation on the flexural strength and phase transformation of zirconia

Statement of problemThe traditional sintering of zirconia takes an extended time, and accelerated treatments have been developed to reduce treatment time and manufacturing costs. Studies evaluating the effect of sintering time on the mechanical properties of zirconia are lacking. PurposeThe purpose of this in vitro study was to evaluate the effect of the sintering condition and the low-temperature degradation (LTD) of zirconia on the flexural strength of monolithic zirconia. Material and methodsZirconia specimens (LUXEN Enamel) were sintered at 1500 °C, 1530 °C, and 1560 °C for 4, 5, 6, 7, and 12 hours and subjected to LTD (n=10). Control specimens were assessed in the nontreated condition. The 3-point flexural strength was measured by using a universal testing machine. The crystal phases of the specimens were compared and quantitatively analyzed through X-ray diffraction (XRD) analysis, and the crystal grain size was measured by using a field emission scanning electron microscope (FE-SEM). Two-way ANOVA and the independent sample t test were used to analyze the experimental results (α=.05). ResultsIn the group not subjected to LTD, there was no difference in flexural strength according to the change in sintering temperature and sintering time (P>.05). The group subjected to LTD showed a difference in flexural strength according to sintering time difference (P<.001). The flexural strength of the zirconia with LTD exposure increased compared with that of the zirconia specimen not subjected to LTD (P<.001). With LTD exposure, cubic and monoclinic crystals increased, tetragonal crystals decreased, and the particle size increased. As the sintering temperature increased, the particle size increased, but not according to the sintering time. ConclusionsAt all sintering times, the flexural strength of zirconia was over 800 MPa, which is the minimum flexural strength of a 4-unit or longer prosthesis as specified in the International Organization for Standardization (ISO) 6872. With LTD exposure, the increase in the flexural strength of zirconia was associated with the phase change from tetragonal to monoclinic.

Effect of sintering process on microstructure, 4-point flexural strength, and grain size of yttria-stabilized tetragonal zirconia polycrystal for use in monolithic dental restorations

Statement of problemModifications have been made in the microstructure and sintering parameters of monolithic zirconia to improve esthetics qualities and avoid chipping of 2-layer restorations. However, how these modifications affect the physical and mechanical properties of zirconia is unclear. PurposeThe purpose of this in vitro study was to compare the influence of different sintering parameters on the microstructure, 4-point flexural strength, density, and grain size of 2 commercially available zirconia advocated for the fabrication of monolithic dental prostheses and 1 commercially available zirconia for use as a core material. Material and methodsThree presintered blocks (Ceramill Zolid, Prettau, and IPS e.max ZirCAD) were used. Specimens were cut and sintered as per the manufacturer's recommendation or as per a modified heating protocol. Ceramill Zolid (Z1450) was sintered at 1450 °C, Prettau (P1600) was sintered at 1600 °C, and IPS e.max ZirCAD (I1530) was sintered at 1530 °C by following the manufacturer's heating protocol. Groups Ceramill Zolid Z1530 and Z1600 were sintered at temperatures higher than the manufacturer's recommendation. Specimens from each group (n=13) were analyzed with X-ray diffraction (XRD), density calculus, average grain size measurement, and 4-point flexural tests. Data were compared by using ANOVA (α=.05). ResultsXRD analysis showed the presence of a tetragonal metastable phase in all groups before and after sintering. No significant differences were found in relative density values for the 3 Ceramill groups (5.98 g/cm3). Groups I1530 (6.03 g/cm3) and P1600 (6.03 g/cm3) had similar density results greater than 6.00 g/cm3. The average grain size of all groups remained lower than 1 μm. P1600 had the highest grain size (0.817 μm), and Z1450 presented the lowest grain size (0.465 μm). P1600 showed the most homogeneous flexural strength and the highest Weibull modulus (m=8.22). Z1530 presented the lowest Weibull modulus (m=4.58). IPS e.max ZirCAD (I1530) had the highest flexural strength (1057.41 ±150.54 MPa), and Ceramill Zolid Z1450 had the lowest (621.01 ±138.08 MPa). ConclusionsThe flexural strength, microstructure, crystal phase, and grain size of the analyzed zirconia varied as per the sintering processing. The IPS e.max ZirCAD had the highest flexural strength (1057.41 ±150.54 MPa), followed by Prettau zirconia (864.18 ±118.21), with a statistically significant difference (P<.05). The Ceramill Zolid zirconia presented the lowest flexural strength, as well as the lowest reliability for all sintering parameters used (Z1450: 621.01 ±138.08 MPa and m=5.42; Z1530: 713.10 ±175.44 MPa and m=4.58; Z1600: 630.15 ±112.08 MPa and m=6.87). At a lower heating rate (8 °C/min), the final density increased and excessive grain growth in group Z1530 was prevented.

Synthesis and Mechanical Properties of Zirconia–Yttria Matrices/Alumina Short Fibre Composites

Yttria tetragonal zirconia polycrystals (YTZP)/alumina short fibre (Al2O3-SF) composites were prepared by wet ball milling. Three different commercial powders of YTZP containing 2, 2.5 and 3 mol% of yttria (denoted as TZ2Y, TZ2.5Y and TZ3YA, respectively) were used as matrices, reinforced with 20 wt% Al2O3-SF. The effect of sintering conditions on the mechanical properties of the composites was studied. XRD and SEM techniques were used for the characterization of the prepared composites. The fracture toughness and hardness were determined by the Vickers indentation technique. The bend strength was measured using a four-point bending test machine. The results showed that both strength and toughness increase with yttria content. The TZ3YA/20 wt% Al2O3-SF composite showed bend strengths up to 760 MPa and fracture toughness of 9.2 MPa√m upon pressureless sintering at 1600 °C. Higher values of the bend strength, up to 855 MPa, were obtained for the post-sintered hipped composites at 1500 °C. The high bend strength and fracture toughness, KIC, result from strong fibre matrix interface. The toughening mechanisms were found to comprise transformation toughening, domain switching and crack deflection toughening. The addition of Al2O3-SF to the matrices of low yttria content was invaluable due to its high monoclinic content upon sintering.

Effect of A Rapid-Cooling Protocol on the Optical and Mechanical Properties of Dental Monolithic Zirconia Containing 3-5 mol% Y2O3.

Many attempts have been made to improve the translucency of zirconia in dentistry. The purpose of this study was to evaluate the effect of a rapid-cooling heat treatment on the optical and mechanical properties of dental monolithic zirconia. Zirconia containing 3, 4, and 5 mol% Y2O3 were sintered, sectioned, and polished. The specimens were rapidly cooled from high temperature inducing a diffusionless cubic-to-metastable tetragonal (t’) phase transformation. The changes in L*a*b* color coordinates, translucency parameter (TP), and total transmittance (T%) were measured. Three-point bending strength, Vickers hardness, and indentation fracture toughness tests were performed. Quantitative phase analyses were carried out by X-ray diffraction with Rietveld refinement. Scanning electron microscopy (SEM) images were obtained. With increasing Y2O3 contents, TP and T% values increased while strength and toughness decreased. The Rietveld analysis showed that the amount of t’-phase increased after rapid-cooling and annealed 5Y-partially stabilized zirconia (PSZ) contained the highest amount of t’-phase (64.4 wt%). Rapid-cooling improved translucency but the translucency of annealed 5Y-PSZ did not approach that of lithium disilicate glass-ceramic. Rapid-cooling decreased flexural strength significantly, being 306.1 ± 61.8 MPa for annealed 5Y-PSZ. SEM revealed that grains tended to get larger after rapid-cooling. A rapid-cooling treatment can produce t’-phase which can contribute to an increase in translucency but has a negative effect on the mechanical properties of zirconia.

Microstructure and Mechanical Properties of Zirconia (3Y-TZP)/Zr Composites Prepared by Wet Processing and Subsequent Spark Plasma Sintering

ZrO2 (3Y-TZP) matrix composites with 30 vol % Zr metallic particles were obtained by spark plasma sintering (SPS) using a colloidal processing method. The microstructure and mechanical properties of this novel ceramic–metal composite have been studied. The fracture toughness of composites is slightly higher than the values corresponding to monolithic zirconia. Scanning electron microscope (SEM) observations of the crack path show that the major contributions to toughening are the resulting crack blunting and branching that occurs at crack tips in the metallic particles before the onset of crack propagation. Plastic deformation of the metallic particles is strongly influenced by the constraint induced by the different phase arrangements. This system can be considered as a particulate composite with a periodic residual stress field, in which the metal phase is under strong compression due to the residual thermal stresses as a consequence of the coefficient of thermal expansion mismatch. Therefore, the plastic deformation of the metallic particles in this composite is likely to be reduced to a large extent.

Improving the mechanical properties of zirconia in instrument bearings

The article presents the issues of replacing leucosapphires in jeweled bearings of the axes of precision instruments with nanostructured crystals of partially stabilized zirconia. The statement is substantiated that doping with rare earth elements provides an improvement in the performance properties of precision instruments by improving the mechanical properties of bearing materials. The efficiency of doping of zirconia crystals with cerium and neodymium oxides is studied. It was found that doped crystals have increased plasticity, which provides an increase in the crack resistance of crystals. Special attention is paid to the issues of increasing the survivability of high-speed rotor bearings by replacing the thrust bearing of leucosapphire with nanostructured crystals of partially stabilized zirconia doped with cerium and neodymium. The efficiency of improving the mechanical properties is confirmed by the X-ray phase analysis of crystals. The phase composition is studied by Raman scattering and the lattice parameters are determined. The increased crack resistance of the thrust bearing is confirmed by tests performed using the kinetic microhardness method.

Microstructure and mechanical behavior of zirconia ceramics by graphene nano-platelets incorporation

Fully densified zirconia ceramics with a uniform dispersion of graphene nanoplatelets (GNPs) were prepared using a field assisted sintering technique (FAST). The results show that the mechanical properties of zirconia with GNPs have improved compared to zirconia without GNPs. GNPs are evenly embedded in grain boundaries with a unique wrinkles structure and closely interfacial bonding inhibit the grain growth. As recognized, performance and structure are inseparable and the interfacial behavior of GNPs-zirconia is a fundamental issue to enhance mechanical properties. Thus, an analytical model was conducted to investigate the stress transfer and the ideal length of GNPs reinforcing zirconia. It is found that the maximum axial and shear is 3.676 GPa and 0.787 GPa, respectively. Moreover, the length of GNPs used in this study is in the ideal length to strengthen zirconia.

The influence of altering sintering protocols on the optical and mechanical properties of zirconia: A review.

As a result of advancements in chairside technology and speed sintering techniques and increased esthetic demands of patients, efforts have been made to produce monolithic zirconia restorations that are highly translucent, strong, and dense. While methods for processing zirconia are well known, there is a tendency to modify the process parameters with the aim of decreasing the overall processing time and, in particular, the sintering time. This review provides clinicians with scientific evidence of the effects of altering sintering parameters used for dental zirconia on its microstructure, phase transformation, and mechanical and optical properties. A systematic search of Embase and Medline using Boolean operators was performed to locate relevant articles. Eleven articles were selected for this review. The following characteristics of monolithic zirconia have been confirmed to be affected by alterations in sintering: the microstructure, mechanical properties, optical properties, wear behavior, and low thermal degradation. The alteration of sintering parameters has been found to alter the grain size, wear behavior, and translucency of zirconia. There is a lack of clinical studies that investigate the influence of altering sintering parameters or methods on the clinical performance of monolithic zirconia restorations. Alteration of sintering parameters alters the microstructural, mechanical, and optical properties of zirconia. This will consequently impact the clinical performance of zirconia prostheses. Future clinical investigations are encouraged to support these in vitro findings.

BIAXIAL FLEXURAL STRENGTH OF UN-SHADED AND SHADEDMONOLITHIC TRANSLUCENT ZIRCONIA

INTRODUCTION: The natural white color of zirconia together with the veneer chipping problem has led to the development of tooth colored monolithic (full-anatomic) zirconia. In order to optimize esthetics shading of monolithic zirconia were done by two main approaches, either by powder mixing method or by infiltration technique. The influence of infiltration technique on mechanical properties of zirconia has been reviewed previously, while the influence of powder mixing method on the mechanical properties of shaded zirconia, specially the biaxial flexural strength has not been widely studied before. OBJECTIVES: To evaluate and compare the biaxial flexural strength and the crystal structure of shaded CAD/CAM monolithic translucent zirconia by powder mixing method with un-shaded ones. MATERIALS AND METHODS: Twenty fully sintered discs of un-shaded [T 0] and shaded [T S] monolithic translucent zirconia of diameter 12 mm and thickness 1 mm has been divided into 2 parallel groups of 10 discs each. Their biaxial flexural strength was measured using a ball-on-ring test fixture and universal testing machine at room temperature. Statistical significance was measured using One-Way ANOVA test. Then crystallographic analysis was done for both groups using X-ray diffraction. Finally the nature of failures of the tested specimens was examined using confocal laser microscopy. RESULTS: Biaxial flexural strength test showed no significant difference between un-shaded and shaded specimens. X-ray diffraction spectrum only showed crystals of tetragonal zirconia with no evidence of neither monoclinic zirconia crystals nor coloring oxides crystal phases. Confocal laser microscopy images of both groups showed the classic fracture patterns of monolithic zirconia materials. CONCLUSIONS: shading of zirconia blocks by powder mixing methods does not significantly (P≥0.05) affect either biaxial flexural strength or crystallographic structure of monolithic translucent zirconia

Mechanical properties of zirconia, doped and undoped yttria-stabilized cubic zirconia from first-principles

Density functional theory calculations investigate the mechanical properties of: cubic (c), tetragonal (t) and monoclinic (m) zirconia (ZrO2); cubic yttria-stabilized zirconia (c-YSZ); c-YSZ doped with TiO2, MnO2, CaO and NiO. These find the elastic constants, elastic compliances, bulk, shear and Young's modulus for the three phases of zirconia together with the ideal strength of c-ZrO2. The ideal strength of c-ZrO2 for strain in the [100] direction (84.3 GPa) being significantly higher than in the [110] (30.5 GPa) and [111] directions (9.87 GPa) is attributed to change in the bond angle reducing the internal strain on the bonds. Adding Y2O3 to c-ZrO2 decreases the ideal strength, particularly in the [100] direction, namely to respectively 11.1 and 28.8 GPa for 6.67 and 14.29 mol % Y2O3. Doping c-YSZ with TiO2, MnO2, CaO and NiO further reduces the ideal strength, with the lowest values for TiO2 (7.16–7.88 GPa). The significant decrease in the ideal strength of c-YSZ and doped c-YSZ compared to c-ZrO2 in the [100] direction is attributed to the weakening of the ZrO2 framework by the oxygen vacancies.

Effects of an etching solution on the adhesive properties and surface microhardness of zirconia dental ceramics

Statement of problemConventional approaches to adhesive bonding are not applicable to zirconia restorations. Recently, an etching solution, Zeta Etching Solution (ZES), has been introduced for etching the surface of zirconia. The effects of this etching solution on the bond strength and mechanical properties of zirconia are unknown. PurposeThe purpose of this in vitro study was to examine the effects of ZES on the bond strength and surface hardness of zirconia. Material and methodsTwo different types of partially stabilized tetragonal polycrystalline zirconia (TZP), Prettau zirconia (group P) and anterior Prettau (group AP), were evaluated with and without ZES etching. Each group was bonded to a zirconia substrate by using an adhesive resin cement. After 24 hours of storage in distilled water, the bond strength of the zirconia was analyzed. Vickers hardness was determined by using a microhardness tester. Scanning electron microscopy was used to analyze the surface microstructure and determine the mode of failure for each specimen. Results were analyzed and compared using 1-way ANOVA and Student t tests (α=.05). ResultsScanning electron microscopy analysis showed that etching the surface of zirconia with ZES etching solution for 60 minutes changed the morphological characteristics and microstructure of zirconia, making the surface more irregular. The changes were more pronounced for AP specimens. Etching with ZES significantly increased the shear bond strength of zirconia (P<.05) in AP specimens. The bond strength of Prettau (P group) specimens after ZES etching did not increase significantly (P>.05). An adhesive failure mode was observed for P zirconia specimens, whereas zirconia specimens exhibited a cohesive mode of failure. No significant decrease (P>.05) was observed in the mean Vickers hardness numbers. ConclusionsWithin the limitations of this in vitro study, it was concluded that etching in ZES for 30 minutes significantly enhanced the shear bond strength of highly translucent anterior Prettau (AP) zirconia restorations. Moreover, etching with ZES did not adversely affect the surface hardness of the zirconia specimens tested.

Comparison between microwave and conventional sintering on the properties and microstructural evolution of tetragonal zirconia

In this research, the comparison between microwave sintering and conventional sintering on the mechanical properties and microstructural evolution of 3 mol% yttria-stabilised zirconia were studied. Green bodies were compacted and sintered at various temperatures ranging from 1200 °C to 1500 °C. The results showed that microwave assisted sintering was beneficial in enhancing the densification and mechanical properties of zirconia, particularly when sintered at 1200 °C. It was revealed that as the sintering temperature was increased to 1400 °C and beyond, the grain size and mechanical properties for both microwave- and conventional-sintered ceramics were comparable thus suggesting that the sintering temperature where densification mechanism was activated, grain size was strongly influenced by the sintering temperature and not the sintering mode.

Influence of Ar-ion implantation on the structural and mechanical properties of zirconia as studied by Raman spectroscopy and nanoindentation techniques

In this study, structural and nanomechanical properties of zirconia polymorphs induced by ion irradiation were investigated by means of Raman spectroscopy and nanoindentation techniques. The zirconia layer have been produced by high temperature oxidation of pure zirconium at 600 °C for 5 h at normal atmospheric pressure. In order to distinguish between the internal and external parts of zirconia, the spherical metallographic sections have been prepared. The samples were irradiated at room temperature with 150 keV Ar+ ions at fluences ranging from 1 × 1015 to 1 × 1017 ions/cm2. The main objective of this study was to distinguish and confirm different structural and mechanical properties between the interface layer and fully developed scale in the internal/external part of the oxide. Conducted studies suggest that increasing ion fluence impacts Raman bands positions (especially characteristic for tetragonal phase) and increases the nanohardness and Young's modulus of individual phases. This phenomenon has been examined from the point of view of stress-induced hardening effect and classical monoclinic → tetragonal (m → t) martensitic phase transformation.

Effects of aqueous and acid-based coloring liquids on the hardness of zirconia restorations

Statement of problemThe effects of the application of aqueous coloring liquids on the mechanical properties of zirconia have not yet been investigated. PurposeThe purpose of this in vitro study was to evaluate the effects of 3 different coloring techniques and the number of coloring liquid applications on the hardness of zirconia. Material and methodsEighty specimens were divided into 8 groups (n=10); nonshaded zirconia, preshaded zirconia, acid-based coloring liquid zirconia, and aqueous coloring liquid zirconia (1, 3, 6). Vickers hardness was measured. Data were analyzed via 1-way and 2-way ANOVAs. Multiple comparisons were performed using a Scheffé test (α=.05). ResultsStatistically significant differences in hardness were found between acid-based coloring liquid zirconia and aqueous coloring liquid zirconia (P<.001). Increasing the number of coloring liquid applications decreased the hardness value of acid-based coloring liquid zirconia (P<.001) but had no effect on the hardness of aqueous coloring liquid zirconia (P>.05). ConclusionsWithin the limitations of this study, the hardness of zirconia was influenced to differing degrees depending on coloring technique. The number of coloring liquid applications affected the hardness of zirconia colored with the acid-based coloring liquid but not the hardness of zirconia colored with the aqueous coloring liquid.

Microstructure and Mechanical Properties of Multiscale Zirconia Ceramics Prepared by Field Assisted Sintering Technique

Two kinds of powders of 3 mol. % yttria stabilized zirconia (3Y–TZP) with different particles sizes; one was 20 nm denoted by N whereas the other was 0.5 µm denoted by M, were mechanically mixed via ball milling machine using different amounts of N wt. % to obtain multiscale zirconia composite powder. Then the mixed powders were sintered by field assisted sintering technique (FAST). The effect of N content on the microstructure as well as on mechanical properties of zirconia is investigated. Results show that the microstructure of M completely surrounded by N emerged in zirconia composites, and tetragonal phase is presented in all the sintered samples. The obtained zirconia ceramics with 15 wt. % N own a highly dense structure (~ 99.9 % relative density) and high flexural strength of 813.59 MPa wherein a 15 % increase in flexural strength compared to zirconia ceramics without adding N, but the fracture toughness of the composites just lightly decreases. The improved flexural strength of the composites is caused by the multiscale effect.

Effect of Infiltration with Ferric Oxide Containing Glass on the Color and Mechanical Properties of Zirconia

This study was to examine the effects of ferric oxide contents, which is one of the components of a newly developed glass, on the color and mechanical strengths of zirconia surfaces after glass infiltration. The composition of bioactive glass contained: SiO2–Al2O3–Na2O–MgO–BaO–CaO–Nb2O5–TiO2–Fe2O3. 84 presintered zirconia discs (diameter 15 mm, height 1.2 mm) were prepared. The experimental groups were divided into 6 groups by Fe2O3 contents of 0, 1, 1.5, 2.0, 2.5 and 2.9 wt%. Non-glass infiltrated zirconia was used as a control. Bioactive glass was coated on the presintered zirconia disc by a spin coating and infiltrated into zirconia by complete sintering at 1450°C for 2 hr. The color of the specimens was measured using a digital spectrophotometer and biaxial flexural strength and fracture toughness was compared. The colors of glass infiltrated zirconia were from yellow to yellowish orange according to ferric oxides contents and those were within the range of natural teeth colors. The mechanical properties of glass infiltrated zirconia were not inferior to those of zirconia. Glass infiltration with ferric oxide into zirconia can improve the color and mechanical properties of zirconia and be applicable for dental purpose.

A Review of the Low-Temperature Degradation of Dental Zirconia

The use of tetragonal zirconia as a dental restorative material has recently increased because of its unique mechanical and optical properties, as well as high biological compatibility with the oral cavity environment. However, the mechanical properties of zirconia can be severely degraded, which leads to the failure of dental restorations. This review focuses on the low-temperature degradation of dental zirconia and its effects on the properties of zirconia and on the oral environment. The purpose is to show the importance of this negative phenomenon and suggest guidelines for minimizing the aging of zirconia that is used as a dental restoration material.