Monolithic Ceramics Research Articles

Comparing the color match of monolithic CAD-CAM dental ceramics with the VITA Classical shade guide

Statement of problemMatching the shade selected and the final color of a ceramic restoration is challenging, and studies on matching monolithic ceramics to the shade selected are lacking. PurposeThe purpose of this in vitro study was to compare the color match of monolithic lithium disilicate (LDS), zirconia-reinforced lithium silicate (ZLS), presintered zirconia-reinforced lithium silicate (PS-ZLS), polymer-infiltrated ceramic network (PICN), and multilayer zirconia with the 3 modes of the VITA Classical shade guide. Material and methodsThis study was performed on 50 rectangular plates (14×12×1 mm) of 5 types of ceramics with A2 shade (n=10). Zirconia specimens were evaluated in 3 locations: incisal, medial, and cervical thirds. The color coordinates of the specimens of all 7 groups were measured on #3 and #8 Ivoclar Natural Die Color material by using a reflective spectrophotometer. The color coordinates of A2 VITA shade were measured in 5 modes: without backing placed in specimen holder, shade tab on the backgrounds #3 and #8, and 1-mm-thick shade tab on the backgrounds #3 and #8. The color difference of each specimen with 3 modes of A2 shade (without backing and on similar backgrounds) was calculated by using the ΔE00 formula, and comparison among groups was performed by using 2-way ANOVA and Tamhane post hoc tests. The comparison of ΔE00 between the values obtained from backgrounds #3 and #8 was performed by using the independent t test (α=.05). ResultsIn both backgrounds, statistically significant differences were found between the studied groups and VITA shade (P<.001). In most situations, the amount of color difference was lowest for the “shade tab on the backgrounds” mode. On background #3, the highest color difference was related to ZLS (6.48 ±0.23), and the lowest values were observed in the PICN group (1.02 ±0.31). On background #8, the highest color difference was related to ZLS compared with the “without backing” mode (8.62 ±0.27), and the lowest values were reported for ZLS compared with the “shade tab on the backgrounds” mode (1.27 ±0.44). The independent t test showed a statistically significant color difference on the 2 different backgrounds for all situations (P<.001). ConclusionsColor selection of monolithic ceramics with the VITA Classical shade guide is improved by placing the VITA tabs on a similar background. Background color has a significant effect on the final shade of the monolithic ceramics. Choosing the correct color for LDS, ZLS, and PS-ZLS requires more care than for PICN and zirconia.

Integrated high strength and high toughness induced by elongated TiB2 grains in reactive sintered TiB2–TiC–SiC ceramics

AbstractAlthough the addition of other phases into TiB2 matrix to form ceramic composites has been widely used to improve the mechanical properties of monolithic TiB2 ceramics, it is still difficult to greatly enhance the flexural strength and fracture toughness simultaneously. In this work, TiB2–TiC–SiC composites were successfully prepared by reactive spark plasma sintering of Ti3SiC2–B4C–Ti powder mixtures. During the sintering process, TiB2 grains grew into an elongated morphology, endowing the composites with integrated high strength and high toughness. The growth mechanism of TiB2 grains was attributed to the evaporation–condensation kinetics induced by the presence of B2O3. These findings can accelerate the exploration of ceramic composites with excellent comprehensive properties.

Restitution of Impacting Projectiles in Ceramic Matrix Composites (CMCs) Subject to Foreign Object Damage

Abstract Accurate assessments of rebound velocity of a projectile in impact events for ceramic matrix composites (CMCs) are important since the rebound velocity affects the degree of resultant impact damage in both CMC targets and projectiles. A series of in-depth characterizations of coefficients of restitution (COR), which is defined as rebound velocity divided by impact velocity of a projectile, was made using various types of gas-turbine grade ceramic matrix composites (CMCs) in conjunction with dynamic imaging and data-acquisition systems. Both the impact aspects and the coefficients of restitution were characterized as a function of impact velocities ranging from 150 m/s to Mach 1 and were analyzed with respect to materials' key properties. An important experimental observation was that regardless of types of CMCs employed, the corresponding CORs at an impact velocity of 350 m/s (i.e., Mach 1) yielded consistently the same value close to 0.1-0.2. The temperature effect in COR was found to be minor to 1100oC as assessed with the specialty SiC/SiCs, also independent of environmental barrier coatings. The coefficients of restitution were also determined in other materials systems such as advanced monolithic ceramics and some metallic materials in an attempt to construct an overall COR map in response to related foreign object damage (FOD) events.

3D printing of crack-free dense polymer-derived ceramic monoliths and lattice skeletons with improved thickness and mechanical performance

Previous research often failed to prepared polymer-derived SiOC ceramic components with dense and thick monoliths/skeletons based on additive manufacturing processes, due to the porosities and cracks generated during the pyrolysis process. Herein, we report a simple solution which combines the introduction of phenolic resin (PR) as an additive and the use of controlled strategy of pyrolysis, for the vat photopolymerization additively manufactured SiOC ceramics. As a result, crack-free dense monolith and lattice skeleton structural polymer-derived SiOC ceramics are successfully prepared despite the low ceramic yield of 19.3 wt% and large linear shrinkage of 50% generated after pyrolysis. The prepared dense monoliths possess a thickness of over 5 mm and the lattices show attainable maximum dense skeletons thickness of ~2 mm. The maximum dense thickness of the samples after pyrolysis is over 7 times that of other samples prepared based on additive manufacturing reported in the literature. As an indicator of dimensional retention, the specific dense thickness to ceramic yield ratio (T/Y) is deduced, resulting maximum values of 101.9 µm/(wt%) for lattice skeletons and 254.7 µm/(wt%) for monoliths. The former is even larger than that for dense monolith SiOC structures prepared by other conventional gel casting and isostatic pressing techniques with much higher ceramic yields of > 80 wt%, and is about 6.1 times the largest T/Y ratio (=16.7 µm/(wt%)) achievable in the AM-based works reported in the literature. This shows predominance of the current work over other types of polymer-derived ceramic structures prepared by additive manufacturing and even conventional methods. The lattice structures’ apparent density and specific strength reached 0.55 g/cm 3 and 6.6 × 10 4 N∙m/kg, respectively. The mechanical performance surpasses other structural polymer-derived ceramic structures with similar apparent density reported in the literature. Through the advanced characterization and analysis of material phase and morphology evolution during the pyrolysis process, the mechanism of defect-free densification is revealed. That is, the introduction of PR enables a highly smooth gas-releasing process due to the generation of ordered gas-releasing channels in the sample bodies during the pyrolysis process. As a result, the generation of cracks and defects was successfully prevented. Moreover, due to the high carbon residue of the PR, the samples containing 15 wt% PR in the preceramic state still possessed amorphous SiOC ceramics after pyrolysis at 1400 ℃, while 0 wt% PR samples showed SiC crystallization. Compared with similar materials reported, the ceramics prepared in this study exhibit enhanced structural and mechanical performance. The strategy investigated in the study can be a viable route for the additive manufacturing of high-performance crack-free and thick monolith and lattice skeleton SiOC ceramic structures based on vat photopolymerization.

Bioinspired PcBN/hBN fibrous monolithic ceramic: High-temperature crack resistance responses and self-lubricating performances

The high strength and toughness of natural materials are mainly determined by a combination of mechanisms operating at different length scales, which can be used as a strategy to reduce the intrinsic brittleness of ceramics. Inspired by the architectures of bamboo, the polycrystalline cubic boron nitride/hexagonal boron nitride (PcBN/hBN) fibrous monolithic ceramics with a long fiber arrangement structure was constructed with PcBN fiber cells and hBN cell boundaries, and its crack resistance responses and tribological performances were investigated. The composite ceramic failed in a non-brittle manner with the rising resistance curve (R-curve) behavior, which was attributed to multiscale crack effects in the hierarchical architecture. The maximum crack growth toughness was extremely high (approximately 21 MPa·m1/2), corresponding to a 270% increase over the crack initiation toughness. Excellent fracture resistance could be retained even above 1000 °C. Moreover, the composite ceramic exhibited low and stable friction coefficients (approximately 0.33) when paired with a Si3N4 pin at high temperature (1000 °C), owing to the lubrication function of hBN cell boundaries with weak van der Waals forces and a small amount of liquid B2O3 produced. As a result, a synergistic improvement of mechanical and tribological properties at high temperature (1000 °C) was realized by combining bionic structure and tribological design. It provides important theoretical and technical support for expanding the application of self-lubricating composite ceramics in harsh environments.

Multiple ballistic damage of segmented SiC/BN laminated ceramic composite armor

This article investigated the structure of the laminated ceramics to improve the multiple ballistic performance of segmented ceramic composite armors. The multiple ballistic experiments were conducted with 5.8 mm caliber steel core bullets at the impact velocity of about 920 m/s. The experiments verified that two laminated SiC/BN structures (GLC and ULC) exhibit higher residual ballistic performances than the monolithic SiC structure (MC). Moreover, through damage evolution analysis, two laminated SiC/BN structures (GLC and ULC) exhibit less sensitivity to the multiple ballistic impacts damages, and possess more energy absorption mechanisms than the monolithic ceramics. The structure design of the laminated of ceramics is beneficial for improving the multiple ballistic performances of composite armors and reducing the crater deformation.

Masking ability of implant abutment substrates by using different ceramic restorative systems

Statement of problemInformation regarding the masking ability of ceramic crowns over different implant abutment materials is scarce. PurposeThe purpose of this in vitro study was to evaluate the masking ability of different monolithic or bilayer ceramic materials with different thicknesses over substrates indicated for implant restorations by using opaque and translucent evaluation pastes. Material and methodsDisk-shaped specimens, shade A1 (VITA Classic; Ø10×1.5 to 2.5 mm), of different ceramics (a bilayer system [yttria-stabilized zirconia infrastructure+porcelain veneer: Zir+Pc] and monolithic systems [lithium disilicate under low, medium, or high translucency: LtLD, MtLD, or HtLD, respectively, and a high-translucent yttria-stabilized zirconia: HtZir]) were made (n=4). The color difference (ΔE00) was assessed by using the CIEDE2000 formula and considering the different ceramic systems over 5 implant abutment materials (A1 shade Zir [Zir A1]; white Zir [White Zir]; A1 low-translucency lithium disilicate [LD]; polyetheretherketone [PEEK]; and titanium [Ti]) when using 2 different evaluation pastes (translucent or opaque). The control comparison was the restorative material positioned over the Zir A1 substrate with a translucent evaluation paste. Statistical analysis was made by using a 2-way ANOVA and Tukey post hoc tests (α=.05) for ΔE00 data considering the restorative material and luting agent factors as their association. Additionally, ΔE00 data were qualitatively analyzed considering the acceptability and perceptibility thresholds. The translucency parameter (TP00) of each restorative material was evaluated, and data were submitted to 1-way ANOVA and Tukey post hoc tests (α=.05). ResultsThe most predictable masking ability was seen with Zir+Pc regardless of the evaluation paste used. Nevertheless, under 1.5-mm thickness, Zir+Pc did not adequately mask Ti (ΔE00>1.77). Most monolithic ceramics did not mask discolored substrates (PEEK or Ti, ΔE00>1.77). The exception was HtZir, which presented acceptable masking ability over PEEK at 2.5-mm thickness with both evaluation pastes (ΔE00<1.77). Regardless of the restorative material thickness, Zir+Pc showed the lowest (P<.05) TP00 values (TP00=3.45 at 1.5-mm thickness; TP00=2.00 at 2.5-mm thickness), and HtLD presented the highest (P<.05, TP00=23.50 at 1.5-mm thickness; TP00=13.36 at 2.5-mm thickness). HtZir showed similar TP00 to MtLD at 1.5-mm thickness and similar TP00 to Zir+Pc when used at 2.5-mm thickness (P>.05). ConclusionsMonolithic ceramics should be used with caution over discolored implant abutments. Bilayer systems (Zir+Pc) were the most predictable approach to adequately masking discolored substrates such as PEEK or Ti. An increased restoration thickness provided higher masking ability for all restorative materials tested.

Effects of surface treatment and shade on the color, translucency, and surface roughness of high-translucency self-glazed zirconia materials

Statement of problemThe impact of different surface treatments and shades on the color, translucency, and surface roughness of high-translucency self-glazed zirconia materials is unclear. PurposeThe purpose of this in vitro study was to investigate the effects of different external surface treatments (self-glazed, milled, polished, and glazed), intaglio surface treatments (milled and airborne-particle abraded), and shades (A1 and A3 shades) on the color, translucency, and surface roughness of high-translucency self-glazed zirconia materials, as well as the correlations among optical parameters, translucency, and surface roughness. Material and methodsEighty shade A1 and 80 shade A3 disks were fabricated with a thickness of 0.80 ±0.02 mm and divided into 16 groups (n=10). Different external and intaglio surface treatments were applied to the specimens. CIELab values were measured with a spectrophotometer, and color differences (ΔE00) and relative translucency parameter (RTP) were calculated. Total transmittance (Tt%) and reflectance (R%) were tested with a spectrophotometer equipped with an integrating sphere. Surface roughness (Ra and Rz) (μm) was measured with a noncontact 3-dimensional laser scanning microscope. One specimen from each group was subjected to scanning electron microscope (SEM) examination. Data were analyzed with ANOVA and the Tukey post hoc test. The correlation among optical parameters, translucency, and surface roughness was investigated by using Pearson correlation analysis (α=.05). ResultsThe effects of external surface treatments, intaglio airborne-particle abrasion, and shades on ΔE00, RTP, and Ra values of the disks were significantly different (P<.001). The smoothest external polishing surface had the greatest RTP and color difference (P<.001). Shade A3 disks had lower RTP and Tt% values than shade A1 disks (P<.001). ΔE00 had a highly positive relationship with the RTP (A1: r=0.884, P<.001; A3: r=0.859, P<.001). SEM images demonstrated that surface treatments affected the surface texture of monolithic zirconia ceramics. ConclusionsDifferent surface treatments affected the surface roughness, translucency, and final color of zirconia materials. The smoothest external polishing surface had the greatest RTP and color difference. Different shades influenced the translucency, as the darker the disk shade, the lower the translucency. The RTP was appropriate as an auxiliary indicator for evaluating the color of a dental ceramic.

Approaches to Preceramic Polymer Fiber Fabrication and On-Demand Applications.

The demand for lightweight, high-modulus, and temperature-resistant materials for aerospace and other high-temperature applications has contributed to the development of ceramic fibers that exhibit most of the favorable properties of monolithic ceramics. This review demonstrates preceramic-based polymer fiber spinning and fiber classifications. We discuss different types of fiber spinning and the advantages of each. Tuning the preceramic polymer chemical properties, molar mass, functional chemistry influences, and incorporation with fillers are thoroughly investigated. Further, we present the applications of preceramic-based polymer fibers in different fields including aerospace, biomedical, and sensor applications. This concise review summarizes recent developments in preceramic fiber chemistry and essential applications.

Effect of firing cycle and aging on long-term chemical degradation of monolithic CAD-CAM ceramics

Statement of problemPrevious studies have shown the susceptibility of dental ceramics to degradation when subjected to certain media. However, knowledge on the effect of repeated firings and thermocycling on the ion elution of computer-aided design and computer-aided manufacturing (CAD-CAM) ceramics is lacking. PurposeThe purpose of this in vitro study was to compare the effect of repeated firings on the ion elution of CAD-CAM materials before and after thermocycling. Material and methodsBar-shaped specimens were prepared from 4 different CAD-CAM materials (monolithic zirconia [Z], zirconia-reinforced lithium silicate glass-ceramic [S], lithium disilicate glass-ceramic [EX], and leucite-reinforced glass-ceramic [E]) and divided into 3 groups according to the number of repeated glaze firings (1 firing [1F], 2 firings [2F], and 4 firings [4F]). Specimens were placed into deionized water (pH 7.4) and stored at 37 °C for 168 hours. Inductively coupled plasma-optic emission spectrophotometry (ICP-OES) was used to measure the baseline values of the eluted ions in immersion. The specimens were then subjected to thermocycling. Then, surface roughness (Ra) and ion elution values were measured. The Kruskal-Wallis and Mann-Whitney U tests were used to analyze the ion elution data before and after thermocycling, and the effect of thermocycling on ion elution was assessed by the Wilcoxon signed rank test. Ra data were analyzed with 2-way analysis of variance (ANOVA) and the Tukey honestly significant difference tests (α=.05). ResultsElution of some ions varied depending on the material-firing pair before (Al, As, B, Ba, Cr, Cu, Li, Mg, Na, P, and Zn) and after (Al, As, B, Ba, Be, Ca, Cd, Co, Cr, Cu, K, Li, Mg, Na, P, Y, and Zn) thermocycling. Before thermocycling, all firing groups within each material showed a similar number of significantly higher eluted ions. After thermocycling, the number of significantly higher eluted ions decreased in all materials, except for EX. The effect of thermocycling on the ion elution of the 1F group of Z (Al, Be, Ca, Cd, Co, Cr, Cu, K, Li, P, Y, and Zn), S (As, Be, Cd, Co, Cr, K, P, and Y), EX (B, Cu, and P), and E (B and Ba); 2F group of Z (Al, Be, Ca, Co, Cr, Cu, K, Li, P, and Y), S (Be, Cd, Co, K, Li, and Y), EX (P), and E (P); 4F group of Z (Al, As, Ba, Be, Ca, Cd, Co, Cr, Cu, K, Li, P, and Y), S (Al, Be, Cd, Co, Cr, Li, Mg, and Y), EX (Be, Ca, Cd, Co, K, Y, and Zn), and E (Ca and P) was nonsignificant (P≥.051). The interaction between material and repeated firings (P<.001) had a significant effect on Ra. For 1F groups, E showed the highest Ra (P≤.003), while Z had higher Ra than S (P=.009). For 2F groups, Z had higher Ra than S (P=.01). The differences among 4F groups were nonsignificant (P≥.677). An increased number of repeated firings (2F and 4F) decreased the Ra of E (P<.001). ConclusionsThe effect of repeated firings and thermocycling on the chemical stability of the tested CAD-CAM materials varied. No clear trend was observed on the elution of different ions within material-firing pairs before thermocycling. However, thermocycling increased the number of significantly higher eluted ions for EX. The effect of thermocycling on the ion elution of materials varied depending on ions. Repeated firings decreased the surface roughness of E.

Evaluating the Effect of Different Polymer and Composite Abutments on the Color Accuracy of Multilayer Pre-Colored Zirconia Polycrystal Dental Prosthesis.

With increasing aesthetic awareness and emphasis on time costs in today’s society, monolithic multilayer precolored zirconia ceramics (M-Zr) facilitate aesthetic restorations in a convenient and straightforward manner without the need for veneering porcelain to modify the color. However, the effect of abutment materials on the final color of M-Zr remains unclear. Herein, we placed Vita A1 Shade M-Zr on six different abutment materials, zirconia (Y-TZP), 3D printed composite resin (CR), dental model resin (MR), polyetheretherketone (PEEK), polyetherketoneketone (PEKK), and cobalt–chromium alloy (Co–Cr), to evaluate their effect on the color accuracy of M-Zr. The color attributes (L*, a*, and b*) were measured using a dental spectrophotometer. The translucency parameter (TP), contrast ratio, color difference (ΔE) between each background substrate and the Vita A1 Shade Guide, and chroma values (C) were calculated to evaluate the color accuracy of M-Zr. A statistical analysis was performed using one-way analysis of variance and post hoc Tukey’s HSD tests (α = 0.05). The experimental results indicate that the TP values and contrast ratio of the M-Zr samples were 14.85 and 0.83, respectively. Co–Cr had the highest ΔE (6.08) and lowest C value (7.52); PEKK had the lowest ΔE (2.60), and PEEK had the highest C value (12.23) (p < 0.05). Notably, the ΔE values of CR (3.13), PEEK (2.86), and PEKK were within clinical indicators (ΔE < 3.7). Based on these results, it can be concluded that the abutment material has a significant effect on the final color of the M-Zr, and PEEK or PEKK resulted in good color accuracy. When choosing the dental MR, traditional zirconia, or metals as abutment materials, colored or opaque cement might be required to eliminate color distortion and achieve desirable optical properties.

Improving the damage tolerance of Si3N4 by forming laminate composites with refractory metals

The objective of this research was to demonstrate that the damage tolerance of Si3N4 could be significantly improved by forming laminate composites with refractory metals, providing materials that undergo graceful failure, rather than the fast-fracture mechanism exhibited by monolithic Si3N4. A damage tolerant Si3N4 could be used as a ring material in an all-ceramic bearing, decreasing the chance for catastrophic failure if the ring is stressed in tension during operation. The technical approach formed a laminate composite material using alternating Si3N4-metallic layers, with both outer layers being Si3N4 to take advantage of its greater wear resistance, chemical stability, and thermal stability. The metallic layers are designed to arrest any cracks in the outer layers, thus producing a toughened Si3N4 and avoiding the catastrophic failure behavior exhibited by monolithic ceramics. The laminate composites were fabricated using a combination of tape-casting Si3N4 and metals from slurries, as well as metal foils, followed by hot pressing at 1500°C. The metallic materials employed were chromium, titanium, and tantalum. Analysis confirmed that the interfaces were well formed, and the laminates with chromium and titanium formed intermetallic compounds more readily than the composites with tantalum. The Si3N4-Ta laminates demonstrated crack deflection and bridging behavior during failure and flexural strength of 800–900 MPa. The hardness and elastic modulus of Si3N4-Ta laminates measured by nanoindentation were similar to those reported in literature. The hardness across the interface of the Si3N4-Ta composite varied according to the composition of the interface, which displayed a profile indicative of a diffusion bond.

Performance evaluation of multilayered ceramic composite armors: New design and advanced predictive method

Novel body armors are designed to protect against ballistic threats in the most vulnerable organs within the thorax and abdomen. Decreasing the armor weight without affecting its total integrity after the impact is one of the most challenging tasks. In this study, we combine advanced numerical simulations and experimental tests to investigate the ballistic performance of multilayered armor systems (MAS) consisting of laminated alumina (Al2O3) ceramic plates with multi-curve form and a hybrid composite backing. The ballistic trauma absorption and ceramic fracturing morphology are considered evaluation criteria. The investigation provides enough data on the measured trauma and the results are compared to advanced monolithic ceramics. The ballistic tests showed that bonding three or two ceramic plates with polymeric interlayer decreases considerably the eroded ceramic mass in comparison to monolithic ceramic tiles. Furthermore, the layup of two thin Al2O3tiles with frontal confinement gives the same trauma-weight index as monolithic silicon carbide and reaction-bonded boron carbide plates. The combination of K129 and KM2 aramid weave fabrics decreases the composite backing weight by 33% and increases its ballistic performance in comparison to homogeneous aramid fabrics. Numerical simulations that involve the use of solid Lagrange and adaptive solid/smooth particles hydrodynamics (SPH) numerical approaches with detailed 3D models of the bullet and the MAS are presented in this work. Based on the statistical analysis, a better prediction of the back face deformation and bullet residual length is obtained by the adaptive solid/SPH method, which is found more suitable for the simulation of multilayered armor impact scenarios.

Mechanical properties–translucency–microstructure relationships in commercial monolayer and multilayer monolithic zirconia ceramics

ObjectivesTo evaluate the phase composition, microstructure, optical properties and mechanical properties of eight commercially available multilayer and monolayer monolithic dental zirconias. MethodsFive commercial 3Y-TZP (GC ST, GC HT [GC, Tokyo Japan]; Katana ML, Katana HT [Kuraray Noritake] and Lava Plus [3M Oral Care]) and three Y-PSZ (Katana STML, Katana UTML [Kuraray Noritake]; GC UHT [GC, Tokyo Japan]) zirconia ceramic grades were cut in plate-shaped specimens, sintered according to the manufacturer’s instructions and mirror polished. The zirconia chemical composition was determined using X-ray fluorescence (XRF), phase composition was characterized using X-ray diffraction (XRD), while the grain size was measured using scanning electron microscopy (SEM). The translucency Parameter (TP) and Contrast Ratio (CR) were measured with a spectrophotometer (n = 10/group). The indentation fracture toughness (n = 10), Vickers hardness (n = 10) and biaxial strength (n = 20) of the sintered ceramics were assessed. The stress distribution during biaxial testing was assessed by Finite element analysis (FEA). Statistical analysis involved one-way ANOVA and post-hoc Tukey’s HSD test and Pearson correlation test (α = 0.05). ResultsFEA showed that the stress distribution in plate shape specimens was the same as for disks, rationalizing the use of plates for biaxial strength testing. As expected, higher quantities of Y2O3 were related to a higher cubic ZrO2 phase content and lower tetragonality t-ZrO2, which improved translucency but diminished flexural strength and toughness. While there was no significant correlation between grain size and other material properties, addition of pigments to the zirconia grade statistically negatively affected hardness. ConclusionEven though an improvement in strength and translucency could be recorded for the last Y-TZP generation, future research still needs to strive for combined improvement of optical properties and mechanical reliability of zirconia ceramics.

Revolution of Current Dental Zirconia: A Comprehensive Review.

The aim of this article is to comprehensively review the revolution of dental zirconia (Zir), including its types, properties, applications, and cementation procedures. A comprehensive search of PubMed and Embase was conducted. The search was limited to manuscripts published in English. The final search was conducted in October 2021. Newly developed monolithic Zir ceramics have substantially enhanced esthetics and translucency. However, this material must be further studied in vitro and in vivo to determine its long-term ability to maintain its exceptional properties. According to the literature, monolithic translucent Zir has had promising results and a high survival rate. Thus, the utilization of this material is indicated when strength and esthetics are needed. Both the materials and methods used for cementation of monolithic Zir have significantly improved, encouraging dentists to use this material, especially when a conservative approach is required. Zir restorations showed promising outcomes, particularly for monolithic Zir crowns supported with implant and fixed dental prostheses.

Enhanced Mechanical Properties and Oxidation Resistance of Zirconium Diboride Ceramics via Grain-Refining and Dislocation Regulation.

Zirconium diboride (ZrB2) is considered as one of the most promising ultra‐high temperature materials for the applications in extreme environments. However, the difficulty in fabrication of ZrB2 limits its industrial applications. In this study, fully dense and grain‐refined ZrB2 is prepared under ultra‐high pressure of 15 GPa at low temperature of 1450 °C. The as‐prepared ZrB2 exhibits excellent mechanical and oxidation‐resistant properties. Compared with raw powder, the grain size decreases 56%. Compared with high‐temperature sintered control specimen beyond 2000 °C, the hardness and fracture toughness increase about 46% and 69%, respectively, the dislocation density increase 3 orders of magnitude, while the grain size considerably decrease 96%. According to work hardening, Hall–Petch and Taylor dislocation hardening effects, the refined grains, substructures, and high dislocation density caused by plastic deformation during sintering can enhance the mechanical properties. The unique structure contributes to a threshold oxidation temperature increase of ≈250 °C relative to the high‐temperature sintered ZrB2, achieving one of the highest values (1100 °C) among the reported monolithic ultra‐high temperature ceramics. A developed densification mechanism of dislocation multiplication with grain refining is proposed and proved to dominate the sintering, which is responsible for simultaneous improvements in mechanical and oxidation‐resistant properties.

A comprehensive review on bonding between monolithic ceramics and tooth structure with different adhesive agents.

Reliable bonding between the prepared tooth and monolithic ceramics can be achieved by various luting agents available on the market. The selection of luting agent and cementation technique plays an important role in the success of the restoration. With the advent of resin-based adhesive systems as luting agents, clinicians' perspectives have changed to a more conservative approach. Recent systems, chemically adhere athe crowns to the prepared tooth structure showing higher bond strength. To reach the aesthetic demands of the patients, all-ceramic restorations were considered over metal-ceramic crowns. Few all-ceramic crowns are brittle, the strength is dependent on the chemical structure and method of fabrication. While some all-ceramic restorations gain strength after cementation. Thus, the choice of luting agent used in cementing all-ceramic crowns is crucial. Even though many luting agents are being introduced no single luting agent fulfilled all the requirements. Among them, adhesive cements showed greater bond strength and enhanced the retention of minimal preparation, which are less retentive. Traditional non-adhesive agents can be used in retentive preparations that bond through mechanical means rather than the chemical bond seen in newer adhesive cements. Also, surface treatments of zirconia showed greater bond strengths irrespective of the luting agent being used. These include air abrasion, acid etching, applying silane couplers, and primers that increase the surface area for adhesion. The use of all-ceramic restorations, the need for surface treatments, types of surface treatments, adhesion and adhesive agents, and evidence from current in vitroresearch on monolithic ceramics and tooth adhesion were all discussed in this review.

Effects of Hydrothermal Treatment on the Phase Transformation, Surface Roughness, and Mechanical Properties of Monolithic Translucent Zirconia.

This study aimed to investigate the effects of hydrothermal treatment on four types of monolithic, translucent, yttria-stabilized, tetragonal zirconia polycrystals (Y-TZPs). Two commercially available Y-TZP brands-SuperfectZir High Translucency (Aidite Technology Co, China) and Katana HT (Kuraray Noritake Dental, Japan) were assessed. For each brand of Y-TZP, materials of four coloring types, including noncolored (NC), colored by staining (CS), precolored (PC), and multilayered (ML) specimens were investigated after hydrothermal aging in an autoclave at 134°C/0.2 MPa for 0 (control group), 5, 10, and 20 hours. The tetragonal-to-monoclinic phase transformation, surface roughness, flexural strength, and structural reliability (Weibull analysis) were measured and statistically analyzed (α=0.05). The subsurface microstructure was analyzed with scanning electron microscopy. The group ML exhibited the lowest flexural strength and Weibull characteristic strength among the four coloring types (p<0.05). Slight increases in the monoclinic phase volume, flexural strength, and Weibull characteristic strength were observed after hydrothermal aging (pall<0.05). Regardless of coloring type, no significant effects of aging on the Weibull modulus or surface roughness were found for the tested materials. Compared with the Katana HT cross-sections, the SuperfectZir High Translucency cross-sections exhibited a similar but thicker transformation zone. The coloring procedure and material type were found to affect the mechanical properties and aging resistance of translucent monolithic Y-TZP ceramics. Regardless of the aging time, the surface roughness of the tested Y-TZP ceramics remained unchanged.

Fracture resistance of lab composite versus all-ceramic restorations in class II inlay cavity preparations: An in vitro study.

Aim:The aim of this study was to evaluate and compare the fracture resistance of inlay preparations restored with indirect lab composite, conventional and translucent monolithic zirconia-based ceramics.Materials and Methods:Fifty freshly extracted human maxillary premolars were selected for the study. Standardized inlay cavities were prepared and restored with indirect lab composite, conventional monolithic zirconia-based ceramic and translucent monolithic zirconia-based ceramic. After restoration each sample was subjected to axial compressive load with Universal testing machine. The force required to induce fracture was recorded in Newton (N).Statistical Analysis Used:The data were analyzed using the one-way ANOVA test and Post hoc Bonferroni multiple comparison test.Results:Results revealed that fracture resistance of prepared inlay cavities restored with conventional monolithic zirconia-based ceramics was found to be best followed by other groups. Group I > Group IV > Group V > Group III > Group II.Conclusion:The fracture resistance of conventional monolithic zirconia-based ceramic inlays and translucent monolithic zirconia-based ceramic inlays were comparable with intact teeth but, indirect lab composite inlays showed lower fracture resistance than all.

Effects of Different Air Particle Abrasion Protocols on the Biaxial Flexural Strength and Fractography of High/Ultra-Translucent Zirconia.

In this study, the biaxial flexural strength (BFS) and fractography of high/ultra-translucent monolithic zirconia ceramics subjected to different mechanical surface pretreatments were evaluated. A total of 108 disc-shaped samples (12 mm diameter, 1.2 mm thickness) of three zirconia materials (5Y-ZP KATANA Zirconia UTML (ML), 3Y-TZP DD Bio ZX2 (DB), and 5Y-ZP DD cube X2 (DC)) were used. The BFS was investigated after subjecting the samples to surface treatment using air abrasion particles of two types (aluminum oxide or glass microbeads). The data were analyzed using two-way analysis of variance, followed by Scheffe’s post hoc test for multiple comparisons. The mean ± standard deviation BFS for DB was highest after treatment with 50 µm Al2O3 (1626.05 ± 31.9 MPa), with lower values being observed following treatment with 50 µm glass microbeads (1399.53 ± 24.2 MPa) and in the control sample (1198.51 ± 21.1 MPa). The mean ± standard deviation (SD) BFSs for DC and ML were the highest in the control groups. Surface air abrasion with 50 µm Al2O3 particles and 2 bar pressure is recommended for 3Y-TZP translucent zirconia, while no abrasion of 5Y-ZP translucent zirconia ceramic.