Recent advances in dental zirconia: 15 years of material and processing evolution.

OBJECTIVES: The objective was to discuss the research on zirconia published in the past 15 years to help the dental materials community understand the key properties of the types of zirconia and their clinical applications. METHODS: A literature search was performed in May/2023 using Web of Science Core Collection with the term "dental zirconia". The search returned 5102 articles, which were categorized into 31 groups according to the research topic. RESULTS: The current approach to improving the translucency of zirconia is to decrease the alumina content while increasing the yttria content. The resulting materials (4Y-, 5Y-, and above 5 mol% PSZs) may contain more than 50% of cubic phase, with a decrease in mechanical properties. The market trend for zirconia is the production of CAD/CAM disks containing more fracture resistant 3Y-TZP at the bottom layers and more translucent 5Y-PSZ at the top. Although flaws located between layers in multilayered blocks might represent a problem, newer generations of zirconia layered blocks appear to have solved this problem with novel powder compaction technology. Significant advancements in zirconia processing technologies have been made, but there is still plenty of room for improvement, especially in the fields of high-speed sintering and additive manufacturing. SIGNIFICANCE: The wide range of zirconia materials currently available in the market may cause confusion in materials selection. It is therefore imperative for dental clinicians and laboratory technicians to get the needed knowledge on zirconia material science, to follow manufacturers' instructions, and to optimize the design of the prosthetic restoration with a good understanding where to reinforce the structure with a tough and strong zirconia.

Effect of titania content and biomimetic coating on the mechanical properties of the Y-TZP/TiO2 composite.

OBJECTIVE: To investigate the effect of titania addition (0, 10 and 30mol%) on the microstructure, relative density, Young's modulus (E), Poisson's ratio (υ), mechanical properties (flexural strength, σf, and Weibull modulus, m) of a Y-TZP/TiO2 composite. The effect of the presence of a biomimetic coating on the microstructure and mechanical properties was also evaluated. METHODS: Y-TZP (3mol% of yttria) and Y-TZP/TiO2 composite (10 or 30mol% of titania) were synthesized by co-precipitation. The powders were pressed and sintered at 1400°C/2h. The surfaces, with and without biomimetic coating, were characterized by X-ray diffraction analysis and scanning electron microscopy. The relative density was measured by the Archimedes' principle. E and υ were measured by ultrasonic pulse-echo method. For the mechanical properties the specimens (n=30 for each group) were tested in a universal testing machine. RESULTS: Titania addition increased the grain size of the composite and caused a significant decrease in the flexural strength (in MPa, control 815.4a; T10 455.7b and T30 336.0c), E (in GPa, control 213.4a; T10 155.8b and T30 134.0c) and relative density (control 99.0%a; T10 94.4%c and T30 96.3%b) of the Y-TZP/TiO2 composite. The presence of 30% titania caused substantial increase in m and υ. Biomimetic coating did not affect the mechanical properties of the composite. SIGNIFICANCE: The Y-TZP/TiO2 composite coated with a layer of CaP has great potential to be used as implant material. Although addition of titania affected the properties of the composite, the application of a biomimetic coating did not jeopardize its reliability.

Dental ceramics: a review of new materials and processing methods.

The evolution of computerized systems for the production of dental restorations associated to the development of novel microstructures for ceramic materials has caused an important change in the clinical workflow for dentists and technicians, as well as in the treatment options offered to patients. New microstructures have also been developed by the industry in order to offer ceramic and composite materials with optimized properties, i.e., good mechanical properties, appropriate wear behavior and acceptable aesthetic characteristics. The objective of this literature review is to discuss the main advantages and disadvantages of the new ceramic systems and processing methods. The manuscript is divided in five parts: I) monolithic zirconia restorations; II) multilayered dental prostheses; III) new glass-ceramics; IV) polymer infiltrated ceramics; and V) novel processing technologies. Dental ceramics and processing technologies have evolved significantly in the past ten years, with most of the evolution being related to new microstructures and CAD-CAM methods. In addition, a trend towards the use of monolithic restorations has changed the way clinicians produce all-ceramic dental prostheses, since the more aesthetic multilayered restorations unfortunately are more prone to chipping or delamination. Composite materials processed via CAD-CAM have become an interesting option, as they have intermediate properties between ceramics and polymers and are more easily milled and polished.

Dental ceramics: a review of new materials and processing methods

Abstract The evolution of computerized systems for the production of dental restorations associated to the development of novel microstructures for ceramic materials has caused an important change in the clinical workflow for dentists and technicians, as well as in the treatment options offered to patients. New microstructures have also been developed by the industry in order to offer ceramic and composite materials with optimized properties, i.e., good mechanical properties, appropriate wear behavior and acceptable aesthetic characteristics. The objective of this literature review is to discuss the main advantages and disadvantages of the new ceramic systems and processing methods. The manuscript is divided in five parts: I) monolithic zirconia restorations; II) multilayered dental prostheses; III) new glass-ceramics; IV) polymer infiltrated ceramics; and V) novel processing technologies. Dental ceramics and processing technologies have evolved significantly in the past ten years, with most of the evolution being related to new microstructures and CAD-CAM methods. In addition, a trend towards the use of monolithic restorations has changed the way clinicians produce all-ceramic dental prostheses, since the more aesthetic multilayered restorations unfortunately are more prone to chipping or delamination. Composite materials processed via CAD-CAM have become an interesting option, as they have intermediate properties between ceramics and polymers and are more easily milled and polished.

Effect of fiber addition on slow crack growth of a dental porcelain.

AIMS: To evaluate the effect of the processing method (conventional sintering, S, and heat-pressing, HP) and addition of potassium titanate fibers, PTF, on the microstructure, mechanical properties (flexural strength, σf, and Weibull parameters, m and σ5%), slow crack growth parameters n (stress corrosion susceptibility coefficient), and optical properties (translucency parameter, TP, and opalescence index, OI) of a feldsphatic dental porcelain. METHODS: Disks (n = 240, Ø12 × 1 mm) of porcelain (Vintage-Halo, Shofu) were produced using S and HP methods with and without addition of 10 wt% (conventional sintering) or 5 wt% (heat-pressing) of PTF. For the S method, porcelain was sintered in a conventional furnace. In the HP technique, refractory molds were produced by lost wax technique. The porcelain slurry was dry-pressed (3t/30s) to form a cylinder with 12 mm (diameter) and 20mm (height), which was heat-pressed for 5 min/3.5 bar into the mold. Specimens were tested for biaxial flexural strength in artificial saliva at 37°C. Weibull analysis was used to determine m and σ5%. Slow crack growth (SCG) parameters were determined by the dynamic fatigue test, and specimens were tested in biaxial flexure at five stress rates: 10(-2), 10(-1), 10(0), 10(1) and 10(2)MPa/s (n=10), immersed in artificial saliva at 37°C. Parameter n was calculated and statistically analyzed according to ASTM F394-78. Optical properties were determined in a spectrophotometer in the diffuse reflectance mode. RESULTS: The highest n value was obtained by the combination of heat-pressing with fiber addition (37.1) and this value was significantly higher than those obtained by both sintered groups (26.2 for control group and 27.7 for sintered with fiber). Although heat-pressing alone also resulted in higher n values compared to the sintered groups, there were no significant differences among them. Fiber addition had no effect on mechanical strength, but it resulted in decreased TP values and increased OI values for both processing methods. Heat-pressing alone was able to reduce the porosity level of the porcelain. CONCLUSIONS: Addition of PTF combined with heat-pressing can reduce strength degradation of a dental porcelain compared to sintered materials with or without fibers. Heat-pressing (HP) alone should be considered as a good alternative for clinical cases where high translucency is required.

Efeito do conteúdo de titânia e da alteração da superfície por meio da aplicação do recobrimento biomimético nas propriedades mecânicas do compósito Y-TZP/TiO2 / Effect of titania content and the change of the surface by applying the biomimetic coating on the mechanical properties of the composite Y-TZP/TiO2

Os objetivos desse trabalho foram: 1) determinar o efeito do conteúdo de titânia em mol % (zero, 10 e 30) na área de superfície específica (SBET), no tamanho dos aglomerados e na intensidade dos picos correspondentes às fases cristalinas presentes no pó cerâmico de Y-TZP/TiO2; 2) determinar o efeito do conteúdo de titânia em mol % (zero, 10 e 30) na microestrutura, densidade, densidade relativa, módulo de elasticidade, coeficiente de Poisson, módulo de Weibull (m) e resistência à flexão (f) de pastilhas cerâmicas sinterizadas de Y-TZP/TiO2 e, 3) determinar o efeito do recobrimento biomimético no módulo de Weibull (m) e na resistência á flexão de pastilhas cerâmicas sinterizadas de Y-TZP/TiO2. Os pós foram produzidos por meio de uma rota de co-precipitação, obtendo-se três composições do compósito Y-TZP/TiO2, que foram de zero (T0), 10 (T10) e 30 (T30) % mol de titânia. O pó produzido foi prensado (50 MPa) para produzir pastilhas de 15 mm de diâmetro e sinterizado a 1400 °C por 2 horas. Após o polimento com solução diamantada de 45 m, as pastilhas (n=60 para cada grupo) ficaram com aproximadamente 12 mm de diâmetro e 1,0 mm de espessura. Metade das pastilhas foram submetidas ao recobrimento biomimético (sete dias em solução de silicato de sódio e sete dias em solução de 1,5 SBF-simulated body fluid). Os pós foram caracterizados por difração de raios-X (DRX), espalhamento a laser, adsorção gasosa e microscopia eletrônica de varredura (MEV). As pastilhas foram caracterizadas pelo método de Archimedes, pulso-eco ultra-ssônico, MEV, DRX e para a análise de Weibull, as pastilhas foram submetidas ao ensaio de resistência à flexão biaxial em saliva artificial a 37°C. Os resultados mostraram que todos os pós apresentaram zircônia monoclínica e tetragonal na sua composição e uma área de superfície específica superior a 42 m2/g. A adição de titânia favoreceu a formação de aglomerados maiores e com uma distribuição bimodal.

Em todas as pastilhas foram detectadas zircônia monoclínica e tetragonal, enquanto no grupo T30 também foi detectada a fase de titanato de zircônia (ZrTiO4). O grupo T0 apresentou os maiores valores de densidade medida (6,05 g/cm3), densidade relativa (99,0%), módulo de elasticidade (213 GPa) e resistência à flexão (815 MPa). A adição de titânia reduziu significativamente a densidade medida (5,45 g/cm3 para T10 e 5,15 g/cm3 para T30) a densidade relativa (94,4% para T10 e 96,3% para o T30) o módulo de elasticidade (156 GPa para T10 e 134 GPa para o T30) e a resistência à flexão (455 MPa para o grupo T10 e 336 MPa para o grupo T30) do compósito Y-TZP/TiO2. O grupo T30 apresentou um módulo de Weibull (11,7) e um coeficiente de Poisson (0,34) significativamente superior ao grupo T0 (6,4 e 0,31, respectivamente). Foi observado que o recobrimento biomimético promoveu a formação de glóbulos de hidroxiapatita distribuídos de forma heterogênea na superfície do material e que esse tratamento não alterou significativamente a resistência à flexão e o módulo de Weibull do compósito Y-TZP/TiO2. Conclui-se que a adição de titânia afetou as propriedades estudas do pó e das pastilhas do compósito de Y-TZP/TiO2. Além disso, o compósito pode ser recoberto com uma camada hidroxiapatita sem ter sua confiabilidade estrutural afetada.

The objectives of this study were: 1) to determine the effect of titania content in mol% (zero, 10 and 30) in the specific surface area (SBET), the size of the agglomerates and the intensity of the peaks corresponding to crystalline phase present in the ceramic powder of Y-TZP/TiO2; 2) to determine the effect of the content in mol% of titania (zero, 10 and 30) in the microstructure, density, relative density, modulus of elasticity, Poisson's ratio, Weibull modulus (m) and flexural strength (f) of ceramic discs sintered from Y-TZP/TiO2 and 3) to determine the effect of biomimetic coating on the Weibull modulus (m) and the flexural strength of the sintered ceramic discs of Y-TZP/TiO2. The powders were produced by a co-precipitation route, in order to obtain the composite Y-TZP/TiO2 with three compositions, containing zero (T0), 10 (T10) and 30 (T30) mol% titania. The produced powder was pressed (50 MPa) into discs of 15 mm diameter and sintered at 1400 °C for 2 hours. After polishing with diamond solution of 45 m, the discs (n = 60 for each group) were approximately 12 mm in diameter and 1.0 mm-thick. Half of the discs were subjected to biomimetic coating (seven days with sodium silicate solution and seven days in 1,5 SBF-simulated body fluid solution ). The powders were characterized by X-ray diffraction (XRD), laser scattering, gas adsorption and scanning electron microscopy (SEM). The discs were characterized by the Archimedes method, ultrasonic pulse-echo, SEM, XRD and for the Weibull analysis, the discs were subjected to the test of biaxial flexural strength in artificial saliva at 37 °C. The results showed that all powders had monoclinic and tetragonal zirconia in their composition, and a specific surface area greater than 42 m2/g.