Development and processing of Al2O3-ZrO2 composites for CAD/CAM prostheses: optical and microstructural characterization

As restaurações monolíticas de Y-TZP (Zircônia Tetragonal Policristalina estabilizada por Itria) se apresentam como uma alternativa interessante devido a suas elevadas propriedades mecânicas, porém existe a preocupação quanto a Degradação em Baixa Temperatura (DBT). Os compósitos ZTA (Alumina reforçada por Zircônia) tem o potencial de atender a esta demanda, apesar do desafio estético uma vez que a passagem de luz pode ser limitada pela combinação de duas fases cristalinas. O presente trabalho teve como objetivo inovar na criação de um compósito ZTA sintetizado com Y-TZP translúcida, na procura de um material com alta resistência mecânica em relação à alumina, resistente à DBT quando comparada à YTZP e com propriedades ópticas melhoradas em relação ao ZTA sintetizado com Y-TZP convencional. Sessenta corpos de prova (discos de 12 mm de diâmetro por 1 mm de espessura) foram confeccionados e divididos em quatro grupos: zircônia convencional (3YSB-E), zircônia translucida (Zpex), compósito ZTA (Al2O3-70%v ZrO2-30%) sintetizado com 3YSB-E (ZTA-3YSB-E) e outro com zircônia translucida Zpex (ZTA-Zpex). Os corpos de prova foram obtidos mediante prensagem uniaxial e isostática dos pós cerâmicos. Após sinterização, o polimento das duas faces foi realizado com discos e suspensões diamantadas de até 1 m. A caracterização óptica foi realizada mediante testes de refletância sobre fundo branco e preto para determinar a razão de contraste (RC) e o parâmetro de translucidez (PT) mediante a diferença de cor (E). Difração de Raios-X (DRX) e Microscopia Eletrônica de Varredura (MEV) foram realizadas para estudo da microestrutura do material. Análise de variância ANOVA e teste de Tukey com nível global de significância de 5% foram utilizados na análises dos dados de propriedades ópticas. A RC mostrou opacidade significativamente menor para o grupo Zpex (0.77; p=0.0001), o grupo 3YSB-E mostrou valores intermediários (0.84; p=0.0001), sendo que os dois compósitos ZTA apresentaram valores maiores de opacidade (ZTA-3YSB-E = 0.99 e ZTA-Zpex = 1) sem diferença significante entre eles (p=0.7433). Para o PT os compósitos ZTA mostraram um E baixo (ZTA-Zpex = 0.22 e ZTA-3YSB-E = 0.43), sem diferença significante entre os grupos (p=0.5). O grupo 3YSB-E apresentou valores intermediários e significativamente diferentes em relação aos outros grupos (E = 7.11 p<0.0001). Já o grupo Zpex apresentou a menor capacidade de mascaramento com E =10.19 (p<0.0001). A DRX mostrou similaridade das fases cristalinas dos grupos 3YSB-E e ZPEX evidenciando que as mesmas foram preservadas na mistura nos compósitos, sem mostrar alterações da estrutura cristalina. A analise no MEV em até 1.500x de aumento evidenciou pouca alteração morfológica entre as zircônias e entre os ZTAs. As propriedades ópticas do ZTA Zpex não foram estatisticamente diferentes do compósito sintetizado com 3YSB-E, sendo que as Y-TZPs apresentaram menor opacidade. As Y-TZPs mostraram estrutura cristalina regular sem a formação de aglomerados e os compósitos ZTAs apresentaram uma mistura uniforme, mantendo as características da estrutura cristalina tanto da Y-TZP quanto da Al2O3, sem formação de aglomerados nem segregação dos grãos dos compósitos. Novos estudos são necessários para avaliar a resistência a DBT e as propriedades mecânicas destes materiais experimentais.Monolithic Yttria stabilized Tetragonal Zirconia Polycrystals (Y-TZP) prostheses are considered an interesting treatment alternative due to their high mechanical properties. Nevertheless there is concern about the Low Temperature Degradation (LTD) process. Zirconia-Toughened Alumina (ZTA) composites seem to be capable of meeting this demand, while facing the challenge of being aesthetically suitable, since the passage of light can be limited by the combination of two polycrystalline phases. The present work aimed to innovate in the synthesis of a ZTA composite with a translucent Y-TZP for dental applications, in the search for a material with high mechanical resistance when compared to alumina, resistant to LTD when compared to Y TZP, and with improved optical properties over ZTA synthesized with conventional Y-TZP. Sixty disc shaped specimens with 12 mm diameter and 1 mm thick, were prepared and divided in four groups: a conventional zirconia (3YSB-E), a translucent zirconia (Zpex), a ZTA composite (Al2O3-70%v ZrO2-30%) synthetized with 3YSB-E (ZTA- 3YSB-E), and a ZTA composite synthetized with translucent zirconia (ZTA-Zpex). The specimens were obtained by uniaxial and isostatic pressing of the ceramic powders. After sintering, polishing of both sides was performed with diamond disks and suspensions up to 1 m. The optical characterization was performed by means of reflectance on a white and a black background to determine the contrast ratio (CR) and the translucency parameter (TP) of the experimental groups. XRD and SEM analyses were performed to study the crystalline structure. Analysis of variance ANOVA and Tukey test with a global significance level of 0.05% were used to analyze the data. CR showed significantly lower opacity for Zpex group (0.77, p = 0.0001), 3YSB-E showed intermediate values of opacity (0.84, p = 0.0001), and both ZTA composites presented higher opacity (ZTA-3YSB-E = 0.99 and ZTA-Zpex = 1) with no statistically significant difference between them (p = 0.7433). The TP showed a low E for ZTA composites (ZTA-Zpex = 0.22 and ZTA-3YSB-E = 0.43), with no statistically difference between the groups (p = 0.5). The 3YSB-E group presented intermediate and significantly different values of TP relative to the other groups (E = 7.11 p <0.0001). The Zpex group presented the lowest masking ability with E = 10.19, also significantly different from the other groups (p <0.0001). The XRD showed similarity of the crystalline phases of 3YSB-E and ZPEX, structure that were preserved in the blends in ZTA composites, without showing changes in the crystalline structure of the materials. SEM analysis (up to 1.500 x) showed low morphologic alteration between Y-TZP and ZTA composites. Optical properties of ZTA-Zpex showed no statistical difference when compared with ZTA-3YSB-E, whereas Y-TZP groups showed less opacity than other groups. The experimental Y-TZPs showed a regular crystalline structure without the formation of agglomerates, and the ZTA composites presented a uniform mixture of the phases, maintaining the characteristics of the polycrystalline structure of both Y-TZPs and Al2O3, without the formation of agglomerates or segregation of the grains in the composites. Future tests evaluating the resistance to LTD and mechanical properties of these experimental materials are warranted

Compósitos experimentais 70%Al2O3-30%ZrO2: caracterização estrutural, topográfica e mecânica antes e após envelhecimento

Objectives: To evaluate the effect of aging on the crystalline structure, surface topography and mechanical properties of an experimental zirconia-toughened-alumina (ZTA) composite comprised by 70% Al2O3 and 30% of a 2nd-generation 3mol% yttria tetragonal zirconia polycrystal (3Y-TZP), compared to its individual counterpart materials. Materials and Methods: Disc-shaped ceramic specimens were divided in four groups (n=10/material): 1) 3YSB-E (1st-generation 3Y-TZP), 2) Zpex (2nd-generation 3Y-TZP), 3) Alumina, and 4) ZTA-Zpex 70/30. X-ray diffraction (XRD) and scanning electron microscope (SEM) were used to characterize the crystalline content and microstructure. Reflectance tests were performed to determine the contrast-ratio (CR) and translucency-parameter (TP). Mechanical properties were assessed by biaxial-flexural-strength (BFS) test to determine Weibull parameters. ZTA and its isolated materials were tested under nanoindentation to record elastic modulus (E) and hardness (H); and Interferometry to assess 3D surface roughness parameters (Sa, Sq). All analyses were conducted before and after autoclave aging (20h, 134oC, 2.2bar). Optical parameters were evaluated through repeated-measures analysis of variance and Tukey tests (p<0.05), BFS data were analyzed using Weibull statistics (95% CI); and nanoindentation and topographic results were analyzed using linear mixed-model and least square difference pos-hoc tests (a=5%). Results: High density values were found for all materials and SEM images exhibited a dense microstructure. While XRD patterns revealed the preservation of crystalline content in the ZTA composite, an increase in the monoclinic phase was observed for pure zirconias after aging. Higher CR and lower TP values were observed for ZTA, followed by Alumina, 3YSB-E, and Zpex. The highest characteristic stress was recorded for 3YSB-E, followed by intermediate values between ZTA and Zpex, and the lowest for Alumina. Conversely, Al2O3 yielded the highest H and E values, followed by ZTA-70/30 and Zpex. Aging affected the optical and mechanical properties of both zirconias, while remained stable for ZTA and alumina. Aging did not affect the surface roughness parameters of ZTA and Alumina, although a significant increase in Sa was recorded for Zpex following aging. Conclusion: The synthesis of the experimental 70-30% ZTA composite was successful and its relevance for dental applications relies on its higher masking ability, aging resistance, and strength similar to zirconia.Objetivo: Avaliar o efeito do envelhecimento na estrutura cristalina, topografia de superfície e propriedades mecânicas de um compósito experimental de alumina reforçada com zircônia (ZTA) composto por 70% de Al2O3 e 30% de uma zirconia de segunda geração, em comparação com os seus materiais individuais. Materiais e métodos: Espécimes em formato de discos foram divididos em quatro grupos (n = 10 / material): 1) 3YSB-E (3Y-TZP de primeira geração), 2) Zpex (3Y-TZP de segunda geração), 3) Alumina e 4) ZTA-Zpex 70/30. Difração de raios X (DRX) e microscopia eletrônica de varredura (MEV) foram usados para caracterizar o conteúdo cristalino e a microestrutura dos materiais. Testes de refletância foram realizados para determinar a razão de contraste (RC) e o parâmetro de translucidez (PT). As propriedades mecânicas foram avaliadas pelo teste de resistência à flexão biaxial (RFB) para determinar os parâmetros de Weibull. ZTA, Zpex e Alumina foram adicionalmente testados sob nanoindentação para obter módulo de elasticidade (E) e dureza (H); e por Interferometria para avaliar parâmetros de rugosidade superficial 3D (Sa, Sq). Todas as análises foram realizadas antes e após o envelhecimento artificial (20h, 134oC, 2,2 bar). Os dados de propriedades ópticas foram avaliados por meio da análise de variância de medidas repetidas e testes de Tukey (p <0,05); os dados da RFB foram analisados pela estatística de Weibull (IC95%); e dados de nanoindentação e resultados topográficos foram analisados usando modelos lineares mistos e testes pos-hoc de diferença de mínimos quadrados (a = 5%). Resultados: Valores de alta densidade foram encontrados para todos os materiais e as imagens de MEV exibiram uma microestrutura densa. Os padrões de XRD revelaram a preservação do conteúdo cristalino no compósito ZTA, enquanto um aumento nos picos monoclínicos foi observado para zircônias puras após envelhecimento. Maior RC e menor PT foram observados para o compósito ZTA, seguido por alumina, 3YSB-E e Zpex. O maior estresse característico foi registrado para 3YSB-E, seguido por valores intermediários entre Zpex e ZTA, e o menor para Alumina. Al2O3 apresentou os maiores valores de H e E, seguido por ZTA-70/30 e Zpex, todos significativamente diferentes. O envelhecimento afetou as propriedades ópticas e mecânicas de ambas as zircônias, enquanto se manteve estável para o compósito ZTA e alumina. O envelhecimento não afetou os parâmetros de rugosidade da superfície de ZTA-70/30 e Al2O3, embora um aumento significativo de Sa tenha sido registrado para Zpex após o envelhecimento. Conclusão: A síntese experimental do compósito ZTA 70-30% foi bem-sucedida e sua relevância para aplicações odontológicas está em sua maior capacidade de mascaramento, resistência ao envelhecimento em todos os parâmetros testados e resistência semelhante à zircônia. O envelhecimento aumentou significativamente o conteúdo monoclínico das zircônias puras e afetou as suas propriedades ópticas e mecânicas, bem como sua rugosidade superficial

Influence of abrasive dentifrices on polymeric reconstructive material properties after simulated toothbrushing

AbstractTo assess the influence of dentifrices with different abrasiveness levels on the properties of dental reconstructive materials. Forty-eight cylinders were obtained from four polymeric materials, being two CAD/CAM acrylic resins (Ivotion-Dent and Ivotion-Base), one injected acrylic resin (IvoBase-Hydrid) and one light-cured resin composite (Empress Direct). Specimens were allocated to four subgroups for toothbrushing simulation according to the dentifrice relative dentin abrasivity (RDA) and silica content: (i) RDA 0 = 0%; (ii) RDA 50 = 3%; (iii) RDA 100 = 10%; and (iv) RDA 120 = 25%. Specimens were then subjected to toothbrushing. Surface analyses [surface roughness Ra (SR) and scanning electron microscopy (SEM)] along with hardness and optical properties [translucency parameter (TP) and contrast ratio (CR)] were evaluated before and after toothbrushing. Statistical analyses were performed using ANOVA and Tukey test. A significant increase in SR was observed after toothbrushing with higher RDA toothpastes for Ivotion-Dent (100 and 120) and IvoBase-Hybrid (120). Ivotion-Base and Empress Direct presented no significant differences in SR when analyzed as a function of timepoint and RDA levels. Hardness was not influenced by toothbrushing with different RDA dentifrices, except for Empress Direct with RDA 0 toothpaste, where a decrease in the hardness was observed. TP of Ivotion-Dent and Empress Direct significantly decreased after toothbrushing with higher RDA dentifrices and CR of Ivotion-Dent, Empress Direct and IvoBase-Hybrid significantly increased with higher RDA dentifrices. The levels of dentifrice abrasiveness affected differently the SR, hardness and optical properties of polymeric reconstructive materials after toothbrushing

Nanomechanical and microstructural characterization of a zirconia-toughened alumina composite after aging

This study's objective was to mechanically characterize and validate the synthesis method of a polycrystalline composite comprised of 80% alumina reinforced with 20% translucent zirconia (zirconia-toughened alumina, ZTA) and compare to an experimental translucent zirconia. Experimental ZTA (ZTA ZPEX 80/20) and translucent Y-TZP (ZPEX) green-state disc-shaped specimens were obtained via uniaxial/isostatic ceramic powder pressing technique. The discs were sintered using a predefined protocol after both sides of the discs were polished. The specimens were subjected to nanoindentation testing to acquire their elastic modulus (E) and hardness (H) before and after a simulated low temperature degradation (LTD) challenge. Subsequently, the fabricated discs had their 3D surface topographical (Sa/Sq) parameters assessed via interferometry before and after exposure to a simulated LTD aging protocol. The specimens were evaluated using X-ray diffraction (XRD) to assess the tetragonal-monoclinic phase transformation and via scanning electron microscopy (SEM) to evaluate the homogeneity of the surfaces and distribution of the grains. The apparent density was measured using Archimedes' principle. All of the data were statistically evaluated through repeated measures ANOVA following post-hoc comparisons using the Tukey test (p 0.05). A significant decrease in the E values after the aging protocol was observed for both groups (p < 0.01). While ZTA ZPEX 80/ 20 did not show statistically significant differences in the hardness values after the aging protocol (p = 0.36), ZPEX demonstrated a significant decrease in the H values (p = 0.03). For ZTA ZPEX 80/20, simulated LTD aging did not affect the tested properties, except for the E values. Although artificial aging did not affect the surface roughness of ZPEX, the E and H values significantly decreased after aging45788408846CONSELHO NACIONAL DE DESENVOLVIMENTO CIENTÍFICO E TECNOLÓGICO - CNPQCOORDENAÇÃO DE APERFEIÇOAMENTO DE PESSOAL DE NÍVEL SUPERIOR - CAPESFUNDAÇÃO DE AMPARO À PESQUISA DO ESTADO DE SÃO PAULO - FAPESP304589/2017-9; 434487/2018-0não tem2012/19078-7; EMU 2016/18818-8; 2016/17793-1; 2017/19362-0; 2018/03072-