Efeito da temperatura de sinterização e de envelhecimentos induzidos sobre a microestrutura, propriedades ópticas e resistência à flexão de duas zircônias monolíticas
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Data
2018-08-01
Autores
Cardoso, Kátia Vieira
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Universidade Estadual Paulista (Unesp)
Resumo
As zircônias monolíticas foram desenvolvidas como alternativa às próteses feitas com zircônia convencional e devido suas propriedades ópticas melhoradas não necessitam cerâmica de cobertura. Diferentes temperaturas de sinterização bem como processos de envelhecimento, podem influenciar sua microestrutura e propriedades ópticas e mecânicas. Este estudo avaliou como diferentes temperaturas de sinterização e envelhecimentos induzidos afetam a microestrutura, propriedades ópticas e mecânicas das zircônias monolíticas. Para a avaliação das temperaturas de sinterização espécimes em forma de barra (25 mm × 5 mm × 2,1 mm) foram obtidos de uma zircônia totalmente estabilizada (Prettau Anterior, Zirkonzahn) e divididos em dois grupos (n=15), de acordo com a temperatura final de sinterização (1450oC ou 1600oC). Os parâmetros ópticos obtidos foram os de refletância média (R), opacidade (O), translucidez (T), soma de absorção e dispersão de luz (A/D) e diferença de cor (ΔE). Foram realizadas as análises em microscopia eletrônica de varredura (MEV) para avaliação microestrutural e de tamanhos de grãos, análise cristalográfica foi feita por meio de difração de raios-x (DRX) e a avaliação mecânica foi através do ensaio de flexão em 3 pontos. Os dados obtidos foram analisados utilizando o teste t-Student. Os resultados mostraram diferença significativa entre os grupos (p<0,05) nos parâmetros R, O, e A/D. A T (p>0,05) e resistência à flexão não apresentaram diferença significativa (p=0,378). O valor de ΔE foi 2,32. O DRX indicou fase cúbica (47,41% para 1450°C; 46,04% para 1600°C) e tetragonal (52,59% para 1450°C; 53,96% para 1600°C). Não foi encontrada fase monoclínica. A imagens de MEV mostraram grãos 4 vezes maiores, além de limites entre os grãos mais definidos no grupo de 1600°C. A avaliação dos envelhecimentos foi realizada primeiramente em espécimes não pintados, através de discos (12 mm Ø e 1,2 mm de espessura) de duas zircônias (Prettau Anterior (ZMA) e Prettau (ZMP), Zirkonzahn), que foram divididos em 3 grupos (n=15) de acordo com o envelhecimento realizado: hidrotérmico (H), em autoclave, por 28h; químico (Q), em ácido acético a 4% por 300h e mecânico (M), até 2x106 ciclos. As propriedades ópticas (parâmetros de R, O, T e A/D), a análise de MEV para avaliação superficial e DRX para obtenção dos padrões de difração foram realizadas antes e após o período final dos envelhecimentos e posteriormente foi realizado o teste de flexão biaxial. Os resultados mostraram que as propriedades ópticas apresentaram alterações parciais dos parâmetros estudados. Na flexão biaxial, ZMP foi significativamente diferente que ZMA em todos os grupos (p<0,05). Entre os grupos do mesmo material ZMP não mostrou diferença significativa entre nenhum dos envelhecimentos e ZMA mostrou diferença significativa apenas do controle para H (p<0,05). Os padrões de DRX mostraram picos constantes para ZMA em todos os grupos e para ZMP houve o surgimento de novos picos sugestivos de fase monoclínica em todos os grupos. As imagens de MEV em ambos materiais mostraram mudanças como espaçamento entre os grãos, espações vazios e zonas de nucleação. Os envelhecimentos induzidos também foram testados progressivamente em espécimes pintados, através de discos (12 mm Ø e 1,2 mm de espessura) das zircônias ZMA e ZMP. Os espécimes receberam uma pintura com líquido na cor A3 do mesmo fabricante antes da sinterização e foram divididos em grupos (n=15) como descrito anteriormente, porém com intervalos de análises: (H) nos tempos: 5h, 8h, 12h e 15h, 20h, 24h e 28h; (Q), nos tempos: 90h, 120h, 150 e 180h, 210h, 250h e 300h e (M), nos intervalos de 2,5x105, 5x105, 7,5x105, 1x106, 1,25x106, 1,5x106 e 2x106 ciclos. As propriedades ópticas e análises de DRX com quantificação das fases foram realizadas após cada período citado. As imagens de MEV foram feitas no período inicial e final. Os resultados mostraram que as propriedades ópticas mudaram significativamente (p<0,05) conforme os tempos de envelhecimento, exceto para a opacidade da ZMP grupo M. As quantificações de fases cristalinas mostraram que não houve conteúdo monoclínico para ZMA em nenhum grupo e para ZMP houve diminuição progressiva da fase tetragonal e aumento principalmente de fase monoclínica. As imagens de MEV mostraram em ambos materiais, mudanças como espaçamento entre os grãos, espaços vazios e zonas de nucleação. O aumento da temperatura provocou alterações na microestrutura, principalmente no tamanho dos grãos da ZMA e nas propriedades ópticas, exceto para translucidez. A resistência à flexão em 3 pontos não foi afetada. Os diferentes protocolos de envelhecimentos mudaram parcialmente as propriedades ópticas em ambos materiais. A resistência à flexão biaxial foi afetada apenas na ZMA no grupo H em relação ao controle. ZMP foi superior a ZMA em todos os grupos estudados. Os envelhecimentos provocaram mudanças microestruturais semelhantes em ambos materiais.
Monolithic zirconias has been developed as an alternative for prostheses made with veneering porcelain, because it’s improved optical properties. However, sintering conditions and aging process could affect its microstructure, optical and mechanical properties. The aim of this study was to evaluate the effect of different sintering temperatures and aging process on the microstructure, optical and mechanical properties of the monolithic zirconias. Sintering protocols were evaluated using bar-shaped specimens (25 mm × 5 mm × 2.1 mm) of a fully stabilized zirconia (Prettau Anterior, Zirkonzahn) divided into two groups (n = 15) according to final sintering temperatures (1450°C and 1600°C). Optical properties parameters of average reflectance (R), opacity (O), translucency parameter (TP), absorption-scattering sum of light (S/A), and color difference (ΔE) were obtained were obtained. Scanning electron microscopy (SEM) was conducted for microstructure analysis, crystalline phase quantification was obtained by x-ray diffraction (XRD) and for mechanical performance, three-point bending was performed. Data were analyzed using Student’s t-test. Significant difference was founded in the R, O, and S/A parameters between groups (p<0.05). TP (p>0.05) and flexural strength (p=0,378) showed no statistical differences. ΔE value was 2.32. XRD indicated cubic (47.41% for 1450°C; 46.04% for 1600°C) and tetragonal content (52.59% for 1450°C; 53.96% for 1600°C). No monoclinic content was found. SEM images showed grains 4 times higher and more definite grain boundaries in the 1600°C group. Aging evaluation was made using discs-shaped specimens (12 mm Ø and 1.2 mm of thickness) of two zirconias(Prettau Anterior (AMZ) e Prettau (PMZ), Zirkonzahn), not painted. Specimens were divided into 3 groups (n=15) according to the aging process: hydrothermal (H), in autoclave for 28h; chemistry (Ch), in 4% acetic acid for 300h and mechanical (M), at 2x106 cycles. Optical properties (R, O, TP and S/A parameters), SEM and XDR analyses were made initially and after final aging times. Biaxial bending was made after final aging times. Optical properties showed partial changes in both material for all parameters. Flexural strength of PMZ was significantly higher than AMZ in all groups (p<0.05). Between groups in each material ZMP showed no statistical difference (p>0.05) and AMZ was different only from control to H (p<0.05). XDR showed constants peaks in all groups and PMZ showed emergence of new peaks, suggestive of monoclinic phase in all groups. SEM showed in both materials changes as spacing between the grains, empty spaces and nucleation zones. Induced aging was also progressively tested on painted specimens, using discs-shaped specimens (12 mm Ø and 1.2 mm of thickness) of AMZ and PMZ. Before sintering, a painting with A3 liquid color were made, then specimens were divided in groups (n=15) and submitted to the same aging protocols as previously described, but with intervals of analysis. (H): 5h, 8h, 12h e 15h, 20h, 24h and 28h; chemical (Ch): 90h, 120h, 150 e 180h, 210h, 250h and 300h (M):2,5x105, 5x105, 7,5x105, 1x106, 1,25x106, 1,5x106 e 2x106 cycles. Optical properties and XRD were made after each aging time; SEM was made at initial and final aging time. Optical properties showed significant changes (p<0.05) in the aging times, except for opacity at PMZ group M. Crystalline phase quantification indicate no monoclinic content for AMZ in all groups and PMZ had a progressively tetragonal phase decrease and an increase mainly of monoclinic content. SEM images showed in both materials changes such as spacing between the grains, empty spaces and nucleation zones. Increased sintering temperature led to changes in microstructure, mainly in grain sizes, and optical properties of AMZ, except translucency. Three-point bending resistance was not affected. The different aging protocols partially changed the optical properties in both zirconias. Biaxial flexural strength was different only in AZM from control to H and PZM was superior to AZM in all groups. Microstructural changes was the same in AZM and PZM.
Monolithic zirconias has been developed as an alternative for prostheses made with veneering porcelain, because it’s improved optical properties. However, sintering conditions and aging process could affect its microstructure, optical and mechanical properties. The aim of this study was to evaluate the effect of different sintering temperatures and aging process on the microstructure, optical and mechanical properties of the monolithic zirconias. Sintering protocols were evaluated using bar-shaped specimens (25 mm × 5 mm × 2.1 mm) of a fully stabilized zirconia (Prettau Anterior, Zirkonzahn) divided into two groups (n = 15) according to final sintering temperatures (1450°C and 1600°C). Optical properties parameters of average reflectance (R), opacity (O), translucency parameter (TP), absorption-scattering sum of light (S/A), and color difference (ΔE) were obtained were obtained. Scanning electron microscopy (SEM) was conducted for microstructure analysis, crystalline phase quantification was obtained by x-ray diffraction (XRD) and for mechanical performance, three-point bending was performed. Data were analyzed using Student’s t-test. Significant difference was founded in the R, O, and S/A parameters between groups (p<0.05). TP (p>0.05) and flexural strength (p=0,378) showed no statistical differences. ΔE value was 2.32. XRD indicated cubic (47.41% for 1450°C; 46.04% for 1600°C) and tetragonal content (52.59% for 1450°C; 53.96% for 1600°C). No monoclinic content was found. SEM images showed grains 4 times higher and more definite grain boundaries in the 1600°C group. Aging evaluation was made using discs-shaped specimens (12 mm Ø and 1.2 mm of thickness) of two zirconias(Prettau Anterior (AMZ) e Prettau (PMZ), Zirkonzahn), not painted. Specimens were divided into 3 groups (n=15) according to the aging process: hydrothermal (H), in autoclave for 28h; chemistry (Ch), in 4% acetic acid for 300h and mechanical (M), at 2x106 cycles. Optical properties (R, O, TP and S/A parameters), SEM and XDR analyses were made initially and after final aging times. Biaxial bending was made after final aging times. Optical properties showed partial changes in both material for all parameters. Flexural strength of PMZ was significantly higher than AMZ in all groups (p<0.05). Between groups in each material ZMP showed no statistical difference (p>0.05) and AMZ was different only from control to H (p<0.05). XDR showed constants peaks in all groups and PMZ showed emergence of new peaks, suggestive of monoclinic phase in all groups. SEM showed in both materials changes as spacing between the grains, empty spaces and nucleation zones. Induced aging was also progressively tested on painted specimens, using discs-shaped specimens (12 mm Ø and 1.2 mm of thickness) of AMZ and PMZ. Before sintering, a painting with A3 liquid color were made, then specimens were divided in groups (n=15) and submitted to the same aging protocols as previously described, but with intervals of analysis. (H): 5h, 8h, 12h e 15h, 20h, 24h and 28h; chemical (Ch): 90h, 120h, 150 e 180h, 210h, 250h and 300h (M):2,5x105, 5x105, 7,5x105, 1x106, 1,25x106, 1,5x106 e 2x106 cycles. Optical properties and XRD were made after each aging time; SEM was made at initial and final aging time. Optical properties showed significant changes (p<0.05) in the aging times, except for opacity at PMZ group M. Crystalline phase quantification indicate no monoclinic content for AMZ in all groups and PMZ had a progressively tetragonal phase decrease and an increase mainly of monoclinic content. SEM images showed in both materials changes such as spacing between the grains, empty spaces and nucleation zones. Increased sintering temperature led to changes in microstructure, mainly in grain sizes, and optical properties of AMZ, except translucency. Three-point bending resistance was not affected. The different aging protocols partially changed the optical properties in both zirconias. Biaxial flexural strength was different only in AZM from control to H and PZM was superior to AZM in all groups. Microstructural changes was the same in AZM and PZM.
Descrição
Palavras-chave
Zircônio, Envelhecimento, Resistência de materiais, Difração de raios X, Fenômenos ópticos, Zirconium, Aging, Material resistance, X-Ray diffraction, Optical phenomena