Caracterização mecânica, microestrutural e óptica de zircônias monolíticas e dissilicato de lítio com diferentes espessuras
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2018-07-13
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Universidade Estadual Paulista (Unesp)
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Para eliminar a aplicação de porcelanas, zircônias com maior translucidez têm sido lançadas no mercado, que assim como o dissilicato de lítio, são indicadas para o uso monolítico. Um exemplo é a zircônia totalmente estabilizada em fase tetragonal, com maior quantidade de fase cúbica. No entanto, o comportamento mecânico, a espessura mínima indicada e a influência da espessura na translucidez destes materiais ainda são incertos. Este estudo avaliou zircônia totalmente estabilizada por ítria (Prettau Anterior), zircônia parcialmente estabilizada (Prettau) e dissilicato de lítio (IPS e.max CAD) através de caracterização mecânica, além do efeito da espessura na resistência à fratura e translucidez. Resistência à flexão biaxial (RFB) e parâmetros de Weibull (n=30) foram realizados. Espécimes em forma de disco nas espessuras de 0,5 mm, 1 mm e 1,5 mm foram analisados em espectrofotômetro para avaliação da translucidez. Posteriormente foram cimentados em substrato de resina epóxi para o ensaio de resistência à fratura (RF) e parâmetros de Weibull (n=30). Para caracterização microestrutural foi utilizado Microscopia Eletrônica de Varredura (MEV). Os valores de RFB (MPa) foram: 683,0 ± 70,23 para Prettau, 438,6 ± 64,1 para Prettau Anterior e 248,6 ± 37,3 para IPS e.max CAD. ANOVA à um fator para RFB mostrou significância (ρ<0,001) e pós-teste de Tukey indicou diferença entre todas as cerâmicas. Houve diferença estatística significante na resistência característica, mas no módulo de Weibull não. ANOVA à dois fatores para RF e para translucidez foi significante para cerâmica (ρ<0,001), espessura (ρ<0,001) e interação (ρ<0,001). Para RF não houve diferença entre as cerâmicas na espessura de 0,5 mm. Prettau obteve os maiores valores de RF em 1 mm e 1,5 mm. IPS e.max CAD de 1,5 mm exibiu maior RF que Prettau Anterior. Para translucidez dissilicato de lítio foi o mais translúcido, seguido de Prettau Anterior e depois Prettau. No entanto, foi encontrada similaridade estatística entre Prettau Anterior e Prettau de 0,5 mm, Prettau Anterior de 1 mm e dissilicato de lítio de 1,5 mm e Prettau 1 mm e dissilicato de lítio 1,5 mm. Prettau de 1,5 mm foi o grupo menos translúcido. Imagem de MEV para dissilicato de lítio apresentou estrutura cristalina de formato típico de agulha. Prettau Anterior apresentou grãos notavelmente maiores que Prettau. Concluiu-se que Prettau tem a maior resistência mecânica e menor translucidez, mas quando cimentado sobre um substrato, os espécimes de 0,5 mm se comportaram de maneira similar as outras cerâmicas nessa mesma espessura. Apesar da menor RFB, IPS e.max CAD teve RF similar ou superior a Prettau Anterior quando cimentado em substrato. Com valores inferiores de translucidez e resistência mecânica próxima em relação ao dissilicato de lítio pode-se concluir que mais análises são necessárias para uma melhor indicação da zircônia totalmente estabilizada por ítria.
In order to eliminate the porcelain veneering, high translucency Y-TZP has been introduced on the market, which as well as lithium disilicate, were developed for monolithic indication. One example is the fully stabilized zirconia, with greater amount of cubic phase. However, the mechanical behavior, the minimum thickness recommended and the influence of the thickness on the translucency of these materials are still uncertain. This study assessed the fully stabilized zirconia (Prettau Anterior), the partially stabilized zirconia (Prettau) and the lithium disilicate (IPS e.max CAD) through mechanical characterization, besides the effect of thickness on fracture load and translucency. Biaxial flexural strength (BFS) and Weibull parameters (n=30) were performed. Disk-shaped specimens with thicknesses of 0.5 mm, 1 mm, and 1.5 mm were analyzed in spectrophotometer to evaluation of translucency. After, they were cemented on an epoxy-resin substrate for the fracture load static test (FLST) and Weibull statistics (n=30). To microstructural characterization, Scanning Electron Microscopy (SEM) was used. The BFS values (MPa) were: 683.0 ± 70.23 to Prettau; 438.6 ± 64.1 to Prettau Anterior, and 248.6 ± 37.3 to IPS e.max CAD. One-way ANOVA for BFS was significant (ρ<.001), and Tukey’s post hoc test showed differences among all ceramics. There was statistical difference in characteristic strength, but there was no difference in Weibull modulus. Two-way ANOVA for FLST and for translucency was significant for ceramic (ρ <.001), thickness (ρ <.001), and interaction (ρ <.001). To FLST, there was no difference among all ceramics at the 0.5 mm thickness. Prettau had higher FLST values for the 1.0 and 1.5 mm. IPS e.max CAD of 1.5 mm exhibited a higher FLST than Prettau Anterior. For translucency, lithium disilicate was the most translucent, followed by Prettau Anterior and then Prettau. However, statistical similarity was found between Prettau Anterior and Prettau of 0.5 mm, Prettau Anterior of 1 mm and lithium disilicate of 1.5 mm and Prettau 1 mm and 1,5 mm. Prettau of 1.5 mm was the least translucent group. SEM image for lithium di-silicate showed typical needle-like crystal structure. Prettau Anterior showed remarkably larger grains than Prettau. It was concluded that Prettau has the highest mechanical strength and lower translucency, but when cemented on a substrate, the 0.5 mm specimens behaved similarly to other ceramics in the same thickness. Despite the lower BFS, IPS e.max CAD had FLST similar or higher than Prettau Anterior when cemented in a substrate. With lower values of translucency and near mechanical resistance in relation to lithium disilicate it can be concluded that further analyzes are necessary for a better indication of fully stabilized zirconia.
In order to eliminate the porcelain veneering, high translucency Y-TZP has been introduced on the market, which as well as lithium disilicate, were developed for monolithic indication. One example is the fully stabilized zirconia, with greater amount of cubic phase. However, the mechanical behavior, the minimum thickness recommended and the influence of the thickness on the translucency of these materials are still uncertain. This study assessed the fully stabilized zirconia (Prettau Anterior), the partially stabilized zirconia (Prettau) and the lithium disilicate (IPS e.max CAD) through mechanical characterization, besides the effect of thickness on fracture load and translucency. Biaxial flexural strength (BFS) and Weibull parameters (n=30) were performed. Disk-shaped specimens with thicknesses of 0.5 mm, 1 mm, and 1.5 mm were analyzed in spectrophotometer to evaluation of translucency. After, they were cemented on an epoxy-resin substrate for the fracture load static test (FLST) and Weibull statistics (n=30). To microstructural characterization, Scanning Electron Microscopy (SEM) was used. The BFS values (MPa) were: 683.0 ± 70.23 to Prettau; 438.6 ± 64.1 to Prettau Anterior, and 248.6 ± 37.3 to IPS e.max CAD. One-way ANOVA for BFS was significant (ρ<.001), and Tukey’s post hoc test showed differences among all ceramics. There was statistical difference in characteristic strength, but there was no difference in Weibull modulus. Two-way ANOVA for FLST and for translucency was significant for ceramic (ρ <.001), thickness (ρ <.001), and interaction (ρ <.001). To FLST, there was no difference among all ceramics at the 0.5 mm thickness. Prettau had higher FLST values for the 1.0 and 1.5 mm. IPS e.max CAD of 1.5 mm exhibited a higher FLST than Prettau Anterior. For translucency, lithium disilicate was the most translucent, followed by Prettau Anterior and then Prettau. However, statistical similarity was found between Prettau Anterior and Prettau of 0.5 mm, Prettau Anterior of 1 mm and lithium disilicate of 1.5 mm and Prettau 1 mm and 1,5 mm. Prettau of 1.5 mm was the least translucent group. SEM image for lithium di-silicate showed typical needle-like crystal structure. Prettau Anterior showed remarkably larger grains than Prettau. It was concluded that Prettau has the highest mechanical strength and lower translucency, but when cemented on a substrate, the 0.5 mm specimens behaved similarly to other ceramics in the same thickness. Despite the lower BFS, IPS e.max CAD had FLST similar or higher than Prettau Anterior when cemented in a substrate. With lower values of translucency and near mechanical resistance in relation to lithium disilicate it can be concluded that further analyzes are necessary for a better indication of fully stabilized zirconia.
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Zircônio, Resistência dos materiais, Cerâmica, Zirconium, Material resistance, Ceramics