Efeito da espessura de zircônia e dissilicato de lítio monolíticos sob fadiga acelerada progressiva
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Data
2021-07-07
Autores
Baldochi, Mariana Ribeiro
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Editor
Universidade Estadual Paulista (Unesp)
Resumo
O lascamento da porcelana de cobertura é um problema recorrente em sistemas totalmente cerâmicos a base de zircônia policristalina estabilizada por ítria (YTZP) e, para eliminar a necessidade do material de recobrimento, foram desenvolvidas zircônias com maior grau de translucidez indicadas para o uso monolítico. No entanto, o comportamento mecânico desses novos materiais sob fadiga e a espessura mínima indicada ainda são incertos. O objetivo deste estudo foi avaliar as zircônias monolíticas Prettau (P) e Prettau Anterior (PA) e o dissilicato de lítio IPS e.max CAD (DL), por meio de ensaio de fadiga acelerada progressiva variando-se a espessura do material. Foram confeccionados discos com as cerâmicas (n=54/material) com as dimensões finais de 12 mm de diâmetro e espessura de 0,5 mm, 1,0 mm e 1,5 mm. Os discos foram cimentados sobre discos de resina epóxi G10 de 12 mm de diâmetro e 3 mm de espessura. Os corpos-de-prova (n=18/grupo) foram submetidos ao ensaio de fadiga acelerada na distribuição 3 x 2 x 1, sendo 9 espécimes testados em regime leve, 6 no regime moderado e 3 no agressivo. A distribuição das falhas e as probabilidades de sobrevida foram submetidos à análise de Weibull de dano acumulado, por meio do software ReliaSoft. O modo de falha foi investigado para identificação do tipo e da origem da fratura. Os resultados de confiabilidade para uma missão calculada de 50000 ciclos a 500 N variaram de 68% a 85% para Prettau Anterior, de 97 a 99% para e.max CAD e 86% a 100% para Prettau. Na espessura de 1,0 mm e 1,5 mm o e.max CAD apresentou confiabilidade superior a Prettau Anterior e na espessura de 1,0 mm houve redução significativa da confiabilidade da Prettau. Houve diferença estatística significante na resistência característica e no módulo de Weibull, sendo que P 1,5 mm apresentou a mais elevada média desses parâmetros. A avaliação do modo de falha revelou que os grupos DL 0,5 mm, PA em todas as espessuras e P 0,5 mm e P 1,5 mm, as trincas foram predominantes radiais, associadas a algumas trincas tipo cone interno. Foram observadas trincas radiais associadas a trincas tipo cone interno em número maior e em diferentes direções para o grupo P 1,0 mm. Concluiu-se que a zircônia totalmente estabilizada por ítria, apresenta menor confiabilidade e resistência característica. Ambos os tipos de zircônia se mostraram sensíveis à variação da espessura, particularmente na medida intermediária. O dissilicato de lítio foi pouco influenciado pela espessura.
Chipping of veneer porcelain is a recurrent problem in all-ceramic systems based on yttria-stabilized polycrystalline zirconia (YTZP) and to eliminate the need for veneer material, monolithic zirconia with a higher translucency have been developed. However, mechanical behavior of these new materials under fatigue and the minimum thickness indicated are still uncertain. The aim of this study was to evaluate different thickness of two types of monolithic zirconias (Prettau and Prettau Anterior) and a lithium disilicate (IPS e.max CAD) by step stress accelerated life testing. Ceramic discs (n=54/material) were made with 12 mm in diameter and 0.5 mm, 1.0 mm, 1.5 mm thickness. The discs were cemented on G10 epoxy resin discs (12 mm of diameter and 3 mm of thickness). The samples (n=18/group) were tested by step stress accelerated life testing in a 3 x 2 x 1 distribution, with 9 samples being tested in mild profile, 6 in moderate profile and 3 in aggressive profile. Failure distribution and survival probabilities were submitted to Weibull analysis of accumulated damage using ReliaSoft software. Failure mode analysis was performed to identify the type and origin of the fracture. Reliability results for a given mission of 50000 cycles under 500 N ranged from 68% to 85% for Prettau Anterior, 97 to 99% for e.max CAD, and 86% to 100% for Prettau. The thickness of 1.0 mm and 1.5 mm of e.max CAD provided greater reliability than Prettau Anterior and Prettau 1.0 mm. There was a statistically significant difference in characteristic strength and Weibull modulus, with P 1.5 mm presenting the highest mean of these parameters. Failure mode evaluation indicated that the groups e.max CAD 0.5 mm, Prettau Anterior in all thicknesses and Prettau in 0.5 mm and 1.5 mm, presented radial cracks associated to inner cone cracks. In the group Prettau 1.0 mm there were radial cracks associated to higher amount of inner cone cracks. It was concluded that the full stabilized zirconia was less reliable and less strong than the other ceramics, particularly when compared to partially stabilized zirconia. Both types of zirconia were sensible to thickness, especially in intermediary thickness. The lithium disilicate ceramic was not markedly affected by thickness.
Chipping of veneer porcelain is a recurrent problem in all-ceramic systems based on yttria-stabilized polycrystalline zirconia (YTZP) and to eliminate the need for veneer material, monolithic zirconia with a higher translucency have been developed. However, mechanical behavior of these new materials under fatigue and the minimum thickness indicated are still uncertain. The aim of this study was to evaluate different thickness of two types of monolithic zirconias (Prettau and Prettau Anterior) and a lithium disilicate (IPS e.max CAD) by step stress accelerated life testing. Ceramic discs (n=54/material) were made with 12 mm in diameter and 0.5 mm, 1.0 mm, 1.5 mm thickness. The discs were cemented on G10 epoxy resin discs (12 mm of diameter and 3 mm of thickness). The samples (n=18/group) were tested by step stress accelerated life testing in a 3 x 2 x 1 distribution, with 9 samples being tested in mild profile, 6 in moderate profile and 3 in aggressive profile. Failure distribution and survival probabilities were submitted to Weibull analysis of accumulated damage using ReliaSoft software. Failure mode analysis was performed to identify the type and origin of the fracture. Reliability results for a given mission of 50000 cycles under 500 N ranged from 68% to 85% for Prettau Anterior, 97 to 99% for e.max CAD, and 86% to 100% for Prettau. The thickness of 1.0 mm and 1.5 mm of e.max CAD provided greater reliability than Prettau Anterior and Prettau 1.0 mm. There was a statistically significant difference in characteristic strength and Weibull modulus, with P 1.5 mm presenting the highest mean of these parameters. Failure mode evaluation indicated that the groups e.max CAD 0.5 mm, Prettau Anterior in all thicknesses and Prettau in 0.5 mm and 1.5 mm, presented radial cracks associated to inner cone cracks. In the group Prettau 1.0 mm there were radial cracks associated to higher amount of inner cone cracks. It was concluded that the full stabilized zirconia was less reliable and less strong than the other ceramics, particularly when compared to partially stabilized zirconia. Both types of zirconia were sensible to thickness, especially in intermediary thickness. The lithium disilicate ceramic was not markedly affected by thickness.
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Palavras-chave
Cerâmica, Zircônio, Resistência de materiais, Ceramic, Zirconium, Material resistance