Influência dos tratamentos térmicos de nucleação na fração cristalina e morfologia dos cristais de dissilicato de lítio LaMaV CAD
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Data
2019-02-28
Autores
Vallerini, Bruna de Freitas
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Editor
Universidade Estadual Paulista (Unesp)
Resumo
Os materiais destinados a próteses odontológicas têm evoluído ao longo dos anos permitindo chegar a materiais cerâmicos com alta qualidade, sendo o dissilicato de lítio um dos materiais mais utilizados devido à sua ampla gama de indicações; isto é possível pois sua microestrutura está diretamente relacionada com suas boas propriedades mecânicas, físicas e óticas. O Laboratório de Materiais Vítreos (LaMaV) da Universidade Federal de São Carlos está desenvolvendo um dissilicato de lítio do tipo fresado que permite obter próteses a um custo futuro mais acessível; porém, estudos ainda são necessários para otimizar a microestrutura. Sendo assim, o objetivo deste estudo foi avaliar a influência dos diferentes tratamentos térmicos de nucleação na fração cristalina e morfologia dos cristais de LaMaV CAD. Para tanto foram confeccionados discos (12 mm de diâmetro x 1,2 mm de espessura) de dissilicato de lítio LaMaV CAD e de IPS e.max CAD (grupo controle, n=3). Os discos de LaMaV CAD foram submetidos a recozimento a 380oC por 2h seguido de diferentes tratamentos térmicos de nucleação, processo no qual se variou o tempo e a temperatura compondo quatro subgrupos (n=3): T1 (1h30 por 500oC), T2 (3h por 500oC), T3 (6h por 500oC) e T4 (6h por 480oC). Os discos de IPS e.max CAD foram cristalizados de acordo com as recomendações do fabricante. Foram obtidas imagens em microscópio óptico de varredura (MEV) para caracterizar a microestrutura e quantificar a fração cristalina. Tal quantificação foi realizada utilizando-se o software ImageJ, pelo qual se obteve uma porcentagem estimada das fases vítreas e cristalina. Difração de raios-X foi realizada para se verificar, por meio do refinamento de Rietveld, as fases presentes nas amostras. As imagens de MEV foram analisadas descritivamente bem como os resultados referentes à fração cristalina. A análise de DRX mostrou picos de aproximadamente 86% de dissilicato de lítio para todos os grupos. As imagens feitas em MEV mostraram morfologia dos cristais em formato acicular e homogêneos para todos os grupos, e o grupo que mais se assemelhou ao grupo controle foi o Grupo T1. O Grupo T4 mostrou uma maior nucleação de cristais em relação ao controle. A fração cristalina (%) foi: C= 59,31; T1= 61,73; T2= 60,13; T3= 55,51 e T4= 57,52, mostrando que os grupos experimentais possuíam fração cristalina próxima à do controle. Concluiu-se que a temperatura de nucleação influenciou no tamanho e na quantidade dos cristais de dissilicato de lítio e que os tratamentos que apresentaram melhores resultados foram os submetidos aos tempos de 1 hora e 30 minutos a 500oC e 6 horas a 480oC.
Materials destined to dental prostheses have evolved over the years allowing reaching ceramics materials with high quality, lithium dissilicate is one of the most used materials due to its wide range of indications, this is possible because its microstructure is directly related to its good mechanical, physical and optical properties.The Laboratory of Vitreous Materials (LaMaV) of the Federal University of São Carlos is developing a lithium disilicate in a milling type that allows prostheses to be obtained at a more affordable future cost, but studies are still necessary to optimize the microstructure. Thus, the aim of this study was to evaluate the influence of the different heat treatments of nucleation on the crystalline fraction and crystal morphology of the LaMaV CAD. Discs (12 mm diameter x 1.2 mm thickness) of LaMaV CAD lithium disilicate and IPS e.max CAD (control group, n = 3) were made. The LaMaV CAD discs were annealed at 380oC for 2h followed by different nucleation heat treatments in which time and temperature were varied by composing four subgroups (n = 3): T1 (1h30/500oC), T2 (3h/500oC), T3 (6h/500oC) and T4 (6h/480oC). The IPS e.max CAD discs were crystallized according to the manufacturer's recommendations. Microscopy electron scanning (SEM) images were obtained to characterize the microstructure and to quantify the crystalline fraction. This quantification was performed using the ImageJ software, in which an estimated percentage of the vitreous and crystalline phases were obtained. X-ray diffraction was performed to verify, through the refinement of Rietveld, the phases present in the samples. SEM images were analyzed descriptively as well as the results concerning the crystalline fraction. XRD analysis showed peaks of approximately 86% lithium disilicate for all groups. The SEM images showed the morphology of the crystals in an acicular and homogeneous format for all groups; the group that most resembled the control group was the T1 group. The T4 group showed higher nucleation of crystals in relation to the control. The crystalline fraction (%) was: C = 59.31, T1 = 61.73, T2 = 60.13, T3 = 55.51 and T4 = 57.52, showing that the experimental groups had crystalline fraction close to the control. It was concluded that the nucleation temperature influenced the size and quantity of the crystals of lithium disilicate, the treatments that presented the best results were those that received treatments at 1 hour and 30 minutes at 500ºC and 6 hours at 480ºC.
Materials destined to dental prostheses have evolved over the years allowing reaching ceramics materials with high quality, lithium dissilicate is one of the most used materials due to its wide range of indications, this is possible because its microstructure is directly related to its good mechanical, physical and optical properties.The Laboratory of Vitreous Materials (LaMaV) of the Federal University of São Carlos is developing a lithium disilicate in a milling type that allows prostheses to be obtained at a more affordable future cost, but studies are still necessary to optimize the microstructure. Thus, the aim of this study was to evaluate the influence of the different heat treatments of nucleation on the crystalline fraction and crystal morphology of the LaMaV CAD. Discs (12 mm diameter x 1.2 mm thickness) of LaMaV CAD lithium disilicate and IPS e.max CAD (control group, n = 3) were made. The LaMaV CAD discs were annealed at 380oC for 2h followed by different nucleation heat treatments in which time and temperature were varied by composing four subgroups (n = 3): T1 (1h30/500oC), T2 (3h/500oC), T3 (6h/500oC) and T4 (6h/480oC). The IPS e.max CAD discs were crystallized according to the manufacturer's recommendations. Microscopy electron scanning (SEM) images were obtained to characterize the microstructure and to quantify the crystalline fraction. This quantification was performed using the ImageJ software, in which an estimated percentage of the vitreous and crystalline phases were obtained. X-ray diffraction was performed to verify, through the refinement of Rietveld, the phases present in the samples. SEM images were analyzed descriptively as well as the results concerning the crystalline fraction. XRD analysis showed peaks of approximately 86% lithium disilicate for all groups. The SEM images showed the morphology of the crystals in an acicular and homogeneous format for all groups; the group that most resembled the control group was the T1 group. The T4 group showed higher nucleation of crystals in relation to the control. The crystalline fraction (%) was: C = 59.31, T1 = 61.73, T2 = 60.13, T3 = 55.51 and T4 = 57.52, showing that the experimental groups had crystalline fraction close to the control. It was concluded that the nucleation temperature influenced the size and quantity of the crystals of lithium disilicate, the treatments that presented the best results were those that received treatments at 1 hour and 30 minutes at 500ºC and 6 hours at 480ºC.
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Palavras-chave
Cerâmica, Tratamento térmico, Cristalização, Microscopia eletrônica de varredura, Difração de raios X, Ceramics, Thermic treatment, Crystallization, Microscopy, electron, scanning, X-Ray diffraction