Processing of Glass-Ceramic Based of Lithium Disilicate With Functional Gradient of Porosity

Objectives: The aim of this study was to investigate the mechanical behavior of an experimental glass ceramic based on lithium disilicate (DL) with functional gradient of porosity.
Methods: A mixture of oxides was homogenized and melted at fusion temperature. The glass frits got by cooling were grinded and passed through heat treatment according to CSD and RXD. Six groups were obtained according to material (lithium disilicate and glass ceramic reinforced by zirconia- YTZP) and substrate simulation (enamel-E, dentin-D, and graded- both E and D): DL-E; DL-D; DL-Grad; YTZP-E; YTZP-D; YTZPGrad. Volumes of 23 and 40% of glass powder were prepared through dispersion in water and submitted to gel casting technique to form functional gradient. The samples with and without functional gradient of porosity were characterized by RXD, FEG, density, apparent porosity, biaxial flexural strength and fractography tests. Data were analyzed by ANOVA and Tukey tests (p<0.05).
Results: The temperature of sintering of DL-E, DL-D and DL-Grad was 910°C; and YTZP-E, YTZP-D, YTZPGrad was 850°C. The development of functional gradient of porosity was observed in micrographs only for DLgroups. There was no difference of density among groups, however YTZP groups showed 10% higher porosity than groups without zirconia. The critical flaw at surface of the ceramics were similar among groups, however the random of internal pores at groups with YTZP resulted in significantly lower biaxial flexural strength than the groups without YTZP (p<0.05). The flexural strength was similar among the dense and graded groups.
Conclusions: It was concluded that the addition of zirconia to SiO -Li O ceramic- based systems changed the temperature of sintering, the standard of porosity, flexural strength, and compromised the development of functional gradient of porosity. The mechanical behavior of lithium disilicate dense and graded ceramics were similar.