An in situ and ex situ study of the microstructural evolution of a novel lithium silicate glass-ceramic during crystallization firing. Issue 5 (May 2020)

• Record Type: Journal Article
• Authors: Ortiz, Angel L.; Rodrigues, Camila S.; Guiberteau, Fernando; Zhang, Yu
• Is Part Of: Dental materials. Volume 36:Issue 5(2020)
• Page Start: 645
• Page End: 659
• Publication Date: 2020-05
• Subjects: Lithia-based glass-ceramics -- Crystallization firing -- Compositional and microstructural developments -- In situ characterization -- Ex situ characterization; Dentistry -- Periodicals; Dental materials -- Periodicals; 617.695
• DOI: 10.1016/j.dental.2020.03.011
• Languages: English
• ISSNs: 0109-5641

Abstract

Abstract: Objective: To elucidate the compositional and microstructural developments of a novel lithium silicate glass-ceramic during its crystallization cycle. Methods: Blocks of a lithium silicate glass-ceramic (Obsidian®, Glidewell Laboratories) were cut into 1 mm thick plates and polished to 1 μm finish. Some of them were crystallized prior to polishing. Firstly, ex situ compositional and microstructural characterizations of both the pre- and post-crystallized samples were performed by wavelength dispersive X-ray fluorescence, field-emission scanning electron microscopy, and X-ray diffractometry. Secondly, the pre-crystallized samples were subjected to in situ compositional and microstructural characterizations under non-isothermal heating by simultaneous thermogravimetry/differential scanning calorimetry, X-ray thermo-diffractometry, and field-emission scanning electron thermo-microscopy. Results: The microstructure of pre-crystallized Obsidian® consists of an abundant population of perlitic-like/dendritic lithium silicate (Li2 SiO3 ) nanocrystals in a glass matrix. Upon heating, the residual glassy matrix does not crystallize into any form of SiO2 ; elemental oxides do not precipitate unless over-heated above 820 °C; and the Li2 SiO3 nanocrystals do not react with the glassy matrix to form typical lithium disilicate (Li2 Si2 O5 ) crystals. Nonetheless, the Li2 SiO3 nanocrystals grow and spheroidize through the solution-reprecipitation process in the softened glass, and new lithium orthophosphate (Li3 PO4 ) nanocrystals precipitate from the glass matrix. Significance: The identification of compositional and microstructural developments of Obsidian® indicates that, by controlling the firing conditions, it is possible to tailor its microstructure, which in turn could affect its mechanical and optical properties, and ultimately its clinical performance.