Angel L Ortiz1, Oscar Borrero-López2, Fernando Guiberteau2, Yu Zhang3. 1. Departamento de Ingeniería Mecánica, Energética y de los Materiales, Universidad de Extremadura, 06006 Badajoz, Spain. Electronic address: alortiz@unex.es. 2. Departamento de Ingeniería Mecánica, Energética y de los Materiales, Universidad de Extremadura, 06006 Badajoz, Spain. 3. Department of Biomaterials and Biomimetics, New York University College of Dentistry, NY 10010, USA.
Abstract
OBJECTIVE: To elucidate the microstructural evolution of a commercial dental-grade lithium disilicate glass-ceramic using a wide battery of in-situ and ex-situ characterization techniques. METHODS: In-situ X-ray thermo-diffractometry experiments were conducted on a commercially available dental-grade lithium disilicate glass-ceramic under both non-isothermal and isothermal heat treatments in air. These analyses were complemented by experiments of ex-situ X-ray diffractometry, field-emission scanning electron microscopy, energy-dispersive X-ray spectroscopy, differential scanning calorimetry, and field-emission scanning electron thermo-microscopy. RESULTS: It was found that the non-fired blue block consists of ∼40 vol % crystals embedded in a glass matrix. The crystals are mainly lithium metasilicate (Li2SiO3) along with small amounts of lithium orthophosphate (Li3PO4) and lithium disilicate (Li2Si2O5). Upon heating, the glassy matrix in the as-received block first crystallizes partially as SiO2 (i.e., cristobalite) at ∼660 °C. Then, the SiO2 crystals react with the original Li2SiO3 crystals at ∼735 °C, forming the desired Li2Si2O5 crystals by a solid-state reaction in equimolar concentration (SiO2 + Li2SiO3 → Li2Si2O5). Precipitation of added colourant Ce ions in the form of CeO2 appears at ∼775 °C. These events result in a glass-ceramic material with the aesthetic quality and mechanical integrity required for dental restorations. It also has a microstructure consisting essentially of elongated Li2Si2O5 grains in a glassy matrix plus small cubic CeO2 grains at the outermost part of the surface. SIGNIFICANCE: It was found that by judiciously controlling the heat treatment parameters, it is possible to tailor the microstructure of the resulting glass-ceramics and thus optimizing their performance and lifespan as dental restorations.
OBJECTIVE: To elucidate the microstructural evolution of a commercial dental-grade lithium disilicate glass-ceramic using a wide battery of in-situ and ex-situ characterization techniques. METHODS: In-situ X-ray thermo-diffractometry experiments were conducted on a commercially available dental-grade lithium disilicate glass-ceramic under both non-isothermal and isothermal heat treatments in air. These analyses were complemented by experiments of ex-situ X-ray diffractometry, field-emission scanning electron microscopy, energy-dispersive X-ray spectroscopy, differential scanning calorimetry, and field-emission scanning electron thermo-microscopy. RESULTS: It was found that the non-fired blue block consists of ∼40 vol % crystals embedded in a glass matrix. The crystals are mainly lithium metasilicate (Li2SiO3) along with small amounts of lithium orthophosphate (Li3PO4) and lithium disilicate (Li2Si2O5). Upon heating, the glassy matrix in the as-received block first crystallizes partially as SiO2 (i.e., cristobalite) at ∼660 °C. Then, the SiO2 crystals react with the original Li2SiO3 crystals at ∼735 °C, forming the desired Li2Si2O5 crystals by a solid-state reaction in equimolar concentration (SiO2 + Li2SiO3 → Li2Si2O5). Precipitation of added colourant Ce ions in the form of CeO2 appears at ∼775 °C. These events result in a glass-ceramic material with the aesthetic quality and mechanical integrity required for dental restorations. It also has a microstructure consisting essentially of elongated Li2Si2O5 grains in a glassy matrix plus small cubic CeO2 grains at the outermost part of the surface. SIGNIFICANCE: It was found that by judiciously controlling the heat treatment parameters, it is possible to tailor the microstructure of the resulting glass-ceramics and thus optimizing their performance and lifespan as dental restorations.
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