HIGH TOUGHNESS TEXTURED DENTAL GLASS CERAMICS

牙科陶瓷具有化学耐久性、生物相容性，并且具有实现上级美学的最大潜力。 它们目前正在获得新的兴趣，而金属基修复产品正在逐步从口腔环境中淘汰。 在过去的五年中，一种新的技术已被引入牙科制造全陶瓷牙科修复体：热压。 然而，大多数目前可用的可压制陶瓷具有较低的断裂韧性，这意味着全陶瓷陶瓷制品可能会失效。 本研究的总体目标是开发高韧性织构微晶玻璃，用于热压全陶瓷微晶玻璃。 织构将在有核玻璃的热压过程中获得。 这种独特的微观结构将与断裂韧性的各向异性增加相关联，这是由于板状晶体在压制方向上的对齐。 研究了氧化镁对Li_2 O-Na_2 O-K_2 O-CaO-MgO-SiO_2-F系统微晶玻璃的热性能和力学性能的影响。 要测试的假设是，增加镁的浓度将增加玻璃的流动性及其工作范围。 玻璃的成核和晶化行为将通过X射线衍射、扫描和透射电子显微镜以及核磁共振谱进行研究。 用差热分析法和差热分析法分析其热性能。 双轴弯曲强度和断裂韧性也将进行研究。 热性能和机械性能的研究将允许选择热压材料。 热压研究将分为两个步骤，首先将所研究的玻璃陶瓷材料的简化的低熔融版本热压作为对照。 其次，玻璃陶瓷材料本身将被热压。 光学散射和吸收系数将根据反射率测量值计算。 测试两种材料在压制方向和法向的力学性能，并通过SEM表征织构程度。 最后研究了退火对所研制的微晶玻璃的裂纹愈合行为和抗弯强度的影响。

Dental ceramics are chemically durable, biocompatible and have the greatest potential for achieving superior esthetics. They are currently gaining new interest while metal-based restorative products are progressively being eliminated from the oral environment. During the past five years, a novel technique has been introduced in dentistry for fabricating all-ceramic dental restorations: hot-pressing. However, most of the currently available pressable ceramics have low fracture toughness, implying possible failure of all-ceramic restorations. The overall objective of the proposed research is to develop high-toughness textured glass-ceramics for hot-pressed all- ceramic restorations. The texture will be obtained during hot-pressing of the nucleated glass. This unique microstructure will be associated with an anisotropic increase in fracture toughness, due to the alignment of the plate-shaped crystals in the direction of pressing. The strategy is to investigate the effect of magnesium oxide on the thermal and mechanical properties of a glass-ceramic in the system Li2O-Na2O-K2O-CaO-MgO-SiO2-F. The hypothesis to be tested is that increasing concentrations of magnesium will increase the fluidity of the glass and its working range. The nucleation and crystallization behavior of the glasses will be studied by x-ray diffraction, scanning and transmission electron microscopy and nuclear magnetic resonance spectroscopy. The thermal properties will be analyzed by differential thermal analysis and dilatometry. The biaxial flexural strength and fracture toughness will also be investigated. The study of thermal and mechanical properties will allow material selection for hot-pressing. Hot-pressing studies will be divided in two steps, first a simplified, low fusing version of the glass-ceramic material studied will be hot-pressed as control. Second, the glass ceramic material itself will be hot-pressed. The optical scattering and absorption coefficients will be calculated from reflectance measurements. The mechanical properties of both materials will be tested in both the direction of pressing and the normal direction, the degree of texture will be characterized by SEM. The effect of annealing on the crack healing behavior and flexural strength of the glass-ceramic developed will be investigated last.