HIGH TOUGHNESS TEXTURED DENTAL GLASS CERAMICS

牙科陶瓷具有化学耐用性、生物相容性和实现卓越美学的最大潜力。它们目前正在获得新的兴趣，而基于金属的修复产品正逐渐从口腔环境中淘汰。在过去的五年里，一种新的牙科修复技术被引入到牙科中来制造全瓷修复体：热压。然而，目前可用的大多数可压制陶瓷的断裂韧性较低，这意味着全瓷修复体可能会失败。本研究的总体目标是开发用于热压全瓷修复体的高韧性织构微晶玻璃。在微晶玻璃的热压过程中将获得织构。这种独特的微观结构将与断裂韧性的各向异性增加有关，这是由于板状晶体在压制方向上的排列。研究了氧化镁对Li2O-Na2O-K2O-CaO-MgO-SiO_2-F系微晶玻璃的热性能和力学性能的影响。需要检验的假设是，增加镁的浓度将增加玻璃的流动性及其工作范围。用X射线衍射仪、扫描和透射电子显微镜和核磁共振波谱研究了玻璃的形核和析晶行为。用差热分析和膨胀法对其热性能进行了分析。还将对其双向弯曲强度和断裂韧性进行研究。热性能和力学性能的研究将为热压材料的选择提供依据。热压研究将分为两个步骤，首先将所研究的简化、低熔点版本的微晶玻璃材料作为对照进行热压。其次，微晶玻璃材料本身将被热压。光学散射系数和吸收系数将通过反射率测量来计算。两种材料的力学性能将分别在压制方向和法向进行测试，织构程度将通过扫描电子显微镜表征。最后研究了退火对微晶玻璃裂纹愈合行为和抗折强度的影响。

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.