Development of SiO2 - Li2O - ZrO2 dental glass-ceramic systems with extended lifetimes: crystallization mechanisms and resistance to subcritical crack growth

基于硅酸锂的微晶玻璃是当今商业上最成功的牙科修复材料。与典型的长石基牙科陶瓷相比，二硅酸锂（Li 2Si 2 O 5）晶体受益于沿晶体学c轴的优选晶体生长沿着。拉长的晶相使得能够定制各向异性的微结构架构，使其与自然设计所采用的那些一致，例如在牙釉质中。微结构特征的刻意定向似乎是生物学实现最佳机械性能的策略的基石，这种方法也适用于无机材料。不幸的是，目前存在的二硅酸锂体系特别容易受到玻璃相中应力辅助的亚临界裂纹生长的影响。玻璃相和晶体相之间的热残余应力的发展加速了这种现象。特别受影响的是SiO2 -Li 2 O-ZrO 2系统中的玻璃陶瓷。向基础玻璃中增量添加ZrO 2改变了二硅酸锂已知的典型成核和结晶动力学，涉及Li 2SiO 3的非均质成核以及随后在较高温度下向Li 2Si 2 O 5的转化。这导致富含ZrO 2的残余玻璃相。在这个过程中涉及的基本机制，SiO2/Li 2 O比的关系，以及它们在形成玻璃网络结构的最终叠瓦，仍然知之甚少。作为跨学科项目的一部分，将彻底研究SiO2 -Li 2 O-ZrO 2玻璃系统中成分变化的影响。成核和结晶的动力学构成了我们感兴趣的中心焦点，包括玻璃网络结构的详细表征和残余玻璃在缓慢裂纹生长阻力和热残余应力的影响方面的性能。局部和全局的力学行为的影响将系统地探讨，重点是优化的微观结构设计和相兼容性，旨在牙科氧化锆含二硅酸锂的发展，延长临床寿命。

Glass-ceramics based on Lithium silicates today constitute the most commercially successful restorative material for dental applications. Compared to typical feldspar-based dental ceramics, lithium disilicate (Li2Si2O5) crystals benefit from a preferred crystal growth along the crystallographic c-axis. Elongated crystal phases enable the tailoring of anisotropic microstructural architectures in congruence with those employed by natural design, such as in dental enamel. The deliberate orientation of microstructural features appears to be a cornerstone in biology´s strategy to achieve optimal mechanical performance, an approach applicable to inorganic materials as well. Unfortunately, the currently existent lithium disilicate systems are particularly susceptible to stress-assisted subcritical crack growth in the glass phase. This phenomenon is accelerated by the development of thermal residual stresses between the glass and crystal phases. Especially affected are glass-ceramics in the system SiO2 – Li2O – ZrO2. The incremental addition of ZrO2 to the base glass alters the typical nucleation and crystallization kinetics known for lithium disilicates, involving the heterogeneous nucleation of Li2SiO3 and the later transformation to Li2Si2O5 at higher temperatures. This results in a residual glass phase enriched with ZrO2. The underlying mechanisms involved in this process, the relationship to the SiO2/Li2O ratio, and their ultimate imbrications in shaping the glass network structure, are still poorly understood. As part of an interdisciplinary project, the effects of compositional variations in the SiO2 – Li2O – ZrO2 glass system will be thoroughly investigated. The kinetics of nucleation and crystallization constitute the central focus of our interest, including a detailed characterization of the glass network structure and properties of the residual glass with respect to slow crack growth resistance and influence of thermal residual stresses. The implications on the local and global mechanical behavior will be probed systematically with focus on the optimization of microstructural design and phase compatibility, aiming on the development of dental ZrO2-containing lithium disilicates for extended clinical lifetimes.