牙科双层瓷结构“拉应力敏感性”疲劳性能及其影响因素的研究

The high fracture strength of core materials does not avoid the fracture of bilayered ceramic fixed partial dentures (FPD). Base on the results of both clinical researches and in vitro fractography analysis, the fracture of bilayered ceramic FPDs predominately occurs due to the cracking within connector areas. Recent study conducted by the present applicant indicated that although the fracture strength of bilayered ceramic structure loaded with core in tension (simulating the stress distrubution of occlusal surface) is significantly higher than that when loaded with veneer in tension (simulating the stress distrubution of connector area), for different bilayered ceramic systems, the differences of fracture strength between the two loading schemes (core in tension vs veneer in tension) demonstrat a quite huge gap. Innovatively, “tensile stress sensitivity” is used to describe this phenomenon. This project proposal aims to clarify the fatigue proterty and the influence factors of “tensile stress sensitivity” with the combination of in vitro test, fractography analysis and finite element analysis. This project mainly consists of two parts; one is to study the influence of fatigure testing on the performance of “tensile stress sensitivity”; the other is to study the the influence of core/veneer thickness ratio and fabracating defects of veneer procelain on the performance of “tensile stress sensitivity”. It is envisaged that the outcomes of the study would explan the fracture sensitivity at the connector area of the bilayered ceramic restorations, additionally optimaze the design and fabricating technique, as well as reduce the clinical fracture rate of the bilayered ceramic restorations.

高强度的核瓷并未有效避免双层瓷固定义齿的断裂失效，临床及体外研究均显示断裂主要发生于连接体处。申请人近期研究指出虽然双层瓷结构正向加载（He面应力分布）断裂强度显著高于反向加载（连接体处应力分布），但不同双层瓷系统正/反向加载间断裂强度差异的大小显著不同。我们创新性地将这种差异用“拉应力敏感性”（tensile stress sensitivity）一词来描述。本项目拟在前期工作基础上采用体外实验、断口形貌分析、有限元分析三者相互结合校验的研究方法，进一步深入探讨“拉应力敏感性”的疲劳性能及其影响因素。研究内容分为两方面：一是探讨循环加载对双层瓷结构“拉应力敏感性”的影响及原因；二是探讨饰核瓷厚度比和饰瓷制作缺陷对“拉应力敏感性”的影响及原因。项目旨在从“拉应力敏感性”入手，解释双层瓷固定义齿连接体处断裂失效的原因及影响因素，为改良修复体设计与制作提供理论依据，减少临床断裂失效的发生。

高强度的核瓷并未有效避免双层瓷固定义齿的断裂失效，临床及体外研究均显示断裂主要发生于连接体处。虽然双层瓷结构正向加载（He面应力分布）断裂强度显著高于反向加载（连接体处应力分布），但不同双层瓷系统正/反向加载间断裂强度差异的大小显著不同。我们创新性地将这种差异用“拉应力敏感性”（tensile stress sensitivity）一词来描述。而不同制作工艺会在双层瓷修复体表面及内部引入各种缺陷，其中一些缺陷是导致修复体崩瓷及断裂失效的重要原因。本项目研究内容分为两方面：一是探讨不同加载模式下双层瓷结构抗疲劳性及“拉应力敏感性”的变化及原因；二是探讨饰瓷制作缺陷对修复体崩瓷及断裂失效的影响及原因。本研究发现，饰瓷的引入大幅降低双层瓷材料的反向加载断裂强度。循环加载可显著降低单/双层全瓷结构的断裂强度，降低幅度高达25% ~ 45%。饰瓷的使用可显著提高双层瓷材料的抗疲劳性，前提是饰瓷不能位于拉应力集中区。而引起双层瓷修复体断裂及崩瓷失效的为位于特定位置，具有一定体积的气孔缺陷，而饰瓷烧结后的慢速降温可减少此类缺陷的产生。项目旨在探究双层瓷固定义齿连接体处断裂失效的原因及影响因素，为改良修复体设计与制作提供理论依据，并明确现有材料及修复体制作工艺的不足之处，为新型牙科全瓷材料工艺的发展及修复体的质量检测提供实验与理论依据，减少临床失效的发生。