牙科氧化锆双层瓷修复体失效本质及饰瓷和饰-核瓷界面因素影响机制的研究

The clinical studies have shown that zirconia-based all-ceramics (ZBAC) restorations exhibit a significantly higher failure rate (30%-42%) over a period of five years than that of porcelain fused to metal restorations (16%), and this has become the main bottleneck problem for wide application of bilayered ZBAC restorations. It has been proved that for ZBAC restorations the veneer or the core-veneer interface is most likely to be the weakest link. A recent study conducted by the present applicant indicated that the roughness at the core-veneer interface can also lead to the veneer chipping in ZBAC restorations. Thus far, however, the failure reason of chipping has not been clarified. This project proposal aims to clarify the influence of the internal defects in veneer, core-veneer fracture toughness, elastic modulus and miss-match of coefficient of thermal expansion on chipping failure of bilayered ZBAC restorations, so as to help solving the tough clinical problem of ZBAC with a high chipping rate. The study will mainly focus on two aspects, one is to characterize the effect of key processing factors in the fabrication of the veneer and core-veneer interface on the chipping behavior of bilayered ZBAC restorations and identify the root causes leading to the failure; and the second is to analyze the fractographic morphology of the clinically failed ZBAC restorations, reconstruct the failed restorations and then conduct fatigue experiments on them, as well as build up finite element (FE) models for numerical modeling; in particular the cross-checking and comparison will be performed among the results from the three parts, i.e., clinical observation, experimental characterization and FE simulations results, and clarify the origin of cracking, crack propagation path and distribution characteristics etc, and finally elucidate the failure mechanism of failure. In the completion of the project, it is envisaged that the outcomes of the study would provide theoretical background for design optimization of bilayered ZBAC restorations, assessment of reliability and durability, and offer a methodology for an accurate prediction of longevity of bilayered ZBAC restorations, as well as promote the clinical application of the restorations.

临床研究结果所显示的氧化锆全瓷冠5年崩瓷率（30%-42%）远高于金属烤瓷冠（16%）已成为限制氧化锆双层瓷修复体推广的瓶颈。研究表明氧化锆双层瓷修复体最弱环可能在饰瓷内部或饰-核瓷界面；申请人近期的研究结果也指出饰-核瓷界面粗糙度是影响其饰瓷崩瓷的因素之一。本项目拟探索饰瓷内部缺陷、饰-核瓷断裂韧性、弹性模量及热膨胀系数匹配关系等对氧化锆双层瓷修复体崩瓷影响的机制，解决其饰瓷崩瓷率高的临床难题。研究内容包括两部分：一是研究饰瓷内部及饰-核瓷界面加工制作因素对氧化锆双层修复体饰瓷崩瓷行为的影响，确定导致失效的根本原因；二是分析临床失效后氧化锆全瓷冠断口形貌，复制该失效修复体并进行疲劳实验及有限元数值模拟，相互校验三者结果，确认裂纹起始部位、扩展路径及分布状况等，阐明崩瓷机制。研究旨在为临床氧化锆双层瓷修复体的优化设计、可靠性和耐久性评价及寿命预测提供实验与理论依据，有力推动其临床应用。

临床研究结果所显示的氧化锆全瓷冠5年崩瓷率（30%-42%）远高于金属烤瓷冠(16%)已成为限制氧化锆双层瓷修复体推广的瓶颈。本项目研究饰瓷内部及饰-核瓷界面加工制作因素对氧化锆双层修复体饰瓷崩瓷行为的影响；继而分析临床失效后氧化锆全瓷冠断口形貌明确裂纹起始部位、扩展路径及分布状况等；随后建立有限元模型，模拟临床失效修复体，并与临床失效分析及体外实验的结果相互校验，确认裂纹起始部位、扩展路径及分布状况等，阐明崩瓷机制。研究发现①机械打磨对氧化锆核瓷-饰瓷双层试件的断裂强度值无显著影响，高粗粒度打磨能提高氧化锆双层瓷材料断裂强度的可靠性；②固定桥连接体区域，基牙全瓷冠切端及颈缘是裂纹起源的常见部位；③修复牙位是影响全瓷冠失效模式的一个因素，前牙全瓷冠主要表现为饰瓷内聚破坏，而后牙全瓷冠主要为饰核瓷的全层断裂；④累积损伤与拉应力集中的共同作用、饰瓷表面或饰-核瓷界面的缺陷是双层氧化锆全瓷冠裂纹发生的主要原因。此研究结果将有力推动氧化锆双层瓷修复体的临床应用，为其优化临床设计、评价可靠性和耐久性及寿命预测提供实验与理论依据。