具有梯度弹性模量特性新型瓷修复体的力学性能及强韧化机制研究

The high fracture resistance of human enamel arises from its structure with graded elastic modulus. In contrast, the commercially available dental ceramic restorations only have uniform elastic modulus, whose fracture and chipping remain a serious concern clinically. Our recent studies have shown that the stress distribution and fracture behavior of ceramics will be altered according to changes in the distribution of elastic modulus. The mechanical properties of dental ceramics for clinical application appear capable of being improved if their elastic modulus can be constructed with a gradient. The aim of the present project is therefore to investigate the general relationship between graded elastic modulus of dental ceramic restorations and their mechanical properties, and try to determine the optimal elastic modulus distribution model as well as identify its strengthening and toughening mechanism. The project comprises two parts focusing on:(i)Constructing and analyzing finite element models with different graded elastic modulus, from which the optimized model will be determined based on their stress distribution and crack propagation characteristics; and (ii)Fabricating standard specimens and anatomical shapes (crowns) with the corresponding graded elastic modulus for static bending and contact loading failure and fatigue experiments, whereby the optimal elastic modulus distribution model would be determined and the strengthening and toughening mechanism clarified by comparing the experimental results with finite element analysis data. The present study will shed light on the use of graded elastic modulus for improving the mechanical properties of dental ceramics, and the data acquired therefrom will provide the theoretical and experimental basis for the development of novel dental ceramic materials.

人牙釉质具有梯度变化弹性模量结构因而抗折破坏能力优异。但目前所用瓷修复体为均一弹性模量材料，临床仍面临崩瓷及断裂失效等重要问题。申请人最新研究结果表明，改变弹性模量分布会影响瓷修复体应力分布及断裂失效行为。将梯度变化弹性模量的特性引入陶瓷材料可望改善瓷修复体的力学性能。据此，本项目拟探索弹性模量梯度变化对瓷修复体力学性能影响的规律及强韧化机制，建立最佳弹性模量分布模型以指导修复体设计。研究内容包括：①构建具有梯度弹性模量变化特性的有限元模型及数学断裂模型，依据应力分布和裂纹扩展特性对模型进行优化；②制作具有梯度变化弹性模量的标准试件及解剖冠进行抗折破坏和疲劳试验，结合有限元分析结果确定优化弹性模量分布的数学物理模型并阐明强韧化机制。本研究以在修复体全层引入梯度变化弹性模量为切入点从而提高其力学性能，可为新型牙科全瓷材料研发提供理论指导并为临床应用提供参考。

人牙釉质具有梯度变化弹性模量结构因而抗折破坏能力优异。但目前所用瓷修复体为均一弹性模量材料，临床仍面临崩瓷及断裂失效等重要问题。申请人最新研究结果表明，改变弹性模量分布会影响瓷修复体应力分布及断裂失效行为。将梯度变化弹性模量的特性引入陶瓷材料可望改善瓷修复体的力学性能。因此，我们利用有限元分析，以人牙釉质弹性模量为优化基准，以降低全冠修复体拉伸应力峰值为优化目标，经多目标遗传算法优化得到弹性模量分布规律更为简单，更易实现，并可更好地改善全冠修复体临床表现的最佳弹性模量分布。此外，我们还研究了另一纵向梯度钇含量氧化锆修复体，由于钇含量的改变，每层氧化锆的微观结构、相含量、力学性能及热力学性能存在差异，但该修复体的力学性能仍介于传统 3钇氧化锆和 5 钇高透氧化锆之间，失效起源与单层材料一致，为颈部和压头下方，未出现分层断裂现象。研究结果为新型牙科全瓷材料研发提供理论指导并为临床应用提供参考。