磷酸酯单体10-MDP调节氧化锆陶瓷的机理：理论化学建模和计算

Zirconia owns high mechanical strength compared to other all ceramic materials, however, low temperature degradation, which leading to a decreasing of strength, is a fatal flaw for long-term clinical performance of zirconia restorations. Bonding improvement of zirconia is an important way to prevent cracking, which can be realized through surface treatments. However, zirconia receive conventional surface treatments would be more susceptible to low temperature degradation for producing stress and high temperature in the procedure. How to improve bonding of zirconia without low temperature degradation worsening is a question worth considering. Presently, conditioning of zirconia with phosphate ester monomers attracts a lot of attention for the advantages of easy handling and little effect to low temperature degradation. Although phosphate group is usually considered to be the active group of a phosphate ester monomer, unfortunately, its chemical mechanism is still not clear. Why phosphate group in phosphate ester monomer provide function of chemical modification of zirconia while the one in phosphate acid can not? Why phosphate groups in different phosphate ester monomers with different molecular structures provide different effects for bonding improvement of zirconia? These kinds of questions still can not be covered by previous studies. Among all the phosphate ester monomers, 10-MDP is the most classical one, which has been used for a longer time compared to the other ones. In current study, chemical mechanism of conditioning of zirconia with 10-MDP would be studied through modeling and computing via theoretical chemistry method. Furthermore, stability of chemical bonds between phosphate groups in various changed structure 10-MDP molecules and zirconia would be analyzed. The research would be more helpful for optimizing molecular structure of phosphate ester monomers and developing stronger modification ability of phosphate ester monomers to zirconia bonding surface.

粘接是弥补氧化锆全瓷材料低温老化效应、降低修复体临床碎裂几率的重要途径。提高氧化锆陶瓷的粘接性能主要通过表面处理来实现。相对传统表面处理来讲，磷酸酯单体调节因操作简便并且不加剧氧化锆陶瓷的低温老化效应而备受关注。然而，尽管研究已经发现磷酸基团是磷酸酯单体分子中的活性基团，但其具体作用机理仍不清楚。为何磷酸基团在磷酸中无法与氧化锆反应而在磷酸酯单体中却可以，为何不同分子结构的磷酸酯单体提高氧化锆粘结的效果也会不一样，诸如此类的问题当前的研究仍无法正面解释。10-MDP分子是当前磷酸酯单体中最经典、应用时间最长、最具代表性的一种，其有效性已经获得公认。本课题拟通过建立10-MDP分子与氧化锆晶体吸附的数字模型来研究该分子中磷酸基团断裂、构建化学键的过程以及分子结构变化对此过程的影响，从而能够深入了解磷酸酯单体调节氧化锆陶瓷的基本作用机理，突破现有的研究瓶颈。

氧化钇稳定四方相氧化锆（Y-TZP）陶瓷是牙科氧化锆基全瓷材料中最为常用的种类。利用磷酸酯单体MDP化学调节Y-TZP陶瓷实现增强粘接性能的方式相对于其它方式来讲具有明显优势而应用日益广泛。研究普遍认为MDP之所以能与此特殊性质的表面形成化学键是因为其中磷酸基团的作用。然而当前研究仍无法直接阐释磷酸酯单体调节Y-TZP陶瓷的化学机理。在本课题的研究中，课题组通过密度泛函方法对MDP与氧化锆晶体化学反应发生的可能性及如果反应发生时所形成的化学键的机理进行了解释和分析，发现MDP理论上能够自发与四方相和单斜相氧化锆晶体发生化学结合，该化学结合通过“MDP在溶剂中的解离”以及“MDP解离后与氧化锆晶体形成配位键”两个反应步骤实现。MDP与两种晶相的氧化锆晶体间的结合以“双配位”为主要形式。另外，课题组通过量子化学方法分析了MDP分子主、侧链结构经过多种类型的变化后的稳定性及其变异分子与氧化锆晶体化学结合的能力，发现缩短MDP的分子主链、在侧链远磷酸端添加羟基或羧基等活性基团，或在分子主链中部添加2个羟基或羧基等活性基团，都将对分子结构的稳定性或是对氧化锆晶体簇的加成产生负面影响，从而降低MDP分子与四方相氧化锆之间的结合能力；而延长分子主链，在分子主链中部添加 1个羟基或羧基等活性基团能够少量提高分子与氧化锆晶体的结合。今后研究可根据本课题的量子化学分析结果合成相应的分子，进行体外粘接试验和分析化学表征，以验证提高氧化锆陶瓷与树脂结合的实际效果。