用于根管器械的超细晶镍钛合金的组织控制及疲劳与生物相容性研究

The ideal material for endodontic instruments should possess not only high strength to prevent the fracture of instrument, but also proper elongation to guarantee the flexibility of instruments, so that the root transportation is reduced and the fatigue resistance is improved. In recent years, to improve the fracture resistance of NiTi endodontic instruments, researchers have developed special thermomechanical processes for manufacturing NiTi instruments. However, the strength and cutting ability are still unsatisfied. Meanwhile, the research results indicated that the mechanical property, shape memory effect and superelasticity of ultrafine-grained NiTi alloy obtained by severe plastic deformation method has been significantly improved. The ultrafine-grained NiTi alloy exhibited higher strength than the conventional thermal-mechanical treated NiTi alloy. Based on the above two points, the applicant put forward a new academic idea of exploring the application of ultrafine-grained NiTi shape memory alloy in the endodontic instrument field. The present project will base on this ultrafine-grained NiTi shape memory alloy wires, and study the structure control of the alloy by means of thermal treatment, so as to optimize the strength and superelasticity of the alloy. The mechanical properties including bending, torsion, cutting ability and fatigue resistance, as well as the corrosion resistance and ion release in the artificial saliva are investigated. This project will explore the feasibility of the ultrafine-grained shape memory alloy used as endodontic instrument, and provide the important theoretical basis and experimental reference for design and developing of the novel endodontic instrument based on ultrafine-grained NiTi shape memory alloy.

理想的根管器械材料，不仅要具有高的抗拉强度来防止断裂发生，而且要具有适当的延伸率以保证器械的柔韧性，降低根管偏移，提高疲劳抗力。近年来国内外开展了大量通过独特的热机械处理工艺来减少并预防镍钛根管器械折断的研究，但其断裂强度和切削效率始终不理想。有研究结果表明，采用剧烈塑性变形工艺制备的超细晶镍钛形状记忆合金的力学性能和形状记忆效应及超弹性获得了极大改善，可以提供传统热机械处理的NiTi合金所不具有的高强度。基于上述两点，申请人提出自己的学术新想法，探索超细晶镍钛形状记忆合金在根管器械材料领域的应用。本项目针对超细晶镍钛形状记忆合金丝材，通过热处理工艺进行组织控制，优化合金的强度和超弹性，并综合考察合金的弯扭特性、切削性能、疲劳性能及其在口腔环境中的耐腐蚀性和离子溶出行为，探索超细晶镍钛形状记忆合金作为根管器械材料的可行性，为开发新型超细晶镍钛合金根管器械提供重要的理论依据和实验参考。

针对镍钛根管器械使用过程中易于折断的问题，采用自行搭建的两种模拟根管体外模型对新型K3XF和CM镍钛根管锉的组织结构、弯曲、扭转、疲劳等力学性能进行了评价，并针对目前新型根管锉材料的强度和切削力不足的问题，探讨了兼具高强度和超弹性的超细晶镍钛合金作为根管器械材料的可行性。研究表明，热机械处理工艺可以通过改变相变温度来调控两种新型镍钛根管锉的组织结构，从而改善了其柔韧性和疲劳性能。失效分析发现新型镍钛根管锉材料的强度和切削力不足，以致影响根管锉的临床使用效率和安全性。采用等径角挤压工艺制备的晶粒尺寸约为290nm的超细晶镍钛合金，屈服强度约为固溶态粗晶合金的3倍，在模拟唾液和EDTA溶液中的耐腐蚀性与粗晶态合金相当，在次氯酸钠溶液中的耐腐蚀性明显优于粗晶合金；在模拟唾液和次氯酸钠溶液中的短期浸泡实验结果表明，在相同浸泡时间下超细晶镍钛合金在模拟唾液和次氯酸钠溶液中镍离子的溶出量更少，且其2个星期浸泡后的总溶出量在人体日均耐受摄入量的范围内，具有应用于根管器械的可行性。另外，Cu元素的加入提高了TiNi合金的相变温度，减小了合金的相变滞后。TiNi3Cu合金具有良好的综合力学性能，在浸泡实验中，TiNiCu合金在常规模拟唾液中的镍离子溶出速率明显低于TiNi合金，且随着浸泡时间的延长，溶出速率减慢，表现出应用于口腔器械领域的可行性。研究结果对于开发高性能新型根管器械材料提供了重要的实验参考和理论依据。