根管治疗术对牙根纵裂发生机制的多尺度研究

Vertical root fracture (VRF) often occurs in teeth after root canal therapy, which will result in treatment failure and tooth extraction. However, whether the root canal treatment is associated with occurrence of VRFs is still not sure. Researches showed that root canal treatment could change the root morphology, reduce the mechanical properties of root dentin, and may made micro-cracks on the root canal wall. The function and status of these factors in the development of VRFs is still controversial. The aim of this project was to study action of root morphological changes caused by treatment and the dentinal microstructure/chemical injury from canal irrigation in the occurrence of VRFs. Multiple scales methods including micro mechanical properties test, macro fracture experiment, the overall loading test and stress analysis will be used. The initiation and development of micro-cracks on root canal wall during treatment will be observed through high-resolution micro-CT. Digital and entity models of endodontic treated root with micro cracks will be established. The laws of crack initiation and propagation will be explored. This project will promote the further studies on VRFs, and provide a theoretical basis for avoiding the iatrogenic injury from root canal treatment to the root and reducing the incidence of VRFs in endodontically treated teeth.

牙根纵裂好发于根管治疗的牙齿，造成治疗失败及患牙拔除。但根管治疗是否与牙根纵裂的发生存在相关目前尚不肯定。研究表明根管治疗改变牙根的结构形态，降低牙本质的力学性能，并可能使根管壁产生微裂纹，这些因素在牙根纵裂产生与发展中的作用与地位目前仍存在争议。本课题拟借助力学方法，从微观力学性能、宏观断裂、整体实体加载及应力分析等多尺度，研究根管治疗造成牙根形态改变及冲洗液对牙本质的微结构和化学成分的损伤在牙根纵裂发生中的作用。利用高分辨micro-CT定点观察治疗中微裂纹的产生发展状况，建立根管壁微裂纹的数字和实体模型，探寻裂纹萌生、扩展的规律。研究将为牙根纵裂发病机制的深入研究奠定基础，为避免治疗因素对牙根的医源性损伤、降低治疗后牙根纵裂的发生提供理论依据。

牙根纵裂好发于根管治疗的牙齿，是造成失牙的重要原因。本研究针对根管治疗中两个关键步骤，即根管预备和根管充填，对牙根力学行为的影响展开研究。牙根裂纹的发生与组织本身的力学性能及牙根的受力状态密切相关。项目通过微观力学性能、宏观断裂、整体实体加载、应力分析及数学公式模型等多尺度，探索了治疗因素对根部牙本质力学性能及牙根应力分布的影响。.研究结果表明根管冲洗液NaClO对根管壁的腐蚀随浓度而升高，其断裂强度的降低与结构改变呈线性正相关。冲洗液造成牙本质微观力学性能降低，从而改变根部牙本质的应力分布状态，通过有限元模拟实体实验预测引起折裂发生的应力值，证实了NaClO对其折裂应力值的降低作用，所得数值与数学公式模型计算的数据吻合。根管预备削弱了牙根的抗折力，而根管充填能在一定程度上弥补预备降低的牙根抗折力。单尖法和热牙胶垂直加压法充填后的牙根抗折力显著提高，而单尖充填牙根的应力分布状况更有利。牙根折裂的裂纹方向多见于颊舌向。.结果提示NaClO通过改变根部牙本质的结构及微观力学性能，改变牙根的受力状态和牙本质的抗折强度，从而降低了牙根的抗折力。这一作用机制与浓度相关，因此在根管治疗中，高浓度NaClO的使用应当谨慎。根管预备降低了牙根的抗折力，但完善的根管充填可以使牙根抗折力得到显著提高，非加压的单尖充填法或可成为预防根管治疗牙发生牙根折裂的选择。本项目成果为牙根纵裂医源性因素作用机制的研究鉴定基础，为临床治疗方案的制定提供理论依据。