目的·结合小视野锥形束CT（cone-beam CT，CBCT）、计算机辅助技术、万能试验机方法，分析长椭圆形根管清洁度与抗折性能的关系，探讨常用镍钛锉系统对二者关系的影响。方法·收集2024年4月至2025年4月于上海交通大学医学院附属新华医院口腔科因正畸拔除的单直根管下颌前磨牙。使用CBCT分析根管形态并筛选40颗长椭圆形根管牙，截冠制备13 mm长的标准牙根样本，平均随机分为A组（X-GOLD，n=10）、B组（Reciproc Blue，n=10）、C组（ProTaper Universal，n=10）和对照组（n=10）；A、B、C组分别使用不同镍钛锉系统进行根管预备。牙根样本使用CBCT扫描预备前后的形态，三维重建并比对前后模型，计算清洁度。实验组采用单尖法根管充填，对照组不充填，包埋固定牙根，使用万能试验机施加静态载荷，测量牙根样本的断裂载荷。分析各组清洁度与抗折性能的差异及变化趋势，以及清洁度与抗折性能的关系。结果·清洁度评测结果显示：C组的整体清洁度显著高于A组和B组，差异均有统计学意义（均P<0.05）；而A组与B组的整体清洁度比较，差异无统计学意义（P>0.05）。根管预备效果三维重建图展现了长椭圆形根管壁近远中向预备过量而颊舌向预备不足的特点。断裂载荷评测结果显示：对照组的断裂载荷显著高于A、B、C组，差异均有统计学意义（均P<0.05）；而A组与B组的断裂载荷比较，差异无统计学意义（P>0.05）；C组的断裂载荷显著低于A组和对照组，差异均有统计学意义（均P<0.05）。长椭圆形根管的清洁度与抗折性能呈负相关（r=-0.379，P=0.039）。结论·镍钛锉系统对长椭圆形根管的清洁度与抗折性能关系存在影响。长椭圆形单直根管的下颌前磨牙的清洁度与抗折性能呈负相关，使用ProTaper Universal镍钛锉系统预备长椭圆形单直根管下颌前磨牙时，具有较高的清洁度，并可保持一定的牙根抗折性能。

Objective ·To investigate the relationship between the cleanliness and fracture resistance of long-oval root canals using small field-of-view cone-beam CT (CBCT), computer-aided technologies, and a universal testing machine, and to explore the effects of commonly used nickel-titanium (NiTi) file systems on this relationship. Methods ·Mandibular premolars with single straight roots extracted for orthodontic reasons between April 2024 and April 2025 in the Department of Stomatology, Xinhua Hospital, Shanghai Jiao Tong University School of Medicine, were collected. CBCT was used to analyze canal morphology, and 40 teeth with long-oval canals were selected. The crowns were removed to prepare standardized root samples with a length of 13 mm. The samples were randomly and equally divided into Group A (X-GOLD, n=10), Group B (Reciproc Blue, n=10), Group C (ProTaper Universal, n=10), and a control group (n=10). Root canal preparation was performed in Groups A, B, and C using different NiTi file systems. All samples were scanned before and after preparation using CBCT, and three-dimensional models were reconstructed to calculate canal cleanliness by comparing pre- and post-preparation morphologies. The experimental groups were obturated using the single-cone technique, while the control group was left unobturated. All roots were embedded and subjected to static loading using a universal testing machine to determine fracture load. Data were analyzed to evaluate differences and trends in cleanliness and fracture resistance among the groups, and to assess their relationship. Results ·Group C showed significantly higher overall cleanliness compared to Groups A and B, and the differences were statistically significant (P<0.05), while no statistically significant difference was observed between Groups A and B (P>0.05). CBCT-based 3D reconstruction illustrated that long-oval canals tended to be over-prepared in the mesiodistal direction and under-prepared in the buccolingual direction. The control group demonstrated significantly higher fracture resistance than Groups A, B and C, and the differences were statistically significant (P<0.05). There was no statistically significant difference in the fracture load between Group A and Group B (P>0.05). Group C had significantly lower fracture resistance compared to Group A and the control group, and the difference were statistically significant (P<0.05). A significant negative correlation was found between canal cleanliness and fracture resistance in long-oval root canals (r=-0.379, P=0.039). Conclusion ·NiTi file systems affect the relationship between cleanliness and fracture resistance in long-oval root canals. In mandibular premolars with long-oval single straight canals, cleanliness is negatively correlated with fracture resistance. The ProTaper Universal NiTi file system achieves higher cleanliness while maintaining a certain level of fracture resistance in such cases.