The purpose of this study was to analyze various characteristics and classification of C-shaped root canals and evaluate the causes of endodontic failure of C-shaped root canals by examining the resected root surface with an endodontic microscope and a scanning electron microscope (SEM). Forty-two teeth with C-shaped root canals were included in this study and had undergone intentional replantation surgery. Before surgery, periapical radiography and cone-beam computed tomography were taken. The root canal configuration was analyzed and classified according to Melton's classification at coronal and apical level. After injection of 1 : 100,000 epinephrine with 2% lidocaine, the tooth was carefully extracted. After the root-end resection, the resected root surface was examined using an operating microscope and SEM. Mandibular second molars were most frequently involved teeth (90.4%). The most frequently observed root canal configurations were C1 at the coronal level (45.2%) and C3 at the apical 3 mm level (45.2%). The most common cause of failure for a C-shaped root canal treatment was a leaky canal (45.2%), followed by an isthmus (23.8%), missing canal, overfilling, and iatrogenic problems. In conclusion, C-shaped root canals were most frequently found in mandibular second molars. The most common cause of failure was a leaky canal and isthmus.

中文翻译：

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C形根管牙髓失败原因分析

本研究的目的是通过牙髓显微镜和扫描电子显微镜（SEM）检查切除的根面，分析C形根管的各种特征和分类，并评估C形根管牙髓失败的原因。42颗具有C形根管的牙齿被纳入本研究，并进行了有意再植手术。手术前进行了根尖周X线摄影和锥形束计算机断层扫描。根据Melton的冠状和根尖水平的分类对根管配置进行分析和分类。注射 1:100,000 肾上腺素和 2% 利多卡因后，小心地拔出牙齿。根端切除后，使用手术显微镜和扫描电镜检查切除的根面。下颌第二磨牙是最常受累的牙齿（90.4%）。最常观察到的根管配置是冠状水平的 C1 (45.2%) 和根尖 3 mm 水平的 C3 (45.2%)。C 形根管治疗失败的最常见原因是根管渗漏 (45.2%)，其次是峡部 (23.8%)、根管缺失、填充过度和医源性问题。总之，C形根管最常见于下颌第二磨牙。失败的最常见原因是漏水的运河和峡部。过度填充和医源性问题。总之，C形根管最常见于下颌第二磨牙。失败的最常见原因是漏水的运河和峡部。过度填充和医源性问题。总之，C形根管最常见于下颌第二磨牙。失败的最常见原因是漏水的运河和峡部。