目的·通过锥形束CT测量分析下颌第一磨牙的根管直径和锥度，探究根管直径和锥度随年龄变化的特征，并为临床根管预备方案提出优化建议。方法·选择2022年10月—2023年10月于中南大学湘雅医学院附属海口医院口腔医学中心就诊的20~59岁患者，采集240例健康的下颌第一磨牙锥形束CT影像，其中三根管型与四根管型各120例，再按年龄分为4组（20~29岁、30~39岁、40~49岁、50~59岁），每组30例。测量根管长度，在冠、中、尖、孔4个层面分别测量根管直径的颊舌径与近远中径，并计算出冠1/3段、中1/3段、尖1/3段颊舌向与近远中向的根管锥度，分别比较各年龄组间的差异。结果·下颌第一磨牙各根管直径均为颊舌径大于近远中径。在多数根管的部分层面，50岁以下年龄组的根管直径显著大于50~59岁组（均P<0.05）。下颌第一磨牙各根管锥度均为颊舌向大于近远中向，不同年龄组冠1/3段近远中向锥度均值范围为0.07~0.34，中1/3段均值范围为0.03~0.09，尖1/3段均值范围为0.05~0.11；在多数根管的部分区段，50岁以下年龄组的根管锥度显著大于50~59岁组（均P<0.05）。结论·下颌第一磨牙根管结构存在增龄性改变，50岁及以上人群根管直径缩窄、锥度变小。初尖锉的选择建议：三根管型远中根管用15号锉，其余根管及四根管型的所有根管用10号锉；对于50岁及以上患者，三根管型远中根管调整为10号锉，四根管型的近颊根管及远舌根管调整为8号锉。根管的预备锥度建议：冠部预备用锥度0.08的开口锉；中下段预备时三根管型近颊、近舌根管及四根管型近舌、远舌根管用锥度0.04的主尖锉，三根管型远中根管及四根管型近颊根管用锥度0.06的主尖锉，四根管型远颊根管用锥度0.08的主尖锉。根管充填推荐大锥度牙胶尖联合生物陶瓷类封闭剂进行垂直加压充填。

Objective ·To analyze the root canal diameter and taper of mandibular first molars using cone-beam CT (CBCT), investigate age-related changes in these parameters, and propose optimized clinical protocols for root canal preparation. Methods ·From October 2022 to October 2023, CBCT images of 240 healthy mandibular first molars (120 three-canal type cases and 120 four-canal type cases) were collected from patients aged 20‒59 years at the Stomatology Center, Haikou Affiliated Hospital of Central South University Xiangya School of Medicine. The three-canal type and the four-canal type samples were respectively divided into four age groups (20‒29, 30‒39, 40‒49, and 50‒59 years), with 30 cases in each group. Root canal length was measured, and buccolingual and mesiodistal diameters were recorded at four levels (coronal, middle, apical, and foramen). The tapers of the coronal 1/3, middle 1/3, and apical 1/3 segments were calculated in both buccolingual and mesiodistal directions. Differences among the age groups were compared. Results ·The buccolingual diameters of all root canals exceeded the corresponding mesiodistal diameters. At several levels of most root canals, the diameters in the <50-year-old groups were significantly larger than those in the 50‒59-year-old group (P<0.05). The buccolingual tapers exceeded the corresponding mesiodistal tapers in all root canals of mandibular first molars. The mean mesiodistal tapers in different age groups ranged from 0.07 to 0.34 in the coronal 1/3 segment, 0.03 to 0.09 in the middle 1/3 segment, and 0.05 to 0.11 in the apical 1/3 segment. At several levels of most root canals, the tapers in the <50-year-old groups were significantly larger than those in the 50‒59-year-old group (P<0.05). Conclusion ·Mandibular first molars exhibit age-related narrowing of root canal diameter and reduced taper in individuals aged ≥50 years. For initial apical file selection, #15 files are recommended for the distal canals in the three-canal type, while #10 files are advised for all other canals in the three-canal type and all canals in the four-canal type. For patients aged 50 years or older, the files for the distal canals in the three-canal type can be adjusted to #10, and the files for the mesiobuccal and distallingual canals in the four-canal type to #8. Regarding preparation taper, a 0.08-taper orifice opener is recommended for the coronal 1/3 segment. During mid-lower segment preparation, 0.04-taper master apical files are suggested for the mesiobuccal and mesiolingual canals in the three-canal type and the mesiolingual and distallingual canals in the four-canal type, 0.06-taper files for the distal canals in the three-canal type and the mesiobuccal canals in the four-canal type, and 0.08-taper files for the distobuccal canals in the four-canal type. Root canal obturation is recommended to be performed using vertical compaction with large-taper gutta-percha cones combined with bioceramic sealer.