目的: 通过应用多层螺旋CT 观察分析内蒙古地区成人下颌第一磨牙的根管形态及其变异情况，为
临床治疗提供解剖学依据，同时探讨下颌第一磨牙根管形态是否存在性别与民族差异。方法: 筛选内蒙古地区
符合双侧健康下颌第一磨牙标准的蒙汉族成年人66 名，共132 颗下颌第一磨牙进行研究，应用多层螺旋CT 扫
描，利用Release 4． 4后处理软件进行三维重建，分析下颌第一磨牙根管形态。结果: 下颌第一磨牙2 根发生率
67． 6%，3 根发生率33． 3%，2 根2 根管发生率6． 1%，2 根3 根管发生率42． 4%，2 根4 根管发生率18． 2%，3 根3
根管发生率7． 6%，3 根4 根管发生率25． 7%。下颌第一磨牙远中舌根个体发生率33． 3%，男女性别间发生率无
统计学差异( P ＞ 0． 05) ，蒙汉族间发生率有统计学差异( P ＜ 0． 05) 。结论:内蒙古地区成人下颌第一磨牙牙根及
根管形态多样且具有较大的变异性，同时变异存在民族差异。

Objective: To provide the anatomy reference about the basic clinical therapy and explore
the mandibular first molars whether there are differences between genders or nationalities，by using
multi － slice computed tomography to evaluate root and canal morphology． Methods: A total of 66
Mongolian and Hans adults with healthy，well － developed mandibular first molars were included． Totally，
anumber of 132 mandibular first molars were studied． The root and canal morphology were evaluated
by multi － slice computed tomography scanning， the data was imported into workstation and made research
on image reconstruction and multiplanar reconstruction by Release 4． 4 software． Results: The
incidence rate of mandibular first molars with two separate roots was 67． 6%， three roots were identified
in 33． 3%of mandibular first molars． Two canals in two separate roots were found in 6． 7%of mandibular
first molars，42． 4%had three canals and 18． 2% had four canals． Three canals in three roots were
found in 7． 6%of mandibular first molars，25． 7%had four canals． The RE( radix entomolaris) individual
incidence of mandibular first molars was 33． 3%． There is no statistical difference( P ＞ 0． 05) of incidence
rate between male and female． There is statistical difference( P ＜ 0． 05) of incidence rate between
Mongolian and Hans． Conclusions: The root and canal morphology of mandibular first molars are diversified
and variability in Inner Mongolia Region． The variability is distinguished between Mongolian and
Hans．

781． 4