Objective To study the application value of cone-beam computed tomography(CBCT)in the location and ex-traction of impacted mandibular third molar (IMTM). Methods Thirty-six patients planning to extract IMTM in the Affiliated Stomatology Hospital of Southwest Medical University from May 2014 to April 2015 were selected and took the surface fault panoramic radiograph before operation. The patients were divided into the class 1 and 2 according to the relation between IMTM and position of inferior alveolar neural tube displayed by the surface fault panoramic radiograph. The class 1 was the non-touch or point-like touch of IMTM and inferior alveolar neural tube. The class 2 was partial or large range of overlap of IMTM and inferior alveolar neural tube. The position relation between IMTM and inferior alveolar neural tube could not be accurately judged in the patients with class 2,then CBCT was further taken. After that the CS 3D imaging software was used to conduct the three dimen-sional reconstruction and axial,coronal and sagittal position layer analysis for determining the condition of bone ambush and root furcation and the relation between the adjacent teeth and the inferior alveolar neural tube. The teeth extraction scheme was accord-ingly formulated for extracting IMTM. Results In 36 cases of IMTM,14 cases were the class 1 displayed by the surface fault panoramic radiograph and directly performed IMTM extraction ,all cases were successfully extracted without the inferior lip numb-ness symptom after operation;22 cases were the class 2 displayed by the surface fault panoramic radiograph ,after taking further CBCT,the CS 3D imaging software was used to conduct the three dimensional reconstruction and axial ,coronal and sagittal posi-tion layer analysis for precisely locating IMTM. The extraction scheme was formulated and IMTM was successfully extracted with the operation time of 40-60 min;postoperative wound had the early healing without the occurrence of complications such as infec-tion,adjacent teeth damage and inferior lip numbness. The consistency of IMTM root furcation condition ,its relation with adjacent teeth and inferior alveolar neural tube displayed by CBTB examination with the intraoperative findings was higher than the surface fault panoramic radiograph,the difference was statistically significant(P<0.05). Conclusion Compared with the surface fault panoramic radiograph,CBCT can precisely locate IMTM(especially the patients with the inferior alveolar neural tube overlap dis-played by the surface fault panoramic radiograph),which should be widely used in clinic.%目的：探讨口腔颌面锥形束CT（CBCT）在定位和拔除下颌阻生第三磨牙（IMTM）中的应用价值。方法选取2014年5月至2015年4月西南医科大学附属口腔医院收治的拟拔除IMTM患者36例，术前均拍摄曲面断层全景片，根据曲面断层全景片显示的IMTM与下牙槽神经管影像关系分为2类，第1类为IMTM与下牙槽神经管不接触或呈点状接触，第2类为IMTM与下牙槽神经管部分和大范围重叠。第2类患者不能准确判断IMTM与下牙槽神经管的位置关系，则进一步拍摄CBCT后利用CS 3D imaging software软件进行三维重建和轴位、冠状位和矢状位层面分析确定骨埋伏、根分叉情况、与邻牙和下牙槽神经管的关系，据此制订拔牙方案，拔除IMTM。结果36例患者中曲面断层全景片显示为第1类14例，直接行IMTM拔除术，均顺利拔除，术后无下唇麻木症状；曲面断层全景片显示第2类22例，进一步拍摄CBCT后应用CS 3D imaging software 进行三维重建及轴位、冠状位和矢状位分析，精准定位IMTM，制订拔牙方案，均顺利拔除，手术时间40～60 min；术后伤口均初期愈合，无感染、邻牙损伤及下唇麻木等并发症的发生。CBCT检查显示的IMTM根分叉情况、与邻牙和下牙槽神经管位置关系等与术中所见一致性高于曲面断层全景片，差异均有统计学意义（P<0.05）。结论与曲面断层全景片比较，CBCT能精准定位IMTM（尤其是曲面断层全景片显示与下牙槽神经管重叠的患者），应在临床中广泛应用。
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