下颌阻生第三磨牙与下颌管位置的曲面体层X线片和锥形束CT观察

Relationship between the impacted mandibular third molar and the mandibular canal on panoramic radiograph and cone beam computed tomography

目的观察分析在曲面体层X线片上人群中下颌阻生第三磨牙（impacted mandibular third molar，IMTM）与下颌管位置关系的类型，并对二者关系密切的病例行锥形束CT（cone beam computed tomography，CBCT）检查，了解二者实际位置关系。为临床制定IMTM拔除手术方案提供参考。方法观察390例（645侧）曲面体层X线片，将IMTM与下颌管的位置关系的影像分为3种类型：①无接触类，二者影像无任何重叠或接触；②点状接触类，二者之间影像仅为点状接触；③部分重叠类，二者影像部分重叠或有较大范围接触。统计3种类型的构成比。曲面体层x线片显示IMTM与下颌管影像呈部分重叠或较大范围接触的部分病例行CBCT检查，观察曲面体层X线片IMTM与下颌管关系密切者中，IMTM实际突破下颌管壁所占的比例。结果390例（645侧）IMTM的曲面体层x线片影像中，无接触类441侧（68．4％）；点状接触类149侧（23．1％）；部分重叠类55侧（8．5％）。对31例（50侧）曲面体层X线片上显示IMTM与下颌管呈部分重叠或较大范围接触的CBCT检查发现，25侧（50％）IMTM突破下颌管壁。结论①曲面体层x线片可以排除90％以上IMTM与下颌管关系不密切的病例；②曲面体层x线片IMTM与下颌管影像呈部分重叠或较大范围接触表现的病例有必要行CBCT进一步检查。

Objective To investigate the actual relationship between the impacted mandibular third molars （IMTM） and the mandibular canals on panoramic radiographs and cone beam computed tomography （CBCT）. Methods A cross-sectional study design was used and panoramic radiographs of 390 patients （645 sides developed IMTM） were included in the present study. The relationship between the IMTM and the mandibular canal on panoramic radiographs was defined in three types： ＇untouched＇, ＇touching in point＇, and ＇superimposition or line touching＇. The IMTM superimposing and line touching with mandibular canals on panoramic radiographs were examined by CBCT. Results The relationship types on panoramic radiographs were as follows： ＇untouched＇ type 441 IMTM （68.4%）,the type of ＇touching in point＇ 149 IMTM （23.1%） and the type of ＇superimposition and line touching＇ 55 IMTM （8. 5% ）. CBCT showed that 25 （50%） of 50 IMTM of superimposition and line touching type impinged on the mandibular canals. Conclusions More than 90% of IMTM which do not have intimate relationship with the mandibular canals can be screened out by panoramic radiographs. The IMTM which belong to the line touching and superposition type on panoramic radiographs should be examined by CBCT.