CBCT评估下颌阻生第三磨牙同下颌管的位置关系

Evaluation of the position and relationship between MITM and MC by CBCT

目的:通过CBCT观察在曲面断层片中牙根与下颌管存在重叠影像的近中或垂直阻生下颌第三磨牙同下颌管的位置关系。方法:对牙根同下颌管在曲面断层片上存在重叠影像的240颗(221例)下颌近中或垂直阻生的第三磨牙,通过CBCT进一步明确其牙根与下颌管的位置及接触关系;并对微创拔牙术中下牙槽神经术中暴露情况进行检查;通过SPSS 18.0软件统计分析。结果:CBCT显示240颗阻生牙中同下颌管实际存在接触关系者有158颗(65.83%);下颌管位于牙根颊舌向不同位置时,下颌管同牙根分离的概率依次为:颊侧时53.13%,牙根之间时22.22%,牙根舌侧时0;从A类到C类牙根同下颌管分离的概率逐渐降低,牙根同下颌管连接或包含的概率逐渐增大。术中下牙槽神经暴露的概率为15.83﹪,而CBCT影像上显示下颌管同牙根存在实际接触关系的病例中,术中下牙槽神经暴露的概率为24.05﹪;垂直向不同位置关系时术中下牙槽神经暴露率:C类(22.22﹪)>B类(17.98﹪)>A类(3.28﹪);颊舌向不同位置时术中下牙槽神经的暴露率:牙根间(48.98﹪)>牙根舌侧(20.41﹪)>牙根颊侧(6.67﹪)。结论:在评估下颌近中或垂直阻生第三磨牙牙根同下颌管的相互关系中,CBCT较曲面断层片更为直观和准确。

Objective：To observe the position and relationship of mandibular mesial or vertical impacted third molar and mandibular canal （MC） which show overlapping image on orthopantomography by cone beam computed tomography （CBCT）.Method：240 teeth from 221 patients,which were diagnosed as the mandibular mesial or vertical impacted third molars,were included in this study.To analyze the position and relationship between the roots of MITM and MC by CBCT,and check up the exposure situation during the minimally invasive extraction of MITM.All statistical analyses were performed using SPSS 18.0.Result：Although all impacted third molar were directly superimposed on the inferior alveolar canal on panoramic radiographs,CBCT showed direct contact or canal involvement in 65.83 ％.When the MC is located in the buccal of root,the frequency of the MC separation from the toot was 53.13 ％,significantly higher than that located between two roots of the impacted tooth 22.22 ％ and on the lingual side 0.With the degree of superposition of MC and the impacted tooth on panoramic photography increasing,the probability of impacted tooth contacting with MC increases.The checking of the IAN exposure situation during the minimally invasive extraction of MITM show that the IAN exposure rate was 15.83 ％,but was 24.05 ％ in the cases which have really contacting relationship showed by CBCT.The exposure rate of IAN during tooth extraction were different in different vertical relationship between the impacted tooth and the MC,and the results showed that：class C （22.22 ％） ＞ class B （17.98 ％） ＞ class A （3.28 ％）.The exposure rate of IAN during tooth extraction were different in different Bucco-lingual relation between the impacted tooth and the MC,and the results showed that：between two roots of the molars （48.98 ％）＞ on the lingual side （20.41％ ＞ on the buccal side （6.67 ％）.Conclusion：CBCT can provide more precise information than panoramic radiography for the analysis of the position and relationship of mandibular mesial or vertical impacted third molar and MC.