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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 relationship between mandibular third molars and mandibular canal by using CBCT to observe the presence or absence of near-medial or vertical occlusion of mandibular canal with overlapping images of root and mandibular canal. Methods: A total of 240 (221 cases) mandibular third molars with overlapping images of the mandibular canal on the surface of the mandibular canal were examined by CBCT to determine the location and the relationship between the root and mandibular canal. Minimally invasive extraction of alveolar nerve during surgery to check the situation; by SPSS 18.0 software statistical analysis. Results: The CBCT showed 158 (65.83%) of the 240 impacted teeth had contact with the mandibular canal. The probability of the separation of the mandibular canal and the root canal was in the order of the buccal 53.13%, 22.22% between roots and 0 on root side. The probability of separation from type A to type C roots in mandibular canal decreased gradually, and the probability of root connection or inclusion to mandibular canal gradually increased. The probability of intraoperative inferior alveolar nerve exposure was 15.83%, while in CBCT images, the probability of lower alveolar nerve exposure was 24.05% in the case of actual contact between mandibular canal and root. In the case of vertical to different position The exposure rate of middle and inferior alveolar nerve was lower in group C (22.22%) than in group B (17.98%) and in group A (3.28%). The exposure rate of inferior alveolar nerve in different positions was 48.98% )> Dental root lingual (20.41%)> Dentinoral buccal (6.67%). CONCLUSION: CBCT is more visual and accurate than the curved surface in assessing the intermolecular relationship between the mandibular third molar root and the mandibular canal.