以下颌神经管为参照的下颌阻生第三磨牙的分类及临床意义

目的：以下颌神经管为参照,探讨与下颌神经管(inferior alveolar canal,IAC)相交的下颌阻生第三磨牙(impacted mandibular third molars,IMTMs)的阻生类型,并观察手术拔除阻生牙后下牙槽神经损伤与阻生类型间的关系。方法：对锥形束CT(cone beam computed tomography,CBCT)确诊为下颌阻生第三磨牙与下颌神经管接触或相交的378例患者共658侧阻生牙,以下颌神经管为参照,将阻生牙分为4类：Ⅰ类位于神经管的上方,Ⅱ类位于神经管的颊侧,Ⅲ类位于神经管的舌侧,Ⅳ类下颌神经管位于牙根之间。所有病例均采用手术拔除,术后观察容易引起下牙槽神经损伤的阻生类型,统计各种类型神经损伤的例数,应用SPSS13.0软件包对数据进行χ²检验。结果：阻生牙拔除后,下牙槽神经损伤率为6.8%(45/658)。其中,第Ⅰ类15例(15/332)发生下唇麻木、第Ⅱ类19例 (19/108) 发生下唇麻木、第Ⅲ类11例(11/210)发生下唇麻木,第IV类未发生下唇麻木(0/8)。统计学分析显示,阻生牙拔除后,第Ⅰ类和第Ⅱ类、第Ⅱ类和第Ⅲ类下牙槽神经损伤率有显著差异(P<0.01),第Ⅰ类和第Ⅲ类之间无显著差异(P>0.05)。结论：以下颌神经管为参照,CBCT冠状位可将下颌阻生第三磨牙与下颌神经管相交的患者分为4类,手术拔除过程中均有损伤下牙槽神经的危险,尤其是位于下颌神经管颊侧的阻生牙。

Classification of the impacted mandibular third molar using the mandibular canal as a reference and its clinical significance

PURPOSE： The purpose of this study was to access the position of third mandibular molar in relationship to the inferior alveolar nerve （IAN） injury during surgical extraction. METHODS： Six hundred and fifty-eight cases were diagnosed with impacted mandibular third molars （ITIMs） which were intersected with the inferior alveolar canal （IAC） by cone beam computed tomography （CBCT）, they were classified using the IAC as a reference, the relationship of tooth root and IAC was divided into four types： （~ The root was located above the IAC （type 1）; （~）The root was located on the buccal side （type 2）; （~）The root was located on the lingual side （type 3）; （~ IAC was located between the roots （type 4）. In all cases, the teeth were surgically extracted, and postoperative observations were performed to determine the category which was more likely to cause IAN damage. The data was analyzed with SPSS13.0 sofeware package for chi-square test. RESULTS： The overall rate of neurosensory impairment following extraction was 6.8% （45/658）. It occurred in 15 patients whose root was located above the IAC （15/332）, in 19 patients whose root was located on the buccal side of the IAC （19/108）, and in 11 patients whose root was located on the lingual side （11/210）. No neurosensory impairment was found in the group where the IAC was located between the roots （0/8）. Statistical analysis showed there was significant difference between type I and type 2, and type 2 and type 3 （x2test, P〈0.01）; and there was no significant difference between the first group and the third group （x2test, P〉0.05）. CONCLUSIONS： The relationship between the IMTM and the IAC was divided into four categories using the IAC as a reference. Risk of IAN damage exists for patients during surgical extractions of IMTM that are intersected with the IAC, especially for those with impacted teeth that are located on the buccal side of the IAC. Supported by High-Tech Research and Development Program of China （2012AA030309） and Research Fund from Bureau of Health, Pudong New District, Shanghai Municipality （PW-2011D-4）.