曲面体层片对下颌第三磨牙阻生的可行性探讨

Feasibility of Application of Panoramic Radiography in Early Prediction of Impacted Mandibular Third Molars

目的探讨下颌第三磨牙阻生时曲面断层片的相关指标,为早期预测下颌第三磨牙阻生提供临床依据。方法选取86例符合条件的病例共166颗下颌第三磨牙作为研究对象,按诊断标准分成阻生组和萌出组。测量曲面断层片的如下指标:①下颌第二磨牙倾角(Am2-m1);②下颌第三磨牙倾角(Am3-m2);③下颌第三磨牙倾斜度(Am3-mp);④下颌角(GoA);⑤下颌骨嵴缘夹角(RP-OP)⑥磨牙拥挤度(CM):⑦磨牙后间隙长度与第三磨牙牙冠宽度比值(SM/MD);⑧磨牙后间隙长度与下颌骨牙槽长度比值(SM/AD)。用独立样本t检验比较下颌第三磨牙萌出组与阻生组各测量项目的差异。以下颌第三磨牙阻生的发生概率为因变量,以上述8项测量项目的变化为自变量,对相关因素进行Logistic回归分析。结果阻生组中Am3-m2、CM、Am2-m1、Am3-mp、SM/MD和SM/AD皆大于萌出组(P<0.01),阻生组GoA与萌出组差异无统计学意义(P>0.05)。Logistic回归分析所得回归方程为:下颌第三磨牙阻生=8.51+5.48×下颌第三磨牙倾角+2.93×磨牙拥挤度-1.40×下颌第三磨牙倾斜度-1.04×下颌第二磨牙倾角。结论下颌第三磨牙不同萌出状态在曲面断层片的测量项目中有不同的表现,可在一定程度上用于预测下颌第三磨牙是否发生阻生。

Abstract： Objective To evaluate the feasibility of application of panoramic radiography in early prediction of impacted mandibular third molars. Methods Eighty six cases of one hundred and sixty six mandibular third molars that meet the criteria of this study are selected and divided into two groups： the impaction group and the eruption group based on diagnostic standards. The following measurements are made： ① the inclination of mandibular second molars（Am2-m1）; ② the inclination of mandibular third molars （Am3-m2）; ③ the inclination degree of mandibular third molars （Am3-mp）; ④ the genial angle （GoA）; ⑤ the crystal marginal angle （RP-OP） ⑥ the crowding degree of molars （CM）; ⑦retromolar space and mesiodistal crown space ratios（SM/MD）; ⑧ retromolar spate and the length of mandibular alveolar ratios （SM/AD）. The independent samples t test is conducted to analyze the differences between the eruption group and the impaction group. Then, logistic regression analysis of relevant factors are made under the condition that the incidence of impacted mandibular third molars and changes in eight test items stated hereinbefore are taken as the dependent variable and the independent variable respectively. Results There are significant differences between the two groups with regard to changes of Am3-m2, CM, A m2-m1, Am3-mp, SM / MD and SM / AD （P〈0.01）. Conversely, there was no significant correlation between the GoA of impaction group and eruption group （P〉0.05）. Regression equation acquired from logistic regression analysis is that occurrence of M3 impaction - 8.51 ＋5.48 ×Am3-m2 ＋2.93 ×CM -1.40×mm3-mp -1.04 ×A m2-mp. Conclusion Different eruption status of mandibular third molars is manifested in panoramic radiographs, which can be used to make an early prediction of impacted mandibular third molars to a certain extent.