不同垂直骨面型骨性Ⅲ类错牙合下颌磨牙后区特征的CBCT研究

CBCT study on the characteristics of mandibular retromolar region in skeleton Class Ⅲ malocclusion with different vertical facial skeletal types

目的应用锥形束计算机断层扫描(CBCT)对成人轻度或中度骨性Ⅲ类错牙合下颌磨牙后区的形态特征进行观察研究。方法选择成人轻度或中度骨性Ⅲ类错牙合30例行CBCT扫描,CBCT生成头颅侧位片,测量眼耳平面与下颌平面的夹角(FMA角度),其中高角组(FMA>32°)、均角组(22°≤FMA≤32°)、低角组(FMA<22°)各10例,应用CBCT专用软件CS 3D Imaging对下颌双侧第二磨牙后间隙和下颌第二磨牙后区牙槽骨宽度的相关参数进行测量,并运用SPSS21.0软件包对测量参数进行统计学分析。结果 3组下颌第二磨牙后间隙和下颌第二磨牙后区牙槽骨宽度单因素方差分析结果差异有统计学意义(P<0.05)。低角组、均角组、高角组下颌第二磨牙后间隙(SRL)与第二磨牙远中4 mm位置距牙槽嵴顶4 mm处牙槽骨宽度(ABW4)两两比较,差异有统计学意义(P<0.05),测量结果均依次减小。低角组第二磨牙远中4 mm位置距牙槽嵴顶8 mm处牙槽骨宽度(ABW8)大于均角组,低角组大于高角组,差异有统计学意义(P<0.05);均角组与高角组比较,差异无统计学意义(P>0.05)。有第三磨牙组SRL、ABW4和ABW8大于无第三磨牙组,差异有统计学意义(P<0.05)。结论骨性Ⅲ类错牙合不同垂直骨面型下颌第二磨牙后间隙及下颌第二磨牙后区牙槽骨宽度的大小存在差异,且与下颌平面角的大小呈负相关;第三磨牙的存在对下颌第二磨牙后区的空间有一定影响。

Objective To observe and study the morphological features of the retromolar region of mandibular in adults with mild or moderate ClassⅢmalocclusion using Cone Beam Computed Tomography(CBCT).Methods 30 cases of mild or moderate ClassⅢmalocclusion with CBCT were selected,the angel between Frankfort horizontal plane and mandibular plane(FMA angles)were measured on lateral cephalometric radiographs generated by CBCT,including 10 cases with high angle(FMA>32°),10 cases with average angle(22°≤FMA≤32°),and 10 cases with low angle(FMA<22°).The relative parameters of the second retromolar space and the width of the alveolar bone in Bilateral mandible were measured by CS 3D Imaging software special for CBCT,and the parameters were analyzed statistically by using SPSS 21.0 software package.Results The results of One-Way ANOVA analysis were statistically significant differences between second retromolar space and alveolar bone width of second retromolar region of mandibular in the three groups(P<0.05).There were statistically significant differences among low angle,average angle and high angle groups in terms of second retromolar space(SRL)and alveolar bone width of 4 mm from the top of alveolar crest in 4 mm distal position of second molar(ABW4)(P<0.05),and which decreased in turn.In term of alveolar bone width of 8 mm from the top of alveolar crest in 4 mm distal position of second molar(ABW8/mm),the low angle group was larger than the average angle group and the high angle group with statistically significance(P<0.05).There was no statistically significant difference between the average angle group and the high angle group in ABW8(P>0.05).The third molar existence group was larger than third molar missing group in SRL,ABW4 and ABW8,and the difference was statistically significant(P<0.05).Conclusion The size of second retromolar space and alveolar bone width of second retromolar region of mandibular are different among various vertical skeletal malocclusions,and they are negatively correlated with the size of mandibular plane angle.The presence of the third molar affects the size of the posterior area of mandibular molars.