骨性Ⅱ类上颌磨牙后间隙解剖特征分析

目的: 比较骨性Ⅰ类与骨性Ⅱ类错患者的上颌磨牙后间隙,探讨骨性Ⅱ类上颌骨前突患者磨牙后移的解剖因素。方法: 对32例骨性Ⅰ类和36例骨性Ⅱ类错患者共136侧上颌骨后段锥形束CT（cone-beam CT,CBCT）资料进行分析。以上颌第一、二磨牙功能尖连线为测量参考线,在上颌第二磨牙远颊根所在平面上,选择上颌第二磨牙的釉-牙骨质界（cemento-enamel junction,CEJ）水平、根分叉水平、距离根分叉2、4、6 mm水平及远颊根根尖水平,测量从上颌第二磨牙到上颌结节远中骨皮质边缘距离。采用SPSS 23.0软件包对数据进行分析,比较骨性Ⅰ类与骨性Ⅱ类错患者上颌磨牙后间隙在不同测量水平处的测量值。结果: 不同性别在各水平测量的磨牙后间隙结果无显著差异;骨性Ⅱ类组测量值均大于骨性Ⅰ类组,2组测量值均在釉-牙骨质界水平最小,分别为（4.18±1.40）和（5.12±2.16） mm;随着测量水平上移,所测得间隙值增长,在根尖处最大,分别为（8.64±2.41）和（10.02±2.27） mm。结论: 骨性Ⅱ类错患者有更大的间隙提供远移。在推上颌磨牙向后时,应更多关注第二磨牙远中沿咬合线的釉-牙骨质界水平的解剖极限。

Anatomical limits of distal displacement of bony maxillary molars in patients with skeletal Class Ⅱ malocclusion

PURPOSE: To compare the posterior space of the maxillary molar with osseous dislocation and investigate the retromolar space available for molar distalization in patients with maxillary prognathism. METHODS: Cone-beam CT (CBCT) data of 136 posterior maxillary segments in 32 patients with skeletal Class I malocclusion and 36 patients with skeletal Class Ⅱ malocclusion were analyzed. The functional tip of the maxillary first and second molars was connected as the measuring reference line, the reference plane for measurement parallel to the reference line, which passed the furcation of the mandibular second molar root, was set as the “0 mm” plane. Four additional planes, which were parallel to the 0 mm-plane and located at 2, 4, 6 mm apical to the 0 mm-plane, cemento-enamel junction (CEJ) and root tip, were named the"2 mm, 4 mm, 6 mm, CEJ and TIP", in order to measure the distance from the maxillary second molar to maxillary tubercle bone cortex in the edge. SPSS 23.0 software package was used to analyze the data. RESULTS: At all levels of measurement, the retromolar space of the values in male and female patients was not significantly different, ClassⅡ malocclusion were significantly greater than those in ClassⅠmalocclusion, with the minimum values at the CEJ level, (4.18±1.40) and (5.12±2.16) mm, respectively. As the measured level moved up, the measured clearance value increased and reached the maximum at the root tip, which was (8.64±2.41) and (10.02±2.27) mm, respectively. CONCLUSIONS: Compared with ClassⅠmalocclusion, patients with ClassⅡmalocclusion have greater retromolar space for maxillary molar distalization along the posterior line of occlusion. More attention should be paid to the anatomical limit of maxillary second molar at the CEJ level along the bite line in the distal direction when maxillary molar is pushed backward.