目的

研究面罩式前方牵引联合快速扩弓治疗骨性Ⅲ类错 合牙 畸形及在调整磨牙近中关系中的作用，并对上颌“A”点的前移和下颌颏部变化在骨性Ⅲ类面型改善中的作用进行分析。

方法

随机选择17 例恒牙列早期（11.6 岁）骨性Ⅲ类错 合牙 患者，使用面罩式前方牵引结合上颌快速扩弓进行治疗，对患者治疗前、后头颅侧位片进行测量分析，使用配对t 检验对数据进行统计分析。

结果

上颌骨“A”点平均前移3.41±1.63 mm，治疗前后有统计学意义。 而代表下颌颏部突缩的Y 轴角的变化则无统计学意义。上颌骨“A”的变化与Y 轴角呈负相关关系。

结论

面罩式前方牵引对骨性Ⅲ类错 合牙 畸形面型改善是通过上颌骨“A”点的前移和下颌平面顺时针旋转共同作用的结果，是一个协调的过程。 在调整Ⅲ类磨牙关系中，前牵引引起上颌磨牙的近中移动和垂直向的伸长起决定作用。

Objective

To investigate the skeletal fuction of face mask maxillary protraction combined with rapid maxillary expansion（RME） and its effect on correction of molar relationship examine the effect of the forward movement of maxillary “A” point and the rotation of mandibular mental region on the profile of class Ⅲmalocclusion.

Methods

Seventeen subjects in early permanent dentition with anterior cross bite treated by face mask and RME were included. Cephalometric radiographs were taken before treatment and after treatment for analysis. Twenty three items were included in the cephalometrics.Paired student t-test was performed to analyze the data.

Results

Maxillary “A” point was measured moving forward by 3.41±1.63 mm，whereas no significant change in Y axis which stood for the prominence of the mental region was observed. The change in A point was negatively related to the Y axis.

Conclusion

Forward movement of maxilla and mandibular clockwise rotation account for the major profile improvement. Mesial movement and the extrusion of the upper molar play an pivotal role in molar relation correction.