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目的    研究不同正畸治疗方法对阻生下颌第三磨牙的影响。方法    选择2005年1月至2008年5月青岛大学医学院附属医院口腔正畸科治疗的第三磨牙阻生青少年患者79例（154颗患牙），按治疗前下颌第三磨牙倾斜角及矫治是否拔牙分为4组：未拔牙A组（非拔牙矫治且倾斜角≤30°），未拔牙B组（非拔牙矫治且倾斜角＞30°），拔牙A组（拔牙矫治且倾斜角≤30°），拔牙B组（拔牙矫治且倾斜角＞30°）。拍摄正畸治疗前后口腔曲面断层片，测量并计算矫治前后下颌第三磨牙倾斜角及萌出间隙的变化。结果    矫治后拔牙A组第三磨牙倾斜角比矫治前平均减小3.36°，且差异有统计学意义（P < 0. 05）；其余各组矫治前后差异均无统计学意义。矫治后各组下颌第三磨牙的萌出间隙均高于矫治前，且差异有统计学意义（P < 0. 05），其中拔牙组矫治前后萌出间隙变化尤为明显。结论    对于原倾斜角较小的下颌第三磨牙，拔牙有利于改善第三磨牙的萌出角度；与非拔牙矫治相比，拔牙矫治更多地增加了下颌第三磨牙的萌出间隙，有利于下颌第三磨牙的萌出。

Effects of the orthodontic treatment on the mandibular third molar with different angulations

Objective To study the effect of different orthodontic treatment on impacted mandibular third molars.Methods Totally 79 adolescent patients were involved in the study.A total of 154 mandibular third molars were divided into four groups according to the mandibular third molar angulation and the extraction conditions.（1）Treatment without extraction,the angulation ≤30°.（2）Treatment without extraction,the angulation30°.（3）Treatment with extraction,the angulation ≤30°.（4）Treatment with extraction,the angulation30°.The pretreatment and posttreatment panoramic radiographs were measured to evaluate the change of angulation and the eruption space of mandibular third molar.Results The angulation of third molar reduced in the third group（P 0.05）while eruption space increased in all groups（P 0.05）.The space increase in extraction groups was significantly larger than that in nonextraction groups（P 0.01）.Conclusion Extraction in orthodontic treatment can improve the erection angle of mandibular third molar with smaller angulation.Compared to nonextraction treatment,extraction can increase the eruption space of mandibular third molar significantly,and promote the eruption of third molar.