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目的    评价正畸拔除第二前磨牙对第三磨牙萌出角度和萌出间隙的影响。方法    选择2007年1月至2010年7月在济南市口腔医院正畸科行直丝弓正畸治疗的41例安氏Ⅰ类错牙合青少年患者，所有患者第二前磨牙及第二磨牙完全萌出，第三磨牙牙冠已形成但均未萌出。按治疗方法分为拔牙组（21例，均拔除4个第二前磨牙）和非拔牙组（20例）。在治疗前后分别拍摄全口曲面断层片，测量第三磨牙的倾斜角度和萌出间隙。结果    治疗前后上、下颌第三磨牙萌出间隙的增加值拔牙组大于非拔牙组，差异有统计学意义（P < 0.001）。上颌第三磨牙萌出角度的增加值拔牙组大于非拔牙组，差异有统计学意义（P < 0.05），而下颌第三磨牙萌出角度的增加值两组间差异无统计学意义（P > 0.05）。结论    正畸拔除第二前磨牙可以增加上、下颌第三磨牙的萌出间隙，并使上颌第三磨牙萌出角度更加直立。

Effect of the second premolar extraction on third molar eruption

Objective To investigate the effects of orthodontic treatment for 4 second premolars extractions on the angulations and eruption spaces of third molars. Methods Totally 41 adolescents were chosen and divided into second premolar extraction and nonextraction groups, with 21 and 20 patients respectively. The angulational changes and eruption spaces of third molars were evaluated on the panoramic radiographs taken before and after orthodontic treatment. Results Compared to nonextraction group, second premolar extraction group demonstrated statistically significant differences for all third molar eruption spaces（P 〈 0.001 ）and the upper third molar eruption angulation（P 〈 0.05） ,but no statistically significant difference for lower third molar eruption angulation （P 〉 0.05）. Conclusion Second premolar extraction could increase the eruption spaces of third molars, and make the upper third molar eruption angulation more upright.