正畸治疗中磨牙的拔除和保留(十一)——拔除第二磨牙与拔除第一前磨牙后第三磨牙牙胚位置的对比研究

目的：比较正畸治疗中拔除第二磨牙与拔除第一前磨牙后第三磨牙牙胚位置的不同改变。方法：选择拔除第二磨牙患者18例及拔除第一前磨牙患者20例，对两组治疗前后X线头颅侧位片进行测量分析。观察矫治前后第三磨牙在垂直方向、水平方向及倾斜角度的改变，比较两组间的差异。结果：两组病例上、下颌第三磨牙垂直位置的改变有显著性差异，拔除第二磨牙组比拔除第一前磨牙组第三磨牙向胎方移动快。水平距离的改变两组之间无差异。拔除第二磨牙组的下颌第三磨牙在矫治后明显竖直，与对照组之间存在显著性差异；矫治后两组上颌第三磨牙的角度均有较大改善，但两组之间的改变无差异。结论：拔除第二磨牙比拔除第一前磨牙加速了第三磨牙向骀方的移动，有利于下颌第三磨牙的竖直，为其以后的萌出创造了有利条件，减少了第三磨牙阻生的可能性。

A comparison of the effects of second molar and first premolar extractions on third molar position

Objective:To compare the changes in third molar position in patients treated with second molar and first premolar extractions. Method:The pretreatment and posttreatment cephalometric radiographs of 18 second molar extraction cases and 20 premolar extraction cases were analyzed. Vertical and horizontal drift and angulation of the third molar were measured. Changes in third molar position from pretreatment to posttreatment for two groups were compared. Result:Student t tests showed more vertical movement of the third molars during treatment in both arches of the second-molar-extraction patients than in the first-premolar-extraction patients. Statistically there were no significant differences in the change in third molar mesial movement. The mandibular third molars of the second-molar-extraction patients showed an improvement in angulation. Conclusion:Our results suggest that second molar extraction therapy may increase the rate of vertical movement of the third molar and improve the angulation of the mandibular third molars.