正畸拔除下颌第一磨牙对第三磨牙位置变化的影响

目的：通过比较正畸采用不同拔牙模式后第三磨牙位置的改变,探讨拔除下颌第一磨牙后对第三磨牙萌出的影响。方法：选择拔除下颌第一磨牙（15例）、第一前磨牙（20例）及非拔牙（20例）的3组青少年病例,3组患者正畸治疗前后及保持2年后拍全颌曲面断层片,对第三磨牙萌出的各项评价指标变化量进行比较研究。结果：在正畸治疗前后,第三磨牙萌出间隙改变量,拔第一磨牙组大于拔第一前磨牙组和非拔牙组,且差异均具有统计学意义。第三磨牙萌出角度改变量,拔第一磨牙组大于拔第一前磨牙组和非拔牙组,且差异均具有统计学意义。正畸保持2年后萌出间隙变化量虽均有增加但不具有统计学意义,第三磨牙萌出角度变化量拔第一磨牙组大于拔第一前磨牙组和非拔牙组,且差异均具有统计学意义。结论：正畸治疗中拔除下颌第一磨牙可增大下颌第三磨牙萌出间隙,第三磨牙更加直立,对第三磨牙的萌出有利。

Effects of Lower First Molar Extractions on Third Molar Position in Adolescent Followed by Orthodontic Treatment

Objective： To study the effects of lower first molar extraction on the third molar position in adolescent. Methods： 55 adolescent cases were selected and divided into lower first molar extraction（15 cases）, first premolar ex- traction（20 cases） and non--extraction（20 cases） groups respectively. The pretreatment, posttreatment and after 2 years retaining panoramic radiographs were measured to analyses the change of the third molar position among these groups. Results： There were significant differences in the changes of the third molar eruption space among three groups （P~0.05）. Space changes in first molar extraction group were larger than that in premolar extraction group and non--extraction group. The changes of lower third molar in first molar extraction group were increased more than that in other groups. After 2 years retaining the changes in eruption space and the angle of first molar extrac- tion group were even larger than other 2 groups. Conclusion： Lower first molar extraction could enlarge the eruption space of third molar and upright the third molar. It was beneficial to third molar eruption.