第一前磨牙减数治疗对第三磨牙角度和萌出间隙的影响

The effect of first premolar extraction on third molar angulation and eruption space

目的:探讨拔除第一前磨牙正畸治疗后对第三磨牙角度和萌出间隙的影响。方法:120例安氏I类错患者按年龄大小分为2组,分别给予拔牙和非拔牙治疗。测量治疗前后的第二、第三磨牙牙尖连线角度(α角)、阻生状态和深度,Rickett’sXi点到下颌第三磨牙远中尖距离(Xi-LTM)、下颌支前缘到第三磨牙远中尖距离(R-LTM)、翼上颌裂切线到上颌第三磨牙后缘的距离(R-LTM)及上、下磨牙的前移量,计算治疗前后各变量的差值,采用SPSS10.0软件包进行统计学分析,α角、Xi-LTM、R-LTM、R-LTM用t检验,阻生状态和深度用χ2检验,比较年龄因素对各指标的影响。结果:拔牙组中,小年龄组的下颌α角和Xi-LTM改变值分别为7.16°和3.22mm,大年龄组分别为2.42°和2.10mm,均大于非拔牙组,差异有显著性(P<0.05);而上颌无显著性差异,拔牙组中下颌第三磨牙的阻生状态明显好转。结论:拔除前磨牙后,下颌第三磨牙前移、竖直,有助于减轻下颌第三磨牙阻生的可能性,但对上颌无明显效果。

PURPOSE：To study the influence of the first premolar extraction on the angulation and eruption space of third molar.METHODS：One hundred and twenty patients cases of Class I malocclusions were divided into 2 groups by age,who were treated with extraction and non-extraction respectively.The following values was measured：angle of cusp line between the second and third molar（α angle）,impact state and depth,distance from Rickett＇s Xi to distal cusp of third mandibular molar along the occlusal plane （Xi-LTM）,anterior border of ramus to the third mandibular molar （R-LTM）,distance from projection of distal contact point of maxillary third molar to intersection of pterygoid vertical on occlusal plane （PTV-UTM）.The change between pre-and post-treatment was calculated and analyzed with SPSS10.0 software package.α angle,Xi-LTM,R-LTM,R-LTM were tested with independent-sample t test,impact state and depth was tested with Chi-square test.Influence of age on the values was also evaluated.RESULTS：In younger group,changes of mandibular α angle and Xi-LTM in extraction group was 7.16°and 3.22mm,but in elder group,these changes was 2.42° and 2.10mm,all values were significantly larger than non-extraction group （P〈0.05）.Impact state and depth of third mandibular molar improved in extraction group,while there was no significant changes in the maxilla.CONCLUSIONS：The third mandibular molar becomes upright and distal movement after first premolar extraction.The possibility of the third mandibular molar impaction is decreased,but the effect on the maxilla is not significant.