Xie Jing-zhong
Department of Orthodontic, Hangzhou Dental Hospital, Hangzhou 310006, Zhejiang Province, China.
Shanghai Kou Qiang Yi Xue. 2009 Dec;18(6):584-7.
To study the influence of the first premolar extraction on the angulation and eruption space of third molar.
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(alpha 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. alpha 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.
In younger group, changes of mandibular alpha angle and Xi-LTM in extraction group was 7.16 degrees and 3.22mm, but in elder group, these changes was 2.42 degrees 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.
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.
研究拔除第一前磨牙对第三磨牙倾斜度及萌出间隙的影响。
选取120例安氏Ⅰ类错牙合患者，按年龄分为2组，分别采用拔牙矫治和非拔牙矫治。测量以下指标：第二、三磨牙牙尖连线夹角（α角）、阻生状态及深度、沿牙合平面从里克特氏X点至下颌第三磨牙远中牙尖的距离（X-LTM）、下颌升支前缘至下颌第三磨牙的距离（R-LTM）、上颌第三磨牙远中接触点投影至牙合平面翼突垂线交点的距离（PTV-UTM）。计算治疗前后各项指标的变化，并采用SPSS10.0软件包进行分析。α角、X-LTM、R-LTM、R-LTM采用独立样本t检验，阻生状态及深度采用卡方检验。同时评估年龄对各项指标的影响。
在年轻组中，拔牙组下颌α角及X-LTM的变化分别为7.16°和3.22mm，而在年长组中，这些变化分别为2.42°和2.10mm，所有数值均显著大于非拔牙组（P<0.05）。拔牙组下颌第三磨牙的阻生状态及深度有所改善，而上颌则无明显变化。
拔除第一前磨牙后，下颌第三磨牙会直立并向远中移动。下颌第三磨牙阻生的可能性降低，但对上颌的影响不显著。
