上颌牙弓形态的主要要素分析

Classification of maxillary dental arches by correlation and principal component analyses

目的:寻找一种快速评价牙弓形态的客观标准。方法:从396副(年龄:18～26岁;男性257副,女性139副)牙模型中选出62副(男性36副,女性26副)具有正常牙列及牙合的模型,设定以下参考点:切嵴的中点,尖牙的牙尖顶,前磨牙的颊尖,第一和第二磨牙的近中颊尖,以及I1R-I1L连线的中点(A)。从A作一个垂直线与M2R-M2L连线相交,形成参考点(B)。A-B连线与CR-CL连线相交,形成参考点(E)。进行以下分析:(1)评价尖牙的突度,指标为①:角I2R-CR-P1R(∠R)+角I2L-CL-P1L(∠L);(2)评价前牙的曲度,指标为②:(A-B)/(CR-CL),③:180°-∠(CR-A-CL)和④:(A-E)/(CR-CL);(3)评价牙弓长度与宽度比,指标为⑤:(A-B)/(M2R-M2L);(4)评价牙弓的圆润程度,指标为⑥:(rθ5-rθ4)R+(rθ5-rθ4)L;(5)通过双侧后牙参考点连线⑦:P1-P2-M1-M2(线i)、P1-M2(线ii)的形态和位置评价Ⅰ型和Ⅱ型方圆形牙弓的特征。其中指标①、②、③、④、⑤和⑥的数据经过分析归纳为3个主要要素:①前牙的弯曲度,②牙弓的突度,和③牙弓的长-宽比。结果:(1)60%的上颌牙列为方圆形牙弓,没有明显显示出主要要素的形态特征;(2)正方形上颌牙弓的参数①∠R+∠L明显较小;(3)圆形牙弓的特征是参数⑥(rθ5-rθ4)R+(rθ5-rθ4)L值偏小;(4)尖圆形牙弓的参数②,③和④值较大。结论:上述评价参数可以归类为3种主要要素(第1要素、第2要素、第3要素),通过分析这些要素,可以有效地评价上颌牙弓的形态,并得出了3类牙弓的各自形态特征。

PURPOSE： To evaluate the morphology of dental arches. METHODS： 62 （male： 36, female： 26） paired casts having normal dentitions and occlusion were selected from 396 （age： 18 to 26 years old; male： 257, female： 139） sets of dental study models. The maxillary dentitions were preliminarily classified as square, round-square, round and round V- shaped arches based on the conventional morphological descriptions. Midpoints of the incisor edge （I1R I1L, I2R, ＆ I2L）, summits of the cuspids （CR ＆ CL）, buccal cusps of the premolars （P1R, P1L P2 R, ＆ P2L）, mesial buccal cusps of the first and second molars （M1R, M1L. M2 R, ＆ M20, and the midpoint （A） of line I1R-I1L were designated as reference points. From A, let a vertical line intersected line M2R-M2L at reference point B. The line A-B intersected CR-CL at reference point E. The following items were evaluated： （1） the protrusion of the cuspids by ① angle 12R-CR-P1R（∠R） ＋ angle I2L-CL-P1L （∠L）; （2） the curvature of the anterior teeth by ② A-B/CR-CL, ③ 180°- ∠CR-A-CL, and ④A-E/CR-CL; （3） the length to width ratio of the dental arch by ⑤ A-B/M2R-M2L; （4） the degree of roundness of the maxillary arch by estimation of ⑥ （rθ5-rθ4）R＋（rθ-rθ）6 and （5） an item ⑦ for the differentiation of type Ⅰ and type Ⅱ round-square arches by relating the bilateral contour and position of break line P1-P2-M1-M2 （i） to line P1-M2 （ii）. The data of items ①, ②, ③, ④, ⑤, and ⑥ were further standardized and summarized into three essential principal components： （1） the curvature of the anterior teeth, （2） the curvilinear contour of the dental arch, and （3） the length-to-width ratio of the dental arch. RESULTS： （1） 60% of the maxillary dentitions were round-square arches which showed no prominent principal component; （2） square maxillary arches distinctly showed a small ①∠R＋ ∠L; （3） round arches were characteristic by small ⑥ （rθ5-rθ4）R＋（rθ5-rθ4）L, values; and （4） round V-shaped arches had large ②, ③ and ④ values. CONCLUSIONS： We concluded that parameters ①,②,③,④,⑤,⑥ and ⑦ were summarized into three principal components （first principal component, second principal component and third principal component）. Through three principal component analysis, we can quickly evaluate the morphology of the dental arches clinically.This methods is simple and of validity. And we can also obtain the characteristics of maxillary dental arches.