Harris Edward F, Dinh Dustin P
Department of Orthodontics, College of Dentistry, Health Science Center, University of Tennessee, Memphis, Tennessee 38163, USA.
Am J Phys Anthropol. 2006 Aug;130(4):514-28. doi: 10.1002/ajpa.20389.
Much of a human molar's morphology is concentrated on its occlusal surface. In view of embryologists' recent attention on the determination of crown morphology by enamel knots that initiate cusp formation, we were interested in the arrangement of cusp apices in the definitive tooth. Computer-assisted image analysis was used to measure intercusp distances and angles on permanent maxillary M1 and M2 in a sample of 160 contemporary North American whites. The intent was to generate normative data and to compare the size and variability gradients from M1 to M2. There is little sexual dimorphism in intercusp distances or angles, even though the conventional mesiodistal (MD) and buccolingual (BL) crown size is 2.0% and 4.0% larger in males, respectively, in these same teeth. Dimensions decreased in size and increased in variability from M1 to M2, but differentially. Cusps of the trigon were more stable between teeth, especially the paracone-protocone relationship. Principal components analysis on the six M1 distances disclosed only one eigenvalue above 1.0, indicating that overall crown size itself is the paramount controlling factor in this tooth that almost invariably exhibits a hypocone. In contrast, four components were extracted from among the 12 angular cusp relationships in M1. These axes of variation may prove useful in studies of intergroup differences. A shape difference occurs in M2, depending on whether the hypocone is present; when absent, the metacone is moved lingually, creating more of an isosceles arrangement for the cusps of the trigon. Statistically, correlations are low between occlusal intercusp relationships and conventional crown diameters measured at the margins of the crowns that form later. Weak statistical dependence between cusp relationships and traditional MD and BL diameters suggest that separate stage- and location-specific molecular signals control these different parts (and different stages) of crown formation.
人类磨牙的大部分形态集中在其咬合面上。鉴于胚胎学家最近关注通过启动牙尖形成的釉结来确定牙冠形态，我们对恒牙中牙尖顶点的排列感兴趣。在160名当代北美白人样本中，使用计算机辅助图像分析来测量上颌第一恒磨牙（M1）和第二恒磨牙（M2）的牙尖间距离和角度。目的是生成标准数据，并比较从M1到M2的大小和变异梯度。牙尖间距离或角度几乎没有性别二态性，尽管在这些相同牙齿中，男性的传统近远中（MD）和颊舌（BL）牙冠大小分别大2.0%和4.0%。从M1到M2，尺寸减小且变异性增加，但存在差异。三角区的牙尖在不同牙齿之间更稳定，尤其是副尖-原尖关系。对六个M1距离进行主成分分析，仅发现一个特征值大于1.0，表明总体牙冠大小本身是该几乎总是呈现远中尖的牙齿的首要控制因素。相比之下，从M1的12个牙尖角度关系中提取了四个成分。这些变异轴可能在群体间差异研究中有用。M2存在形状差异，这取决于远中尖是否存在；当不存在时，远中颊尖向舌侧移动，三角区牙尖形成更等腰的排列。从统计学上讲，咬合面牙尖间关系与稍后形成的牙冠边缘处测量的传统牙冠直径之间的相关性较低。牙尖关系与传统MD和BL直径之间的统计依赖性较弱，表明不同阶段和位置特异性的分子信号控制牙冠形成的这些不同部分（和不同阶段）。
