Genetic variability of crown structure in the molar

我们比较了异性双胞胎(OS)和同性双胞胎(SS)的第一磨牙大小，以分析环境对牙齿大小变化的影响。在上颌骨中，OS组女性的平均值比SS组大，而SS组男性的平均值比OS组大。在下颌，牙齿大小的性别差异在SS和OS双胞胎中显示出相同的模式。邓普西等人。(1999)报告说，OS雌性的牙齿比SS双胞胎的牙齿大。他们推测，性激素在子宫内从男性向女性同卵双胞胎扩散，可能是OS女性牙齿尺寸增加的原因。他们的假设与我们的上颌磨牙的结果是一致的，但我们对下颌磨牙的结果并不一致。我们的结果表明，遗传效应在下颌磨牙中比在上颌中受到更大的影响。牙尖面积是在标准的咬合面照片上测量的。进行结构方程建模。牙尖面积的变异在性别之间没有异质性的证据。遗传模型表明，结合加性遗传和独特环境变异的模型(AE模型)适用于大多数尖端和树冠区域。在其中一些情况下，包含共同的和独特的环境变化的模型(CE模型)提供了适当的拟合。遗传力的估计在47%到85%之间。总体冠层面积和冠层联合面积的遗传力估计值高于各尖端面积。在测量中，副锥体区域的遗传力估计最低。副牙尖在个体发育和系统发育中都是第一尖，也是灵长类中最稳定的磨牙尖。这一结果表明，在整个人类进化过程中，稳定的尖端受到几乎常见的基因类型的控制。

We compared the first molar sizes between opposite-sexed (OS) and same-sexed (SS) twins to analyze the environmental contributions to tooth size variation. In the maxilla, the mean values of the females were tended to be large in OS than in SS, but the mean values of males were larger in SS than in OS. In the mandible, the sexual differences in the tooth size showed the same pattern in both SS and OS twins. Dempsey, et al. (1999) reported that OS females had larger teeth than SS twins. They supposed that diffusion of sex hormones from male to female co-twins in utero might account for the increased tooth size in OS females. Their hypothesis was accord with the maxillary molars of our results, but our results of the mandibular molars were not accord. Our results indicated that the genetic effect was more affected in the mandibular molars than the maxilla.The cusp areas were measured on standardized photographs of the occlusal surface. Structural equation modeling was performed. There was no evidence of heterogeneity in variances of the cusp area between sexes. Genetic modeling indicated that a model incorporating additive genetic and unique environmental variation (AE model) was adequate for most of the cusp areas and crown areas. In some of these instances, a model incorporating common and unique environmental variance (CE model) provided an adequate fit. Estimates of heritability ranged from 47 to 85%. Overall crown area and crown unite areas showed higher heritability estimates than each cusp area. The paracone area showed the lowest heritability estimate in the measurements. The paracone is the first cusp in both ontogeny and phylogeny, and the most stable cusp of molars in primates. This result indicated that a stable cusp has been controlled by almost common genotypes throughout the human evolution processed.