Eggen S
Acta Odontol Scand. 1989 Dec;47(6):409-15. doi: 10.3109/00016358909004810.
Torus mandibularis has frustrated several attempts to make family patterns of variation fit modifications of Mendelian models. It is suggested that the quasi-continuous model of inheritance provides a rational explanation for the diverging opinions. The model implies an underlying continuous and normally distributed variable, 'liability', with a threshold value beyond which individuals will be affected. Both genetic and environmental factors determine liability, making the system multifactorial. The incidence of variable degrees of torus was examined in two groups of patients with different stresses on the jaws: one group with bruxism and one comparison group. The transformation of incidences to group means and variances of liability was demonstrated. Muscular forces during bruxism were shown to influence liability. The relative importance of environmental and genetic components of variance could, however, not be estimated directly from the entire groups, since both were mixed with regard to the genetic predisposition. To achieve materials with uniform genotypes, all individuals without torus were omitted. The estimate of the genotypic variance (VG) was obtained by subtracting the variance of the bruxism sub-group--the environmental component associated with bruxism (VEB)--from the total phenotypic variance of the comparison sub-group (VP). The estimate of the genetic determination of torus (VG/VP) turned out to be about 30%, whereas approximately 70% of the causes seemed to be attributable to environmental influence in terms of occlusal stress. Gene effects on the morphologic level are usually pleiotropic, and it is suggested that the correlation of torus mandibularis with other clinical variables might make an interesting subject for further investigation.
下颌隆突使人们多次尝试将家族变异模式与孟德尔模型的修正相匹配的努力受挫。有人认为，准连续遗传模型为不同观点提供了合理的解释。该模型意味着存在一个潜在的连续且呈正态分布的变量“易感性”，具有一个阈值，超过该阈值个体就会受到影响。遗传和环境因素都决定易感性，使该系统具有多因素性。在两组颌部承受不同压力的患者中检查了不同程度下颌隆突的发生率：一组患有磨牙症，另一组为对照组。展示了发生率到组均值和易感性方差的转换。磨牙症期间的肌肉力量被证明会影响易感性。然而，由于环境和遗传方差成分在遗传易感性方面相互混杂，无法直接从整个组中估计它们的相对重要性。为了获得具有统一基因型的材料，所有没有下颌隆突的个体都被排除。通过从对照组的总表型方差（VP）中减去磨牙症亚组的方差——与磨牙症相关的环境成分（VEB），得到基因型方差（VG）的估计值。结果表明，下颌隆突的遗传决定度（VG/VP）约为30%，而就咬合压力而言，约70%的病因似乎可归因于环境影响。基因在形态学水平上的效应通常是多效性的，有人认为下颌隆突与其他临床变量的相关性可能成为进一步研究的一个有趣课题。
