Interpreting Heritability Estimates in the Orthodontic Literature

Analysis of family members is central to understanding the causation of biological variation, either genetic or environmental. Rarely, however, is the answer one or the other; variation in the craniofacial complexes, including occlusal variation (“malocclusion”), is almost always some complex combination of nature and nurture. Heritability is the proportion of a trait's variation that, under ideal, simplified conditions, is due to genetic variation. It, in fact, implies nothing about trait size or treatment limits based on some presumed genetic “predetermination.” This article overviews the genetic and environmental sources of variation that generate a trait's phenotype to help clarify the interpretation and limitations of a trait's “heritability,” which is a term often overinterpreted in the orthodontic literature. Applications of genetic studies to the causation of malocclusion also are reviewed, showing that skeletal variation has a substantial genetic component, but there is little or none for “tooth-based” variations such as tooth positions, rotations, and displacements.