Classification and genetics of numeric anomalies of dentition.

A suggested classification of numeric anomalies of teeth is a trimodal classification: anodontia, hypodontia, and hyperdontia. A subclassification into nonsyndromic and syndromic cases would allow for uniform analysis. The limited data on anodontia and hyperdontia have made the genetic analysis of these anomalies difficult. The most suitable data for analysis on the genetics of numeric anomalies of dentition are on hypodontia. A reevaluation of this data, as presented in this report, suggests hypodontia follows an autosomal dominant mode of inheritance. However, the fact that penetrance is not complete suggests the presence of a mechanism whereby epistatic genes interfere with the phenotypic expression of the hypodontia gene. How this occurs is uncertain, but the available evidence suggests a major single gene defect, which is modified by genetic or environmental factors.