Variables and criteria in prevalence studies of dental anomalies of number, form and size.

Prevalence studies of dental anomalies of number, form and size have varied greatly in their findings. The purpose of this paper is to demonstrate from published studies the effect of variables in sampling techniques and examination methods and to suggest diagnostic criteria. In sampling the ethnic background, the sex distribution, age and derivation of the group studied are shown to be important, but the consumption of near optimum concentrations of fluoride in drinking water does not appear to influence findings. For the examination, a dental history is important and full radiographic coverage essential. Findings should be recorded separately for each dentition, while these anomalies should be studied as a group rather than singly. Diagnostic criteria are proposed for supernumerary teeth, hypodontia, invaginated teeth, double teeth, megadontia and microdontia.