[Determining the average posteruptive age of teeth from the results of cross-sectional studies (author's transl)]

If results of cross-sectional studies must be used as a basis for setting up models of development of caries in permanent teeth, then the average rather than individual posteruptive age of teeth has to be resorted to. Data available for this purpose had been obtained from a total of 54,000 children living in two G.D.R. cities, namely, Plauen and Karl-Marx-Stadt, as well as from two surveys made in 1959 and 1971, respectively. Calculation of the average posteruptive age of teeth assumes good knowledge of the distribution of dates of eruption in a population. Of the three types of distribution considered, namely, normal, lognormal, and log-logistic distribution, the log-logistic model proved to be superior to others because of better adaptation to the data available. The method of calculating the posteruptive age of teeth is described and illustrated by use of a number of examples. Since one of the two surveys (namely that which was made in Karl-Marx-Stadt in 1971) was made after twelve years' drinking water fluoridation, it was possible to study the effect of fluoridation upon the eruptive behavior of permanent teeth. The results of this study confirmed those obtained during previous investigations.