[Radiographic study of formation and calcification of the third molar].

A total of 500 orthopantomographic X-rays of Mexican children and teenagers of either sex, aged 7-18, were studied in order to ascertain the development and calcification stages of their third molars, as well as the most frequent anomalies related with them. It was observed that the dental bud appears between ages nine and eleven, and that the third molar is absent in 32.4% of the population, with a predominance of females over males. It was also found that 7.4% of molars evidenced malposition during their early stages of development. In view of such findings, the authors consider that a diagnosis of oligodontia and malposition of the third molar, cannot be established before age 13.