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Third molar agenesis in the Burlington Growth Centre in Toronto.

Serial and cross-sectional cephalograms were read and the treatment files reviewed, for 521 children of a representative sample, the Burlington Growth Centre sample, to determine the frequency of congenially missing third molars. All the children had at least two cephalograms taken between the ages of 3 and 21 years, and one of these was taken around 16 years. Of the 521 children studied, 22.3 % had congenially missing third molars. There was no sex-specificity with respect to congenitally missing third molars or to the number of missing third molars in the maxilla and the mandible. Generally, more teeth were absent when third molars were congenitally missing. A relationship was found to exist between congenitally missing teeth and congenitally missing third molars in females. Thus, when third molars were absent, there was a sex-specificity for other congenitally missing teeth. The probability of specific teeth being missing was higher for those individuals with missing third molars than in the 1,191 10- to 12-year-old children of the overall Burlington Growth Centre sample.