Posteruptive tooth age in children with Down's syndrome and their sibs.

The accumulated posteruptive tooth age was calculated for 212 children with Down's syndrome and 124 of their unaffected sibs. Posteruptive tooth age was shown to vary widely with different morphological permanent tooth types at the same chronological age. Girls in both groups had greater accumulated posteruptive tooth age than boys at each age. Sibs of both sexes generally exceeded the exposure experience of the children with Down's syndrome.