Third molar agenesis in Down syndrome.

The frequency, gender, and maxillary/mandibular occurrences of third molar agenesis have been studied in a Danish population of Down syndrome individuals (39 F and 31 M). The study was based on radiological examination and compared with 2 control groups of normal Caucasian populations. We found that the occurrence of third molar agenesis in Down syndrome individuals was around 4 times greater than in a normal population and higher than in corresponding previous studies. The agenesis occurred more often in the maxilla than in the mandible, and the frequency was not significantly higher in females than in males. The present study stresses the importance of focusing on the dental germs in the phenotypic discussion, as different genes are involved in tooth formation. The absence of teeth can contribute to an understanding of the interaction between genotype and phenotype.