Prevalence of tooth transposition, third molar agenesis, and maxillary canine impaction in individuals with Down syndrome.

Alterations in the size, morphology and number of teeth are among the many inherited disorders that have been reported in individuals with Down syndrome. By contrast, third molar agenesis and tooth transposition have been largely ignored and the prevalence of canine impaction has not been reported. The intention of this study was to quantify the occurrence of these anomalies in a group of individuals with Down syndrome, using standardized records, which included a clinical examination, dental casts, and a panoramic radiograph. The results show a notably high prevalence of third molar agenesis (74% of individuals older than 14 years), canine impaction (15%), and maxillary canine/first premolar transposition (15%), compared to published figures from random population samples. These anomalies should not be seen as separate, independent entities, but as associated phenomena. The slow rate of cell growth and a consequent reduced cell number that characterize this syndrome may be responsible for the underdevelopment of the upper jaw, the delayed dental development, the reduction in teeth number and size, and the altered path of canine eruption. No explanation, other than genetics, is immediately available to explain why the maxillary canine/first premolar transposition should represent another phenotypic expression of this trisomy.