- Down Syndrome (DS) (Trisomy 21) is a relatively common anomaly occurring in one in every 600-700 live births and characterized by impaired growth and development and early senescence. Signs of abnormal development have been observed on ultrasound as early as the first trimester. By the second trimester additional signs are evident on ultrasound, affecting skeletal growth as well as other organ systems. Dental anomalies include reduced tooth size and number, thin enamel and abnormal crown form as well as taurodont roots and a high frequency of missing teeth. The severity of the dental defects varies along the tooth row with later developing teeth most severely affected. Recent studies carried out on exfoliated (shed) deciduous teeth using a combination of serial microCT scans and SEM have enabled us to reconstruct the chronology and extent of intrauterine and infant growth insults in DS infants, expressed in growth and differentiation of the developing teeth. Our results for the deciduous teeth show that in DS, there is accelerated dental development in the first trimester followed by progressive growth retardation associated with impaired differentiation of the dental tissues. These changes appear to primarily affect cells derived from ectoderm affecting cell division and differentiation resulting in a smaller modified tooth germ and impaired enamel matrix formation and bio-mineralization. The resulting enamel is thin and hypomineralized and this may contribute to the severe abrasion seen in the teeth of DS children despite the associated lack of muscle tone.