Dentin dysplasia type I: a scanning electron microscopic analysis of the primary dentition.

Dentin dysplasia type I (DD-I) is a rare autosomal dominant disorder which affects both the deciduous and permanent dentitions. The affected deciduous and permanent teeth have short conical roots with sharp, apical constrictions and frequently periapical radiolucencies in the absence of caries. Apical to a thin layer of normal coronal dentin are large, calcified, dentin masses which nearly obliterate the pulp chamber and canals. Presented here are light microscopic and scanning electron microscopic observations of deciduous teeth from three unrelated persons with the disorder. In general, the deciduous teeth had (1) normal enamel, (2) a thin layer of normal dentin adjacent to the dentinoenamel junction, (3) a crescent-shaped pulpal remnant below the normal dentin, (4) dysplastic dentin masses (ranging from atubular to a few small tubules) between which are spaces presumed to previously have contained smaller remnants of the original mesenchymal dental papilla, and (5) root dentin, which is dysplastic throughout. The SEM-defined phenotype, however, was noticeably variable among all three persons. Based on the current concepts of tooth morphogenesis, it is most likely that the abnormal root morphology of DD-I teeth is secondary to the abnormal differentiation and/or function of the ectomesenchymally derived odontoblasts.