Single maxillary central incisors in the midline.

A single maxillary central incisor in both the primary and the permanent dentition is a rare phenomenon. Attempts to explain the etiology of this condition included "fusion across the midline", "conation" and "double tooth". Three cases are presented with morphologically normal single incisors in the permanent dentition, and evidence of single central incisors in the primary dentition. Agenesis seems to be the preferred etiologic explanation.