A child has less than the normal number of teeth, and one of the mandibular incisors is larger than usual, showing two roots and two root canals on an X-ray. What is the likely diagnosis?

The situation describes a condition where there is a reduced number of teeth in a child, accompanied by a mandibular incisor that is larger than the typical size and exhibits two roots and two root canals. This presentation is characteristic of gemination.

In gemination, a single tooth bud attempts to split into two crowns, resulting in a tooth that has a larger appearance than usual, often with a fused appearance. The presence of two canals indicates that this irregular formation may result in additional root structures due to the incomplete division of the tooth bud, leading to the abnormal morphology observed in the X-ray.

While dilation (or taurodontism) involves a different issue concerning the shape and size of the pulp chamber and root system, and fusion involves two separate tooth buds developing together into a single tooth, the presence of an unusually larger tooth with bipartite root structures strongly indicates gemination as the probable diagnosis in this context. Thus, the larger mandibular incisor with dual canals suggests an anomaly resulting from gemination.