Enamel in odontodysplasia.

Microradiographs of a tooth affected by odontodysplasia showed a clear delineation between the hypoplastic enamel and dentin. Two different zones, one presenting a prismatic structure and the other a globular structure, were found in the enamel layer. In areas where normal prismatic enamel was found, a scalloped dentinoenamel junction and a normal mantle dentin layer were present. Crystallites in those areas were of normal size but the intercrystalline spaces were enlarged. Hypoplastic globular enamel consisted of smaller, closely packed crystallites resembling a type of enameloid found in teleost fishes. Round calcified bodies attached or unattached to the hypoplastic enamel were composed of still smaller irregularly distributed crystallites. It is suggested that the outer hard tissues in odontodysplasia involve different processes. The prismatic enamel zones are formed by the first differentiated ameloblasts. The hypoplastic enamel is due to a decrease in the number of ameloblasts. A localized loss of ameloblasts induces lack of enamel in places. The round calcified bodies attached or unattached to the hypoplastic enamel are most likely formed without any involvement of the ameloblasts.