Cases and Comments

Hereditary opalescent dentin has the following characteristics: (1) It is inherited as a domi­ nant trait; (2) the teeth have a bluish or amber opalescence; (3) there is a dispropor­ tion in size of the crown and root, and the root length may be considerably diminished; (4) the pulp tissue is partially or completely obliterated; (5) the enamel is easily worn and fractured. There are other signs which are sometimes associated with hereditary opalescent dentin, such as the presence of numerous periapical rarefactions, small crown size and structural changes in the formation of the dentin. Not every instance of hereditary opalescent dentin embraces this whole cluster of characteristics. There probably are modifying genes which'are transmitted along with the dominant gene and which alter the final expression of the phenotype. Because of the variations, the classification of hereditary dysplasias of dentinal tissue has not been as precise as could be wished. For example, hereditary opalescent dentin is also known as “ dentinogenesis imperfecta,” “odon­ togenesis imperfecta” and “ hereditary opal­ escent dentine associated with osteogenesis im­ perfecta.” Each of these has a slightly differ­ ent connotation, yet the term “ hereditary opalescent dentin” is used to cover them all. Perhaps a more definitive classification may evolve as additional cases are described, and more histological studies made. In the case presented, both the opalescence and the enamel fragility are missing, but with regard to the remaining features the condi­ tion most nearly resembles hereditary opal­ escent dentin.