Failure of root development of human permanent teeth following irradiation.

Complete absence of root formation of the upper incisors, canine and first premolar was reported in a 27-year-old female who had received radiation therapy for a retinal glioma of the right eye at age of 3 years 1 month. Ground and decalcified sections showed no remarkable changes in enamel and dentin of the crowns, but the pulp floor was closed by irregular dentin deposit despite the absence of root formation. The outer surface of the irregular dentin was covered by acellular cementum, and the periodontal membrane was undeveloped. A slight degree of fibrosis was seen in the pulp, but the coronal part of the dentin was lined by odontoblasts. The theory that tooth eruption is caused by the growth of the root is not substantiated by the observation in this case.