The influence of traumatic intrusion of primary teeth on their permanent successors. A radiographic and histologic study in monkeys.

Intrusion of maxillary central primary incisors was performed in 18 green vervet monkeys (Cercopithecus aethiops) with the purpose of studying early and late histologic changes in odontogenesis of permanent tooth germs and the effect of treatment of primary tooth injury. Immediate changes were studied in five monkeys where both maxillary central primary incisors were intruded. The monkeys were sacrificed 10-15 min after intrusion. The immediate changes in the permanent tooth germ consisted of contusion and displacement of the reduced enamel epithelium and slight displacement of the hard dental tissue in relation to the cervical loop, or Hertwig's epithelial root sheath. Late changes and effect of treatment were studied in 13 monkeys where both maxillary central incisors were intruded. One central primary incisor was removed 1 hour after intrusion while the other incisor was allowed to remain in the jaw. The monkeys were sacrificed 6 weeks after injury and the anterior portion of the maxilla was examined histometrically. The late changes consisted of metaplasia of the reduced enamel epithelium into a stratified squamous epithelium and, in most cases, changes in morphology of the dentin and enamel matrices. On the side where the injured tooth was preserved, significantly larger areas of epithelial metaplasia of the reduced enamel epithelium were present compared with the extraction side. Changes in morphology of the enamel matrix and dentin were found with the same frequency in the two groups, but tended to be less severe in the extraction group. It is concluded that more studies are needed on the effect of metaplasia of the reduced enamel epithelium on complete mineralization of the enamel before an optimal treatment of intruded primary incisors can be determined.