Primary failure of eruption: a case report.

The long-term effect of extracting infra-occluded (submerged) first permanent molars on the subsequent movement of the second permanent molars was studied in a member of a family with previously noted primary failure of tooth eruption. The case is described with the use of radiographs and diagrams and the conclusion reached that in some pathological conditions tooth movement takes place in an apical direction, an observation that may be termed 'paradoxical' tooth movement.