The extent of infraposition of replanted and subsequently ankylosed permanent incisors was examined in a longitudinal study of 52 patients. Study cast models were made during the follow-up period. Infraposition was evaluated on frontal photos of the study cast models taken parallel with the occlusal plane. The extent of infraposition was defined as the difference between the position of the incisal edge of the replanted incisor and the adjacent non-injured incisor in apico-coronal direction, measured with a digital caliper at 50x magnification of the negatives. The precision of this measuring procedure was 2.9% and the accuracy 2.0%. Marked infraposition was identified if the tooth was traumatized before the age of 16 in boys and before the age of 14 in girls. In addition, infraposition was observed when ankylosis developed in patients aged 20-30 years, with a yearly mean infraposition rate of 0.07 mm/year (range: 0.02-0.21 mm/year) in males and 0.07 mm/year (range: 0.00-0.12 mm/year) in females. The latter findings supported the concept of slow continuous eruption of the teeth. This phenomenon may have implications not only for the treatment of traumatized teeth but also for the treatment of tooth loss by osseointegrated implants, which represent an analogue to the ankylosed replanted tooth.