Mandibular incisor stability after bimaxillary orthodontic treatment with premolar extraction in the upper arch.

To evaluate long-term changes in the lower incisor region, a comparison was made between children with large overjet treated with extraction of the upper first premolars and fixed appliances in both jaws and untreated children with normal occlusion. The treatment group consisted of 26 children and was studied with plaster models on 5 occasions: before treatment, at the end of active treatment, at the end of retention, after 1 year out of retention and at the last registration 4 to 5 years out of retention. The total time from the start of treatment to the last registration was 9 years and 10 months. Cephalometric registrations were made at the first and last registrations. The group of untreated children, the control group, consisted of 19 individuals. They were also studied with plaster models and lateral headfilms during a period of 10 years. The age of the treatment group and the control group at the last registration was 21.7 years and 20.4 years, respectively. At the first registration there was an available space in the lower anterior region of -0.06 mm (+/- 1.73) in the treatment group and + 0.4 mm (+/- 2.00) in the control group. At the last registration the available space for the treatment group was -1.4 mm (+/- 1.31), an extra space loss of 0.8 mm; in the control group the space loss was 1.3 mm and the available space was thus -0.9 mm. No significant difference in anterior lower jaw crowding could be seen between the treatment and control group at the last registration. Subjective ranking of the plaster models from the final registrations according to the amount of crowding in the lower anterior region showed no significant difference between the treatment and the control group.