Mandibular incisor stability after orthodontic treatment in the upper arch.

The aim of this study was to observe longitudinally the anterior region of the lower jaw when treating only the upper jaw. A comparison was made between a group of 35 children treated with extraction of the maxillary first premolars and a fixed appliance in the upper jaw and a control group of 19 untreated children. The treatment group was studied with plaster models on five occasions: before treatment, at the end of active treatment, at the end of retention, after one year out of retention and at the last registration, in total over about a seven year period. Cephalometric registrations were made before treatment and at the last registration. The control group was studied with plaster models and lateral head films during a period of nine years and their age at the last registration was the same as for the treatment group. The space loss in the anterior region of the lower jaw increased from a mean of 0.4 mm (s.d. 0.82) to 2.5 mm (s.d. 1.52) in the treatment group and from 0.1 mm (s.d. 0.16) to 0.5 mm (s.d. 0.81) in the control group: an extra space loss of 2.0 mm for the treatment group. The main increase was registered during treatment and after retention. Subjective ranking of the plaster models from the final registrations according to the amount of crowding in the lower anterior region also showed a significant difference between the treatment group and the control group, the treatment group showing the largest of crowding. In cases where maxillary protrusion is treated by extraction in the maxilla only, stabilization of the lower arch with fixed orthodontic appliances seems justified.