Follow-up control of patients with unilateral posterior cross-bite treated with expansion plates or the quad-helix appliance.

The aim of this study was to evaluate the long-term stability of the occlusion after correction of posterior cross-bite with either a removable expansion plate or a quad-helix appliance and to compare the transversal development of the jaws in the plate group, the quad-helix group and a control group. At the start of treatment there were 22 children in each of the treated groups. Two children in the plate group and 1 child in the quad-helix group discontinued the treatment. Two children treated with the quad-helix appliance and 1 child in the plate group could not be reached for the follow-up registration, so the collective finally consisted of 30 boys and 27 girls: 19 subjects in the plate group, 19 in the quad-helix group and 19 controls. The treatment groups were studied with the help of plaster models before treatment, immediately after treatment and at the last registration about 5.5 years after treatment. The control group was studied with the help of plaster models on 2 occasions, at the mean age of 8.8 years and 15.9 years respectively. This was about the same age as the first and the last registrations in the treatment groups. In all children, the posterior cross-bite was corrected by the end of the treatment. At the last registration, the corrected posterior cross-bite had relapsed in 1 child in the plate group and in 3 children in the quad-helix group. The degree of expansion was similar for both groups. The mean treatment time was longer in the plate group than in the quad-helix group: 12.5 months and 7.7 months respectively. Despite a transversal expansion in the treatment groups, the width of the maxillary dental arch did not reach the mean width in the control group, and even at the last registration the width of the maxillary dental arch was significantly greater in the control group than in the treated groups. The conclusions of this study are: 1. The long-term treatment effect in children with posterior cross-bite was somewhat better when they were treated with the removable expansion plate in comparison with treatment with the quad-helix appliance. 2. Both immediately after treatment and at the last registration 5.5 years later, the width of the maxillary dental arch was significantly greater in the control group than in the plate group or the quad-helix group while the width of the mandibular dental arch was equal in all 3 groups.