Evaluation of orthodontic treatment after 1 year of retention--a randomized controlled trial

The aim of this study was to use a randomized controlled trial methodology to evaluate and compare three different retention methods. The capacity of the retention methods to retain orthodontic treatment results was in this first phase analysed on a short-term basis, i.e. after 1 year of retention. The subjects were recruited from adolescents undergoing fixed appliance treatment at an orthodontic clinic in the National Health Service (NHS) in Sweden between 2001 and 2007. Seventy-five patients (45 girls and 30 boys with a mean age of 14.4 years at the start of retention) were randomized into three retention systems; a vacuum-formed retainer in the maxilla and bonded canine-to-canine retainer in the mandible (group V-CTC), a vacuum-formed retainer in the maxilla combined with stripping of the 10 proximal surfaces of the lower mandibular anterior teeth (group V-S), and a prefabricated positioner covering the teeth in the maxilla and mandible (group P). The main outcome measures were: Little's irregularity index (LII), intercanine and intermolar width, arch length, overjet, and overbite. Registrations were made before orthodontic treatment, when the fixed orthodontic appliance was removed, and after 12 months in retention. Differences in means between groups were tested by one-way analysis of variance. After 1 year of retention, no clinically significant difference in retention capacity was found between the three retention methods. Small but significant differences (P < 0.05) were observed between the V-CTC and V-S groups regarding mandibular canine width, mandibular arch length, and overbite. In group P, two patients failed to co-operate.