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Comparison of three different retention strategies 5 years or more postretention.Randomized, prospective, single-centre controlled trial. Forty-nine patients (33 girls and 16 boys) were randomly assigned to one of three retention methods during 2 years by picking a ballot shortly before start of retention treatment. Inclusion criteria were no previous orthodontics, permanent dentition, normal skeletal sagittal, vertical, and transversal relationships, Class I dental relationship, space deficiencies, treatment plan with extractions of four premolars followed by fixed straight-wire appliance. Maxillary and mandibular Little's irregularity index (LII), intercanine and intermolar width, arch length, and overbite/overjet were recorded in a blinded manner, altogether 10 measurements on each patient. Significant differences in means within groups assessed by t-test and between groups by one-way analysis of variance.Retention methods: removable vacuum-formed retainer (VFR) covering the palate and the maxillary anterior teeth from canine-to-canine and bonded canine-to-canine retainer in the lower arch (group V-CTC); maxillary VFR combined with stripping of the lower anterior teeth (group V-S); and prefabricated positioner (group P).Maxillary mean LII ranged from 1.8 to 2.6mm, mean intercanine width 33.6–35.3mm with a significant difference between groups V-S and P, mean intermolar width 46.8–47.4mm and mean arch length 21.8–22.8mm. Mandibular mean LII ranged from 2.0 to 3.4mm with a significant difference between groups V-S and P, mean intercanine width from 25.4 to 26.6mm, mean intermolar width from 40.8 to 40.9mm and mean arch length from 16.9 to 17.3mm. Mean overbite ranged from 1.8 to 2.7mm and mean overjet from 3.7 to 4.1mm.A single centre study could be less generalizable.The three retention methods disclosed equally favourable clinical results.This trial was not registered.The protocol was not published before trial commencement.