Clinical procedure
During the orthodontic treatment, three experienced orthodontists treated the patients with a pre-adjusted fixed appliance in the maxilla and mandible (0.022 slot size, MBT prescription, Victory Series, 3M Unitek, Monrovia, California, USA). After removing the fixed appliances, post-treatment records, including study casts, were taken (T1). After 2 years of retention, the patients were asked to approve the removal of the retention appliances. Post-retention records and study casts were then taken (T2). All patients in group C handed in the VFR to the clinic after the retention period. One year after the removal of the retainers, additional records and study casts were taken (T3).