Stability of Orthodontic Treatment Outcome in Relation to Retention Status: An 8-Year Follow-Up
Our aim was to evaluate the stability of orthodontic treatment outcome and retention status seven or more years after active treatment in relation to post-treatment or post-retention time, type of retention appliance, and duration of retainer use. The subjects were former patients who completed orthodontic treatment with fixed appliances from 2000 to 2007. The pre-treatment eligibility criteria were anterior crowding of 4mm or more in the maxilla or the mandible and Angle Class I or Class II sagittal molar relationship. Acceptable pre-treatment and post-treatment dental casts were required. A total of 67 patients participated, 24 men and 43 women, with a mean age of 24.7 years (range, 20.0-50.0 years). All participants had a follow-up clinical examination, which included impressions for follow-up casts, and each completed a questionnaire. Data were obtained from pre-treatment, post-treatment, and follow-up (T2) casts as well as from the patients' dental records. Treatment stability was evaluated with the peer assessment rating (PAR) index and Little's irregularity index. The participation rate was 64%. The average post-treatment time was 8.5 years (range, 7.0-11.0). All participants had received a retainer in the mandible, maxilla, or both after active treatment. At T2, the PAR score showed a mean relapse of 14%. The majority (78%) of participants still had a fixed retainer at T2 (retainer group), and 22% had been out of retention for at least one year (post-retention group). The relapse according to the PAR did not differ significantly between participants with and without a retainer at T2. From post-treatment to T2, the irregularity of the mandibular incisors increased almost three times more in participants with no retainer in the mandible compared with those with an intact retainer at T2 (P = 0.001). In the maxilla, no corresponding difference was found. Our results suggest that occlusal relapse can be expected after active orthodontic treatment irrespective of long-term use of fixed retainers. Fixed canine-to-canine retainers seem effective to maintain mandibular incisor alignment whereas, in the maxilla, a fixed retainer may not make any difference in the long term.