Stability of orthodontic treatment outcome in relation to retention status: An 8-year follow-up

Abstract

Introduction: Our aim was to evaluate the stability of orthodontic treatment outcome and retention status 7 or more years after active treatment in relation to posttreatment or postretention time, type of retention appliance, and duration of retainer use.

Methods: The subjects were former patients who completed orthodontic treatment with fixed appliances from 2000 to 2007. The pretreatment eligibility criteria were anterior crowding of 4 mm or more in the maxilla or the mandible and Angle Class I or Class II sagittal molar relationship. Acceptable pretreatment and posttreatment 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 pretreatment, posttreatment, 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.

Results: The participation rate was 64%. The average posttreatment 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 1 year (postretention group). The relapse according to the PAR did not differ significantly between participants with and without a retainer at T2. From posttreatment to T2, the irregularity of the mandibular incisors increased almost 3 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.

Conclusions: 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.