Does quality of orthodontic treatment outcome influence post-treatment stability? A retrospective study investigating short-term stability 2 years after orthodontic treatment with fixed appliances and in the presence of fixed retainers.

Objective: The present study aimed to evaluate stability 2 years after orthodontic treatment and to investigate the influence of various pre-treatment and post-treatment prognostic factors on stability.

Setting And Sample Population: Consecutive patients treated with full fixed appliance and retained with fixed retainers were retrospectively assessed for eligibility.

Materials And Methods: Digital models were analysed at treatment start (T0), end of treatment (T1) and 2 years post-treatment (T2). The Peer Assessment Rating (PAR) index, Little's Irregularity Index (LII), arch width and length, overjet, overbite and presence of unexpected post-treatment changes were assessed. Multiple regression analyses were conducted to model the relationship of all outcomes with several prognostics simultaneously.

Results: The sample consisted of 287 subjects (mean treatment time: 25.1 months, standard deviation [SD] 7.5; mean post-treatment follow-up: 27.5 months, SD 6.1) with a mean weighted PAR score of 29.5 (SD 8.6) at T0, 1.8 (SD 2.9) at T1 and 3.2 (SD 3.6) at T2. At T1, 95% of the subjects had a perfect LII versus 86% at T2. An increased LII at T1 correlated with increased LII and PAR changes from T1 to T2. PAR at T1 as well as overjet at T0 was a significant prognostic factor for PAR at T2. At T2, five cases (1.7%) showed unexpected post-treatment changes related to fixed retainers.

Conclusion: Short-term post-treatment stability with fixed retainers was very good. Prognostic factors for stability included LII and PAR at T1, suggesting that high-quality treatment outcome in the presence of fixed retainers may ensure post-treatment stability.