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.