Fixed and removable orthodontic retainers and periodontal health

Data sourcesMedline, PubMed, Cochrane Central Register of Controlled Trials, LILACS and BBO databases with no language restrictions; unpublished literature was searched in Proquest Dissertations and Theses database, clinicaltrials.gov and controlled-trials.com.Study selectionRandomised and nonrandomised controlled clinical trials, prospective cohort studies, and case series (with a minimum sample size of 20 patients) in patients who underwent fixed or removable appliance orthodontic therapy with a minimum follow-up period of six months. The primary outcome was periodontal health; while failure rates, impact of orthodontic retainers on patient-reported outcomes and cost-effectiveness served as secondary outcomes.Data extraction and synthesisFull texts of relevant abstracts were retrieved and data extracted using pre-piloted data collection forms by two authors. Study quality was assessed with Cochrane Collaboration's Risk of Bias tool (RCTs) and Newcastle-Ottawa Scale (NOS) for non-randomised studies. Only RCTs at low or unclear risk of bias and non-randomised studies of moderate or high methodological quality were included in the meta-analysis (MA). If moderate to high heterogeneity was present (I² > 50%), MA was not performed.ResultsOut of the 18 included RCTs, 11 were assessed to be of low risk of bias while five out of six prospective cohort studies were considered high quality using the NOS. The authors did not perform MA because of significant heterogeneity that existed among different studies.With regards to periodontal health, there was no significant difference in probing depth and bleeding on probing between fixed mandibular stainless steel (SS) retainers (bonded to anterior teeth or canines only), fibre reinforced composite retainers or Hawley retainers at three-year follow-up. However, there was increased plaque accumulation around fibre reinforced composite retainers compared to SS retainers. The failure rates of mandibular stainless steel fixed retainers bonded from canine to canine was 0.29 (95 % confidence interval [CI], 0.26, 0.33) over a follow-up period of six to 36 months. The failure risk for mandibular stainless steel fixed retainers bonded to canines only was 0.25 (CI, 0.16, 0.33) over a follow-up period of one to three years. A meta-regression showed that follow-up period was not a predictor of failure rate for mandibular stainless steel fixed retainers. The failure rates of removable retainers (Hawley's or vacuum formed retainers) are lower than the bonded fixed retainers. Removable Hawley's retainer was associated with increased discomfort as well as higher levels of embarrassment with speech and aesthetics. In terms of cost-effectiveness, vacuum-formed retainers were found to be significantly more cost-effective than Hawley retainers or mandibular stainless steel fixed retainers bonded to canines.ConclusionsThere is a lack of high-quality evidence to endorse the use of one type of orthodontic retainer based on their effect on periodontal health, risk of failure, patient-reported outcomes and cost-effectiveness.