The effects of fixed orthodontic retainers on periodontal health: A systematic review

•Eleven RCTs, 4 prospective cohort studies, 1 retrospective cohort study, and 13 cross-sectional studies were eligible for inclusion. •Because of the high amount of heterogeneity identified across the included studies and the lack of high-quality evidence, a meta-analysis was deemed inappropriate. •In contrast to the general consensus, 2 RCTs, 1 prospective cohort study, and 2 cross-sectional studies reported poorer periodontal conditions in the presence of a fixed retainer. •Orthodontic fixed retainers seem to be a retention strategy rather compatible with periodontal health. Introduction The objective of this systematic review was to assess the available evidence in the literature for the effects of fixed orthodontic retainers on periodontal health. Methods The following databases were searched up to August 31, 2019: Medline, EMBASE, the Cochrane Oral Health Group's Trials Register, CENTRAL, ClinicalTrials.gov, the National Research Register, and Pro-Quest Dissertation Abstracts and Thesis database. Randomized controlled trials (RCTs), controlled clinical trials, cohort studies of prospective and retrospective design, and cross-sectional studies reporting on periodontal measurements of patients who received fixed retention after orthodontic treatment were eligible for inclusion. The quality of the included RCTs was assessed per the revised Cochrane risk of bias tool for randomized trials (RoB 2.0), whereas the risk of bias of the included cohort studies was assessed using the Risk Of Bias In Nonrandomized Studies of Interventions tool. A modified version of the Newcastle-Ottawa scale was used for cross-sectional studies. Results Eleven RCTs, 4 prospective cohort studies, 1 retrospective cohort study, and 13 cross-sectional studies fulfilled the inclusion criteria. The quality of evidence was low for most of the included studies. In contrast to the general consensus, 2 RCTs, 1 prospective cohort study, and 2 cross-sectional studies reported poorer periodontal conditions in the presence of a fixed retainer. The results of the included studies comparing different types of fixed retainers were heterogeneous. Conclusions According to the currently available literature, orthodontic fixed retainers seem to be a retention strategy rather compatible with periodontal health, or at least not related to severe detrimental effects on the periodontium.