Data sources The following electronic databases were searched from 1946 to 31 August 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.Study selection The following study designs were eligible: randomised controlled trials (RCTs), controlled clinical trials, cohort studies of prospective and retrospective design, and cross-sectional studies that reported periodontal measurements on patients who received fixed retention after orthodontic therapy. Studies irrespective of their language were selected by two reviewers independently.Data extraction and synthesis Data extraction from the selected studies and risk of bias assessments were performed by two reviewers independently. Specific risk of bias tools were used according to the pertinent research designs of the included studies. Criteria for conducting a meta-analysis were not met and a qualitative synthesis was conducted.Results Twenty-nine studies fulfilled the eligibility criteria; that is, 11 RCTs, four prospective cohort studies, one retrospective cohort study and 13 cross-sectional studies. The quality of the evidence was low for most of the studies included in this review. Contrary to the general consensus, two RCTs, one prospective cohort study and two cross-sectional studies identified poorer periodontal health in patients with fixed orthodontic retainers.Conclusions The authors of this systematic review concluded that fixed orthodontic retainers in the majority of the 29 included studies seemed to be a method of retention that is rather compatible with periodontal health, or at least not related to severe detrimental consequences for the periodontium. No recommendations on the best type of fixed retainer to use could be given. High-quality evidence from long-term studies is necessary to provide definitive conclusions on the relationship between fixed retainers and periodontal health.