title: The effects of fixed and removable orthodontic retainers: a systematic review.
abstract: OBJECTIVE
  In the view of the widespread acceptance of indefinite retention, it is important to determine the effects of fixed and removable orthodontic retainers on periodontal health, survival and failure rates of retainers, cost-effectiveness, and impact of orthodontic retainers on patient-reported outcomes.
  
  
  METHODS
  A comprehensive literature search was undertaken based on a defined electronic and gray literature search strategy (
  CRD42015029169). The following databases were searched (up to October 2015); MEDLINE via OVID, PubMed, the Cochrane Central Register of Controlled Trials, LILACS, BBO, ClinicalTrials.gov, the National Research Register, and ProQuest Dissertation and Thesis database. Randomized and non-randomized controlled clinical trials, prospective cohort studies, and case series (minimum sample size of 20) with minimum follow-up periods of 6 months reporting periodontal health, survival and failure rates of retainers, cost-effectiveness, and impact of orthodontic retainers on patient-reported outcomes were identified. The Cochrane Collaboration's Risk of Bias tool and Newcastle-Ottawa Scale were used to assess the quality of included trials.
  
  
  RESULTS
  Twenty-four studies were identified, 18 randomized controlled trials and 6 prospective cohort studies. Of these, only 16 were deemed to be of high quality. Meta-analysis was unfeasible due to considerable clinical heterogeneity and variations in outcome measures. The mean failure risk for mandibular stainless steel fixed retainers bonded from canine to canine was 0.29 (95 % confidence interval [CI] 0.26, 0.33) and for those bonded to canines only was 0.25 (95 % CI: 0.16, 0.33). A meta-regression suggested that failure of fixed stainless steel mandibular retainers was not directly related to the period elapsed since placement (P = 0.938).
  
  
  CONCLUSIONS
  Further well-designed prospective studies are needed to elucidate the benefits and potential harms associated with orthodontic retainers.
authors.affiliation: Barts and The London School of Medicine and Dentistry, Queen Mary University of London, London, E1 2AD, UK. d.almoghrabi@qmul.ac.uk.
authors.forename: Dalya
authors.identifier: http://orcid.org/0000-0002-6733-748X
authors.initials: D
authors.lastname: Al-Moghrabi
authors.affiliation: Dental School, Medical Faculty, University of Bern, Bern, Switzerland.
authors.forename: Nikolaos
authors.initials: N
authors.lastname: Pandis
authors.affiliation: Barts and The London School of Medicine and Dentistry, Queen Mary University of London, London, E1 2AD, UK.
authors.forename: Padhraig S
authors.initials: PS
authors.lastname: Fleming
mesh_terms: D003362:Cost-Benefit Analysis; D006801:Humans; D008334:Mandible; D015201:Meta-Analysis as Topic; D065228:Non-Randomized Controlled Trials as Topic; D018704:Orthodontic Retainers / Q000009:adverse effects / Q000145:classification; D009971:Orthodontics, Corrective / Q000379:methods; D010510:Periodontal Diseases; D016032:Randomized Controlled Trials as Topic; D013193:Stainless Steel / Q000737:chemistry; D016896:Treatment Outcome
chemical_list: D013193:Stainless Steel
keywords: Cost-effectiveness; Failure rate; Orthodontic retainer; Patient-reported outcomes; Periodontal; Survival rate