Data sources The Cochrane Oral Health Group Trials Register, CENTRAL, Medline and Embase were searched to May 2005. Key journals were searched by hand, together with bibliographies of all retrieved papers and review articles. No language restrictions were applied. Authors of trials were contacted to identify unpublished trials.Study selectionInclusion criteria specified randomised and quasi-randomised controlled trials which involved children or adults who had retainers fitted or adjunctive procedures undertaken, following orthodontic treatment with braces to prevent relapse. The outcomes were amount of relapse, survival of retainers, adverse effects on oral health and quality of life.Data extraction and synthesis Screening of eligible studies, assessment of the methodological quality of the trials and data extraction were conducted independently and in duplicate. For dichotomous outcomes, the estimate of effect of an intervention was expressed as risk ratios together with 95% confidence intervals. For continuous outcomes, mean differences and 95% confidence intervals were used to summarise the data for each group.ResultsThe search identified 27 articles, of which five met the inclusion criteria. These trials all compared different interventions. There was weak unreliable evidence, based on data from one trial, that a statistically significant increase in stability occurs in both the mandibular (P<0.001) and maxillary anterior segments (P<0.001) when the circumferential supracrestal fiberotomy is used in conjunction with a Hawley retainer, compared with a Hawley retainer alone. There was also weak, unreliable evidence that teeth settle quicker with a Hawley retainer than with a clear overlay retainer after 3 months. The quality of the trial reports was generally poor. No data were available from any study on quality of life assessment. Meta-analysis could not be undertaken as no two studies compared the same retention techniques.Conclusions There are insufficient research data on which to base our clinical practice on retention at present. There is an urgent need for high quality randomised controlled trials in this crucial area of orthodontic practice. © 2006 EBD.