Data sources The Cochrane Oral Health Group's Trials Register, The Cochrane Central Register of Controlled Trials (CENTRAL), Medline and Embase were searched. Several journals were searched by hand (American Journal of Orthodontics and Dentofacial Orthopedics (formerly American Journal of Orthodontics), Angle Orthodontist European Journal of Orthodontics, Journal of Orthodontics (formerly British Journal of Orthodontics)). No language restrictions were applied. Authors of published reports of randomised controlled trials (RCT) were identified and contacted to identify further unpublished trials. The most recent search made was in December 2002.
Study selection Only RCT were chosen for inclusion. Studies included children and adults who had retainers fitted or adjunctive procedures undertaken after orthodontic treatment with braces to prevent relapse. The outcomes were how well the teeth were stabilised, survival of retainers, adverse effects on oral health and quality of life.
Data extraction and synthesis Screening of eligible studies, assessment of methodological quality of the trials and data extraction were conducted in duplicate and independently by two reviewers. Because no two studies compared the same retention strategies (interventions), it was not possible to combine the results of any studies.
Results Four trials satisfied the inclusion criteria. These trials all compared different interventions: circumferential supracrestal fiberotomy (CSF) combined with full-time removable retainer versus a full-time removable retainer alone; CSF combined with a nights-only removable retainer versus a nights-only removable retainer alone; removable Hawley retainer versus a clear overlay retainer and three types of fixed retainers versus a removable retainer. There was weak unreliable evidence, based on data from one trial, that there was a statistically significant increase in stability in both the mandibular (P<0.001) and maxillary anterior segments (P<0.001) when the CSF was used, compared with when it was not used. There was also weak, unreliable evidence that teeth settle quicker with a Hawley retainer than a clear overlay retainer, after 3 months. The quality of the trial reports was generally poor.
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 RCT in this crucial area of orthodontic practice.