Outcomes assessed in clinical trials concerning orthodontic retention: A scoping review

Objectives

To assess outcomes and outcome measurement tools used in randomized controlled trials (RCTs) concerning orthodontic retention, and to evaluate the study and sample characteristics.

Methods

A comprehensive search was undertaken to identify RCTs concerning orthodontic retention in participants of any age, published up to May 17th, 2025. Primary and secondary outcomes were grouped into main domains with associated outcome measurement tool recorded. Data relating to sample characteristics, type of intervention, dropout rate, study setting and duration, and recall intervals were obtained.

Results

Of 1526 papers identified, 129 were included. Dental alignment (n = 38) and arch width changes (n = 30) were the most prevalent primary and secondary outcomes, respectively. Patient-centred outcomes were evaluated in only 33 studies (25.6%). Heterogeneity in outcome measurements was evident for both periodontal and dental alignment outcomes. Most participants were adolescents (n = 63; 48.84%) with most included studies involving comparisons between variants of removable retainers (n = 38; 29.5%). The effects of retainer use were considered in both arches (n = 61; 47.3%) or the mandibular arch alone (n = 51; 39.5%). The average follow-up was 13.04 months with moderate dropout rates (> 10%) reported in 27.9% of the studies.

Conclusions

Orthodontic retention trials primarily focused on short-term dental alignment in the lower arch and generally overlooked patient-centred outcomes. Prolonged follow-up remains the exception with moderate dropout rates typical even in short-term studies.