We aimed at comparing the performance of vacuum-formed thermoplastic retainers (VFR) worn either full-time or part-time, in maintaining orthodontic treatment results in terms of tooth alignment, arch form and occlusion. We reviewed randomized and prospective controlled clinical trials comparing VFR wearing protocols and searched databases, without restrictions, for published and unpublished literature. The risk of bias was assessed using the Cochrane Risk of Bias tool and the overall level of certainty in the evidence following ADA methodology. 184 studies were initially identified and reduced to the 3 randomized controlled trials included in the systematic review by means of specific criteria. One study followed patients 1 year into retention, and the other two for 6 months. Little's Irregularity Index, intermolar and intercanine width, arch length, overjet and PAR score did not differ significantly between the patients wearing their retainers part time or full time. We observed a slight increase in the overbite in the part-time group in only one trial. With a moderate level of certainty, we found that during the observation period, full-time VFR wear is not superior to part-time, bearing in mind the potential implications for health burden, retainer longevity and cost-effectiveness, as well as patient satisfaction and compliance.
Keywords: Clear; Orthodontics; Retainers; Systematic review; Thermoplastic; Vacuum-formed.