Aim of this systematic review was to assess the efficacy of preventive interventions against the development of white spot lesions (WSLs) during fixed appliance orthodontic treatment. Nine databases were searched without limitations in September 2018 for randomized trials. Study selection, data extraction and risk of bias assessment were done independently in duplicate. Random-effects meta-analyses of mean differences (MDs) or relative risks (RRs) with their 95% confidence intervals (CIs) were conducted, followed by sensitivity analyses, and the GRADE analysis of the evidence quality. A total of 24 papers (23 trials) were included, assessing preventive measures applied either around orthodontic brackets (21 trials; 1427 patients; mean age 14.4 years) or molar bands (2 trials; 46 patients; age/sex not reported). Active patient reminders were associated with reduced WSL incidence on patient level compared to no reminder (3 trials; 190 patients; RR: 0.4; 95% CI: 0.31-0.64; Number Needed to Treat [NNT]: 3 patients), flat surface sealants were associated with reduced WSL incidence on tooth level than no sealant (5 trials; 2784 teeth; RR: 0.8; 95% CI: 0.63-0.95; NNT: 33 teeth), and fluoride varnish was associated with reduced WSL severity on tooth level (2 trials; 1160 teeth; MD: -0.32 points; 95% CI: -0.44 to -0.21 points). However, the quality of evidence was low according to GRADE, due to risk of bias. Some evidence indicates that active patient reminders and flat surface sealants or fluoride varnish around orthodontic brackets might be associated with reduced WSL burden, but further research is needed.