DATA SOURCES: Sources were the Cochrane Oral Health Group's Trials Register, the Cochrane Central Register of Controlled Trials (CENTRAL), Medline and Embase. The authors of identified trials were contacted for further data. STUDY SELECTION: Studies were selected if they were randomised clinical trials (RCT) or quasi-RCT, involved the use of a fluoride-containing product compared with no use or use of a non-fluoride control, and if enamel demineralisation was assessed during or after orthodontic treatment. DATA EXTRACTION AND SYNTHESIS: Six reviewers independently, in duplicate, extracted data. The primary outcome was the difference in the presence or absence of white spots between experimental and control patients for parallel design studies, and between experimental and control quadrants, for split-mouth design studies. Potential sources of heterogeneity were examined. Sensitivity analyses were undertaken for the items assessed for quality and publication bias. RESULTS: A total of 15 trials, with 723 participants, provided data for this review. None of the studies fulfilled all of the methodological quality assessment criteria. There is some evidence, however, that a daily sodium fluoride mouthrinse reduces the severity of enamel decay surrounding a fixed brace [weighted mean difference for lesion depth, −70.0 μm; 95% confidence interval (CI), −118.2 to −21.8 μm]. Use of a glass ionomer cement for bracket bonding reduces the prevalence (Peto odds ratio, 0.35; 95% CI, 0.15-0.84) and severity of white spots (weighted mean difference for mineral loss, −645 vol% μm; 95% CI, −915 to −375) compared with composite resins. CONCLUSIONS: There is some evidence that the use of topical fluoride or fluoride-containing bonding materials during orthodontic treatment reduces the occurrence and severity of white spot lesions, but there is little evidence regarding which method or combination of methods is most effective for fluoride delivery. Based on current best practice in other areas of dentistry for which there is evidence, we recommend that patients with fixed braces rinse daily with a 0.05% sodium fluoride mouthrinse. More high-quality, clinical research is required into the different modes of delivering fluoride to the orthodontic patient.