ObjectiveThe aim of this study was to assess the effects of three different fluoride-releasing agents on preventing white spot lesions that occur during treatment with full coverage rapid maxillary expanders.Materials and methodsA total of 48 patients with transverse maxillary deficiency were randomly assigned to four equal groups. A fluoride-containing agent was applied to teeth before cementation of the full coverage acrylic-bonded rapid maxillary expanders in the three experimental groups (gel, varnish, and sealent in groups 1, 2, and 3, respectively), while the control group received no agent application. Quantitative light-induced fluorescence (QLF) images of the patients were obtained before cementation and after decementation of the appliances. Four parameters (Delta F, Delta F-max, A, and Delta R) were evaluated on maxillary ten anterior teeth.ResultsIn the fluoride gel group, upper central and lateral incisors, right first and left second premolars showed significant decreases in fluorescence levels indicating demineralization. Right central and left lateral incisors showed significant white spot lesion formation in the fluoride varnish group. Right and left central incisors and left first premolar were the teeth that mineral loss was observed in the sealent group, while all of the teeth except canines and first premolars showed significant demineralization in the control group.ConclusionsMultifluorid varnish and Proseal sealant were effective on preventing demineralization and should be applied to teeth clinically before appliance cementation.Clinical relevanceDemineralization is a major problem during orthodontic treatment. The application of effective fluoride-releasing agents could prevent this major iatrogenic complication.