Purpose: To confirm that the quantitative light-induced fluorescence-digital (QLF-D) system is an adequate tool for monitoring changes in the mineral contents of white spot lesions. Materials and Methods: Twenty-three anterior teeth from five orthodontic patients were selected for the samples. Initial fluorescent images were taken with the QLF-D system immediately after removing the fixed orthodontic appliances, and the white spot lesions were visualised in the fluorescent images that were selected. Subsequently, a fluoride varnish containing 0.1% fluoride was applied to all white spot lesions, and the final QLF-D images were taken two weeks after fluoride treatment. Finally, the following four parameters were compared between the images taken at baseline and two weeks after the treatment with paired t-tests: the mean fluorescence loss (∆F), maximum fluorescence loss (∆Fmax), lesion area (area), and lesion volume (∆Q). Results: All the parameters obtained by QLF-D after two weeks had improved significantly when compared with baseline (p 0.01). The recovery rates of the ∆F, ∆Fmax, area, and ∆Q were 11.4%, 17.1%, -37.5%, and 42.1%, respectively. Shallow lesions (∆Fi ≥ -15%) were better remineralized than deep lesions (∆Fi -15%). The ratios of the ∆F, ∆Fmax, area, and ∆Q parameters between the shallow and deep lesions were 2.86, 3.30, 2.20, and 1.88, respectively. Conclusion: The QLF-D system is a sensitive tool for the assessment of small levels of mineral changes in carious lesions after the removal of orthodontic appliances. Keywords: dental caries, diagnosis, quantitative light-induced fluorescence-digital system, white spot