Aim: To assess the use of the Quantitative Light-induced Fluorescence-Digital BiluminatorTM (QLF-DTM) as an oral hygiene evaluation tool to detect demineralisation and plaque during orthodontics Design: Randomised clinical trial Settings: Liverpool University Dental Hospital Subjects: 33 patients (21 females, 12 males) currently undergoing upper and lower fixed orthodontic appliance treatment were recruited. The median age of patients was 14.6 years with a range from 11.0 to 37.4 years. Methods: The patients were randomly allocated, stratified by the presence of demineralisation at baseline (T0), to receiving oral hygiene reinforcement (OHR) at four consecutive appointments (T1-T4) using the White light (WL) or Quantitative Light-induced Fluorescence (QLF) images, taken with the QLF-DTM device (Inspektor Research Systems BV, Amsterdam, The Netherlands), as visual aids. The standard of oral hygiene was assessed on the QLF images using customised software to provide quantitative scoring of fluorescence loss (ΔF) and plaque coverage (ΔR30) at each appointment. Inter-examiner reliability assessments were conducted by 4 examiners using QLF and WL images from 7 patients. One examiner assessed the images on a second occasion two weeks later to ascertain the intra-examiner reliability. A debriefing questionnaire, distributed on completion of the study, was used to ascertain the patients’ perspectives of the QLF-DTM images. Results: There were no significant differences in demineralisation (ΔF: P=0.56) or plaque accumulation (ΔR30; P=0.95) between the WL and QLF groups from T0 to T4. There were no significant reductions in ΔF in the WL or the QLF group from T0-T4 (P > 0.05), however there was a significant reduction in ΔR30 (P < 0.05). The inter-examiner reliability of QLF image assessment, using ICC, was 0.994 and 0.998 for ΔF and ΔR30 respectively. The inter-examiner reliability of WL image assessment, using kappa, ranged from 0.504 to 0.785. The intra-examiner reliability scores were additionally high with an ICC of 0.988 and 1.0 for ΔF and ΔR30 respectively on the QLF images. The kappa score of demineralisation assessment on the WL images was 1.0. All of the participants found being shown the images helpful and were able to see areas of demineralisation and plaque accumulation. 100% of the QLF group thought it would be useful to be given OHR for the full duration of orthodontic treatment compared to 81% of the WL group (OR 2.3, 95% CI: 1.5-3.5). Conclusion: QLF-DTM can be used to detect and monitor demineralisation and plaque during orthodontics. The image analysis demonstrated high levels of inter- and intra-examiner reliability. OHR at consecutive appointments using the WL or QLF images as visual aids is effective in reducing plaque coverage. Whilst there was no apparent statistical benefit in terms of reducing levels of demineralisation or plaque of using QLF images over WL images, patients reported that they were more informative.