Efficacy of Dual-Light Photodynamic Therapy on Oral Health in Adolescents Undergoing Fixed Orthodontic Treatment: A Randomized, Assessor-Blinded and Controlled Trial

Background/Objectives: Patients with fixed orthodontic appliances are at increased risk of plaque accumulation, gingivitis, and caries because brackets and bands hinder mechanical hygiene. This study evaluated whether regular home use of dual-light antibacterial photodynamic therapy (aPDT) supports oral hygiene during fixed orthodontic treatment in adolescents. Methods: In a single-center, randomized, assessor-blinded trial, forty-one adolescents starting fixed orthodontic treatment were randomised to a Control group (standard hygiene) or a Test group (standard hygiene plus home-use dual-light aPDT). Visible Plaque Index (VPI%), Bleeding on Probing (BOP%), and Orthodontic Plaque Index (OPI) were assessed at baseline and 12 weeks by an assessor blinded to allocation. After two protocol-driven exclusions, 39 participants (20 Test group, 19 Control group) were analysed. Site-level proportions were compared using the chi-square test. Results: VPI decreased in both groups, with a larger mean within-group reduction in the Test group (−7.0%) than in the Control group (−3.7%); exploratory site-level analysis showed a greater reduction in plaque-positive sites in the Test group at 12 weeks (p < 0.001). BOP increased in both groups but to a smaller extent in the Test group (mean +2.4% versus +5.7%), and a higher proportion of Test-group participants maintained BOP ≤ 10% (85% versus 58%); bleeding-positive sites were lower in the Test group at 12 weeks (p < 0.001). The Test group also showed a flatter distribution of OPI scores around orthodontic brackets. No device- or protocol-related adverse events were reported. Conclusions: In adolescents undergoing fixed orthodontic treatment, regular home use of dual-light aPDT was safe and associated with better site-level plaque and bleeding control, with directional but non-significant trends at the participant level. The findings support further evaluation of dual-light aPDT as an adjunct to mechanical hygiene during this vulnerable treatment period.