Expression of Genes Related to Bone Metabolism in Saliva of Patients During Early Fixed Orthodontic Treatment: A Prospective Longitudinal Observational Study

Introduction: This study evaluated the early gene expression of crucial bone metabolism markers (receptor activator of nuclear factor kappa-Β ligand [RANKL], osteoprotegerin [OPG], tartrate-resistant acid phosphatase [TRAP], alkaline phosphatase [ALP], runt-related transcription factor 2 [RUNX2]) during fixed orthodontic therapy. Methods: Twenty-four patients (mean age: 18.5 ± 3.2 years) undergoing fixed orthodontic treatment were enrolled in this longitudinal observational study. Saliva samples were obtained at baseline (T0), 24  h (T1), 7 days (T2), and 30 days (T3) after initial arch wire activation. Results of protein and gene expression analysis were obtained by quantitative real-time PCR. Results: Salivary expression of RANKL and TRAP significantly peaked at T1 before gradually declining. Conversely, OPG, ALP, and RUNX2 showed delayed upregulation, increasing significantly from T2 to T3. The RANKL/OPG ratio spiked at T1 and declined significantly below baseline values by T3. Conclusion: Salivary gene expression markers effectively capture the temporal shift of bone remodeling during early orthodontic tooth movement, offering a noninvasive tool to monitor alterations of bone metabolism during early phases of orthodontic treatment.