Photobiomodulation Supports Postorthodontic Molar Space Maintenance by Enhancing Alveolar Bone Remodelling in a Murine Model

Introduction Orthodontic relapse is influenced by incomplete alveolar bone remodelling after active tooth movement. This study evaluated whether 650 nm photobiomodulation treatment prevents postorthodontic relapse by preserving the retained molar distance and enhancing osteogenic activity in alveolar bone. Methods Sixty-four male Wistar rats underwent orthodontic tooth movement of the left maxillary first molar for 14 days using a 10-g nickel-titanium closed-coil spring. After appliance removal, the animals were assigned to four postorthodontic protocols: relapse control without space maintainer or photobiomodulation, space maintainer only, photobiomodulation only, and combined space maintainer with photobiomodulation. Each protocol was evaluated at 7 and 14 days after appliance removal. Histological molar distance was measured to assess relapse tendency. Woven bone formation was evaluated using haematoxylin and eosin staining, while Bmp2, Runx2, alkaline phosphatase, and Collagen-type I expression were analysed by immunohistochemistry. Results The relapse control group showed the smallest retained molar distance and the lowest woven bone formation at both time points. Photobiomodulation alone maintained the molar distance at a level comparable to the space maintainer at 7 days and greater than the space maintainer at 14 days. The combined treatment showed the strongest early maintenance effect and the highest woven bone formation. Photobiomodulation also increased Bmp2, Runx2, alkaline phosphatase, and Collagen-type I expression, indicating enhanced osteogenic differentiation, osteoblast activity, and collagen matrix formation. Conclusion A total of 650 nm photobiomodulation prevent orthodontic relapse tendency by maintaining the molar distance and promoting alveolar bone remodelling. Photobiomodulation may serve as a biological adjunct to mechanical space maintenance for improving postorthodontic stability. Clinical relevance Photobiomodulation may be a noninvasive biological adjunct to conventional orthodontic retention by promoting alveolar bone remodelling and improving postorthodontic stability. However, clinical translation requires further studies to confirm its effectiveness, safety, and optimal irradiation protocol in human orthodontic patients.