Effect of photobiological regulation of green laser on orthodontic tooth retention in rats

Green lasers have a stronger effect on promoting osteoblast differentiation, which is critical for orthodontic tooth retention. This study investigated the impact of green laser photobiomodulation on orthodontic tooth retention in rats. A total of 100 male Sprague-Dawley rats were divided into two groups: Group A (control) and Group B (green laser irradiation). The left upper first molar was moved using a 0.20-mm nickel-titanium coil spring applying a force of 50 g for 3 weeks. The coil spring was then replaced with a 0.25-mm ligature wire to establish an orthodontic tooth retention model. Group B received green laser irradiation on the periodontium surrounding the molars. Retention devices were removed on days 1, 4, 10, 13, and 21. After 3 days of recurrence, the rats were sacrificed on days 4, 7, 13, 16, and 24. The left maxillary molar region was scanned using 3Shape to assess recurrence, and micro-computed tomography was used to evaluate alveolar bone density. Tissue staining was performed to observe periodontal remodeling and bone morphogenetic protein-2 (BMP-2) expression. Over time, the recurrence rate of the molar decreased significantly in both groups (P < 0.01), while alveolar bone density and BMP-2 expression increased (P < 0.01). Group B showed a lower recurrence rate and higher bone density, BMP-2 expression, and osteoblast counts than Group A. Green laser photobiomodulation promoted periodontal tissue remodeling, increased osteoblast numbers, stimulated new bone formation, and reduced the recurrence rate during orthodontic tooth retention in rats.