Recombinant human insulin-like growth factor-1 promotes osteoclast formation and accelerates orthodontic tooth movement in rats

Abstract Background: IGF-1 may be an important factor in bone remodeling, but its mechanism of action on osteoclasts during orthodontic tooth movement is complex and unclear. Methodology: The closed-coil spring was placed between the left maxillary first molar and upper incisors with a force of 50 g to establish an orthodontic movement model. Eighty SD rats were randomized to receive phosphate buffer saline or 400 ng rhIGF-1 in the lateral buccal mucosa of the left maxillary first molar every two days. Tissue sections were stained for tartrate-resistant acidic phosphatase (TRAP), the number of TRAP-positive cells was estimated and tooth movement measured. Results: The rhIGF-1 group exhibited evidential bone resorption and lacuna appeared on the alveolar bone compared to the control group. Moreover, the number of osteoclasts in compression side of the periodontal ligament in the rhIGF-1 group peaked at day 4 (11.37±0.95 compared to 5.28±0.47 in the control group) after the orthodontic force was applied and was significantly higher than that of the control group (p<0.01). Furthermore, the distance of tooth movement in the rhIGF-1 group was significantly larger than that of the control group from day 4 to day 14 (p<0.01), suggesting that rhIGF-1 accelerated orthodontic tooth movement. Conclusion: Our study has showed that rhIGF-1 could stimulate the formation of osteoclasts in the periodontal ligament, and accelerate bone remodeling and orthodontic tooth movement.

Research progress on microRNA-21 in regulating osteoclast and osteogenic differentiation in orthodontic treatment / 口腔疾病防治

@#In the process of orthodontic treatment, the balance between the modeling of alveolar bone and the mechanical stress exerted by the appliance is key to the effective movement of orthodontic teeth. Alveolar bone modeling involves many regulatory factors, and microRNAs (miRNAs), as posttranscriptional regulatory factors, play an important role in the occurrence of bone modeling. As an important member of the miRNA family, miRNA-21 promotes the differentiation of periodontal ligament stem cells into osteoblasts and plays an important role in maintaining bone balance and preventing bone resorption as a regulator of osteoclast formation and a promoter of osteoclast differentiation. A literature review showed that miRNA-21 can regulate osteoclast function and promote bone resorption through programmed cell death 4 (PDCD4), phosphate and tension homology deleted on chromosome ten (PTEN), receptor activator of nuclear factor-κB ligand (RANKL) and osteoprotegerin (OPG). MiRNA-21 is highly sensitive to external mechanical stress in the process of orthodontic tooth movement. After orthodontic force is applied, miRNA-21 can promote osteoclast formation and accelerate orthodontic movement; through targeted regulation of periodontal ligament associated protein-1 (PLAP-1), it can regulate periodontal ligament remodeling in the late stage of tooth movement and improve the potential of tooth movement. In addition, miRNA-21 mediates orthodontic tooth movement (OTM) and alveolar bone remodeling in the periodontal inflammatory microenvironment. miRNA-21 can upregulate the expression of hypoxia-inducible factor-1α (HIF-1α) in periodontal ligament stem cells in a hypoxic environment. It can promote the expression of osteogenic markers, such as osteopontin (OPN), osteocalcin (OCN), alkaline phosphatase (ALP) and runt-related transcription factor 2 (Runx2), and promote osteogenic differentiation during orthodontic tooth movement.