AbstractObjectivesmiR‐21 can promote osteoblast differentiation of periodontal ligament stem cells. However, the effect of miR‐21 on bone remodelling in the midpalatal suture is unclear. This study aimed to elucidate the effects of miR‐21 on the midpalatal suture bone remodelling by expanding the palatal sutures.Materials and methodsmiR‐21 deficient (miR‐21−/−) and wild‐type (WT) mice were used to establish animal models by expanding the palatal sutures. Micro‐CT, haematoxylin‐eosin (HE) staining, tartrate‐resistant acid phosphatase (TRAP) staining, fluorescence labelling and immunohistochemistry were used to investigate the function of miR‐21 in midpalatal suture bone remodelling. Besides, bone mesenchymal stem cells (BMSCs) derived from both miR‐21−/− and WT mice were cultured. The MTT, CCK8, EdU analysis, transwell and wound healing test were used to assess the effects of miR‐21 on the characteristics of cells.ResultsThe expression of ALP was suppressed in miR‐21‐/‐ mice after expansion except 28 days. The expression of Ocn in WT mice was much higher than that of miR‐21‐/‐ mice. Besides, with mechanical force, miR‐21 deficiency downregulated the expression of Opg, upregulated the expression of Rankl, and induced more osteoclasts as TRAP staining showed. After injecting agomir‐21 to miR‐21‐/‐ mice, the expression of Alp, Ocn and Opg/Rankl were rescued. In vitro, the experiments suggested that miR‐21 deficiency reduced proliferation and migration ability of BMSCs.ConclusionsThe results showed that miR‐21 deficiency reduced the rate of bone formation and prolonged the process of bone formation. miR‐21 regulated the bone resorption and osteoclastogenesis by affecting the cell abilities of proliferation and migration.