Orthodontic tooth movement is a complex biologically driven process of asynchronous bone remodeling. Fibromodulin (FMOD), a small leucine-rich proteoglycan, participates in periodontal tissue remodeling and root resorption. This study aimed to determine the effects of FMOD on orthodontic tooth movement (OTM) and orthodontically induced root resorption (OIRR) in rats.

Male Sprague-Dawley (SD) rats were randomized into three groups: control, model, and model + FMOD. OTM was induced in the model and FMOD treatment groups by applying 100 g of orthodontic force to the maxillary right first molar using a nickel-titanium closed-coil spring for 14 days. Concurrently, the model + FMOD group received local periodontal injections of FMOD every two days, whereas the control group received saline injections without force. After 14 days, tooth movement distance, root resorption pit volume, and alveolar bone mineral density (BMD) were analyzed by micro-CT. Immunohistochemistry and RT-qPCR were performed to assess the expression of osteogenic (IGF-1, OCN, Osterix, Runx2) and osteoclast-related markers (RANKL and OPG). FMOD expression was detected using immunofluorescence.

Compared with the control group, the model group exhibited significant increases in both OTM distance and OIRR. FMOD treatment effectively attenuated these changes. Furthermore, the expression of osteogenic markers was downregulated, whereas RANKL expression was upregulated in the model group. However, FMOD treatment reversed these changes. FMOD immunoreactivity was decreased in the model group, and increased following local FMOD administration.

FMOD restrains orthodontic tooth movement and alleviates orthodontically induced root resorption, accompanied by altered expression of osteogenic and osteoclast-related protein markers in periodontal tissues.