Objectives: To explore the effects of matrix metalloproteinase-2 (MMP-2) on the development of orthodontic root resorption in rats and to provide a theoretical basis for prevention and treatment of root resorption in clinical diagnosis.Methods: Thirty-five 6-8-week-old male SD rats were randomly divided into 7 groups, each with 5 rats weighing approximately 200 g±20 g. An orthodontic traction device was applied between the right first molar and the maxillary incisor in the experimental rats,

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... a mesial tractive force of 60 g was applied. Five rats were used for the control group without orthodontic applications. After 0, 1, 3, 5, 7, 14, and 21 days, the maxillae were abducted, and immunohistochemical analysis was performed. We used hematoxylin eosin staining to observe root resorption. The expression of MMP-2 was also assessed by immunohistochemical staining. SPSS17.0 statistical software was used to process the data.Results: Forcing 3 d was observed in the formation of bone resorption lacunae, which were confined to the cementum. After that, it becomes more serious. The most serious damage in 7 days. In 14 d, root absorption was relieved, and osteogenic cells aggregated at the root absorption site. Root resorption lacuna visible dentin repair phenomenon. With the extension of the force application time, the expression of MMP-2 was raised gradually, reached the peak at 7 d, and then gradually declined, 21d tends to be stable, but still stronger than controls.Conclusion: MMP-2 is involved in the metabolism of extracellular matrix in the process of root absorption.