Abstract: Objective To observe the changes of the contents of matrix metalloproteinase (MMP-2) and tissue inhibitor of metalloproteinase (TIMP-2) in the gingival crevicular fluid (GCF)varying with the differences of orthodontic traction on human teeth,and to explore the relationships between MMP-2 and TIMP-2 functions and the orthodontic traction in the process of tooth movement. Methods Twenty four patients were selected as subjects and divided into three groups randomly:control group (0 N),mild force group (0.5 N),and moderate force group (1.5 N).The traction of canine tooth to distal ends was exerted for 0 days,7 days,14 days and 28 days,and then GCF was collected and the changes of MMP-2 and TIMP-2 contents in GCF were measured by western blot. Results In the experimental groups,MMP-2 and TIMP-2 contents have demonstrated volatility changing feature and were time-dependent; there were significant differences between groups ( P< 0.05). Conclusions Firstly,the expressions of MMP-2 and TIMP-2 demonstrate volatility changing feature,and are time-dependent under mild and moderate forces.Secondly,MMP-2 and TIMP-2 participate in the process of periodontal tissue remodeling and their dynamic balance plays an important role in tooth movement.

Key words: orthodontics；GCF； MMP-2；TIMP-2；tooth movement