Abstract: Objective To preliminarily study the expression of MMP-2 in the process of the movement of the orthodontic root of rats under the function of Gushukang, to explore its role in the development of root absorption, and to provide theoretical reference basis for the prevention and treatment of orthodontic clinical root absorption. Methods 60 male SD rats were randomly divided into experimental group (30) and control group (30).The experimental group used Gushukang to fill the stomach, while the control group used distilled water to fill the stomach, the given dose was 2.1 g/kg body weight, lavaged once every morning. Experimental group and control group were respectively divided into strength 0 d, 3 d, 7 d and 14 d and 21 d and 28 d groups, each group with five. Two groups of animals were given to 0.6 N force to pull the right maxillary first molar mesial movement.Orthodontic tooth mobility of rats root absorption model was set up. The experimental rats were put to death according to the time schedule respectively. HE staining was used to observe morphological changes of root absorption, and immunohistochemistry was used to observe the expression of MMP-2 in the root absorption area. Results By the comparison of two groups of rats with different tooth movement time and root absorption index, it was found that with the extension of time, the root absorption indexes increased gradually, and the root absorption began to appear on the third day, then gradually increased. After 14 d root absorption rate slowed down, through the same time comparison between groups, root absorption degree of Gushukang group was lighter than the control group.Except for the fact that root absorption indexes of 0 d, 3 d groups had no statistical significance (P＞0.05), the rest groups were statistically significant (P<0.05). Immunohistochemical results showed that the expression of MMP-2 in the strength 0 group was weaker, with the extension of time, the number of MMP-2 positive cells increased. The two groupshad a strong positive expression on 7 d in peak, after 14 d began to gradually decline. The expression of MMP-2 of Gushukang group on 21 d was weak. In the control group, MMP-2 expressed weakly on 28 d and tended to the level of normal tissue. Conclusion MMP-2 is one of the main inflammatory mediums absorbed by the root and is involved in the process of root absorption. The Gushukang is effective in inhibiting the absorption of orthodontic movement roots.

Key words: orthodontic tooth movement and , root absorption , Gushukang , MMP-2