Objective      To investigate the repair situation of periodontal tissue during the repair process following experimentally induced tooth movement in SD rats.       Methods      The upper left first molars were moved mesially in 72 12-week-old male Wistar rats using a coil spring with a force of 0.49 N. After 14 d

the appliance was removed and the animals were killed in groups of 8 immediately after withdrawal of the force and 3

5

7

10

14

and 28 d later. Histological staining and scanning electron microscopy (SEM) were used to observe changes of periodontium histomorphology. Tartrate-resistant acid phosphatase (TRAP) staining was used to detect changes of cementoclast around the root.       Results     

There were more and more repair cells appearing in periodontal tissue after withdrewing the coils

and there was statistically significant differences in 0 to 5 days groups and control group(

P

<

0.05)

but not in 7 to 28 days group and control group (

P

>0.05).       Conclusion      Absorbent periodontal tissue will gradually complete a certain degree of repair after removing the force

and the longer the time is

the better the repair outcome.