The extraction rate in orthodontic practice changes from different ages,areas,doctors or patient groups.Every ways and means has its advantages and disadvantages,so has different indications.The discussion of extraction or nonextraction is always a focus in orthodontic practice.It is not only pure science but also has some relations with philosophy,ethics aesthetics,moral philosophy so we not only need professional knowledge and techniques,but also need to be responsible and serve the giant population.

OBJECTIVE To investigate the potential mechanism of procyanidin on rats with gingivitis by regulating phosphoinositide 3-kinase （PI3K）/protein kinase B （Akt）/vascular endothelial growth factor （VEGF） signaling pathway. METHODS The rat model of gingivitis was constructed by sewing the neck of the first maxillary molar with silk thread+applying maltose on the gum+feeding with 20% sucrose solution and soft food. Forth-eight model rats were randomly divided into model group， procyanidin group （160 mg/kg）， 740Y-P group （PI3K/Akt signaling pathway activator， 0.02 mg/kg）， and procyanidin+ 740Y-P group （procyanidin 160 mg/kg+740Y-P 0.02 mg/kg）， with 12 rats in each group； another 12 rats were selected as control group； each medication group was treated with corresponding drugs intragastrically or/and intraperitoneally， once a day， for 7 consecutive days. Twenty-four hours after the last administration， the gingival index of rats was measured； the levels of interleukin- 18 （IL-18）， inducible nitric oxide synthase （iNOS） and alkaline phosphatase （ALP） in gingival crevicular fluid， as well as the levels of superoxide dismutase （SOD）， catalase （CAT） and reactive oxygen species （ROS） in gingival tissues of rats were detected； the pathological changes in gingival tissues were observed； the expression levels of PI3K/Akt/VEGF signaling pathway- related proteins in gingival tissues of rats were detected. RESULTS Compared with control group， the gingival tissues of rats in the model group had severe pathological damage，which was manifested as local tissue expansion and congestion， new capillaries， degeneration and loss of collagen fibers and disorder of arrangement， and a large number of inflammatory cell infiltration in the gingival sulcus wall. The gingival index， the levels of IL-18， iNOS， ALP in gingival crevicular fluid， the level of ROS in gingival tissues， the phosphorylations of PI3K and Akt， as well as the protein expression of VEGF in gingival tissues were significantly increased； the levels of SOD and CAT in gingival tissues of rats in model group were significantly decreased （P＜0.05）. Compared with model group， the pathological damage to the gingival tissues of rats in procyanidin group was reduced， and all quantitative indicators were significantly improved （P＜0.05）； 740Y-P could reverse the improvement effect of procyanidin on various indicators （P＜0.05）. CONCLUSIONS Procyanidin may alleviate gingival tissue damage， and improve gingival inflammation and oxidative stress in rats with gingivitis by inhibiting PI3K/Akt/VEGF signaling pathway.