Effects Of Aging Factors On The Change Of Dental Pulp Tissue During Orthodontic Tooth Movement

Objective: To observe the expression of HIF-1α,VEGF and apoptosis level of dental pulp tissue of different age groups in the process of orthodontic tooth movement in rats,and the influence of aging factors on these factors,so as to further explore the differences of adolescent and adult during orthodontic tooth movement.Methods: 5-week-old(25)and 8~9-month-old(25)SD male rats were selected to establish the orthodontic tooth movement model.Both groups of rats were executed after 1 days,3 days,7 days,14 days and 28 days respectively,then HE staining and immunohistochemistry and TUNEL staining methods were used to detect the expression of HIF-1α,VEGF and apoptosis level of dental pulp tissue.Conclusions are as follows:1.The tooth movement was observed in both groups,but the tooth movement speed of adult group was slower,and the moving distance was less.2.In youth group we observed obvious expansion of blood vessels and formation of new blood vessels on Day1,then cell aggregation and proliferation appeared on Day3.The pulp tissue returned to normal on Day28.In adult group,the pulp tissue began edema and vasodilatation on Day3,aggregation of pulp cells were observed on Day7 and Day14.On Day28,the pulp tissue returned to normal practicallyexcept for increased number of vessels.The youth group reacts more rapidly,and the metabolic cycle is shorter than adult group.3.Expression of HIF-1α of youth group was gradually increased from Day1,reached the peak at Day3,then weakened gradually.While the adult group was increased gradually from Day3,reached the peak at Day7,then decreased.We hypothesized that aging factors may slow the rate of regulation of pulp tissue to hypoxia and prolong the regulation period.4.Expression of VEGF of youth group was gradually increased from Day1,reached the peak at Day7,and then weakened gradually.While the adult group was increased gradually from Day3,reached the peak at Day14,and then decreased.The expression of VEGF in the pulp tissue in youth group was higher than that in adult group,and all the difference was statistically significant except Day28.We hypothesized that the aging factors slowly increased the expression of VEGF in dental pulp tissue of adult rats,and decreased the amount of expression,which led to the lag reaction of pulp tissue to orthodontic force and the extension of the reaction cycle.5.The pulp cell apoptosis rate of youth group increased on Day3,then gradually decreased,and restore to the normal level on Day14.Apoptosis rate of adult group increased from Day3,reached the peak on Day7,and then gradually decreased.The apoptosis rate of dental pulp cells in adult group was higher than that in youth group at each time point.We speculate that the aging factors can increase the apoptosis rate of dental pulp tissue,but the regulation cycle is prolonged.The pulp tissue maintains the balance between cell proliferation and cell death may through activating cell apoptosis during orthodontic tooth movement.To eliminate useless and harmful cells in time,so as to regulate the number of cells and maintain the stability of the environment within the pulp tissue.