| Objective:In this experiment,humicacids(HAs)combined with low level laser(LLL)were applied to the maintenance stage of orthodontic teeth in rats.By comparing the recurrence rate,periodontal tissue remodeling and the expression of bone morphogenetic protein 2(BMP-2)in the upper left first molar of rats,to investigate whether the combined application of the two methods has synergistic effect on the maintenance of orthodontic teeth in rats compared with the single condition.To provide a scientific basis for its application in the clinical field of orthodontics.Methods:A total of 120 8-week-old male SD rats were selected to establish the mesial movement model of the left upper first molar.After 3 weeks,the afterweight device was removed and the ligating wire was twisted into a twist shape to establish the left upper first molar retention model,which was randomly divided into 4 groups with 30 rats in each group.Group A(control group):No measures were taken;Group B(simple humic acid group):After the establishment of maintenance model,rats were given 80mg/kg humic acid solution at the rate of 0.5mL/d,once a day;Group C(simple laser irradiation group):low energy laser irradiation was applied on the 0th,2nd,6th,13th,and 20th day after the establishment of the holding model;Group D(laser irradiation combined with humic acid group):The low energy laser combined with humic acid.On the 1st,3rd,7th,14h,and 21th day,6 rats in each group were removed the left upper first molar fixation device.The retainer was removed and allowed to recur for 3 days.Maxillary silicone rubber impressions of 120 rats before and after the movement of the left upper first molar and after the recurrence were obtained by using a two-step method of making individual trays with self-solidification materials.The 3-shape software was used to measure the amount of movement and recurrence(mm),and the recurrence rate was calculated(recurrence rate=amount of recurrence/amount of movement).The rats were sacrificed on the 4th,6th,10th,17th,and 24th day,and the maxillary samples were collected immediately in the left molar area.osteoblast(OB),osteoclast(OC)and periodontal membrane fiber arrangement were observed by HE staining.The expression of BMP-2 was detected by immunohistochemical staining.Statistical analysis was conducted with SPSS 22.0 software.All measurement data were represented by(x±s).One-way analysis of variance was used for all data.For the reliability of the measurement,the experimental data were measured three times by the same operator and averaged.Results:1.After removal of the retaining device,the molar recurrence rate of rats in the same group showed a decreased trend with the extension of retention time,and the difference was statistically significant(P<0.001).In different groups,the recurrence rate of molar in the 1 day group was group D<group C<group B and group A,the difference was statistically significant(P<0.001).After 3 days,7 days,14 days,21 days,molar recurrence rates were group D<group C<group B<group A,the difference was statistically significant(P<0.001).2.After the removal of the oral internal fixation holding device,HE staining showed that the arrangement of periodontal membrane fibers became more regular and dense,the number of bone resorption lacunae of alveolar bone gradually decreased,and the number of osteoblasts gradually increased in the same group with the passage of time.Periodontal tissue changes were different in different groups.The arrangement of periodontal membrane fibers in group A was relatively disordered,and obvious osteoclast-like cells were observed in the distal alveolar bone of the root,while osteoblasts were rare.In group B,the periodontal membrane fibers of the first molar were arranged in a relatively regular and dense manner,and more osteoclast-like cells could be seen in the distal root of the tooth,but they were less active than the control group,and osteoblasts were relatively less.Compared with group B,the fibers of periodontal membrane in group C were arranged more regularly,dense bone trabeculae could be seen,the deposits of new bone in the distal side of the root significantly increased,and a small number of osteoclasts and bone resorption could be seen.In group D,there were no obvious abnormalities in the periodontal membrane,and a good periodontal membrane width was maintained in the distal region.There were almost no osteoclast-like cells in the distal side of the root,and more osteoblasts were distributed in the new bone matrix.3.The results of immunohistochemical staining showed that the expression of BMP-2 in the same group showed a trend of increasing gradually with the increase of time,and the difference was statistically significant(P<0.001).The expression of BMP-2 positive cells was different in different groups of rats in the distal side of the left upper first molar.After 1 day,BMP-2 positive cells could be observed in the periodontal membrane on the surface of the distal alveolar bone,but there was no significant difference in the positive expression of BMP-2 among groups A,B,C and D(P>0.05).At 3,7,14 and 21 days,the number of BMP-2 positive cells in each group increased compared with that at 1 day,and new bone was formed on the surface of distal alveolar bone.The positive expression of BMP-2 was in group D>Group C>group B>group A,with statistical significance(P<0.001).Conclusion:1.In the presence of a fixed retention device,both humic acid and low energy laser alone can reduce the recurrence rate of molar teeth in rats,and the combination of the two can have a synergistic effect to increase the stability of teeth after movement and reduce the recurrence of molar teeth.2.Fixation and maintenance combined with humic acid and low energy laser can effectively promote periodontal tissue remodeling in the relapse stage after tooth movement in rats,and the combination of the two has a synergistic effect to increase the activity of osteoblasts,inhibit the activity of osteoclasts,and reduce the possibility of molar recurrence.3.Both humic acid and low energy laser can promote the expression of BMP-2 in distal molar periodontal tissue of rats at the stage of orthodontic tooth recurrence,and the combined effect of the two is greater than that of low energy laser irradiation alone than that of humic acid alone,which can play a synergistic role in promoting periodontal tissue bone remodeling and effectively reducing the rate of molar tooth recurrence. |
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