Anabolic Effect Of Intermittent Pth(1-34) During The Phase Of Tooth Root Repair In A Rat Model Of Tooth Root Resorption

Abstract Objectives:Orthodontic tooth movement can induce different degrees of root resorption, and many studies have shown that root resorption is inevitable in orthodontic treatment. Doctors have found some ways to reduce root resorption currently,for example: low orthodontic force,short orthodontic time ; and so the root resorption is circumscriptus now which can be partially repaired by itself, but the effect of repair is not perfect. The inevitability of orthodontic tooth root resorption has made oral experts study the tooth root repair gradually by their best over years in order to explore ways to promote root repair and drug rehabilitation. Researches have demonstrated that parathyroid hormone (1-34) is effective to promote bone formation, and a small amount of application of intermittent parathyroid hormone (1-34) can promot the bone tissue repair,and so according to the researches we infer that a small amount of PTH (1-34) through the intermittent application can promote root repair, the current domestic and foreign researches are lack of intravital experimental studies in this area.Intermittent application of PTH (1-34) to promote root repair is a neoteric research method, but also a way worth exploring. Therefore, firstly in this study we established tooth root resorption model during tooth movement in rats. Secondly, we give subcutaneous injections of a small amounts of intermittent PTH (1-34) to rats after discontinuation of orthodontic force, to study the surface of root resorption and their surrounding tissue in order to demonstrate that intermittent PTH (1-34) has an effect on tooth root repair ,through changes of TRAP stained osteoclast number in different time; relative area of repair cementum in different time; immunohistochemical determination of the expression of osteoprotegerin (OPG) and its ligand (RANKL) in the root resorption lacunae and their surrounding tissues in different time. Methods :1. Root resorption model in Wistar rats and group. After 63, 6-8 week-old male adult Wistar rats with weight of 200-250g were fed normally for 7 days , a 0.012mm nickel titanium extension spring with 0.5N extension force was fixed between the first maxillary molar and anterior teeth. After the maxillary first molars moved forward 10 days, the devices in rats were dismantled and rats were re-weighed, divided into 3 groups, the negative control group,the control group,experimental groups of 21 groups, each group 3 randomly by using random number table according to the Weights。2,The following experimental treatments were done on rats in each group: rats in the control group were not given injections for any drugs, and then 3 rats were sacrificed on the day: 0 ,7, 10, 14, 17, 21, 25; The negative control group were given injections for normal saline 5ml/Kg subcutaneously every other day after removal of the device and 3 rats were killed on the day: 0 ,7, 10, 14, 17, 21, 25. the experimental group were given injections for PTH (1-34) 5ml/Kg(PTH:1ug/ml) subcutaneously every other day; 3 rats were killed on the day: 0 ,7, 10, 14, 17, 21, 25. Remove all the above organizations, including the integrity of all molars and alveolar bone tissue; 3,Under sterile conditions organizations were in fixation, dehydrated, embedded in paraffin, sagittal serial sections, slice thickness3-5um ,for the purpose of detect of the root resorption areas. HE staining ,select complete sections which includes the first molar and periodontal tissue for HE staining ; Select the central root and distal root of the first molar and their compression side as the experimental region; After HE staining use Motic Images Advanced 3.2 image analysis software to analyze the relative area of repair cementum; TRAP staining, select as points from root surface and adjacent periodontal tissues of compression side of the roots in high magnification field (×200) for counting TRAP-positive staining osteoclasts, calculating the mean; By OPG and its ligand RANKL immunohistochemistry, select as the points the periodontal tissues of each of the 15 high magnification view (×200) randomly, using Image-pro-plus image analysis system to measure the average optical density value of compression side.4,Statistical analysis: application of statistical software,SPSS13.0, to analyze SPSS13.0 data, continuous data were expressed as means±SEM. Multiple group comparisons were made by one-way ANOVA with Student–Newman–Keuls post hoc analysis. Two groups comparisons were made by Student's test. Statistical significance was accepted at P<0.05. Comparison of the same sample at different times using repeated measures analysis of variance, p<0.05, indicated statistical significance. Results: 1, Model: On the day of discontinuation we observe through HE section, the bone resorption on the surfaces of alveolar bone and tooth root resorption on root compresion side occurred each group; root resorption occurred in the root furcation and root adjacent tip zone, and the absorption lacunae were only confined to the cementum and shallow dentin, and multinucleated osteoclasts were seen in multinucleated osteoclasts. Periodontal fiber were deranged ,and periodontal ligament were narrowed on the compression side of tooth root; Periodontal ligament were widened with periodontal fiber in a row, consecutive inherent alveolar bone and more cellular components on the tension side of tooth root; All of which proved that tooth root resorption model in rats were made successfully.2, Relative repair area of the cementum changes: in any groups ,from the day of discontinuation of force to 7 day did not change, and from 7 day began to increase. Compared with 0-7 days ,17-25 days significantly different (p<0.05); 0-17 days the control group,the negative control group and the experimental group there were no significant differences (p>0.05);but 21-25 days significantly different(p<0.05), the experimental group increased significantly; 3,TRAP staining: on the day of discontinuation of force a large number of positive osteoclasts were visible on the root surface and in the periodontal tissue, with the time past the number of positive osteoclasts gradually decreased,14 days rare positive osteoclasts, 17 days positive osteoclasts were invisible. 0-25 days osteoclasts between every two arrays there were no significant statistic differences (p>0.05);4,OPG immunohistochemistry: 0-25 days in each group, the root and adjacent periodontal tissues showed positive expression; 0-25 days between any two groups: control group, negative control group were no significant statistic differences (p>0.05); the experimental group and control group, the experimental group and the negative control group, 0-17 days there were no significant statistic differences (p>0.05), 21-25 experimental group were significantly higher, there were significant differences(p<0.05).5, RANKL immunohistochemistry: 0-25 days in each group, root surface and adjacent periodontal tissues on compression side showed positive expression. 0-25 days, pairwise comparison between control group and the negative control group there were no significant statistic differences (p>0.05); the experimental group and control group, experimental group and the negative control group, 7-10 days the experimental group significantly increased, there were significant differences (p<0.05); 21-25 days, significant reduction in the experimental group, there were significant differences (p<0.05).6,OPG/RANKL ratio change results: 0-25 days in each group compared itself, the ratio of the group21-25 days compared with the 0-17days the ratio increased significantly, significant statistic differences (p<0.05). 0-25 days, the experimental group and control group, experimental group and the negative control group, 7 days significantly decreased ,but21-25days significantly increased,statistic differences were significant(p<0.05), there were no significant statistic differences in other days(p>0.05).Conclusions:1, Intermittent subcutaneous injection of a small amount of PTH (1-34) can not promote tooth root repair in rats during the early phase.2, Intermittent subcutaneous injection of a small amount of PTH (1-34) can promote tooth root repair in rats during the late phase.