| Background and Objective: The speed of the world's population aging was faster than expected. At present, the elderly accounted for 10% of the world's population, and the growth of the world's aging population was 2% higher than that of the world's total population. It was estimated that by 2050 there was one aged over 60 years old in five people, and it was the first time in human history that the population of the elderly would be more than that of people aged below 14. The periodontal disease, was one of the main diseases inducing tooth missing, whose prevalence significantly increased after 35 years old. With the growth of age, it became more and more severe. More than 75% adult patients over the age of 40 in the search for orthodontic treatments had periodontal disease. In recent years, more and more elderly patients with periodontitis or not request orthodontic movement. The purpose of this study was to discuss the difference in the orthodontic tooth movement between the young and the aged, and the difference in the reaction to the orthodontic force between the periodontas healthy and peridontitis affect rats,thus provided experimental support for orthodontic treatment in the elderly.Methods: Twenty 7-week SD rats were included in group A. And forty 12-month SD rats were randomly divided into two groups: normal group (group B) and periodontitis model group (group C). The orthodontic tooth movement of the first molars were performed using maxillary incisors as anchorage. Five rats were sacrificed randomly at 3, 7, 14, 21 d after applying orthodontic force. The width of the PDL on the pressure side was measured and the X-ray film was saved. The changes of the periodontal ligament width were measured with histological observation through HE and Masson staining. The number of osteoblasts and osteoclasts on both sides was sumed. The results were analyzed by SPSS13.0 software package, using t- test, Mann-Whitney rank sum test and nonparametric test's rank sum test if indicated. A P value <0.05 was considered to indicate statistical significance.Results1. Compare group B with group Aâ‘ The distance of tooth movement: at 3d,1w,2w,3w after applying orthodontic force, there was significant difference between group A and group B in every time period.â‘¡Histological observation: Compared with young rats, the bone density of elderly rats was lower than normal. Bone marrow cavity turned to be smaller, the bone wall was covered with osteoclasts, periodontal ligament became narrower, and fibroblasts in periodontal ligament were rare and disordered.â‘¢The periodontal ligament width: Group B in each time period were significant narrower than that in Group A(P<0.05).â‘£Osteoblasts and osteoclasts: Two groups showed clear signs of stress and tension zone area. At 1w after applying orthodontic force, the osteoclasts on the pressure side of group B were significant less than that in group A(P<0.01).At 3w, the osteoblasts on the tension side of group B were significant less than that of group A(P<0.05).2. Compare group C with group Bâ‘ The distance of tooth movement: at 3d,1w,2w,3w after applying orthodontic force, there was significant difference between group B and group C in every time period except 3d.. â‘¡Histological observation: Two groups had the same characteristics: the width of the periodontal ligament on the pressure side became narrow with the osteoclasts appearing;the periodontal ligament on the tension side became wider with more osteoblasts.â‘¢The periodontal ligament width: At 1w after applying force, the periodontal ligament width in group B was wider than that in group C(P<0.05).â‘£Osteoblasts and osteoclasts: At 2w after applying orthodontic force, the osteoclasts on the both sides of group B were significant less than that in group C(P<0.01).At 3w, the osteoclasts on the tension side of group B were significant less than that of group C(P<0.05).Conclusion:1. Elderly rats'teeth could be moved like the young rats',but the speed of movement and the reaction of the periodontal ligament ,osteoblasts and osteoclasts were different from the young rats,thus orthodontic force application should be paid more attention to the periodontal tissue.2. Teeth with periodontitis in elderly rats moved faster than the health teeth,but the reaction of the tissue (the changes in the width of the periodontal ligament, and the number of osteoblasts and osteoclasts) showed no significant difference between two groups. It suggested that the teeth with periodontitis in elderly adults could be done with the clinical orthodontic treatment after carrying out periodontal treatment.
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