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[Assessment of cell proliferation during distraction osteogenesis of peridental ligament in rats].

PURPOSE
To establish an animal model of orthodontic rapid tooth movement through distraction osteogenesis of the periodontal ligament and assess the cell proliferation including osteoblasts, osteoclasts and bone cells.


METHODS
Forty rats were randomly divided into experimental and orthodontic control group, and received BrdU injection at the beginning of distraction intraperiotoneally. Traditional orthodontic model was established in the control group. In the experimental group, after some parts of mesial alveolar bone of the upper right second molar grinded, self-made distraction device was installed between the second molar and central incisors, the distraction frequency was 1mm/2d , and after one week , there would be a consolidation phase. Four animals in each group were randomly selected to be sacrificed at 5 time points. After obtaining specimens, immunohistochemical examination was done. Then BrdU labeled cells were observed in the regenerated tissue specimens and the positive cells were counted and analyzed with paired-samples t test by SPSS 16.0 software package.


RESULTS
BrdU positive cells were found in both tension and pressure sides, mainly bone cells, osteoblasts, osteoclasts and fibroblasts. BrdU-positive fibroblasts and osteoblasts reached a peak at day 10, and the expression at day 5 and 10 in the experimental group was higher than in the orthodontic treatment group. Osteoclasts reached a peak at day 20, but in the orthodontic treatment group it reached a peak at day 5. The number of positive bone cells was gradually rising over time, but the expression in the orthodontic treatment group was lower than that in the experimental group at day 20 and 30.


CONCLUSIONS
Intramembranous ossification is the main pattern during periodontal ligament distraction osteogenesis; Active bone remodeling occurs at the early and middle consolidation, new bone formation is ongoing, and osteoclast activity is more active. BrdU positive cells are able to survive throughout the entire experimental period of 30 days.