The European Journal of Orthodontics Advance Access originally published online on March 26, 2008
The European Journal of Orthodontics 2008 30(3):320-326; doi:10.1093/ejo/cjm133
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Time-lapse observation of rat periodontal ligament during function and tooth movement, using microcomputed tomography
* Department of Orthodontics, Tsurumi University School of Dental Medicine, Yokohama
** Department of Oral Anatomy, Tsurumi University School of Dental Medicine, Yokohama
*** Department of Oral Health, National Institute of Public Health, Wako-city, Japan
Address for correspondence Yoshiki Nakamura, Department of Orthodontics, Tsurumi University, 2-1-3, Tsurumi, Tsurumi-ku, Yokohama 230-8501, Japan, E-mail: nakamura-ys{at}tsurumi-u.ac.jp
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Abstract |
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The aim of this study was to observe the time-lapse changes in the rat periodontal ligament (PDL) during function and tooth movement. Under Nembutal anaesthesia, time-lapse changes in the thickness of the PDL of the first molars were investigated in five 12-week-old adolescent rats with microcomputed tomography. Three-dimensional (3D) images were reconstructed from the data. Histological observation was also performed, using undecalcified frozen sections of the maxillary first molar area.
The PDL appeared as a radiolucent furrow on the 3D images. A slight change in the thickness of the PDL was observed 1 hour after initiation of orthodontic force loading, which became significant after 6 hours, with the appearance of pressure–tension zones during the tooth movement. These changes were more significant 3 days after orthodontic loading.
Histological observation of the lingual cervical PDL (pressure zone) in nine 12- to 13-week-old rats demonstrated that the periodontal space had become narrow and the cellular elements appeared to be densely packed in the narrowed PDL 6 hours after orthodontic loading. Degeneration of tissues appeared 3 days after loading. Observation of the buccal cervical PDL (tension zone) demonstrated that the PDL was extended 6 hours after orthodontic force loading, and the extension continued for up to 3 days. Alkaline phosphatase activity was distributed in the PDL, except for the degenerating tissues in the pressure zone 3 days after loading.
The results suggest that the periodontal reaction was initiated within 6 hours after orthodontic force loading, which was related to the structural changes of the PDL. The changes probably induced an early response in individual cells of the PDL.