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The European Journal of Orthodontics Advance Access originally published online on December 10, 2008
The European Journal of Orthodontics 2009 31(1):37-45; doi:10.1093/ejo/cjn075
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© The Author 2008. Published by Oxford University Press on behalf of the European Orthodontic Society. All rights reserved. For permissions, please email: journals.permissions@oxfordjournals.org.

Morphological changes in the rat periodontal ligament and its vascularity after experimental tooth movement using superelastic forces

Koji Noda*, Yoshiki Nakamura*, Kyotaro Kogure* and Yoshiaki Nomura**

* Department of Orthodontics, School of Dental Medicine, Tsurumi University, Tsurumi, Yokohama
** Department of Oral Health, National Institute of Public Health, Wako-shi, Saitama, Japan

Address for correspondence Dr Koji Noda, 2-1-3, Tsurumi, Tsurumi-ku, Yokohama, Kanagawa 230-8501, Japan, E-mail: noda-k{at}tsurumi-u.ac.jp


  Abstract

The aim of this study was to statistically assess the morphological changes of the rat periodontal ligament (PDL) and its vascularity in relation to varied magnitudes of superelastic force in experimental tooth movement using nickel–titanium (NiTi) alloy wire. Forces of 0.8, 1.6, 4, 8, and 18 g were applied to the upper first molars of five groups of 10-week-old male Wistar rats (300–320 g) for 1, 7, 14, 21, and 28 days. A control group with no orthodontic appliance application was assessed in accordance with the five experimental periods. The specimens were observed under light microscopy, processed by computer imaging, and analysed statistically with Tukey's HSD non-parametric test.

One day after the start of the experiment, a few blood vessels could be seen in the compressed PDL with forces of 0.8 and 1.6 g. The cross-sectional areas of blood vessels (CAV) and periodontal ligament (CAPL) in the experimental groups where a force of over 4 g was applied were significantly smaller than those where 0.8 and 1.6 g forces were used, and in the control group. On day 7, large CAV were seen in the 1.6, 4, and 8 g groups. On day 28, the 8 and 18 g groups showed significantly larger CAPL than the 0.8, 4 g, or control groups.

The findings suggest that a light continuous force, under 1.6 g, maintains the vascular structure during experimental tooth movement. In contrast, a heavy continuous force over 4 g causes the vascular structure to be absent in the early stages of tooth movement, but a dynamic regeneration of the PDL with vascularity and expansion follows.


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