Experimental tooth movement under light orthodontic forces: rates of tooth movement and changes of the periodontium

Abstract

Aim: To investigate light forces for experimental tooth movement.

Method: Light orthodontic forces of 1.2, 3.6, 6.5, and 10 g force (gf) were applied for 14 days to move rat molars, and the effects of the forces on the rate of tooth movement and changes of the periodontium were examined.

Results: In the early period, despite the different levels of force used in each group, there were no significant differences in tooth displacement. From hour 56 to day 14, the tooth displacement in the 1.2 gf group was significantly smaller than that in the other groups and the rate was nearly constant. The rates of tooth displacement in the 3.6, 6.5, and 10 gf groups fluctuated repeatedly, while the orthodontic forces gradually decreased.

Conclusion: Experimental tooth movement in rats, tipping without friction under light forces, were either constant or fluctuated in cycles of several days' duration. This is in contradiction to the three-phases-theory of tooth movement described in previous investigations using heavy forces.

Keywords:

• Experimental tooth movement
• light orthodontic force
• rate of tooth movement
• titanium-nickel alloy wire

Acknowledgments

We wish to acknowledge the helpful advice of Professor Yasumasa Baba (Institute of Statistical Mathematics, Japan) and Professor Junichiro Iida (Department of Oral Functional Science, Graduate School of Dental Medicine, Hokkaido University, Japan). This work was supported by Grants-in-Aid for Scientific Research (12671988, 12771271) from the Ministry of Education, Culture, Sports, Science and Technology in Japan.