Effects of gradually increasing force generated by permanent rare earth magnets for orthodontic tooth movement.
OBJECTIVE
To examine the effects of gradually increasing force generated by permanent rare earth magnets for orthodontic tooth movement by using a novel experimental rat model and computer simulation.


METHODS
Fifty-five male rats (age 18 weeks) were used as animal experiments. Magnetic (experimental groups) or titanium (control group) cuboids (1.5 x 1.5 x 0.7 mm) were bonded to the lingual surface of the maxillary first molars. The initial distance between materials was 1.0 mm, generating 4.96 gf (experimental group I), or 1.5 mm, generating 2.26 gf (experimental group II). Tooth movement was measured and periodontal structures were observed with microfocus x-ray computed tomography radiographs.


RESULTS
The distance between the magnets decreased with time in experimental groups I and II (P < .001), whereas there was no tooth displacement in the control group. Experimental group I showed rapid tooth movement in the initial phase followed by slower tooth movement. Experimental group II showed gradual tooth movement. Horizontal sections on microfocus computed tomgraphy radiographs revealed no pathological changes, such as root resorption, on the compressed side in the experimental groups.


CONCLUSIONS
The initial light force and gradual increasing force in magnetic attractive force induced effective tooth movement in rats without inducing any pathological changes.
Tomizuka
Ryo
R
Division of Orthodontics and Dentofacial Orthopedics, Tohoku University Graduate School of Dentistry, Sendai, Japan. ryotommy@mail.tains.tohoku.ac.jp
Kanetaka
Hiroyasu
H
Shimizu
Yoshinaka
Y
Suzuki
Akihiro
A
Igarashi
Kaoru
K
Mitani
Hideo
H
D000704:Analysis of Variance; D000818:Animals; D003198:Computer Simulation; D003799:Dental Stress Analysis; D008280:Magnetics / Q000295:instrumentation*; D008297:Male; D008674:Metals, Rare Earth; D009967:Orthodontic Appliances; D051381:Rats; D017208:Rats, Wistar; D014087:Tooth Movement Techniques / Q000295:instrumentation*
D008674:Metals, Rare Earth