Force magnitude and duration effects on amount of tooth movement and root resorption in the rat molar.
OBJECTIVE
To test the hypothesis that there is no difference in the effect of different continuous moderate to very heavy forces on root resorption or amount of tooth movement.


METHODS
In the study, 10, 25, 50 and 100 g mesial force were applied to the maxillary first molars of rat using nickel titanium closed-coil springs for 3 days, 14 days, and 28 days. The molars were extracted and the surface areas of the root resorption craters were measured using scanning electron microscope. The depths of the root resorption craters were measured using a three-dimensional laser scanning microscope. Tooth movement of the maxillary first molar was measured in relation to the maxillary second molar on digitized lateral cephalometric radiographs.


RESULTS
Three days after force application, the tooth movement was not proportionally related to force magnitude. However, 14 days of force application resulted in significantly more tooth movement in the 10, 25, and 50 g force groups than in the 100 g force group. A force application of 10 g produced significantly more tooth movement at 28 days than all the other three force applications. The largest and deepest resorption craters were observed in the disto-buccal root followed by disto-palatal, middle-buccal, middle-palatal, and mesial root. Root resorption and tooth movement increased over time from 3 to 28 days. As heavier forces were applied, greater root resorption occurred.


CONCLUSIONS
The hypothesis is rejected. The light mesially oriented forces, as applied in this study, produced more tooth movement and less root resorption compared with heavier forces.
Gonzales
Carmen
C
Division of Orthodontics and Dentofacial Orthopedics, Nagasaki University Graduate School of Biomedical Sciences, Nagasaki, Japan.
Hotokezaka
Hitoshi
H
Yoshimatsu
Masako
M
Yozgatian
Joseph H
JH
Darendeliler
M Ali
MA
Yoshida
Noriaki
N
D000818:Animals; D002508:Cephalometry / Q000379:methods; D003722:Dental Alloys; D003739:Dental Cementum / Q000473:pathology; D007091:Image Processing, Computer-Assisted / Q000379:methods; D021621:Imaging, Three-Dimensional / Q000379:methods; D008297:Male; D008437:Maxilla; D018613:Microscopy, Confocal / Q000379:methods; D008855:Microscopy, Electron, Scanning; D008963:Molar / Q000473:pathology*; D009532:Nickel; D009969:Orthodontic Wires; D051381:Rats; D017208:Rats, Wistar; D012391:Root Resorption / Q000209:etiology* / Q000473:pathology; D013314:Stress, Mechanical; D013997:Time Factors; D014025:Titanium; D014087:Tooth Movement Techniques / Q000009:adverse effects / Q000379:methods*; D014092:Tooth Root / Q000473:pathology
D003722:Dental Alloys; C040654:titanium nickelide; D009532:Nickel; D014025:Titanium