An In Vivo 3D Micro-CT Evaluation of Tooth Movement After the Application of Different Force Magnitudes in Rat Molar

Abstract

Objective:To investigate the precise longitudinal change in the periodontal ligament (PDL) space width and three-dimensional tooth movement with continuous-force magnitudes in living rats. Materials and Methods: Using nickel-titanium closed-coil springs for 28 days, 10-, 25-, 50-, and 100-g mesial force was applied to the maxillary left first molars. Micro-CT was taken in the same rat at 0, 1, 2, 3, 10, 14, and 28 days. The width of the PDL was measured in the pressure and tension sides from 0 to 3 days. Angular and linear measurements were used to evaluate molar position at day 0, 10, 14, and 28. The finite element model (FEM) was constructed to evaluate the initial stress distribution, molar displacement, and center of rotation of the molar. Results: The initial evaluation of PDL width showed no statistical differences among different force magnitudes. Tooth movement was registered 1 hour after force application and gradually increased with time. From day 10, greater tooth movement was observed when 10 g of force was applied. The FEM showed that the center of rotation in the molar is located in the center of five roots at the apical third of the molar roots. Conclusion: The rat's molar movement mainly consists of mesial tipping, extrusion of distal roots, intrusion of mesial root, palatal inclination, and mesial rotation. Although the initial tooth movement after the application of different force magnitudes until day 3 was not remarkably different, 10 g of force produced more tooth movement compared with heavier forces at day 28. (Angle Orthod. 2009;79:703-714.)

Effects of different types of tooth movement and force magnitudes on the amount of tooth movement and root resorption in rats

“…The center of resistance was determined in the same study as being located near the center of rotation. 19 When a force is applied to the center of resistance, bodily tooth movement will result, as proven by theoretical calculations 20 and clinical experiments. 21 Displacement of the center of resistance may represent the most accurate measure of the amount of tooth movement.…”

“…The center of rotation was theoretically determined in a rat model 19 ; in this study, the crown of the tooth was inclined mesially as a result of tipping tooth movement. The center of resistance was determined in the same study as being located near the center of rotation.…”

Tooth movement and root resorption; The effect of ovariectomy on orthodontic force application in rats

“…These springs were to move the maxillary left first molar mesially as described previously. 9,15 The maxillary right first molars served as the negative controls. After the close-coil springs were set, self-curing resin (Super Bond, Sun Medical, Shiga, Japan) was applied ( Figure 1A-C).…”

“…The linear and angular measurements are used for superimposition techniques to analyze the effect of different orthodontic force directions and magnitudes. 9 For these reasons, micro-CT is a useful threedimensional method that makes it possible to discover the novel information in orthodontics that could not be approached by a conventional radiographic technique.…”

Tooth Movement in Demineralized Area by Etchant in Rabbits

“…In the case of rats, the rotation center of the first molar also exists right at the root side of the root furcation and close to the mesial root 31) . The rotation center is located close to the alveolar crest due to resistance of cortical bone at the cervical region so an area limited to the rooth of first molar and frontal alveolar crest where tooth moved was demineralized in this study.…”