Rate of Orthodontic Tooth Movement (OTM) in a Rodent Model Using Light Forces

Objectives: Animal models have been extensively used to understand the biological mechanisms of OTM. Typical force used for OTM range from 10- 100gm. Lower forces are probably more appropriate in a rodent model due to the size of animal and it is possible that the histologic response will vary with the strain transmitted to the surrounding structures. The objective of this study was to determine the rate of tooth movement using light forces.
Methods: All protocols had IACUC approval. 54 Sprague-Dawley rats were divided in to 3 groups (3 days, 7 days and 14 days). A mixture of ketamine and xylazine were used for anesthesia. 18 rats in each group (12 experimental and 6 sham) were subjected to orthodontic force using a ~3cN custom-fabricated and calibrated coil spring anchored to a miniscrew placed disto-lateral to maxillary incisor laterally and to maxillary first molar. Sham group received mini-implant and spring delivering 0cN load. Immediately after sacrifice, maxilla was dissected and fixed in formalin and then scanned (mCT 40, Scanco, Switzerland). High resolution images were imported into Dolphin Imaging and smallest distance between the first and second molar crowns were measured. ANOVA with Bonferroni correction were conducted for data analysis.
Results: Three animals died prior to end of experiment in the 3 day group. The mean (±SD) amount of tooth movement (mm) over the duration of the 3d, 7d and 14d as follows: 0.1 (±0.04), 0.17 (±0.08), 0.21 (±0.13). 3d was significantly different (p<0.05) for 14d in the amount of tooth movement. The amount of tooth movement is lower than those reported in other studies in which higher forces were used but greater than studies where incisor was used as anchor.
Conclusions: Validation and description of a rodent model using a skeletal anchor to obtain predictable tooth movement with light (<5cN) forces is important in tooth movement studies and to study mechanobiology in response to force application.