Implementation of an Analytical Model for Orthodontic Tooth Movement and Periradicular Bone Morphometry in Mice

Objectives: Basic research in orthodontics is commonly done in rats, which precludes the use of transgenic-models available in mice. Studies on orthodontic-tooth-movement (OTM) in mice are lacking a standard method to examine OTM and periodontal changes. The gold-standard in bone-morphometry is microcomputed-tomography (µCT); however its use in orthodontic research is still limited. We aimed to implement a unifying protocol for OTM analysis and associated bone microarchitectural changes in mice.
Methods: Twenty-nine C57BL/6 12-weeks-old male mice were divided into 3 groups: untreated-WT (n=10), WT-OTM (n=10) and TNFα^-/--OTM (n=9) in which Ni-Ti closed-coil springs pulled the upper-left-first-molar (ULM1) towards the upper-incisors for 12 days. The maxillae were scanned using µCT. The amount of mesial-displacement of ULM1 was measured by 5 different methods based on dental or skeletal landmarks. The upper-right-first-molar (URM1) served as control.
We developed an algorithm to define standardized regions-of-interest (ROIs) in both the pressure and tension sides of ULM1 and URM1 and calculated a series of 3D morphometric parameters.
Results: Among the 5 different methods to assess OTM, the ULM1-ULM2 diasthema-measurement showed the lowest standard-deviation in all experimental groups (0.0±0.0 µm; 252.1±72.3 µm and 61.4 ±36.3 µm; respectively). Our new algorithm defined reproducible ROIs with minimal operator bias. Using this method, we found statistically-significant differences for all selected morphometric parameters between the OTM and control sides (p<0.05) in the two OTM groups (in both tension and pressure sides) with no differences between OTM and control sides in the untreated group. Moreover, significant correlation was found between these parameters and the amount of OTM.

Conclusions: We found that ULM1-ULM2 diasthema-measurement, based on μCT, was the most reliable method for OTM-measurement. Furthermore, our algorithm was able to detect significant morphometric differences associated with distinct OTM rates. We therefore propose this protocol as a standardized-method for OTM analyses in mice.