Microanatomical responses of the periodontal complex to calibrated mechanical forces

Objectives: The objective of this study was to quantify 2D/3D movement when orthodontic tooth movement (OTM) was induced in mice.
Methods: Silicone elastic bands with a stiffness of 3 N/mm were placed between the 1^st and 2^nd maxillary molars of mice at age of 6-week. For OTM group, the band was placed only at one side leaving the contralateral side as a “control”. After 7 days, the mice were sacrificed and the maxillae was dissected and processed for X-ray tomograms using a micro CT (http://bbct.ucsf.edu). For RELAPSE group, bands were placed on both sides. After 7 days, one band was removed whereas the contralateral side was untouched and served as a “control”. After an additional 7 days, the mice were sacrificed and processed.
Results: The displacements of the molars were evaluated by registering “control” and “experimental” tomograms from respective groups. Their 3D distributions were also mapped on the surface of respective “experimental” side. A difference of ~150µm between “experimental” and “control” sides from respective groups was also calculated in a 2D field and plotted as a function of normalized tooth height using custom-built code.
Conclusions: From fundamental science and engineering perspectives, deformation gradients were observed, and on average only ~150 µm of total tooth movement retained while orthodontic tooth gap of ~600 µm between 1^st and 2^nd molars occurred. Data analysis also suggested that the largest changes were associated with the root of a tooth. Analysis through high resolution microscopy for matrix molecules leading to mineral formation and resorption are necessary and will be discussed to elucidate the cause and effect relationship due to local strains.