Micro-anatomical responses in periodontal complexes of mice to calibrated orthodontic forces on the crown.

OBJECTIVE: Correlating mechanical forces with quantifiable physical changes in the dentoalveolar complex.

SETTING AND SAMPLE POPULATION: Male 6-week C57BL/6 mice (N=3), micro X-ray-computed tomography; post-analysis software to extract physical changes in periodontal ligament (PDL)-space.

MATERIALS AND METHODS: Silicone-elastic bands were placed between maxillary molars for 1 week, with the contralateral side as internal control. Average displacements between crowns and roots, and changes in PDL-spaces were evaluated by registering X-ray tomograms of experimental and control hemi-maxillae. Histology illustrated mineral formation and resorption-related events within narrowed and widened volumes of the PDL-space.

RESULTS: 3D maps of changes in PDL-space between molars illustrated coronal and root displacements of 640 μm and 180 μm, respectively, compared to 70 μm in controls. Orthodontic tooth movement (OTM) specimens exhibited an average net change of -20 μm in narrowed and +30 μm in widened PDL-spaces. Bone and cementum were affected by the force on molars, and primary cementum was more affected than secondary cementum.

CONCLUSIONS: This novel approach illustrates the importance of 3D-imaging and analysing 3D alveolar socket subjected to OTM otherwise omitted by 2D micrographs. A measured force on the crown elicits a response related to narrowed and widened regions in the 3D complex. OTM that exceeds PDL-space can illicit biological responses that attempt to restore physiologic PDL-space via remodelling of the periodontium. Regenerated weaker bone due to aseptic inflammation caused by orthodontics could leave patients at a higher risk of bone loss or root resorption if they later develop periodontitis, a form of septic inflammation.