Changes of Alveolar Bone Layers due to Orthodontic Treatment

Objectives: Orthodontic tooth movement results from active processes of bone modeling and remodeling of the alveolar bone surrounding the teeth. As such, the structure and bone mineral density (BMD) of the alveolar bone may change during orthodontic treatment. Therefore, the objective of this study was to investigate how the volume and BMD of the alveolar bone layers changes due to orthodontic treatment.
Methods: Following IRB approval, clinical cone-beam computed tomography (CBCT) images were obtained from 40 patients (12 male, 14 ± 2.5 years old and 28 female, 15 ± 4.5 years old) who had completed orthodontic treatment (treatment duration ranged from 9 to 24 months). Three voxel layers of alveolar bone surrounding the left and right maxillary first molars were digitally isolated before and after orthodontic treatment using ITK-SNAP imaging software. A gray value proportional to BMD was obtained for each voxel. A mean gray value and volume, computed by multiplying bone voxel counts by voxel size, were obtained. A paired t-test was performed to compare the volume and mean gray value before and after orthodontic treatment. Significance was set at p<0.05.
Results: The mean gray value of the layer closest to teeth significantly increased after orthodontic treatment (p<0.001), while its volume remained unchanged (p=0.54). Those of the two outermost layers significantly increased after orthodontic treatment (p<0.04).
Conclusions: The current findings suggest that the strong cortical lamina dura layer immediately surrounding the teeth maintains its structure during orthodontic treatment.