Objective: To investigate the remodeling of alveolar bone and the changes of roots after anterior retraction with maximum anchorage by analyzing CBCT data from adult cases.
Methods: The sample comprised 48 incisors and 24 canines from 12 patients (18 to 40 years of age) with problems of maxillary protrusion or upper arch protrusion. CBCT scans were exposed before and after treatment, and lateral cephalometric images as well as multiple planar reconstruction images were reconstructed. Tracing superimpositions of sagittal sections and three-dimensional reconstructions were done for qualitative analysis. For all maxillary anterior teeth, changes of root length, alveolar bone height and labial-palatal thicknesses at different levels were evaluated. The average of measurements taken by the same tester in three times was processed by SPSS 17.0 statistical package.
Results: In 6 of the 12 cases, alveolar thickness became thinner on labial side [apical area: (-0.64±1.18) mm] while thicker on palatal side [apical area: (0.93±2.0) mm] and the root length decreased[(-0.95±0.79) mm]. In the other 6 cases, the incisors' alveolar bone became thicker on labial side [apical area: (2.12±1.46) mm] while thinner on palatal side [apical area: (-2.88±0.58) mm]and the loss of root length was obvious[(-2.12±1.43) mm]. In all the 12 cases, the canines' alveolar bone became thinner on labial side especially on the apical level[(-0.27±1.86) mm] while greatly thicker on palatal side [apical area: (6.40±6.00) mm]and the root resorption was slight [(-1.12±1.19) mm]. For all the anterior teeth, the height of alveolar bone reduced around them after retraction.
Conclusion: When the root apical moved more palatally, more root resorption would occur and the alveolar bone would get thicker on labial side but thinner on palatal side and thinner as a whole after anterior retraction with maximum anchorage.In the vertical direction, the height of the alveolar bone generally decreased on all sides and decreased the most on the palatal side.