Alveolar Bone Remodeling In Response to Orthodontic Tooth Movement

Objective: Dental protrusion and retrusion are common malocclusions in clinical orthodontics. When teeth are moved orthodontically, the alveolar bone surrounding the teeth remodels. In the past, incisor retraction-associated alveolar bone remodeling has been studied. However, less is known about the alveolar bone remodeling after incisors are proclined. This study aimed to assess the changes in alveolar bone thickness after proclination of maxillary incisors. The null hypothesis was that there is no difference in the surrounding alveolar bone thickness after orthodontic tooth movement. Materials and Methods: Patients were selected under the inclusion criteria of moderate-to-severe bimaxillary dental retrusion (U1-SN < 97°, L1-MP < 88.0°), absence of craniofacial anomalies, non-extraction, absence of missing teeth, with quality pre-and post-treatment lateral cephalometric images. Nineteen patients (10 males, 9 females; mean age 14.7 years) were selected, and their pre-treatment and post-treatment lateral cephalograms were digitally traced using a customized cephalometric analysis to compare changes in labial and lingual alveolar bone thickness (ABT) after orthodontic treatment. A two-sample t-test with R statistical software version 4.1.2 was used to measure the differences between the pre- and post-treatment cephalometric measurements. A p value less than 0.05 was considered statistically significant. Results: According to the SN-7° measurement method, ABT increased at the labial(b) SN-7 (0.27mm ± 0.70; p<0.05) and U1 labial(c) SN-7 (0.79mm ± 1.56; p<0.05) levels; however, ABT decreased at the U1 lingual (c) SN-7 (1.13mm ± 1.35; p<0.05) level. According to the perpendicular of the long axis of U1 root measurement method, ABT increased at the U1 labial(c) ⊥U1 (0.55mm ± 1.35; p<0.05) level while ABT decreased at the U1 lingual (b) ⊥U1 (0.79mm ± 1.03; p<0.05) and U1 lingual (c) ⊥U1 (1.61mm ±1.39; p<0.05) levels. Statistically significant changes were also found in post-treatment incisor angulation U1-SN° (8.05° ± 8.25; p<0.05), U1 – NA° (7.44° ± 8.08; p < 0.05) and post-treatment incisor position U1 – NA (mm) (1.64mm ± 2.63; p<0.05). Conclusion:The null hypothesis was rejected based on our results. There are statistically significant changes to the labial and lingual alveolar bone (ABT) after proclination of the maxillary incisors. Our data support previous findings in orthodontics literature. Further studies should be conducted that can employ larger sample sizes with imaging methods that overcome the limitations of conventional two-dimensional imaging.