Horizontal impact of extensive incisor retraction on alveolar bone

To explore the horizontal impact of extensive incisor retraction on alveolar bone and to investigate the relationship of changes in alveolar bone thickness (ΔBT) with horizontal retraction distance of the incisal edge (HRD) and horizontal retraction distance of alveolar ridge crest (HRD') in orthodontic treatment.

This retrospective study included 84 patients who underwent orthodontic extraction treatment, involving extensive incisor retraction (≥ 3 mm). Pre-treatment (T0) and post-treatment (T1) cone-beam computed tomography (CBCT) data were collected. The samples were divided into adult (> 18 years) and adolescent (≤ 18 years) groups. Changes in the horizontal alveolar bone thickness in the incisor region, as well as changes in HRD and HRD', were measured at T0 and T1. Data were statistically analyzed using SPSS 27.0, utilizing paired and independent samples t-tests.

After extensive retraction, both upper and lower central incisors exhibited increased buccal alveolar bone thickness, while lingual and total alveolar bone thicknesses decreased. The horizontal plane near the root apice exhibited overall thickening of the alveolar bone. The tooth roots consistently remained upright within the alveolar bone, maintaining a stable relative position. The magnitude of ΔBT was smaller compared to the changes in HRD and HRD'.

Alveolar bone thickness decreased during extensive retraction, especially near the alveolar crest, with less noticeable variations closer to the tooth root apices. The stable positioning of incisors within the alveolar bone indicates that the alveolar bone changes were primarily morphological, and suggests that partial tooth movement resulted from bone deformation. (Registration Number: ChiCTR2000034288; Approval Date: 01/07/2020).