How teeth moved and alveolar bone changed after mandibular incisor retraction with intrusion: A retrospective cephalometric and CBCT study

Purpose To investigate the changes of mandibular incisors in position and alveolar bone thickness and height after retraction with intrusion in adults.Materials and Methods Cephalometric radiograph tracings were evaluated before and after retraction and divided into two groups: pure retraction (PR) and retraction with intrusion (RI). Distances of tooth movements and alveolar bone changes were recorded in cephalograms. Tooth movements in anteroposterior and vertical directions were measured at the incisal edge (IE) and root apex(AXE). Changes of labial bone thickness (LaBT), lingual bone thickness (LiBT) and bone height (BH) were assessed at crestal (S1), mid-root (S2), and apical (S3) levels from 86 Cephalograms (46PR/40RI) and 33 CBCT (17PR/16RI). T-tests were applied for cephalometric group (Ceph-M) and non-parametric tests for CBCT groups (CBCT-M).Results Retraction distances at IE were not different between PR and RI but significant intrusion was observed in RI. Amount of retraction and intrusion at AXE was greater in RI. In PR, LaBT was maintained at S1 and S2 in Ceph-M but only S2 in CBCT-M, whereas S3 exhibited significant bone gain. In RI, LaBT was maintained at S1 in Ceph-M but at S2 in CBCT-M, significant bone gain occurred at S2 and S3 in Ceph-M but at only S3 in CBCT-M. LiBT in both groups showed significant bone thinning at all three levels. LaBH and LiBH in both groups exhibited BH loss. RI showed significantly greater bone gain in LaBT at S3.Conclusions RI provided more lingual and apical movement at AXE with comparable labial and lingual bone response to PR with more apical labial bone gain in RI.