Long-term remodeling of anterior alveolar bone from treatment to retention

Bone remodeling in orthodontic treatment has been one of the most concerned issues. The purpose of this study was to characterize the changes in bone remodeling on both labial and lingual aspects of the anterior teeth during treatment and retention. Data of 55 extraction cases (41 females and 14 males) were collected at pretreatment, post-treatment, and follow-up stages. Bone thickness on both labial and lingual aspects of the upper and lower incisors were measured at the level of the center of resistance (UC and LC) and that of 3 mm apical to the upper and lower incisors’ center of resistance (UAC and LAC). For LC, with the significant lingual movement of point LIR (center of resistance of lower incisor; P < 0.001), no statistically significant changes in alveolar width on the labial aspect were detected, whereas the reduction of lingual alveolar width was statistically significant (P < 0.001). In retention, no significant movement of point LIR appeared to occur, while an increase in alveolar width on the lingual aspect was found at this stage. For LAC, the changes in alveolar width as well as the displacement of point LIA (apex of lower incisor) were similar to those of LC. On the maxilla, with the control lingual tipping movement of upper incisor, most of the anterior alveolar changes surrounding the upper incisor were analogous to those of lower incisor. But differently, during treatment, labial bone thickness was increased significantly as the upper incisor moved lingually, and in retention, no statistically significant changes were found on both labial and lingual bone thickness as the upper incisor labially proclined. It was concluded that, with lingual movement of the incisors, bone apposition on the lingual aspect may lag behind the incisor movement. In retention, the lower incisors are in a stable position, with sequential bone apposition being presented on the lingual aspect. However, the upper incisors turn out to be labially relapsed along with the lingual bone resorption and labial bone apposition occurring simultaneously.