Objectives: To test the null hypothesis that there is no difference in bone dehiscence formation before and after orthodontic tooth movement through an atrophic alveolar ridge. Material and Methods: This longitudinal retrospective study evaluated pretreatment and posttreatment cone-beam computed tomography imaging of 15 adult patients. Twenty-five teeth were moved through the atrophic alveolar bone, whereas 25 teeth not subjected to translational movement were considered controls. The distances between the cementoenamel junction and the alveolar bone crest were assessed at the mesial, distal, buccal, and lingual surfaces of all of these teeth. Data were compared using the Wilcoxon test. The Spearman correlation test and multivariate linear regression analysis were also performed. Results: In general, crestal bone height was reduced around 0.5 mm in all groups in every direction. Median buccal dehiscence increased significantly (þ2.25 mm) (P , .05) in teeth moved through the atrophic ridge. Control teeth also had buccal crest loss (þ0.83 mm), but this was not statistically different from that of the experimental teeth. Lingual dehiscence increased significantly for the experimental (þ0.17 mm) and control (þ0.65 mm) groups. Mesial bone height decreased more in the control group (-0.44mm) than in the experimental group (-0.14mm). There was moderate correlation between amount of tooth movement and alveolar bone loss. Conclusions: The null hypothesis was rejected as dehiscence increased after tooth movement through an atrophic alveolar ridge, mainly in the buccal plate. (Angle Orthod. 2020;90:321-329.) KEY WORDS: Alveolar bone loss; Cone-beam computed tomography a Associate Professor,

Objectives The objectives were to evaluate and compare the presence of bone dehiscence before and after orthognathic surgery. Materials and Methods In this retrospective study, 90 cone-beam computed tomography (CBCT) scans from 45 patients were evaluated. Class II (n = 23) and Class III (n = 22) orthodontic patients who were being prepared for orthognathic surgery were measured. CBCT scans were obtained about 30 days prior to (T0) and 6 months after (T1) double jaw orthognathic surgery. The distance between the cemento-enamel junction (CEJ) and the alveolar bone crest was assessed at the buccal and lingual surfaces of all teeth, on both sides and arches, except for the second premolars and the second and third molars. A total of 1332 sites were measured for Class II (644) and Class III (688) patients. The software used was OsiriX (version 3.3 32-bit). Data were compared with Wilcoxon and McNemar tests at the 5% level. Results Bone dehiscence before surgery was present in 26% and 15% of the Class II and III groups, respectively. The presence of dehiscence increased to 31% in the Class II and 20% in the Class III patients after surgery (P < .05). Conclusions The prevalence of dehiscence increased slightly in Class II and Class III surgical-orthodontic patients after orthognathic surgery. Temporary vascular supply reduction and oral hygiene difficulties may explain these results; however, more studies are needed.