INTRODUCTION: Arch development is a common occurrence in orthodontic treatment to expand dimensions of the dental arch form to accommodate proper alignment of teeth. Less attention has been spent in the literature on the changes within the posterior region and the limitation of movement that exists in this area. The purpose of this study was to assess the consequence of using preformed arch wires for posterior arch development has on the surrounding periodontium during routine orthodontic treatment. MATERIAL AND METHODS: A retrospective CBCT study of 49 adult patients orthodontically treated with fixed appliances resulting in a change of arch. The measurements of interest were made on each CBCT scan at pretreatment (T1) and post treatment (T2) for the maxillary and mandibular first premolars (U/L4), second premolars (U/L5), and mesiobuccal (U/LM6) and (U/LD6) distobuccal roots of first molars. The parameters were: (1) alveolar bone height (ABH), (2) alveolar bone thickness (ABT), (3) transverse width Palatal-Palatal (P-P) cusps, (4) root inclination, and (5) the presence and/or absence of dehiscences/fenestrations. RESULTS: The percentage of fenestrations and dehiscences in the maxilla at T1 was 50.8% and it increased by 11.3% at T2, while in the mandible at T1 it was 66.6% and it increased by 10.3% at T2. The transverse width change was significant post-treatment. Post-nonextraction orthodontic treatment where posterior dental arch forms were expanded, there is a higher tendency to: (1) increase ABH (bone loss), (2) thinning of ABT and (3) expansion was mostly achieved by tipping rather than bodily movement. CONCLUSIONS: The results indicate that the routine practice of orthodontic arch development results in significant alterations in the dimensions of the alveolar bone. On average, all posterior teeth experienced bone loss in both the vertical and horizontal dimensions following orthodontic treatment. It is therefore strongly recommended that prior to initiating treatment of adult patients requiring uprighting posterior teeth and/or dental expansion, adjunctive treatment modalities, including orthognathic surgery, skeletal expansion and periodontal bone augmentation, be considered to prevent such dimensional changes.