Three-dimensional evaluation of surgically assisted asymmetric rapid maxillary expansion G€ ulden Karabiber, a,b Hanife Nuray Yılmaz, a S ¸ irin Nevzato glu, a,c Faysal U gurlu, a and Tuna Akdo gan a,d Istanbul, Turkey Introduction: Unilateral posterior crossbite is classified as true unilateral posterior crossbite (TUPC) or func- tional posterior crossbite (FPC). The differential diagnosis between TUPC and FPC is of utmost importance for the decision of expansion protocol because conventional expansion methods have some shortcomings for TUPC. The aim of this retrospective study was to 3-dimensionally evaluate the effects of asymmetric rapid maxillary expansion combined with unilateral osteotomy. Methods: This study sample comprised 16 patients (mean age 18.38 6 1.45) with TUPC. A Hyrax acrylic cap included the maxillary premolars and molars on the constricted side, and all teeth up to the central incisor were included on the other side to increase anchorage. Unilateral surgically assisted rapid maxillary expansion was performed and included anterior (aperture pirifor- mis), lateral (zygomatic buttress), and posterior (pterygomaxillary junction) osteotomies on the constricted side and separation of the midpalatal suture. Cone-beam computed tomographic scans taken just before the operation and after 6 months of retention were used to assess skeletal, dental, and periodontal changes. Results: Expansion was seen on both sides; however, the amount of expansion and tipping was higher on the osteotomy1 side. Because the canines were not included in the acrylic cap on the osteotomy1 side, they did not present the same amount of tipping as the ipsilateral posterior teeth. More teeth were affected periodon- tally on the osteotomy side; however, there were no clinically significant differences between the osteotomy1 and osteotomy sides (mean differences range 10.54 to 0.57 mm). The aperture piriformis width increased significantly on the osteotomy1 side. Conclusions: The treatment mechanics had no clinically detrimental effects on the supporting alveolar bone of the maxilla on either side, and it was thought to be effective in cases with TUPC; however, case selection is crucial. (Am J Orthod Dentofacial Orthop 2019;155:620-31) P osterior crossbite is a prevalent malocclusion that occurs in the presence of maxillary transverse deficiency. Its etiology is multifactorial. Etiologic factors include nasal airway obstructions (enlarged ton- sils and adenoids), 1 long-term pressure on the palatal area (sucking habits), 2 abnormal swallowing habits, 3 occlusal interferences that lead to a mandibular shift, cleft lip and palate, malformations in the head and neck area, juvenile rheumatoid arthritis, unilateral condylar abnormalities, long-term use of a pacifier, a decrease in muscular tonus, and mouth breathing. 4 Posterior crossbite can be classified as skeletal, dental, or functional. It can also be either unilateral or bilateral. 5 Unilateral posterior crossbite can be divided into 2 groups as true unilateral posterior crossbite (TUPC) and functional posterior crossbite (FPC), 6 which have different characteristics and treatment modal- ities. 6,7 From 67% to 79% of unilateral posterior crossbites are functional, and they occur as a result of bilateral maxillary constriction and occlusal interferences, which lead the mandible to shift for maximum intercuspidation. 8-10 During intercuspidation, upper and lower midlines do not coincide, whereas with the open-mouth position upper and lower midline coincidence is observed. 8,11 Bilateral maxillary expansion is recommended for the treatment. Untreated FPC may morphologically change into TUPC a Department of Orthodontics, Marmara University Faculty of Dentistry, Istanbul, Turkey. b Currently: Department of Orthodontics, Medeniyet University Faculty of Dentistry, Istanbul, Turkey. c Faculty of Dentistry, Beykent University, Istanbul, Turkey. d Faculty of Dentistry, Okan University, Istanbul, Turkey. All authors have completed and submitted the ICMJE Form for Disclosure of Potential Conflicts of Interest, and none were reported. Previous presentation: Oral presentation at XVth International Congress of the Turkish Orthodontic Society, October 1-5, 2016, Antalya, Turkey. Address correspondence to: G€ ulden Karabiber, Fahrettin Kerim Gokay Cad. Hos- goru Sok. Orhon Ap., No: 17/3, Postal code: 34732, Kadık€ oy, Istanbul, Turkiye; e-mail, guldenkarabiber@hotmail.com. Submitted, June 2017; revised and accepted, May 2018. 0889-5406/$36.00 Ó 2019 by the American Association of Orthodontists. All rights reserved. https://doi.org/10.1016/j.ajodo.2018.05.024 620 ORIGINAL ARTICLE