Comparison of root resorption after bone-borne and tooth-borne rapid maxillary expansion evaluated with the use of microtomography Mucahid Yildirim a and Mehmet Akin b Konya and Antalya, Turkey Introduction: Root resorption was compared between bone-borne and tooth tissue–borne rapid maxillary expansion patients with the use of microtomography. Methods: The study included 20 patients (ages 11–16 years) requiring fixed orthodontic treatment who underwent extraction of their first premolars after rapid maxillary expansion with the use of modified appliances. One side of the appliance covered the teeth with acrylic, while the other side was fixed to the palatal bone by means of a miniscrew. After 3 months’ retention, the appliance was removed and teeth were extracted and examined with the use of microtomography. Results: When the apical, middle, and cervical thirds, as well as the buccal and lingual sides, were compared, the volume loss was significantly higher in the tooth tissue–borne group than in the bone-borne group (P \0.01). The least volume loss occurred on the cervical third lingual surface in the tooth tissue–borne group and on the middle third buccal surface in the bone-borne group. In the former group, least resorption occurred on the cervical third and highest resorption on the buccal side. In the latter group, surfaces showed no significant changes. Conclusions: More root resorption occurred in the tooth tissue–borne group, mostly in the apical and middle thirds. The amount of resorption on the buccal surface was higher than that on the lingual surface. (Am J Orthod Dentofacial Orthop 2019;155:182-90) A n abnormal buccolingual relationship between the buccal tubercles of maxillary teeth and those of the mandibular teeth is expressed as posterior crossbite. 1 Rapid maxillary expansion (RME), used in the treatment of posterior crossbite, is a treatment method with important orthopedic and orthodontic effects. In this method, midpalatal suture separation and buccal tipping over the alveolar base in the teeth are observed after the expansion force is applied to the maxilla. Thus, an expansion occurs in the transversal direction in the upper arch and in the basal bone bearing the alveolar base. The orthopedic effect obtained with the separation of the midpalatal suture results from applying a strong force (unilateral 0.9-4.5 kg) over a short period of time. 2 However, because of the heavy forces required to open the midpalatal suture, buccal tipping and gingival recession may occur in the abutment teeth and palatal mucosa, and fenestration in the buccal bone and resorption in the abutment teeth may occur as well. 3 The idea of expanding the maxilla by providing only bone support has been suggested by researchers to minimize such side-effects. 3-5 Tooth root resorption occurring after orthodontic tooth movement is observed as root shortening in the apical re- gions on x-ray images. 6 To date, researchers have exam- ined the root resorption occurring after orthodontic treatment with the use of 2-dimensional radiographic methods, 7 histologic methods, 8 scanning electron micro- scopy (SEM), 9 cone-beam computerized tomography (CBCT), 10,11 and microtomography (micro-CT). 12 It is diffi- cult to acquire accurate results via 2-dimensional examina- tions of 3-dimensional (3D) resorption lacunas, although there are advantages in using this approach, namely, panoramic and periapical radiographs are commonly a Department of Orthodontics, Faculty of Dentistry, Konya Necmettin Erbakan University, Konya, Turkey. b Department of Orthodontics, Faculty of Dentistry, Alanya Alaaddin Keykubat University, Antalya, Turkey. Both authors have completed and submitted the ICMJE Form for Disclosure of Potential Conflicts of Interest, and none were reported. Address correspondence to: M€ ucahid Yildirim, Ortodonti AD, Necmettin Erbakan € Universitesi Dis ¸ Hekimli gi Fak€ ultesi, 42050, Karatay/Konya, Turkey; e-mail, mucahidyildirim@konya.edu.tr. Submitted, September 2017; revised and accepted, March 2018. 0889-5406/$36.00 Ó 2018 by the American Association of Orthodontists. All rights reserved. https://doi.org/10.1016/j.ajodo.2018.03.021 182 ORIGINAL ARTICLE