This retrospective study assessed the CBCT records of 30 adult patients (mean age, 27.5 years; range 18.7–39.7 years; 19 females and 11 males) with maxillary transverse deficiency greater than 5 mm and unilateral or bilateral posterior crossbite. Patients with cleft lip and palate or congenital craniofacial syndromes were excluded. This study was approved by the Ethics Committee of the Araraquara School of Dentistry, UNESP, (protocol 14484713.1.0000.5416).
Surgery and treatment protocol
Surgery was carried out under general anesthesia in hospital environment by two surgeons (V.A.P-F. and E.S.G.). SARME was performed with Subtotal LeFort I osteotomy, midpalatal suture separation, and pterygomaxillary disjunction. Patients were treated with Hyrax type appliance and activation rate of one quarter turn (0.2 mm) three times a day until the crossbite correction. The appliance activation was initiated 7 days post-operatively. After achieving the intended expansion of the maxilla width, the appliance was blocked and left in place for about 4 months. Afterward, it was removed and replaced by a transpalatal arch.
CBCT analysis
CBCT scans were acquired preoperatively (T1), immediately after expansion (T2) and 6 months after expansion (T3) using an iCAT CBCT scanner (Imaging Sciences International, Hatfield, PA, USA) set up at 120 kVp, 36 mA, 0.3 mm voxel, and FOV of 17 × 23 cm. The patients were positioned sitting upright in the natural head position, and they were instructed to occlude in maximum habitual intercuspation during the CBCT scanning. The DICOM files were imported into Dolphin 3D (version 11.5, Dolphin Imaging, Chatsworth, CA, USA) for further analysis. In order to maintain the same reference planes in all time points, head orientation of each data set was standardized using orientation tool in Dolphin 3D software. The 3D orientation was performed according to three reference planes obtained from stable landmarks such as porion, orbitale, and nasion. The Frankfurt horizontal plane was defined by the right and left orbitale and the right and left porion landmarks. The transporionic plane was defined by the right and left porion landmarks, perpendicular to Frankfurt horizontal plane. The midsagittal plane was defined as the plane orthogonal to axial and coronal planes passing through nasion landmark [14]. Then, the head was moved so that the previously defined planes were coincident with the reference planes. The Frankfurt horizontal plane was oriented to match the axial plane, the transporionic plane was oriented to match the coronal plane, and the midsagittal plane was moved to match the sagittal plane (Fig. 1). Afterward, the mandibular landmarks (Menton, the right and left condylion and the right and left gonion) were defined using volume rendering and multiplanar reconstruction (Fig. 2). In order to assess the changes in mandibular position at the three time points, linear and angular measurements were performed between the mandibular landmarks and the reference planes (Fig. 3).
Data analysis
Eighteen CBCT images were randomly chosen and assessed twice by the same calibrated examiner, with a minimum interval of 30 days. Reliability was confirmed by the intra-class correlation coefficient (ICC), which ranged from 0.929 to 0.996. The Shapiro-Wilk test was used to investigate assumptions of normality. Longitudinal changes were evaluated using repeated measures ANOVA, Greenhouse-Geisser corrections were applied for data that violated sphericity assumptions. In statistically significant results, the Bonferroni multiple comparison test was used to assess differences between time points. Data analysis were performed using SPSS 16.0 (SPSS, Chicago, IL, USA) with a significance level of 5% (α = 0.05).
