- Model of palatal expander. 

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... mean age at the time of the first imaging ap- pointment in this study was 12.3 ± 2.6 (8.3 to 17.8 years). The second CBCT image was taken on an average of 22.8 ± 5 days after the first image (14 to 37 days). Each patient was treated with a tooth-borne rapid maxillary expander (Hyrax). The expansion appliance consisted of a 7-millimeter Dentaurum expansion screw (Dentaurum, Ispringen, Germany) with 0.051-inch diameter stainless steel arms welded to orthodontic bands on the maxillary first molars, and a 0.051-inch diameter supporting wire placed palatal to the dentition and bands so as to increase the rigidity of the appliance and extend the force of the expander to the canines as well as first and second premolars, if they were present ( Fig 3). The expander was activated two-quarter turns of the expansion screw (0.2 mm each turn) at the time of delivery, followed by a one-quarter turn twice a day. Activation of the screw continued until the transverse discrepancy was overcorrected to the point in which the palatal cusps of the maxillary molars were in edge-to-edge contact with the buccal cusps of the opposing mandibular teeth. Cone beam computed tomography scans were taken using the Classic i-CAT ® (Imaging Sciences International, Inc., Hatfield, USA) cone beam CT scanner. All scans were taken by the same technician using either the 16 x 13 or the 16 x 22 centimeter field of view with a voxel size of 0.4 millimeters. Patients were positioned in a vertical seat with their head stabilized in the headrest to prevent any unwanted movement during the 20-second scan, teeth together in centric occlusion, and the Frankfort Horizontal plane parallel to the floor, as determined by the external auditory meatus and soft-tissue orbitale. Each patient was scanned at two different time points: T and T . The first image (T ) was obtained 0 1 0 prior to the delivery of the expander and represented the subject’s baseline condition prior to expansion. The second time point (T ) was taken at the ap- 1 pointment immediately following the last activation of the expansion appliance. The analysis measured changes of the alveolar bone and maxillary sutures following rapid maxillary expansion with consistent landmark identification using the Dolphin 3-D software (Dolphin Imaging & Management Solutions, Chatsworth, USA). Each scan had a number randomly assigned and loaded into the three-dimensional software so that each scan was analyzed without the operator identifying the patient. First, each scan was oriented by locating the midpoint between both foramina spino- sum (ELSA), and assigning to it x = 0, y = 0, and z = 0 coordinates (Fig 4). The following points were then located: 1) the superior-lateral border of the external auditory meatus (SLEAM) on both right and left sides, and 2) the mid-dorsum of the foramen mag- num (MDFM). An axial-horizontal plane (x-y plane) was determined by using the right and left SLEAM points and ELSA. A sagittal-vertical plane (z-y plane) was determined perpendicular to the x-y plane and passing through points ELSA and MDFM. These points have shown a high intra-reliability when located with 3D images, which makes the x-y and z-y planes formed by these points an adequate way to standardize the orientation of 3D images. Two-dimensional axial images were created perpendicular to the coronal plane and used to measure the amount of midpalatal and transpalatal suture separation on the external surface of each suture. The midpalatal suture was measured adjacent to four locations: the first molar, the contact area between the first and second premolars, the canine, and the most anterior point of the maxillary dental arch. The central groove of each first molar was identified by locating the crown of the molar on an axial image and marking the central groove. An axial section through the hard palate was then created, and the mesial edge of the midpalatal suture was marked on both right and left sides. The same procedure was followed for the other areas of the midpalatal suture, as described above (Fig 5). To verify if the external surface of the suture was being marked, coronal slices were viewed for the places where the suture edges were marked and corrected if necessary. The transpalatal suture was measured at five areas along the suture. The first area identified was in the midline, established by the junction of the midpalatal and transpalatal sutures. The proximal and distal edges of the transpalatal suture were marked at the midline, as well as at 6, 12, and 18 millimeters to the left (Fig 6). The mil- limetric grid on the axial image was used to determine the landmarks to the left of the midline. To verify if the external surface of the suture was being marked, coronal slices were viewed for the places where the suture edges were marked and corrected if necessary. The displacement of the frontonasal suture was determined by locating and marking the superior and inferior edges of the frontonasal suture on the external surface in the midline on a sagittal section (Fig 7). Axial sections were used in the appropriate locations to locate and measure the mesial edges of the intermaxillary suture at ANS (Fig 8) as well as the proximal and distal edges of the zygomaticomaxillary sutures which were located and marked on both inferior (Fig 9) and superior (Fig 10) borders of the zygomaticomaxillary suture on both right and left sides. To determine the amount of appliance expansion, the outer edges of an unactivated 7-mm Dentaurum expansion screw (Dentaurum, Ispringen, Germany) were measured with digital calipers. In the post-ex- pansion scans, the outer edges of the expansion screw were marked in the coronal slice at the maxillary first ...