Skeletal and dental changes after rapid maxillary expansion: a computed tomography study.

To investigate the skeletal and dental changes induced by rapid maxillary expansion, using computed tomography (CT) scans and three-dimensional (3-D) reconstructed images. Twenty patients (Mean age: 12.3 +/- 1.9 years) who required rapid maxillary expansion as a part of their comprehensive orthodontic treatment underwent pretreatment (T1) and post-treatment (T2) CT scans. The T2--T1 differences between selected skeletal and dental measurements on the coronal CT and 3-D volumetric images were compared using the Wilcoxon signed ranks test. At T2 the Maxillary alveolar width (4.5 +/- 3.5 mm) was greater than the Maxillary base width (1.7 +/- 0.9 mm). The greatest transverse dental change was in the Intermolar width (6.3 +/- 2.1 mm and 2.7 +/- 1.9 mm at the crown and the apex, respectively). On the 3-D volume, significant increases occurred in the Bicondylar width (1.2 +/- 1.3 mm), Bimaxillo-mandibular width (2.1 +/- 2.3 mm) and the Maxillary width (2.5 +/- 1.6 mm). The greatest change in the dental measurements was in the Maxillary first molar width (6.4 +/- 0.1 mm). The Maxillary central incisor angle decreased significantly (-7.9 +/- 8.4 mm), indicating an increase in the distance between the apices of the central incisors. Volumetric 3-D CT scanning provides a useful method for assessing skeletal and dental changes after rapid maxillary expansion. Although significant increases occurred in most skeletal and dental measures, it appears that dental tipping explains most of the expansion.