Treatment and posttreatment skeletal effects of rapid maxillary expansion investigated with low-dose computed tomography in growing subjects

Introduction: The aim of this study was to use low-dose coronal computed tomography (CT) scans to evaluate the treatment and postretention effects of rapid maxillary expansion (RME) on the maxillary central incisors, midpalatal suture, and nasal cavity. Methods: Multi-slice coronal CT scans of 17 subjects (7 boys, 10 girls; mean age, 11.2 years) were taken before RME (T0), at the end of active expansion phase (T1), and after the retention period of 6 months (T2). Measurements were made on 3 coronal scans perpendicular to the occlusal plane and passing through anterior nasal spine (anterior scan), the midpoint between anterior nasal spine and posterior nasal spine (middle scan), and posterior nasal spine (posterior scan). Statistical analyses were performed with analysis of variance (ANOVA) for repeated measures with post-hoc tests. Results: The transverse dimensions of the midpalatal suture and nasal cavity showed statistically significant T0 to T1 increments in all 3 coronal scans. The roots of the maxillary central incisors were more divergent than the crowns at both T1 and T2. All T0-to-T1 measurements at the sutural and nasal levels decreased from the anterior to the posterior measurements. Between T1 and T2, all measurements exhibited statistically significant decreases with the exception of nasal width on the middle scan. Conclusions: When analyzed on coronal CT scans, the maxillary halves were separated by RME in a parallel manner and not in a triangular shape. At T2 after RME therapy, the suture appeared reorganized, and the expansion of the nasal cavity was stable. (Am J Orthod Dentofacial Orthop 2010;138:311-7)