• Lorenzo Franchi, Tiziano Baccetti, Roberta Lione, Ezio Fanucci, and Paola Cozza.
• Department of Orthodontics, University of Florence, Via del Ponte di Mezzo 46-48, Florence, Italy.
• Am J Orthod Dentofacial Orthop. 2010 Apr 1; 137 (4): 486-8; discussion 12A-13A.

IntroductionThe aim of this study was to evaluate the density of the midpalatal suture as assessed by low-dose computed tomography (CT) before rapid maxillary expansion (RME) (T0), at the end of active expansion (T1), and after a retention period of 6 months (T2).MethodsThe study sample comprised 17 prepubertal subjects (mean age, 11.2 years) with constricted maxillary arches and unilateral or bilateral posterior crossbite. The total amount of expansion was 7 mm in all subjects. Multi-slice low-dose CT scans were taken at T0, T1, and T2. On axial CT scanned images, 4 regions of interest (ROIs) were placed along the midpalatal suture (anterior [AS ROI] and posterior [PS ROI]) and in 2 regions of palatal bone (anterior and posterior). Density was measured in Hounsfield units. The Mann-Whitney U test and Friedman analysis of variance (ANOVA) with post-hoc test were used (P <0.05).ResultsThe densities in the AS and PS ROIs were significantly smaller than the reference bone densities before RME therapy. Both AS and PS ROIs showed significant decreases in density from T0 to T1, significant increases from T1 to T2, and no significant differences from T0 to T2.ConclusionsThe effective opening of the midpalatal suture by RME in prepubertal subjects was associated with a significant decrease in sutural density. The sutural density after 6 months of retention post-RME indicated reorganization of the midpalatal suture, since it showed values similar to the pretreatment ones.Copyright (c) 2010 American Association of Orthodontists. Published by Mosby, Inc. All rights reserved.

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