Long-term effects of orthodontic therapy on the maxillary dental arch and nasal cavity

Introduction: Rapid maxillary expansion (RME) can enlarge the maxillary dental arch while increasing nasal cavity volume and nasal valve area, and decreasing upper airway resistance over time. However, the long-term effects of RME on arch morphology and nasal cavity geometry in patients treated with RME compared with the general population are unclear. Methods: Three-dimensional morphometic analysis and acoustic rhinometry were used to evaluate the maxillary dental arches and nasal cavities in a post-RME-treatment group (n = 25) and a control group (n = 25). Results: Palatal area and volume increased substantially after expansion and remained stable until posttreatment. Small increases in intermolar distance were not significant between the time points. Nasal airway resistance significantly decreased after RME and remained stable until posttreatment. Nasal cavity volume was stable during expansion and posttreatment. It increased significantly during expander stabilization and 9-12 months after expander removal. The minimal cross-sectional area significantly increased between the end of expansion and expander removal and remained stable until posttreatment. All measurements were comparable with those of the matched controls at posttreatment except for palatal area, which was smaller in the treatment group. Conclusions: RME is a powerful tool to normalize most of the variables investigated. Edgewise orthodontic treatment and a retention regimen that consisted of maxillary circumferential or traditional Hawley retainers met satisfactory standards to stabilize the achieved outcomes. Future studies should include morphometric, functional, and skeletal analyses so that the effects of growth and remodeling are better elucidated. (Am J Orthod Dentofacial Orthop 2009;136:490.e1-490.e8)