Maxillary expansion in an animal model with light, continuous force. 
Maxillary constriction is routinely addressed with rapid maxillary expansion (RME).  However, the heavy forces delivered by most RME appliances to expand the palate may lead to deleterious effects on the teeth and supporting tissues.  The objective of this study was to explore a more physiologic maxillary expansion with light continuous force.  Twenty 6-week-old Sprague-Dawley rats were equally divided into experimental (EXPT) and control (CTRL) groups.  A custom-fabricated archwire expansion appliance made from 0.014-inch copper-nickel-titanium wire was activated 5 mm and bonded to the maxillary molar segments of animals in the EXPT group for 21 days.  The force applied to each maxillary segment was 5 cN. Microfocus x-ray computed tomography and histological analyses were used to compare the tooth movement and bone morphology in the midpalatal suture and buccal aspect of the alveolar process between the EXPT and CTRL groups.  Descriptive statistics (mean ± standard error of the mean) and nonparametric statistical tests were used to compare the outcomes across groups.  Compared to the CTRL group, there was a statistically significant increase in buccal tooth movement and expansion of the midpalatal suture in the EXPT group.  There was no difference in the bone morphologic parameters between groups.  The mineral apposition rate was increased on the buccal surface of the alveolar process in the EXPT group.  Application of light, continuous force resulted in maxillary osseous expansion due to bilateral sutural apposition and buccal drift of the alveolar processes.  This animal experiment provides a more physiologic basis for maxillary expansion.