Objectives: Orthodontic arch development expands and broadens the dentition beyond the confines of the original arch perimeter. This is often accomplished by means of self-ligating fixed appliances. When movements take the teeth outside those confines, without adoption, the muscular forces are unbalanced and may lead to dental relapse. Muscle spindles and associated reflex loops within the tongue provide feedback to arch perimeter changes that may produce postural changes to the new archform. Resting posture has long been accepted as aiding in tooth position. The objective of this study was to assess the oral and pharyngeal postural changes that result from arch development with the Damon system and report the amount of expansion accomplished. Methods: Pre- and post-treatment models and lateral cephalograms were collected on 69 previously treated orthodontic patients from four different private practices. Expansion was measured from the buccal cusp tips of the first and second premolars and first molars. A new cephalometric analysis was implemented to diagnose both variations in malocclusion and variations in posture of the head, neck, pharynx, hyoid bone and tongue. Results: Both tongue height and length increased, 2.9mm (P-value 0.001, SEM=1.06) and 3.76mm (P-value 0.00002, SEM=0.62) respectively, following posterior dental arch expansion using Damon archwires. Hyoid position was not significantly different. Conclusion: As dental arches are expanded the tongue increases in both length and height to fill the space and therefore may aid in stability during the retention phase of treatment. The lack of change in hyoid bone position, as one would expect with a rise in tongue position, might be explained by either slight changes in head position or the need to maintain the airway. / Oral Biology