The use of self-ligating brackets has gained popularity recently in orthodontic treatment. The Damon philosophy is a system that employs passive self-ligation with the use of light forces to achieve arch development and to relieve dental crowding. The philosophy of the system is that the use of light forces does not overpower the forces of the lips, tongue, and other peri-oral soft tissue thereby allowing for optimal equilibration of forces that is customized to every individual. If this actually occurs, changes in the posture of the tongue and hyoid would be expected as is seen after orthognathic surgery and rapid maxillary expansion. The purpose of this study was to evaluate if these postural adjustments do occur, and, if they do, to assess if there is a stratification of treatment effect based on dental classification. A customized cephalometric evaluation was designed from an amalgamation of previous cephalometric studies. This cephalometric study not only evaluated changes due to treatment but also assessed changes in cervical postural position to validate the quality of the measurements and to verify that radiographs were taken in a correct and repeatable head position. Cephalometric measurements were correlated with measurements of posterior dental expansion at the premolars and molars. Results of the study showed a correlation in tongue length and hyoid to mandible measurements. Lack of significance in the cervical posture cephalometric changes validated the cephalometric design and the quality of radiograph included in the study. Significant posterior dental expansion was documented although this expansion was limited to the premolar regions. Changes in tongue length correlated with dental expansion, particularly in the lower premolars. Lastly, increases in upper airway space correlated with dental expansion, particularly in Class III patients. This finding is very interesting and suggests the need for further research in this area. Additionally, replication of this study with more subjects may yield very interesting results. Overall, this study supports the fact that studies of soft tissue changes in relation to orthodontic treatment need further investigation as these tissues are involved in the equilibrium of forces and are directly related to the stability of orthodontic treatment. / Oral Biology