Patient demands for esthetic orthodontic treatment outcomes have grown to include esthetic appliances during treatment. In the last several decades, appliances such as lingual braces, plastic brackets, ceramic brackets, and clear tray materials have been developed to improve the appearance of appliances used during treatment. A better understanding of the material properties could lead to better sequencing of tooth movement and more efficient treatment. Material properties may even affect the treatment outcome, as it was found that patients wearing a harder aligner material for a two week...