Methods of forming arch adjustment dental appliances

A method of forming a dental appliance, comprising:

• forming a virtual arch element based on a virtual dental arch of a patient, wherein the virtual arch element is wider than an arch width across a palate of the virtual dental arch;
• forming one or more virtual tooth engagement structures connected to the virtual arch element and configured to engage with teeth on opposing sides of the virtual dental arch, wherein the virtual arch element extends from a lingual side of the one or more virtual tooth engagement structures so that, when the one or more virtual tooth engagement structures are engaged with the teeth on opposing sides of the virtual dental arch, the virtual arch element spans across the palate and the virtual arch element and the one or more virtual tooth engagement structures applies a virtual force on the teeth on opposing sides of the virtual dental arch in accordance with a stage of a treatment plan;
• and
• fabricating the dental appliance by forming a physical arch element based on the virtual arch element and one or more physical tooth engagement structures based on the one or more virtual tooth engagement structures.