A removable dental appliance comprising: an appliance body configured to at least partially surround a plurality teeth of a dental arch of a patient , wherein the appliance body comprises: a first shell shaped to engage a first tooth of the plurality of teeth in an initial position of the first tooth; and a second shell shaped to engage a second tooth of the plurality of teeth in an initial position of the second tooth, wherein the second tooth is adjacent to the first tooth; and an interproximal reinforcement (102A-102E) on the exterior surface of a respective shell extending from a first gingival edge of the appliance body on a labial side of the appliance body along an interproximal region between the first tooth and the second tooth to a second gingival edge of the appliance body on a lingual side of the appliance body, wherein the interproximal reinforcement results in the appliance body at the interproximal region being stiffer than a labial face and a lingual face of the first shell, and wherein the interproximal reinforcement is configured to engage at least one of a lingual surface of the first tooth below a height of contour of the first tooth or a labial surface of the first tooth below the height of contour to enable the appliance body to apply a force vector at a contact point on the first tooth to cause movement of the first tooth toward a desired position of the first tooth when the removable dental appliance is worn by the patient. an appliance body configured to at least partially surround a plurality teeth of a dental arch of a patient , wherein the appliance body comprises: a first shell shaped to engage a first tooth of the plurality of teeth in an initial position of the first tooth; and a second shell shaped to engage a second tooth of the plurality of teeth in an initial position of the second tooth, wherein the second tooth is adjacent to the first tooth; and a first shell shaped to engage a first tooth of the plurality of teeth in an initial position of the first tooth; and a second shell shaped to engage a second tooth of the plurality of teeth in an initial position of the second tooth, wherein the second tooth is adjacent to the first tooth; and an interproximal reinforcement (102A-102E) on the exterior surface of a respective shell extending from a first gingival edge of the appliance body on a labial side of the appliance body along an interproximal region between the first tooth and the second tooth to a second gingival edge of the appliance body on a lingual side of the appliance body, wherein the interproximal reinforcement results in the appliance body at the interproximal region being stiffer than a labial face and a lingual face of the first shell, and wherein the interproximal reinforcement is configured to engage at least one of a lingual surface of the first tooth below a height of contour of the first tooth or a labial surface of the first tooth below the height of contour to enable the appliance body to apply a force vector at a contact point on the first tooth to cause movement of the first tooth toward a desired position of the first tooth when the removable dental appliance is worn by the patient. <EOS>