An orthodontic appliance, comprising: a shell including a plurality of cavities shaped to receive teeth; a discontinuity formed in the shell; and an elastic member having a first portion directly coupled to the shell at a first attachment point and a second portion directly coupled to the shell at a second attachment point, and positioned to interact with the discontinuity by applying a force on or in a region of the discontinuity when the appliance is worn, wherein said discontinuity comprises one or more of: a flap; or a window or notch, formed in a buccal, lingual, occlusal and/or gingival surface of the shell, and wherein said interaction between said elastic member and said discontinuity comprises: where said discontinuity is a flap, exertion of forces directly on said discontinuity by pressing or pulling against said flap, or where said discontinuity is a window or notch, exertion of forces on portions of the shell surrounding said window or notch; wherein the discontinuity is between the first attachment point and the second attachment point or wherein the elastic member extends around the discontinuity. a shell including a plurality of cavities shaped to receive teeth; a discontinuity formed in the shell; and an elastic member having a first portion directly coupled to the shell at a first attachment point and a second portion directly coupled to the shell at a second attachment point, and positioned to interact with the discontinuity by applying a force on or in a region of the discontinuity when the appliance is worn, wherein said discontinuity comprises one or more of: a flap; or a window or notch, formed in a buccal, lingual, occlusal and/or gingival surface of the shell, and wherein said interaction between said elastic member and said discontinuity comprises: where said discontinuity is a flap, exertion of forces directly on said discontinuity by pressing or pulling against said flap, or where said discontinuity is a window or notch, exertion of forces on portions of the shell surrounding said window or notch; wherein the discontinuity is between the first attachment point and the second attachment point or wherein the elastic member extends around the discontinuity. a flap; or a window or notch, formed in a buccal, lingual, occlusal and/or gingival surface of the shell, and wherein said interaction between said elastic member and said discontinuity comprises: where said discontinuity is a flap, exertion of forces directly on said discontinuity by pressing or pulling against said flap, or where said discontinuity is a window or notch, exertion of forces on portions of the shell surrounding said window or notch; wherein the discontinuity is between the first attachment point and the second attachment point or wherein the elastic member extends around the discontinuity. where said discontinuity is a flap, exertion of forces directly on said discontinuity by pressing or pulling against said flap, or where said discontinuity is a window or notch, exertion of forces on portions of the shell surrounding said window or notch; wherein the discontinuity is between the first attachment point and the second attachment point or wherein the elastic member extends around the discontinuity.