A computer implemented method for designing a removable orthodontic aligner, which comprises operating a digital scanner to obtain a digital image of a patient's dentition and operating a computing environment, which comprises a central processor, memory, imaging software, and graphical user interface, to: (a) receive a copy of the digital image; (b) create a reference plane relative to one or more teeth (36, 38, 46, 48, 54, 56) featured within the digital image; (c) position a line that runs perpendicular from the reference plane and runs tangential to a height of maximum convexity of each of the one or more teeth (36, 38, 46, 48, 54, 56); (d) measure an area of undercut (24, 32, 34) between such perpendicular line and an exterior surface of each of the one or more teeth (36, 38, 46, 48, 54, 56); (e) repeat steps (a) - (d) at a plurality of points along a perimeter of each of the one or more teeth (36, 38, 46, 48, 54, 56); (f) construct a three-dimensional model that represents a compilation of each area of undercut (24, 32, 34) calculated by the system for each of the one or more teeth (36, 38, 46, 48, 54, 56); and (g) translating the three-dimensional model into a set of dimensions that are correlated to preferred interior dimensions of a removable orthodontic aligner, wherein the preferred interior dimensions of the removable orthodontic aligner are configured to cause the removable orthodontic aligner to mate with and retentively sit adjacent to areas of undercut (24, 32, 34) for each of the one or more teeth (36, 38, 46, 48, 54, 56), and the removable orthodontic aligner further comprises one or more anti-relapse features, wherein the anti-relapse features are configured to discourage or prevent relapse movement of an underlying tooth (36, 38, 46, 48, 54, 56). (a) receive a copy of the digital image; (b) create a reference plane relative to one or more teeth (36, 38, 46, 48, 54, 56) featured within the digital image; (c) position a line that runs perpendicular from the reference plane and runs tangential to a height of maximum convexity of each of the one or more teeth (36, 38, 46, 48, 54, 56); (d) measure an area of undercut (24, 32, 34) between such perpendicular line and an exterior surface of each of the one or more teeth (36, 38, 46, 48, 54, 56); (e) repeat steps (a) - (d) at a plurality of points along a perimeter of each of the one or more teeth (36, 38, 46, 48, 54, 56); (f) construct a three-dimensional model that represents a compilation of each area of undercut (24, 32, 34) calculated by the system for each of the one or more teeth (36, 38, 46, 48, 54, 56); and (g) translating the three-dimensional model into a set of dimensions that are correlated to preferred interior dimensions of a removable orthodontic aligner, wherein the preferred interior dimensions of the removable orthodontic aligner are configured to cause the removable orthodontic aligner to mate with and retentively sit adjacent to areas of undercut (24, 32, 34) for each of the one or more teeth (36, 38, 46, 48, 54, 56), and the removable orthodontic aligner further comprises one or more anti-relapse features, wherein the anti-relapse features are configured to discourage or prevent relapse movement of an underlying tooth (36, 38, 46, 48, 54, 56).