Systems and methods for designing thermoformed removable orthodontic aligners and improving the retention of such aligners to patient teeth are disclosed. The systems generally include a digital scanner that is configured to obtain a digital image of a patient's dentition and a computing environment that is configured to receive a copy of the digital image; create a reference plane relative to one or more teeth featured within the digital image; 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; measure an area of undercut between such perpendicular line and an exterior surface of each of the one or more teeth; repeat the foregoing steps at a plurality of points along the perimeter of each of the one or more teeth; and construct a three-dimensional model of an undercut area for each of the one or more teeth.