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.
