Methods, systems, and apparatuses are described for determining a boundary between teeth and gingiva of an archform and/or between teeth and other teeth. Curves may be defined on the surface of teeth and gingiva in the archform. An indication of curvature at various points on the curves may be determined. A predicted likelihood parameter that each of the points corresponds to the boundary between the teeth and gingiva may be determined based on the indication of curvature. A smoothing function and the predicted likelihood parameter may be used to determine a boundary point for each curve. The boundary points may be connected to form the boundary between the teeth and gingiva.
