A method for forming a model of dentition for a patient obtains a 3D surface contour image of the patient dentition and segments the 3D surface contour image. Design parameters of a dental appliance for the patient dentition are obtained and a region of interest of the segmented 3D surface contour image identified according to the dental appliance. The model including the region of interest is generated, excluding one or more portions of the segmented 3D image.