Because of the crestal area’s variability,how can I segment it precisely apart from mandible in slicermorph?
Please share screenshots that are showing the types of challenges you are facing? Also segmentation is a core feature of 3D Slicer, and not part of SlicerMorph extension.
I don’t think there is anything automatic to help you remove those regions. You can use a number of effects in the Segment Editor (paint and threshold) to delete them.