How to make a smooth transition between different areas?

I am working on the creation of a 3D reconstruction of a tooth for a presentation and I need the transition between the enamel and the root to be as smooth as possible, but at the same time, so that these structures do not layer on top of each other in any way. If they are layered, then I can really achieve the effect I want, but if these two anatomical areas are separated, then on the 3D reconstruction the boundaries between them look rounded and rough.
The first image is what I get, and the second is approximately what I would like to achieve in terms of the transition of two anatomical areas. Of course, I won’t achieve a perfect transition, but I want it to look at least more anatomical.


it wont go smooth unless you overlap it to each other