The auto masking will just allow you to sculpt in the part of the mesh where you first clicked on. So if you clicked on the green tooth to sculpt on it and you keep holding the click down and move to any of the other teeth, with auto masking on they wont be affected. This is most useful when two separate meshes inside the same object are intersecting and you don’t want your stroke to affect any other part other than the one you are sculpting on.
So in your case, when you say linked, you mean join? You joined all the teeth as a single mesh? It may be that the purple ones have a mask? Try clearing all the masks. You can upload your file if you want us to take a closer look and help troubleshoot.