In animation we use targets for the Eyes. So you add a Target Helper to point the eyes to the right position, thats why the eye are parented to the base mesh. Morphs in eyes are used to adjust pupil morphs and other things.

If you use to model the eye inside d emesh, you can create one and simple duplicate the mesh, in this case you will need to use bones to animate them.

Teeth can be a mesh inside the base mesh, since exopressions are based in morphs too, so you can adjust the teeths according to the morphs.

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