For the teeth and gums, you need to have the upper and lower teeth (like a set of dentures) as separate polygon meshes or groups.
Location. Teeth should be accurately placed within the mouth, such as the front of teeth matching the inside of the lip.
Teeth and gums should be modeled as far as they will be visible, likely including the gums and reaching into the rear of the mouth.
Teeth and gums need to be shaded.
The lower teeth set needs to be parented to the jaw bone.
