A number of ways to do this. If I was doing it, I would probably use the grouping tool to spawn a prop of the teeth and gums. I would then make a morph so that when 0 the figure teeth and gums are hidden (by scaling the mesh down to the point it is invisible - or you can just make the materials transparent). I would make a similar morph for the false teeth prop, or maybe just use the scale dial since that would do the same thing. I might also make a morph so that the false teeth open and close like in genny's animation. You can now use the prop teeth in combination with the figure. If this is an animation, when you want the teeth to pop out, make the normal teeth and gums invisible, and bring the false teeth into play.