Haven't tried it, but in observing humans, I have noted that not everybody shows teeth when smiling.

Of course, some people have the opposite problem ....

http://freefall.purrsia.com/ff400/fv00354.htm

ronstuff, there's a quick tutorial here in the forum that describes using the grouping tool to morph specific parts of a mesh. You could apply this technique by creating a new group selected from the teeth material.

http://www.renderosity.com/messages.ez?Form.ShowMessage=1322689