Here's an example of low-poly teeth from the FaceTopology wiki page, might help you. http://wiki.polycount.com/FaceTopology?action=AttachFile&do=view&target=JuliusHettig_game-teeth.jpg
Making teeth look right especially if they are showing a lot is really tough. To be honest, it just takes a lot of patients, tweaking and looking at reference. When I sculpt teeth and gums, I always open max and make a curved evenly subdivided block for the gums (top and bottom). Then I make sub divided blocks for the…