I've been puzzling over how to get teeth to look like something other than a row of peppermints or badly made dentures. They don't really want any AO because that gives grey-black shadows which you never see on real teeth. Shadows between teeth (if present at all) are lust slightly darker tooth-colour. They also vary in colour from yellower at the gum (where they are thicker) to more blue-ish at the tips where they are much more translucent. I reckon they need a bit of translucence, sss or something, but not enough to make them 'glow in the dark' further back in the mouth. Maybe some sort of translucence map/mask? Gums too, can sometimes be surprisingly pale where they meet the tooth (I guess from being stretched quite thin over a light-filled white thing).