Two things I do to spruce up a smile.. add a touch of ambiant light to the teeth.. not much, just .1 or so.. it'll be enough to brightedn the smile, without making them look like they are glowing. (Actually, in amny renders, I'll do that to the tongue, gums, and inner mouth as well.) Another good technique, is to use a spotlight aimed JUST on the mouth itself (I also will do that with eyes sometimes, one spotlight for each eye.)

Way too many people take way too many things way too seriously.