Darkening mouth textures is defintely another tool, which I use also, especially if the figure is distant from the camera and closeup mouth details are indistinct. (I didn't mean to overlook your good suggestion earlier.) The trouble with just darkening the textures though, is that unless you remap the mouth, teeth and tongue in variable sections, you have to darken them uniformly; When you're going for true photoreal shadowing in a closeup image, the front facing teeth, the front of the tongue, and sometimes even the front-facing back wall of the throat need to be brighter, with a gradient intensity falloff to the innermost non-facing concave portions of the inner mouth -- and this becomes even more tricky when the light is coming from side, high, or low angles relative to the head position. That's why I thought using some kind of a semi-translucent, layered, and positionable "darkmouth blob" object might be the thing to do, if I can figure out a useable implementation of it. Obviously, all of this is getting very picky for shadow realism -- but that's the kind of stuff the professional occlusion passes achieve, and I'm just trying to figure out how to match that level of quality. When you see a CG creature with and without occlusion darkening, you'd be amazed at the comparative extra level of realism you get from a relatively subtle change like this.