There seems to be no combination of controller settings that will completely close Woot's lips, so that no teeth are visible. It's most visible when his head is tilted up slightly.

Click to view attachment

This tends to leave him with either a bucktoothed or a slackjawed look.

Some slight closing is had by curling the lips in, but the result is not a normal mouth-closed look.

Any solutions?

Do the teeth show in Final/Quick render?

Also -"page up" - ie, increase polys/patch - shows mouth closed

well, I used the "Lips" controllers to make the "mm,b" shape and that closed the center but made for a frown appearance. When I tried to counter that with a bit of a smile the sides of his mouth opened up.

I opened Woot model, now I see what you're talking about. Do they have braces in the land of Oz? Maybe Woot is meant to have an overbite?

It's possible to move the lower jaw out by using the jaw null on the FACE rig.

I tried it, didn't work. It looks like Robert may have to actually move some lip CP's to cover up the teeth.

The simple solution would be to close the jaw bone more, but it has a rotation limit on it.

Would it mess things up just to extend the rotation limit?

As long as you keep the 0% pose the same as it is now, I don't see why it should. Can controls have negative value % ?

The pose can have a negative side and the limits can be extended...then, the Smartskin for that control would need to be modified.

The weighting might be able to handle it if there's only a small movement needed.