Open Mouth Smiling Faces look horrible wrong in anything outside of Manga. You will never see an Open Mouth non-manga CGI smile that looks right.
I will bet you 100-1 that is the exact reason why they won't show him with his mouth open and smiling.
Here are the problems associated with open mouth smiling:
1. 3d texturing
2. 3d depth.
3. Shadowing.
Apply those to a wire mesh and you will not be able to create a 3d open mouth smile that looks even remotely close to what you're going for.