I don't like that there is blackness in his humongous gaping goblin jaw. First off, there really shouldn't be that much space in the first place, the cheek will have covered most of that, but I can appreciate a bit of abstract anatomy.
I don't understand why you could see to the other side however, which would get rid of the black. The only way that could happen is if one side lacked a cheek and the other had one? But that'd be pretty silly, and I doubt thats what you were going for. If so, it could be a lot more apparent.