I also have issues with clenching my jaw at all times. I think for me, it's a lot to do with constant anxiety, especially in social situations. I don't even notice I'm clenching my jaw, but I'm almost always doing it, even when I'm trying to fall asleep or alone at my house watching TV. I've tried to stop, but it's hard to keep reminding myself to check the muscles in my face to stop tensing up. Once I am able to relax them, they clench right back up. It's hard to stop! I notice that when I am stuttering, I almost always close my eyes. I almost 'flutter' them. Sometimes I shake my head. I kind of hate it, because I think it makes the person notice that I am stuttering even more. Especially if I'm really stuck on a word, I know it looks weird that I am fluttering my eyes, and it makes me feel even worse after the encounter.