Bikram Yoga...and Clenching My Teeth

Does anyone else notice they hold a lot of tension in their jaw when they are in Bikram Yoga class? Lately in class I have been noticing that while I try to stay calm in class by breathing in and out of my nose, I am clenching my teeth like I am fighting not to even open my mouth.

I grind my teeth in my sleep, so I guess I already have a lot of tension in my jaw to begin with. How can I help myself loosen my jaw while I practice Yoga without switching to mouth breathing?

Yesterday in class I tried to tell myself to loosen up my jaw, but I couldn't find the place. Any ideas???