One big advantage of going the full face mask route is that there is nothing you need to bite down on...Along with others, such as, the mask defogs itself with every breath you take, the mask can afford you an extra chance at life if you ever happen to have a seizure or go unconscious underwater, can keep your face warm in cold water, our mask has a double seal to fit a larger variety of faces (better than 9 out of 10). The mask also has a semi-positive pressure inside the mask (is still a demand regulator), but because of this, even if the mask is pulled up to an inch away from your face, air will come out and water won't come in, which makes getting water in the mask difficult. And of course, you also have the ability for communications if you are interested in that. A lot of divers use the mask without communications for the other benefits.
We work with wounded veterans for this exact purpose. Some have jaw problems from combat or other military related injuries. I myself, have a case of TMJ and biting down on something for hours is pretty uncomfortable. The only thing I dive is the Guardian, and won't go back to conventional SCUBA if I can help it.
Full face masks are making their way into the recreational space more and more and may be something worth checking out.
If you're interested you can take a look at our mask here :
Shop | Ocean Technology Systems
We also have a variety of training videos here :
Videos | Ocean Technology Systems
If you have any questions about The Guardian FFM or our underwater communications, ask away and I'd be glad to help you out in anyway I can.