I used to get jaw fatigue, which means I was clamping down on the mouthpiece without realizing it. At first I thought it was from the hoses tugging to one side, so I got a swivel, but that didn't help. Next I tried the SeaCure mouthpiece. I've had the same SeaCure mouthpiece now for six years or so, and I never need to bite down any more. Never have any tension in my face from the regs at all, even after days on end of multiple dives.