The comfo bite has a webbed portion arching between the sides of the mouthpiece that rests against the roof of your mouth and holds the second stage in place even if you are essentially slack jawed. I prefer them to the sea cure mouthpiece as the sea cure mouthpiece is excessively long, is hard and does not work well for your OOA buddy when he or she steals your primary.
An old fashioned metal cased regulator is very hard to beat in terms of dry mouth prevention. Dry mouth was pretty rare before the scuba industry was infected with plastic cased second stages. Essentially the entire inside of the metal case and air barrel catches moisture and recycles it. The Scubapro Balanced Adjustable fits the bill. It is all metal, uses the same internal poppet assembly as the current G250HP and S600 and offers virtually identical performance. They show up on e-bay for under $50.00 and are still fully supported by SP parts wise (with the possible exception of the rubber exhaust Tee - rumor has it SP made more of them, but I have not ordered one lately.)
One thing most people don't always realize is how much difference the second stage low pressure hose lenght makes. If the hose is too long, it will push the second stage to the left and if it is too short, it will pull the second stage to the right. Either one will require a great deal more force on the bite tabs to keep the reg in place. If one or the other is happening to you, try a hose 2 inches shorter or longer as appropriate.
A good mouthpiece and a low pressure hose of the proper lenght will do far more to reduce or eliminate jaw fatigue than a "lighter" plastic second stage.