A therapeutic exercising device that can simultaneously increase temporomandibular joint range of motion and strengthen jaw muscles comprises two bite members with bite portions for insertion between a users teeth and a bellows between the bite members that moves them relative to each other toward an open position that separates the users upper and lower jaws. A spring exerts a predetermined opening force on the bite members open, and one or more elastic members attached between the bite members exert an opposing closing force. A user-operated pneumatic pump introduces air under pressure into the bellows to open the bite members when the closing force is sufficient to overcome the opening force. The device can be used with air bladders that massage the jaw muscles, with the optional application of heat or cold. The device is usable with a mandible translation adapter to exercise a users mandible in the posterior-anterior direction.
