A Night Guard or Stess Guard is a horseshoe-shaped, retainer-like, plastic appliance with shallow borders that can be worn on either the top or the bottom arch. It is designed to protect the teeth from the pressure of clenching and grinding by providing a protective cushion between the upper and lower teeth. A night guard can be an excellent solution for protecting your teeth and jaws from the damaging effects of bruxism. When properly made, it can help reduce clenching, grinding, broken or cracked teeth and TMJ problems by helping to relax the muscles in the jaw.