Night guard is indicated for preventing clenching and/or grinding teeth at night. It could be worn either on upper or lower teeth. It is a thicker rubbery material that will prevent wearing of the teeth (you will be grinding on the plastic instead). At the end of orthodontic treatment night guards can also function as a retainer.
Sport Mouth Guards
Whether you have braces or not the teeth should be protected during contact sports. Otherwise they are in danger of trauma. While undergoing orthodontic treatment loosely fitting sports guards should be worn otherwise the mouthguard will break the braces and/or prevent proper movement of teeth.