The night guard protects your teeth from grinding and clenching. It is designed to establish a free space. When your lips come together, your teeth will be apart which initiates muscle relaxation process. When muscles are relaxed, your teeth will rest on the bite pads.
Mouth guard uses tissues retention between your lips, cheek, and tongue to be held in place. There are no hooks that attach to the teeth and there is no need to use the teeth to hold the appliance in place.