An occlusal “night guard” is a clear, plastic ‘horseshoe-shaped’ wafer that sits over the tops of teeth (either upper or lower), and most often worn at night.  It has a flat biting surface that keep clenching/grinding from wearing down the surfaces of teeth, and can help prevent fractures. It also puts the lower jaw in a more comfortable (resting) position, which can reduce TMJ symptoms. Because they are clear, some folks (who are under a lot of stress) wear them during the day as well.