The Doctor's NightGuard Advanced Comfort dental protector is a moldable, custom-fit dental protector that fits over your top teeth. Its patented design has a soft upper layer to cushion and absorb, and a firm lower layer to prevent grinding. And it's slim and flexible, so you can sleep comfortably. Dental protector was designed by a dentist who saw the damage that nighttime teeth grinding (bruxism) could do. He also saw the need for a dental protector that's not only protective, but also comfortable. After all, even the most protective dental protector won't help if you won't wear it. Mouth size and body type don't always correspond but as a general rule, choose the size based on the closest description of your height. Medium: Men - Less than 5 ft 8 in tall, Women - Less than 5 ft 7 in tall.