Obviously we all have different teeth so this will not fit exactly. Can't be returned either. Oh, well.Night guards can cost upwards of $175 -$500 when molded to your own teeth. These are the MOST comfortable ones out there! I love that they have both to or bottom choices AND that they are pre molded silicone. Totally how I would have designed them myself! THANK YOU!Unless you have a tiny mouth with teeth that perfectly fit the pre-molded tray it will not stay in or work for you.Too small. Won't even go down onto teeth.‘Upper” (not big upper) was too small at the back jaws- it won’t fit in molars at all. Where front area might fit but so it won’t stay. Would be painful to leave on all night. Sizing just clearly it will not work when I see it. Material is not cheap. Seems like a good idea if you hate hard mouth guard like from the dentists. Might try reorder big size with hope to find a right silicone night guard.