You may wonder why you need to clean the case if you only ever put the clean retainer, dentures, snore guard, or other oral appliance into the case. The fact is, whatever is floating around in the air, including viruses or bacteria, land on the case the during the day. These tiny, even microscopic bits of yuck add up over the days, and eventually, you can see that the case is dirty. But before you can even see them, there are dangerous germs that can transfer from the case to your dental bridge, sports mouthguard, retainer, or nightguard onto your teeth.