The normal balance of oral flora in our mouths changes when we wear a removable dental appliance. If you do not clean your retainer, aligner or mouth guard daily it is the perfect place for plaque bacteria to multiply and grow. Wearing a dental appliance can lead to increasing the risk of plaque bacteria. If you do not clean your retainer, aligner or mouth guard properly it can cause plaque bacteria to grow. In fact, a study showed that more than 50% of retainers, aligners and mouth guards are often covered in some sort of oral bacteria.