If plaque bacteria are not regularly removed and cleaned from your teeth and removable dental appliance, they can impact your oral health, leading to problems like bad breath or other oral care issues. In a 2011 study from The Society for Applied Microbiology found that up to two thirds of retainers and retainer-wearer mouths contain Candida species, a type of yeast. Candida species is found naturally in the mouth and our saliva usually keeps levels under control. However, if you do not clean your retainer, aligner or mouth guard daily the balance of Candida species levels in your mouth may increase leading to an infection known as oral thrush. The same study also found about half of retainers contained Staphylococcus – a type of bacteria which can cause dental infections. If you have a healthy immune system, both Candida and Staphylococcus are present and rarely cause problems. If your immune system is compromised, you'll need to be very diligent and care for your appliance and mouth routinely.