A retainer must be worn until late teens or early twenties if you want your teeth to stay straight after orthodontic treatment. A spurt of late facial growth where the jaws grow down and forward into the facial musculature can occur at any time during this period, pushing the teeth into the facial musculature and causing crowding. We used to think this crowding was caused by wisdom teeth. We now know that wisdom teeth do not cause post-treatment crowding. For the first one or two appointments, the retainer must be worn every night and whenever you are at home. If you see any movement of the teeth you must wear it more to keep them straight. If the retainer falls out at night, it means that it is uncomfortable for you to wear and you must wear it more hours during the day until it stays in. If the retainer still falls out at night, you must wear full time over a weekend or until youare able to wear it all night long. If the retainer is falling out at night, your teeth will move and you will be back in braces. Never wrap your retainer in a napkin, it will get thrown away. Do not leave it where your dog can get it. Many patients have told me that their dog never jumped on the table to get food, but did jump up on the table to get their retainer. You must brush your retainer with tooth paste every time you take it out. Do not let your saliva dry on it too many times. You may soak it in denture cleaning tablets to help keep it clean. After a few months, if it starts to yellow, you may soak it in undiluted bleach for a few hours followed by thoroughly rinsing and brushing with toothpaste to remove the bleach taste.